Directional Drilling Method and System

Abstract

The present invention relates to a change in the concentration of abrasive particles (92) in a flow (90) of a drilling fluid mixed with abrasive particles, as an abrasive jet of abrasive particles passes through an abrasive nozzle of a drill bit (10) as the drill bit rotates, to change the erosive force of the flow (90) along an angular sector of a wellbore (4a') for directional drilling. During subsequent time periods, most of the abrasive particles (92m1, 92m2) are alternately deflected into two parallel channels (21, 22) having different flow resistances. The velocity difference generated between the most parts causes the most parts deflected subsequently to recombine downstream of the channels, thereby forming a high-concentration flow portion (90h) of the combined most parts, which is alternated with a low-concentration flow portion (90l). Synchronizing the frequency of the flow portions with the rotational speed of the drill bit results in the erosive force of the abrasive jet (90) within a selected angular sector (4a”) of the wellbore (4a) always being higher than outside thereof.

Description

Field of the Invention

[0001] The present invention relates to the field of drilling into an object, particularly into a soil layer, such as a subterranean soil layer. Specifically, the present invention provides a method and a system for the directional mechanical drilling of a wellbore into said object. Background Art

[0002] Directional mechanical drilling involves drilling into said object in a generally curved manner, thereby creating a curved wellbore section therein. This enables the establishment of a wellbore trajectory in the object using one or more curved sections, e.g., the one or more curved sections being contiguous with straight wellbore sections, such that they extend at an angle to one another. The ability to create a wellbore in a subterranean soil layer having such a curved trajectory allows, in practice, for example, the drilling of a subterranean reservoir in a non-vertical direction (e.g., at an inclined or even horizontal direction). For directional drilling, a drilling device is used that is capable of removing material from the end of the wellbore in a desired direction that is inclined relative to the forward direction of the wellbore. Performing directional drilling continuously over a certain wellbore length results in a predetermined wellbore trajectory that is tangential or curved.

[0003] During directional drilling, the drilling direction is finely controlled to establish the desired curved trajectory. In practice, a well path is provided for most directional drilling rigs used in subterranean soil layers, which is pre-determined by engineers and geologists prior to the start of drilling. When the directional drilling rig begins the drilling process, downhole instruments are used to make periodic measurements to provide measurement data, such as the inclination and azimuth of the wellbore. During critical angle and direction changes, measurement-while-drilling tools (MWD tools) are typically added to the drill string to provide continuous updated measurements that can be used for real-time adjustment. This data indicates whether the well is following the planned path and whether the direction of the drilling assembly is causing the well to deviate from the plan.

[0004] In some conventional drilling processes, after drilling a straight vertical wellbore section, the drill string is first pulled to replace the bottom hole assembly (BHA) used for straight drilling with a dedicated directional drilling BHA. After directional drilling until the completion of the curved section, if straight drilling is to be resumed from the end of the curved section, the straight drilling BHA and the directional drilling BHA are swapped again, and the drill string is rotated therein again.

[0005] Common drilling equipment for directional drilling includes bent sub, downhole motor, and rotary seal. When using this equipment, during the curved section of the wellbore, only the downhole part of the drill string rotates - driven by a separate motor. The non-rotating drill string further slides into the hole. In these drilling processes, the same BHA with a bent sub is used for both the straight and curved sections of the wellbore. When drilling the straight section, the drill string rotates with the bit.

[0006] Among other things, to avoid the necessary BHA interchange and / or the drill string sliding in the borehole, newer equipment includes rotary steerable systems (RSS) that can operate while the entire drill string rotates during the drilling of a curved wellbore section. These systems direct the bit towards the desired drilling direction that is inclined relative to the forward wellbore direction, or push the bit towards the desired drilling direction through an expandable thrust pad. Deviation of the wellbore in the desired direction can be achieved through the lateral cutting ability of the bit - for example, by using cutters on the side of a conventional polycrystalline diamond compact (PDC) bit in addition to the front cutters.

[0007] When using a type of bit that forms a cylindrical sidewall, drill face, and circumferentially extending gauge angle, directional drilling is typically achieved by causing the rotary drilling equipment to remove a predetermined and different amount of gauge angle material at the bottom of the wellbore in a selected angular sector during each rotation of the bit. Among them, in the desired, relatively inclined drilling direction, the amount of material removed in the angular sector is less than the amount of material removed in the remaining angular sectors at the bottom of the wellbore. Therefore, the slight lateral force exerted on the bit by the front angular sector forces the bit towards the desired direction. When this technique is continuously applied over a certain wellbore length, a curved wellbore section is produced over this wellbore length, the radius of which depends on the difference between the removal amounts at the angular sectors at the bottom of the wellbore.

[0008] Among them, the difference in the amount of material removed at the angular sectors at the bottom of the wellbore can be achieved by purposefully controlling the flow rate of the drilling fluid through the nozzles in the bit, changing this flow rate during each rotation to create a difference in the effectiveness of the bit at the angular sectors.

[0009] To achieve such control of the drilling fluid flow rate, US4637479 proposes to sequentially open and close the nozzles in the drill bit while the drill bit is rotating. During rotation of the drill string with the drill bit, on the wellbore side in the expected drilling direction, fluid communication is always possible through the nozzles outside a predetermined angular sector at the bottom of the wellbore, while fluid communication is blocked within said angular sector. Thus, the nozzles operate only outside said angular sector, thereby improving the cutting of the drill bit within said sector - and thus the path deviation of the drill bit in the expected direction - towards said angular sector.

[0010] For roller cone bits, US4211292 proposes to extend one of the nozzles to a position normally occupied by a conventional wash nozzle with a fluid injection nozzle. This extended jet nozzle injects pressurized fluid onto the gauge angle of the drilled wellbore. Pressurized fluid is selectively directed to the fluid injection nozzle only during a predetermined part interval of each drill bit rotation to increase the cutting at the bottom of the wellbore outside a selected angular sector of the wellbore and to deflect the wellbore towards said angular sector.

[0011] GB2284837 discloses a roller cone bit with three nozzles between the cones, one of which is adapted to direct the fluid of the drilling fluid to the corners of the drill bit face to make the fluid asymmetric with respect to the drill bit. The flow rate of the drilling fluid is pulsed and synchronized with the rotational frequency of the adapted nozzle. Thus, when the adapted nozzle is azimuthally oriented - that is, at an angular position with respect to an axis tangentially oriented along the center through the wellbore at the bottom of the wellbore - outside a selected angular sector of the wellbore, the fluid flow rate is high, while for the remaining part of the drill bit rotation - deflecting the path of the drill bit towards the selected angular sector, the fluid flow rate is low.

[0012] Specific systems for straight and directional drilling use abrasive particles mixed with the drilling fluid to remove material at the end of the wellbore. Such systems include jet devices for generating an abrasive jet of the mixture and ejecting said jet into an impact with an object within an impact area at the bottom of the wellbore, especially at the gauge angle of the wellbore, thereby (further) eroding the object in the impact area. A longitudinal channel is provided in the drill string for conveying the drilling fluid mixture including abrasive particles to the drill bit.

[0013] These systems can be used to achieve directional drilling by synchronizing the erosion force of the abrasive jet (e.g., by adjusting the velocity of the abrasive particles and / or its mass flow rate during drill bit rotation) with the rotational speed of the drill bit.

[0014] The abrasive jet can be used in combination with mechanical cutters, for example, in addition to wash nozzles, also through abrasive jet nozzles on PDC or tricone drill bits, thereby achieving drilling by both cutting and abrasive jet.

[0015] Abrasive jets can in particular be applied in a special abrasive jet drill bit mounted at the lower end of a drill string. Such a drill bit comprises injection means and one or more nozzles, the injection means being arranged to generate an abrasive jet in an injection direction and to impinge on an object in an impact area, the one or more nozzles guiding the jet - the drill bit having no mechanical cutting tools, whereby drilling is achieved solely by means of said impact.

[0016] The abrasive jet applied in a combined or dedicated system can advantageously contain magnetic abrasive particles, such as only magnetic particles. For example, these particles can have the form of steel shot. The use of magnetic abrasive particles enables improved control of the flow rate of the abrasive particles by using a magnetic field acting on said particles.

[0017] Generally, these particles are ferromagnetic (e.g., martensitic steel) and have a remanent magnetization, especially considering the transportability through a generally ferromagnetic conduit (e.g., drill pipe).

[0018] The control improved by magnetism advantageously enables a downhole recycling system for abrasive particles, wherein, after the abrasive particles have been subjected to an erosive impact, magnets provided in the drill string above the drill bit (e.g., in a sub-bit) capture the particles from the return flow of the drilling fluid and particles towards the surface, said return flow flowing upwards between the drill string and the well wall. After being captured, the abrasive particles are transported downhole through the drill string to a mixing location, at which the abrasive particles are remixed with a fresh mixture of drilling fluid and abrasive particles supplied from the surface through the drill string.

[0019] WO2008 / 119821 discloses such a recycling system, which uses static magnets for capturing and transporting abrasive particles. Such magnets attract the abrasive particles from the return flow above the magnet, and then these abrasive particles move again along an inclined plane in the direction of the drill bit, in order to subsequently be mixed in a mixing chamber with a fresh mixture of drilling fluid and abrasive particles supplied through the drill string.

[0020] The magnetic field can also be used to control the erosive force of the abrasive particles, for example by the velocity and / or mass flow rate of the abrasive particles, and thus for achieving its directional drilling and directional control by selectively changing the erosive force along the impact area.

[0021] The prior art discloses several solutions for manipulating the erosive force of magnetic abrasive particles along the impact area for directional drilling.

[0022] The system disclosed in WO2005 / 005767 utilizes the magnetic field of its recycling system for magnetic abrasive particles to regulate the erosion force of the abrasive jet. Among them, the magnets of the recycling system are arranged as a rotatable conveyor that attracts abrasive particles to be recovered on its upper side and transports these abrasive particles to the mixing chamber. The regulating device in the form of a controllable drive of the conveyor is arranged to regulate the recycling rate synchronously with the rotational speed of the nozzle of the drill bit, thereby regulating the number of abrasive particles in the abrasive jet at the jetting device. Therefore, the erosion force varies along the angular sectors at the bottom of the wellbore. Reference is also made in this regard to WO2005 / 05766.

[0023] This prior art solution is not entirely satisfactory because the regulation is based on and thus requires the presence of a rotatable magnetic conveyor in the recycling system. Maintaining a rotating magnetic field downhole not only consumes a large amount of energy but is also disadvantageous for components that need to move continuously at that location, which can damage the robustness of the system. In view of the latter, in a directional drilling system using magnetic abrasive particles, it will generally be more preferable to use the recycling system with static magnets disclosed in WO2008 / 119821. However, this will remove the possibility of such regulation.

[0024] To solve this problem, US2012 / 0255792 and US20130292181 propose to regulate the erosion force of abrasive particles independently of the recycling system. The disclosed systems regulate the concentration of magnetic abrasive particles in the mixture in the case of supplying drilling fluid to the nozzle.

[0025] The system of US2012 / 0255792 achieves this in a dedicated abrasive jet drill bit with a single nozzle by capturing magnetic particles on a magnetically activated particle collection surface. The collection surface is arranged along the channel through which the drilling fluid mixture leads to the drill bit. The magnetic field on the collection surface is manipulated such that the surface sequentially captures magnetic particles from the fluid mixture and releases these magnetic particles into the fluid mixture. The nozzle rotates at a selected rotational frequency, and the regulation of the supply concentration by the way of capturing and releasing particles on the collection surface is regulated at a regulation frequency equal to the rotational frequency or an integer part of the rotational frequency. Therefore, a single jet nozzle can selectively jet a reduced or increased concentration of abrasive particles at a specific angular position in the wellbore.

[0026] However, this solution also turns out to be unsatisfactory. Magnetic abrasive particles usually move at a relatively high speed, especially at speeds far higher than 2 m / s. Therefore, in such a case for capturing particles, the system still requires a high energy supply. In addition, capturing particles requires a relatively long interaction length.

[0027] The system of US20130292181 provides alternative solutions, including multiple nozzles in the drill bit. The magnetic abrasive particles are transferred geosynchronously by a controlled magnet or other means, in particular by sequentially aligning the supply channels of each nozzle and the outlets of the geosynchronous deflectors along each rotation of the drill bit.

[0028] This solution has similar drawbacks to US2012 / 0255792. When the drill bit rotates, in order to make the diversion geosynchronous, the deflector must compensate for the rotation of the drill bit with nozzles. This requires advanced control mechanisms within the bearings and rotating tubes. In addition, the energy required for rotational compensation still unfavorably requires a high energy supply.

[0029] In summary, in order to achieve a controlled flow of drilling fluid (e.g., drilling fluid mixed with abrasive particles, such as magnetic abrasive particles) for directional drilling, currently known techniques thus require significant modifications to conventional drill bits, such as nozzle modifications (e.g., US4211292, GB2284837) or the implementation of rotary seals and / or bearings (e.g., US4637479, US2012 / 025792, US20130292181), and / or an undesirably high energy requirement for downhole components (e.g., WO2005 / 005767, US2012 / 0255792, US20130292181).

[0030] The modifications are not desirable because this reduces the drill rig's choice of drill bits and requires the use of such drill bits even in the straight sections of the wellbore trajectory. In addition, modifying the nozzles in a conventional drill bit will reduce the overall drilling performance, and clogging the nozzles (e.g., US4637479, US4211292) will also reduce the overall drilling performance. Rotary seals and bearings are prone to damage and are thus not an ideal choice for downhole components. Using actively moving components, especially rotating components, downhole is not a preferred option because it makes the system more vulnerable (e.g., WO2005 / 05766, US20130292181).

[0031] The high energy requirement for downhole components requires a downhole power source, for example, in the form of a battery or a downhole generator. Considering the harsh downhole environment, this is a tricky complication for any system. Summary of the Invention

[0032] A first object of the present invention is to provide at least one alternative to currently known directional drilling systems and methods.

[0033] A second object of the present invention is to provide a controlled flow of abrasive particles (e.g., magnetic abrasive particles) in the drilling fluid for directional drilling, which forms a suitable alternative to currently known systems and methods.

[0034] A third object of the present invention is to provide a system and method for establishing a controlled flow of abrasive particles (e.g., magnetic abrasive particles) in the drilling fluid of a directional drill hole, which is more robust than currently known systems and methods.

[0035] A fourth object of the present invention is to provide a system and method for establishing a controlled flow of magnetic abrasive particles in the drilling fluid of a directional drill hole, which involves a lower downhole energy supply than currently known systems and methods.

[0036] To this end, in a first aspect, the present invention provides the method according to claim 1 and the system according to claim 11.

[0037] The method for directional drilling of a wellbore according to the present invention comprises:

[0038] - providing a drill bit connected to the lower end of a drill string and comprising:

[0039] - a drill bit face which faces the bottom of the wellbore during use,

[0040] - one or more abrasive jet nozzles configured to direct a flow of drilling fluid mixed with abrasive particles to impact the bottom of the wellbore in the form of an abrasive jet, and if plural, the abrasive jet nozzles are arranged at different adjacent azimuthal positions,

[0041] - an intermediate space between the drill bit fluid inlet of the drill bit and the one or more abrasive jet nozzles,

[0042] Each of the one or more abrasive jet nozzles has a nozzle inlet for fluid communication with the intermediate space, and each nozzle inlet extends from the intermediate space;

[0043] - upstream of the drill bit fluid inlet, passing a flow of drilling fluid mixed with abrasive particles through a supply channel having a supply channel outlet at a substantially constant supply rate,

[0044] - simultaneously, rotating the drill bit at a rotational speed so as to rotate the one or more abrasive jet nozzles, and while passing the flow of drilling fluid mixed with abrasive particles through the supply channel outlet and the drill bit fluid inlet, continuously passing the flow through the intermediate space, the one or more nozzle inlets, and the one or more abrasive jet nozzles to impact the bottom of the wellbore, thereby deepening the wellbore; and

[0045] - during rotation of the drill bit and while passing a flow of drilling fluid mixed with abrasive particles, varying the concentration of the abrasive particles along a subsequent flow portion of the flow passing through the abrasive jet nozzles of the drill bit such that the concentration of the abrasive particles is alternately higher in a first flow portion and lower in a subsequent second flow portion.

[0046] According to the present invention, varying the concentration of abrasive particles in the flow of a drilling fluid mixed with abrasive particles includes:

[0047] - upstream of the drill bit fluid inlet, subsequently causing the flow to pass parallelly through a first channel and a second channel from the supply channel outlet to a first outlet and a second outlet respectively, and alternately entering the drill bit fluid inlet from the first outlet and the second outlet,

[0048] - during a first time period, deflecting a majority of all the abrasive particles in the flow passing through the supply channel outlet into the first channel, and

[0049] during a second time period after the first time period, not deflecting a majority of all the abrasive particles in the flow passing through the supply channel outlet into the first channel, and

[0050] - subsequently causing the flow to enter the one or more abrasive jet nozzles from the first outlet and the second outlet,

[0051] wherein a difference between the flow resistance of the drilling fluid mixed with abrasive particles in the first channel and the flow resistance of the drilling fluid mixed with abrasive particles in the second channel results in a difference between a first velocity of the drilling fluid mixed with abrasive particles flowing through the first channel and a second velocity of the drilling fluid mixed with abrasive particles flowing through the second channel,

[0052] wherein the difference between the first velocity and the second velocity causes, downstream of the first outlet and the second outlet,

[0053] a majority of the abrasive particles deflected into the first channel during the first time period and the abrasive particles entering the second channel during the second time period are combined with the drilling fluid entering the first channel and the second channel during the first time period and the second time period respectively to form a first flow portion, and

[0054] the abrasive particles entering the first channel during the second time period and the abrasive particles entering the second channel during the first time period after the second time period are combined with the drilling fluid entering the first channel and the second channel during the second time period and the first time period after the second time period respectively to form a second flow portion.

[0055] According to the invention claimed, the flow of the drilling fluid is split into two sub - flows. A first sub - flow through a first channel and a second sub - flow through a second channel. The first channel and the second channel have different flow resistances, whereby one of the sub - flows takes longer to pass through the corresponding channel than the other sub - flow. Further, within a time interval, the particles in the flow of the drilling fluid deflect into the first sub - flow at the inlets of the first sub - channel and the second sub - channel. Thus, within a first time period, the concentration of the particles in the first sub - flow increases, while the concentration of the particles in the second sub - flow decreases. During a subsequent second time period, the particles do not deflect into the first channel. In this way, each sub - flow is provided with flow portions having a high particle concentration alternating with flow portions having a low particle concentration.

[0056] The first time period and the second time period, and the lengths of the first sub - channel and the second sub - channel are configured such that when the sub - flows recombine into a single flow at the outlets of the first channel and the second channel, the flow portions having a high particle concentration of the first sub - flow at least partially, preferably substantially completely, overlap with the flow portions having a high particle concentration of the second sub - flow. Thus, the single flow resulting from the combination of the first sub - flow and the second sub - flow also includes flow portions having a low particle concentration alternating with flow portions having a high particle concentration, wherein the high particle concentration is greater than the particle concentration in the flow before it was split into two sub - flows, and the low particle concentration is less than the particle concentration in the flow before it was split into two sub - flows.

[0057] In addition, the deflection is timed such that the increase in the concentration of the abrasive particles is synchronized with the rotation of the drill bit. More specifically, when one or more abrasive jet nozzles (more specifically, the flow through said one or more abrasive jet nozzles) are directed towards a part of the wellbore (more specifically, the bottom of the wellbore), the deflection is timed such that the abrasive particles with an increased concentration flow through one or more abrasive jet nozzles, which requires an enhanced erosive force to generate a deflection in the drilling direction and thus generate a curved wellbore trajectory.. In a preferred method, during the second time period, the particles deflect into the second channel, thereby increasing the particle concentration in the second sub - flow, and do not deflect into the first channel, thereby decreasing the particle concentration in the first sub - flow.

[0058] Thus, according to the present invention, by passing a drilling fluid comprising abrasive particles through two channels having different flow resistances and by controlling the periodic passage of the majority of the abrasive particles through one of the two channels, preferably by controlling the alternating passage of the majority of the abrasive particles through the first channel and the second channel, flow portions having alternating high and low concentrations of abrasive particles are produced.

[0059] In an embodiment of the method according to the present invention, varying the concentration of the abrasive particles in the flow of the drilling fluid mixed with the abrasive particles comprises:

[0060] - During a first time period, deflect a first major portion of all abrasive particles in the flow through the supply passage outlet into a first channel, and

[0061] - During a second time period after the first time period, deflect a second major portion of all abrasive particles in the flow through the supply passage outlet into a second channel, and

[0062] - Subsequently, cause the flow to enter the abrasive jet nozzle from a first outlet and a second outlet.

[0063] Wherein, the difference between the first speed and the second speed causes, downstream of the first outlet and the second outlet, the first major portion and the second major portion that are deflected into the first channel during the first time period and into the second channel during the second time period to combine with the drilling fluid that enters the first channel and the second channel during the first time period and the second time period respectively to form a first flow portion. A small amount of non-deflected abrasive particles combine with the drilling fluid that enters the first channel and the second channel during the second time period and the first time period respectively to form a second flow portion.

[0064] Therefore, according to this embodiment of the present invention, by controlling the majority of abrasive particles to deliberately alternate through two channels with different flow resistances, flow portions with alternately high and low concentrations of abrasive particles are generated, whereby the speed differences generated by the majority of the two channels through the channels cause them to meet downstream of the channel outlet. Then, the combined two major portions form a high-concentration pulse of abrasive particles within the high-concentration flow portion. The remaining small amount of particles that are not deliberately introduced into the two channels in the two channels combine downstream of the channel outlet into a low-concentration pulse within the low-concentration flow portion. In this way, in the flow continuously reaching the abrasive nozzle of the drill bit downstream of the channel, the high-concentration flow portion and the low-concentration flow portion alternate with each other.

[0065] In the method of the present invention, the generation of the pulse is based on the following principle: Assuming that the pressure drops across the two channels are equal, the starting position of the abrasive particles released into the first channel during the first time period is after a certain length of the first channel and the second channel that is compensated by the greater speed of the subsequent abrasive particles relative to the abrasive particles subsequently released into the second channel during the second time period. Thereby causing the two flow portions passing through the first channel and the second channel to merge again downstream of the channel into a single flow moving at a single speed, and thus combining the abrasive particles released into the first channel and the second channel in the single flow to flow together as a single pulse in the high-concentration flow portion to the drill bit and into the nozzle.

[0066] By adopting this working principle, the present invention provides an alternative to known systems that adopt other working principles.

[0067] Embodiments are envisioned in which deflection is controlled such that the flow through the drill bit includes flow portions having more than two abrasive particle concentration levels. For example, a first flow portion having a high concentration, a second flow portion having a low concentration, and a third flow portion having a concentration intermediate the concentrations of the first and second flow portions. For example, subsequently repeating the generation of the first flow portion, the third flow portion, the second flow portion, and the third flow portion may result in an abrasive particle concentration through the drill bit that is closer to a sine wave. In an embodiment, the time periods of deflection into a first channel, no deflection into any channel, and deflection into a second channel are applied to generate the first, second, and third flow portions.

[0068] The particle concentration in an alternating flow of drilling fluid and abrasive particles can be repeated a number of times, for example continuously during a directional drilling operation, to alternate the particle concentration in the flow through the drill bit during bit rotation.

[0069] Since the present invention provides pulses of high-concentration abrasive particles generated upstream of the drill bit—and thus upstream of the nozzles—the present invention advantageously does not require significant modification of its drill bit or nozzles and does not involve any clogging of the nozzles. In addition, the dependence of the selection of the drill bit of the drilling rig on the method of guiding the particles can be reduced, and the overall drilling performance remains at a high level.

[0070] Compared with currently known solutions, the pulses generated upstream of the drill bit—and thus upstream of the nozzles—further enable the energy-consuming components for this purpose to be located further away from the bottom of the wellbore and involve fewer moving—especially rotating—components and the components that facilitate this movement. This can reduce the overall vulnerability of the downhole system and thus improve its robustness.

[0071] According to the present invention, the drill bit can be a mechanical drill bit, such as a PDC drill bit or a roller cone drill bit. Wherein, the drill bit further includes one or more cleaning nozzles on the bit face. Wherein, the rotation of the drill bit involves, after the abrasive flow passes through the abrasive jet nozzle, mechanically cutting the bottom of the wellbore through the mechanical drill bit, especially through the mechanical cutting tools arranged on the bit face, to deepen the wellbore. The drill bit can also be an abrasive jet drill bit without any cleaning nozzles.

[0072] It should be noted that the term "deepen" includes extending the wellbore in all directions, that is, it also includes extending the wellbore in a substantially horizontal direction.

[0073] Variations in the abrasive particle concentration, in the form of alternating high and low concentration portions within the drilling fluid, can be advantageously generated consistently along the angular sectors of the wellbore bottom that are impacted by the abrasive particles within the flow portion as the drill bit rotates. By adjusting the timing of these high concentration flow portions through the abrasive jet nozzles to the rotational speed of the drill bit, and thus to the rotational speed of the abrasive jet nozzles, an impact of the high concentration flow portion with a specific angular sector of the wellbore bottom can be achieved, that is, the high concentration flow portion passes through the abrasive jet nozzle when being directed to a specific angular sector of the wellbore, and an impact of the low concentration flow portion with another angular sector of the wellbore bottom can be achieved, that is, the low concentration flow portion passes through the abrasive jet nozzle when being directed to other angular sectors. The adjustment means that the frequency is set to correspond to the number of rotations of the drill bit per unit time, or is an integer part of the number of rotations of the drill bit per unit time.

[0074] In an embodiment of a method employing this principle, a first flow portion and a second flow portion pass through one or more abrasive jet nozzles with timing synchronized to the rotational speed of the drill bit. The first flow portion passes through the abrasive jet nozzle when the abrasive jet nozzle is directed to a selected angular sector of the wellbore bottom, and the second flow portion passes through the abrasive jet nozzle when the one or more abrasive jet nozzles are not directed to the selected angular sector of the wellbore bottom.

[0075] The present invention further provides a directional drilling system for implementing the method according to the present invention.

[0076] In an embodiment of such a directional drilling system, the directional drilling system is for directional drilling of a wellbore using the wellbore bottom in an object, such as a soil layer, such as a subsurface soil layer, the directional drilling system can be connected to a tubular drill string, and the directional drilling system includes a drill bit and a sub.

[0077] The drill bit includes:

[0078] - a bit face that faces the wellbore bottom during use,

[0079] - a bit fluid inlet,

[0080] - one or more abrasive jet nozzles configured to eject a flow of drilling fluid mixed with abrasive particles in the form of an abrasive jet for impact with the wellbore bottom, and if plural, the one or more abrasive jet nozzles are arranged at different azimuthal positions, and

[0081] - an intermediate space between the bit fluid inlet and the one or more abrasive jet nozzles, each of the one or more abrasive jet nozzles having a nozzle inlet for fluid communication with the intermediate space, and each of the nozzle inlets extending from the intermediate space.

[0082] The well bottom end of the joint is connected to or can be connected to a drill bit, for example, so as to be able to rotate with the drill bit, and the other end of the joint is connected to a tubular drill string. The joint includes:

[0083] - A joint fluid inlet, which can be fluidly connected to a supply channel through the drill string to receive a flow of drilling fluid mixed with abrasive particles from the supply channel when the system is connected to the drill string, and

[0084] - A joint fluid outlet, which is fluidly connected or can be connected to a drill bit fluid inlet.

[0085] According to the present invention, the joint further includes an adjustment unit that is fluidly connected downstream thereof to the joint drill bit inlet, and the adjustment unit is configured to vary the concentration of abrasive particles along a flow portion of the flow received from the supply channel, and the flow portion then enters the drill bit fluid inlet through the joint drill bit fluid outlet.

[0086] The adjustment unit includes:

[0087] - A first channel having a first flow resistance to the drilling fluid mixed with abrasive particles, a first inlet, and a first outlet fluidly connected to the joint drill bit fluid outlet,

[0088] - A second channel arranged in parallel with the first channel and having a second flow resistance to the drilling fluid mixed with abrasive particles, a second inlet, and a second outlet fluidly connected to the joint drill bit fluid outlet,

[0089] - A particle deflection device between the joint drill bit fluid inlet and the first inlet and the second inlet, the particle deflection device including one or more actuators and being connected to a control unit of the system,

[0090] The particle deflection device is configured to periodically, preferably based on a control signal received from the control unit,

[0091] - In a first time period, deflect most of all the abrasive particles received from the supply channel through the joint drill bit fluid inlet into the first inlet, and

[0092] - In a second time period after the first time period, cause most of all the abrasive particles in the flow received from the supply channel through the joint drill bit fluid inlet not to be deflected into the first inlet.

[0093] The first channel and the second channel are configured such that the difference between the first flow resistance and the second flow resistance results in a velocity difference between the drilling fluid mixed with abrasive particles passing through the first channel and the drilling fluid mixed with abrasive particles passing through the second channel.

[0094] The velocity difference causes abrasive particles deflected into the first channel in the first time period and abrasive particles entering the second channel in the second time period in the combined section downstream of the first and second outlets to combine with any of the drilling fluids entering the first and second channels in the first and second time periods respectively to form one of the flow portions, and abrasive particles entering the first channel in the second time period and abrasive particles entering the second channel in the first time period after the second time period combine with any drilling fluids entering the first channel in the second time period and entering the second channel in the first time period after the second time period respectively to form a subsequent one of the flow portions.

[0095] Accordingly, in accordance with the present invention, by passing a drilling fluid including abrasive particles through two channels having different flow resistances and by controlling the majority of the abrasive particles to periodically pass through one of the two channels, preferably by controlling the majority of the abrasive particles to alternately pass through the first channel and the second channel, flow portions with alternately high and low abrasive particle concentrations are produced.

[0096] In a preferred system, in the second time period, the particles are deflected into the second sub-channel, thereby increasing the particle concentration in the second sub-flow while reducing the particle concentration in the first sub-flow. In such a system, the control unit and the deflector are configured to

[0097] - in the first time period, deflect a first majority of all the abrasive particles in the flow passing through the outlet of the supply channel into the first channel, and

[0098] - in the second time period after the first time period, deflect a second majority of all the abrasive particles in the flow passing through the outlet of the supply channel into the second channel, and

[0099] - then cause the flow to enter the one or more abrasive jet nozzles from the first and second outlets.

[0100] Wherein, the velocity difference causes abrasive particles deflected into the first channel in the first time period and abrasive particles entering the second channel in the second time period in the combined section downstream of the first and second outlets to combine with any of the drilling fluids entering the first and second channels in the first and second time periods respectively to form one of the flow portions, and abrasive particles entering the first channel in the second time period and abrasive particles entering the second channel in the first time period after the second time period combine with any drilling fluids entering the first channel in the second time period and entering the second channel in the first time period after the second time period respectively to form a subsequent one of the flow portions.

[0101] Thus, according to the present invention, by controlling a majority of the abrasive particles to deliberately alternate through two channels having different flow resistances, flow portions having alternately high and low concentrations of abrasive particles are produced, whereby a velocity difference generated by the majority of the two channels as they subsequently pass through the channels causes them to meet downstream of the channel outlets. Then, the two majorities combine to form a high-concentration pulse of abrasive particles within the high-concentration flow portion. The remaining small amount of particles that do not deliberately enter the two channels in the two channels combine downstream of the channel outlets into a low-concentration pulse within the low-concentration flow portion. In this way, in the flow that continues downstream of the channels to reach the abrasive nozzle of the drill bit, the high-concentration flow portion and the low-concentration flow portion alternate with each other.

[0102] In an embodiment of the system, the adjustment of the timing of these high-concentration flow portions passing through the abrasive jet nozzle is achieved by the configuration of the control unit and is thus adjusted to the rotational speed of the drill bit and, accordingly, to the rotational speed of the abrasive jet nozzle. The control unit is configured such that the signals from the control unit received by the particle deflection device cause the actuator of the particle deflection device to deflect the first and second majorities of the particles into the first and second channels for a period of time synchronized with the rotational speed of the drill bit, such that a subsequent one of the flow portions passes through one or more abrasive jet nozzles while the abrasive jet nozzle is directed to a selected angular sector at the bottom of the wellbore together with any of the drilling fluid entering the first and second channels during the first and second time periods, respectively, and a subsequent one of the flow portions passes through one or more abrasive jet nozzles while the abrasive jet nozzle is not directed to the selected angular sector at the bottom of the wellbore.

[0103] By adjusting the concentration variation of the abrasive particles, as described previously with respect to the prior art, the erosive force of the high-flow and low-flow portions is adjusted. Thus, in the described embodiment, the erosive force of the flow is relatively high within the selected angular sector and low outside the selected angular sector at the bottom of the wellbore. Therefore, within the selected angular sector, the wellbore is deepened at a faster rate than outside it, resulting in a deviation of the drilling direction from the selected angular sector.

[0104] The concentration variation along the subsequent flow portions can be continuous during a certain number of rotations of the drill bit, whereby the first and second flow portions are alternately produced and ejected through the abrasive jet nozzle, and when the frequency of the produced flow portions is equal to the frequency of the drill bit rotation, the concentration variation occurs during each rotation; or when the frequency of the produced flow portions is equal to an integer part of the frequency of the drill bit rotation, the concentration variation occurs during one of multiple rotations, for example, during every second, every third, every fourth, etc. rotation. The lower the ejection frequency of the high-concentration flow portion, the smaller the drilling difference, that is, the smaller the difference in drilling speed between the inner bend and the outer bend of the curved wellbore section being drilled, or vice versa. Therefore, the frequency can be adjusted to regulate the drilling difference.

[0105] As an example, as required for a pure abrasive jet drilling system with a single nozzle, the concentration of abrasive particles in the stream reaching the drill bit can be constant (i.e., 100% of the supplied abrasive concentration) and vary sinusoidally over time. If a desired directional effect is expected to be achieved through a 4% hole-making difference, i.e., the rate of rock removal on one side of the wellbore is 4% faster than on the other side of the hole, the steering joint is adjusted to produce a constant 100% abrasive concentration with a sinusoidal vibration of 2% amplitude superimposed thereon. Alternatively, an amplitude of 4% can be used every second bit rotation, or an amplitude of 8% can be used every fourth bit rotation, and so on.

[0106] It is also conceivable that, in order to adjust the hole-making difference, for example, a first high-concentration stream portion and a second low-concentration stream portion can be ejected at each rotation of the drill bit for a number of rotations, and then the sinusoidal variation along the ejected stream portions is stopped for a number of rotations. Deflection during a number of rotations can only be further used to correct or fine-tune the steering action.

[0107] The hole-making difference can be further adjusted by adjusting the concentration of abrasive particles in the stream upstream of the deflection of the majority of the abrasive particles. For example, in the case of mechanical drilling, where the continuous hole-making action can come from mechanical rock cutting and all the steering action can come from the change in the concentration of abrasive particles in the abrasive jet, the steering action can be reduced, for example, by a factor of 4 by reducing the supplied abrasive concentration by a factor of 4 or, for example, by reducing the amplitude of the abrasive concentration fluctuation by a factor of 4. If the control unit (e.g., downhole control unit) obtains direct feedback on the variation of the abrasive concentration over time, including the concentration difference, the control unit can automatically respond to any change in the abrasive concentration of the stream supplied from the supply channel.

[0108] The portions of the abrasive particles exiting the supply channel and deflected into the first channel and the second channel during a first time period and a second time period respectively determine the concentration difference of the abrasive particles between the first stream portion and the second stream portion. Thereby, it determines the difference in the erosive force of the abrasive jet in the selected first angular sector and the second angular sector at the bottom of the wellbore, and thus determines the hole-making difference. At least the majority of the particles should be deflected into the first channel during the first time period to achieve the concentration difference. Preferably, the majority of the particles are deflected into the first channel and the second channel during the first time period and the second time period respectively to achieve the concentration difference.

[0109] If the first major portion of the particles and the second major portion of the particles are deflected into the first channel and the second channel during a first time period and a second time period, respectively, the first major portion and the second major portion contain at least 50% and at most 100% of the abrasive particles in the streams received from the supply channel during the first time period and the second time period, respectively, so as to achieve a concentration change between subsequent stream portions downstream of the first outlet and the second outlet. This means that the concentration of abrasive particles in the high-concentration stream portion (i.e., the first stream portion) is higher than 100% and at most 200% of the concentration of abrasive particles upstream of any deflection of the abrasive, while the concentration of abrasive particles in the low-concentration stream portion (i.e., the second stream portion) is less than 100%.

[0110] In the case of pure abrasive jet drilling, for example using a dedicated abrasive jet bit, the concentration difference of the abrasive particles between the first stream portion and the second stream portion is preferably much less than 200% of the concentration of the abrasive particles upstream of the deflection, so as to achieve continuous forward drilling - since the deepening of the wellbore is achieved only by the erosive force of the abrasive jet. This means that the concentration in the first high-concentration stream portion should be less than 200% of the concentration in the stream before deflection, while the concentration in the second low-concentration stream portion should be greater than 0%. Ultimately, the second stream portion should still have a certain erosive force to form the inner bend of the wellbore.

[0111] In particular, in the case of pure abrasive jet drilling, the steering action can be achieved by a concentration difference between the first stream portion and the second stream portion that is 50% lower than the concentration of the abrasive particles upstream of the deflection, e.g., 0% to 40%, so as to achieve a favorable ratio of drilling rates between the inner bend and the outer bend. In an exemplary steering action, the concentration difference is about a few percentage points, e.g., 2% - 10%. For example, in the case of a concentration difference of 8%, this means that the concentrations of the first stream portion and the second stream portion are 104% and 96%, respectively, and the major portion contains 52% of the abrasive particles in the stream received from the supply channel. For example, in another case, for a large steering action of a 10 cm diameter wellbore's curved trajectory along a radius of more than 10 m, using pure abrasive jet drilling, a concentration change of 4% between the first stream portion and the second stream portion is sufficient. Short-radius sidetracking forms an application of abrasive jet drilling and may require constructing a portion with a curved radius less than 10 m, and the operator may desire a concentration change of around 10% between the first stream portion and the second stream portion.

[0112] In the case of a combination of mechanical drilling and abrasive jet drilling, for example using a PDC or roller cone bit with one or more abrasive jet nozzles, the concentration difference can be up to 200% - the value of the concentration difference depends on the relative contribution of the abrasive jet and the tool to the drilling rate. Generally, the abrasive jet is only used to produce a steering effect in this case and the value is preferably as close as possible to 200%, the value changing from the deflection of the abrasive received from the supply channel to as close as possible to 100%. In particular, 70% to 100% of the abrasive particles are deflected into the channels, resulting in a concentration difference between the first flow portion and the second flow portion of between 80% and 200%. In a practical embodiment, approximately 80% of the abrasive particles are deflected, whereby the concentrations of the first flow portion and the second flow portion are 160% and 40% respectively of the flow received from the supply channel, and the concentration difference is 120%.

[0113] The hole-making difference is approximately the ratio between the radius of the hole and the radius of curvature of the curved wellbore section. As an example, in the case of a radius of curvature of 5 m and a bit radius of 5 cm, a hole-making difference of 0.5% - 2% is sufficient.

[0114] After the curved wellbore section of the directional drill, when drilling a straight wellbore section, it is possible to completely stop the deflection of most of the inlet channels while continuing to pass the flow and rotate the bit, whereby the concentration of abrasive particles is substantially constant along each rotation of the bit. When operating the system according to the invention, the regulating device can be switched off to achieve this - for example, by stopping the power supply to the regulating device. When using a mechanical bit, it is also possible to completely stop the supply of abrasive particles when drilling a straight wellbore section, but it is preferably to continue the supply of abrasive particles (e.g., at a relatively low concentration) while stopping the deflection.

[0115] In one embodiment, the deflection of abrasive particles into the first and second channels is achieved by mechanical means (e.g., a mechanical barrier).

[0116] In particular, the deflection can be achieved by strain. Wherein, one or more movable filters can be provided upstream of the first and second inlets, which are adapted to allow any drilling fluid in the flow to pass through, while reducing or preventing the entry of abrasive particles into the first and second channels respectively during a first time period and a second time period, so that they alternately move along the cross-section of the outlet of the supply channel to cover the first and second channels respectively. The movement can be in the form of pivoting or sliding, for example.

[0117] In another example, a movable chute-shaped or funnel-shaped element may be arranged directly upstream of the first and second inlets, which covers a part of the cross-section of the flow and is adapted to deflect at least most of the abrasive particles passing through the first and second channels by guiding the flow of abrasive particles along its guiding surface while avoiding the drilling fluid behind it, the guiding surface moving alternately towards the first and second channels during a first time period and a second time period, respectively, such as by sliding or pivoting.

[0118] In an embodiment employing a mechanical deflection device, the first and / or second inlets may be moved radially relative to the supply channel outlet, e.g., the first and / or second channels may be moved as a whole relative to the supply channel outlet. In these examples, the particle deflection device may be passive, i.e., continuously moving the particles in a specific direction while actively supporting the first and / or second inlets, i.e., the first and / or second channels are movably supported at their inlet ends and the inlets of the first and / or second channels are moved into and out of the flow of particles deflected by the particle deflection device.

[0119] In one embodiment, the first and / or second channels are movably supported at their inlet ends and the particle deflection device includes a particle concentrating device which is arranged directly upstream of at least the first inlet and between the supply channel outlet and the channel inlet. The concentrating device deflects the particles received from the supply channel such that the supply concentration of the abrasive particles in a first cross-sectional part of its outlet is higher than in a second cross-sectional part of the outlet. The concentrating device may utilize a sieve or filter and / or a magnetic field for deflecting the particles towards the second cross-sectional part of the outlet.

[0120] The relative radial movement of at least the first inlet, and optionally also the second inlet, relative to the first and second cross-sectional parts of the concentrating device causes a reduction or increase in the cross-sectional part of the corresponding inlet within the contours of the first and second parts of the outlet of the concentrating device, whereby the corresponding inlet receives a higher or lower concentration of particles. In one example, the relative radial movement is achieved by moving at least the first inlet radially relative to the first and second parts of the concentrating device outlet. In another example, in addition to or instead of the radial movement of the channel inlet, the radial movement is achieved by moving the concentrating device radially relative to at least the first inlet.

[0121] In one embodiment, the relative radial movement is actively driven by an actuator mechanism of the deflection device.

[0122] The concentrating device includes an inlet and an outlet, the inlet being fluidly connected to the outlet of the supply passage for receiving a flow of drilling fluid mixed with abrasive particles from the supply passage. The concentrating device is configured to deflect most of the abrasive particles of the supply flow to a first portion of the outlet and a minority of the abrasive particles to a second portion of the outlet, such that the concentration (and thus the flow rate) of the abrasive particles is higher in the first portion of the outlet and lower in the second portion of the outlet. For example, such a concentrating device is a filter. In fact, the concentrating device may form an extension of the supply passage.

[0123] In one embodiment, the first passage is movable such that its inlet is in a first position, in which the first passage is at least partially radially within the profile of the first portion of the outlet of the concentrating device during a first time period, for example axially aligned with the first portion, such that the first inlet receives a high concentration of abrasive particles of the supply flow. The first passage is further movable such that, during a second time period, its inlet is in a second position, in which the first passage is at least partially radially outside the profile of the first portion of the outlet of the concentrating device during the second time period, for example not axially aligned therewith, such that the first inlet does not receive or receives fewer high-concentration (and thus high-flow rate) abrasive particles of the supply flow, and thus receives a lower concentration of abrasive particles. For example, the first inlet is in a second position at least partially within the profile of the second portion of the cross-section of the outlet of the concentrating device during the second time period so as to receive a lower concentration of abrasive particles of the supply flow.

[0124] In one embodiment, the first passage or at least its inlet end may pivot about a radial extension axis away from the inlet to move the first inlet between the first position and the second position. In one embodiment, the first passage may be translated radially to move the first inlet between the first position and the second position.

[0125] In an embodiment, similar to the first passage, the second passage is movable to receive low-concentration particles during a first time period and high-concentration particles during a second time period.

[0126] In one example, the second passage may move simultaneously with the first passage, for example together, such that, at the second position of the first inlet, the second inlet is at least partially radially within the profile of the first portion of the cross-section of the outlet of the concentrating device during the second time period, for example axially aligned with the first portion. The effect of this is that the first passage and the second passage alternately - during the first time period and the second time period - receive high-concentration abrasive particles of the supply flow.

[0127] In an alternative embodiment, the supply channel (e.g., its downstream portion, e.g., its outlet, e.g., provided with a concentrator) can be moved relative to the first and second channels for alternately introducing high-concentration particles and low-concentration particles into the first and second channels. In one example, to this end, the concentrating device is movable.

[0128] In one embodiment, the first and second portions of the concentrator outlet are adjacent portions of the cross-section - one portion does not surround the other portion. In another embodiment, the first portion of the concentrator outlet is radially surrounded by the second portion of the concentrator outlet, e.g., the first and second portions are concentric.

[0129] In an embodiment where the first portion of the concentrator outlet is radially concentrically surrounded by the second portion of the concentrator outlet, the first channel is correspondingly arranged within the second channel such that the inlet of the first channel is radially surrounded by the second channel and is concentric with the second channel at a first position of the first channel. Thus, at the first position of the first channel, the first channel is axially aligned with the first portion of the concentrator outlet. Wherein, the actuator mechanism of the deflection device is preferably arranged in the second channel and is configured to move the first channel between a first position and a second position of its inlet, e.g., configured to pivot the first channel about a pivot axis radially extending axially away from its inlet (e.g., near the outlet of the first channel). Thus, at the second position of the inlet of the first channel, the first channel is eccentrically arranged within the second channel and is not axially aligned with the first portion. At least a smaller portion (preferably, no portion at all) of the inlet of the first channel is within the contour of the first portion, and at least a larger portion of the inlet of the first channel is within the contour of the second cross-sectional portion of the concentrator outlet to receive abrasive particles of a lower-concentration stream. At the same time, at the second position of the first inlet, the first channel is eccentrically arranged within the second channel such that at least a smaller portion of the second inlet is within the contour of the second portion and at least a larger portion is within the contour of the first portion - preferably, at the second position of the first inlet, the contour of the first portion is completely radially covered by the second inlet. In this embodiment, by only moving the first channel, both the first inlet and the second inlet are moved between their first and second positions.

[0130] Another embodiment is envisioned where the particle concentrating device (e.g., not the first and second channels) is movable such that the first and second portions of the outlet are radially moved relative to the first and second inlets to a first position and a second position thereof, at the first position, the first inlet is at least partially radially within the contour of the first portion during a first time period, at the second position, the first inlet is at least partially radially outside the contour of the first portion during a second time period, thereby receiving abrasive particles of high-concentration and low-concentration supply streams, respectively.

[0131] In one embodiment, the actuator mechanism of the deflection device (in this case, configured to move the first channel within the second channel) is disposed within the second channel. In one example, the actuator mechanism includes an electric motor, such as a linear motor, which is controlled by a control unit that is directly or indirectly connected to both the first and second channels, as described herein, to drive the movement of the first channel within the second channel. The actuator mechanism may include a transfer mechanism to convert the output movement of the motor into the relative movement of the first channel.

[0132] For example, the transfer mechanism includes a cable and a cable guide fixed to either the first or second channel, with the cable extending from the motor to the first channel through the cable guide. For example, the motor is a linear motor with a linear output movement in the axial direction, and the cable guide guides the cable to engage the first channel in the radial direction, such that the operation of the linear motor pulls the first channel in the radial direction. The transfer mechanism further includes an elastic element, such as a spring, which acts between the first and second channels at a position diametrically opposite or at the same radial position where the cable engages the first channel, and counteracts the pulling effect of the cable at a certain axial distance. Wherein, the first channel preferably can pivot about a pivot axis extending radially away from its inlet (e.g., near or at its outlet), and the cable of the actuator mechanism engages the first channel at or near the first inlet. Alternatively, the first channel can be translated in the radial direction.

[0133] In another example, the transfer mechanism includes a channel wall guide coupled to the motor and an elastic element, such as a spring. In this case, the channel wall guide cooperates with the outer wall of the first channel to convert the output movement of the motor into the relative movement of the first channel. The wall guide and the first channel wall engage at complementary inclined surfaces in the axial-radial direction, such that the axial movement of the motor causes the inclined surfaces to slide along each other, thereby inducing the radial movement of the first channel. The elastic element interconnects the first and second channels at the same position or at a diametrically opposite radial position where the cable engages the first channel to counteract the pulling effect of the cable.

[0134] The present invention further relates to a mechanical actuator mechanism used in a directional drilling system according to any of the above embodiments, and a particle deflection device including such a mechanical actuator system.

[0135] In one embodiment, the deflection of particles into the first and second channels is achieved by a magnetic device, rather than or in addition to a mechanical device.

[0136] As is known in the art, in an embodiment, the abrasive particles can be magnetic abrasive particles, such as steel shots. In this case, the deflection of the abrasive particles into the first channel and the second channel is achieved by changing (e.g., reversing) the direction of the magnetic field in the cross-section of the flow immediately upstream of the first channel and the second channel, respectively, in the plane of the cross-section, in the direction towards the first channel and in the direction towards the second channel.

[0137] In an embodiment of the system according to the invention, such a magnetic field is generated by a capture device placed immediately upstream of the first inlet and the second inlet as disclosed in US2012 / 0255792.

[0138] In another preferred embodiment of the system according to the invention, the deflection into the first channel and the second channel is achieved by alternately guiding the magnetic field in the cross-section of the flow immediately upstream of the first inlet and the second inlet towards the first channel and towards the second channel in a first time period and a second time period.

[0139] The amount of energy required to create a concentration difference between subsequent flow portions depends to a large extent on the manner in which the abrasive particles are deflected. Deflecting the particles by switching the magnetic field in the cross-section advantageously reduces the energy consumption compared to using the capture device or using mechanical deflection.

[0140] Due to induction by the magnetic field in the cross-section, the magnetic abrasive particles are magnetized to adapt to the magnetic field. The induced N pole of the particle tends to move towards the S pole of the magnet generating the magnetic field, or vice versa. When the magnetic field is non-uniform, the particles tend to move towards the part of the magnetic field with a higher magnetic line density. Utilizing this principle, by establishing a magnetic field in the cross-section of the flow (the magnetic field being denser in the part covering the corresponding channel than in the other channel), the particles can be directed towards the corresponding channel in the first channel and the second channel.

[0141] In an embodiment of the method, the magnetic field is thus changed such that in a first time period, the magnetic field density in the part of the cross-section of the flow covering the first channel is higher than the magnetic field density in the part covering the second channel, and in a second time period, the magnetic field density in the part of the cross-section covering the second channel is higher than the magnetic field density in the part covering the first channel.

[0142] Embodiments of the system according to the present invention provide for an actuator of a deflection device, including a magnetic switch configured to generate a non-uniform magnetic field in a cross-section immediately upstream of a first inlet and a second inlet during a first time period, the non-uniform magnetic field guiding abrasive particles towards the first inlet in the plane of the cross-section, and during a second time period, generate a non-uniform magnetic field in a cross-section immediately upstream of the first inlet and the second inlet, the non-uniform magnetic field guiding abrasive particles towards the second inlet in the plane of the cross-section. Wherein, the magnetic field generated during the first time period is non-uniform because the density of the magnetic field is higher in the part covering the cross-section of the first channel than in the part covering the second channel. The density of the magnetic field generated during the second time period is higher in the part covering the cross-section of the second channel than in the part covering the first channel.

[0143] In an embodiment, the magnetic switch includes a plurality of magnets arranged at different azimuthal positions along the outer circumference of the flow immediately upstream of the first inlet and the second inlet (e.g., along the circumference of the channel accommodating the flow at that position), and the plurality of magnets together generate a non-uniform magnetic field.

[0144] In one embodiment, the plurality of magnets are permanent magnets, and the actuator further includes drive means connected to the magnets. The drive means is configured to move the magnets as a whole along the circumference when switching between respective time periods to determine that the magnetic field guides abrasive particles towards respective channels during respective time periods.

[0145] In another embodiment, the plurality of magnets arranged along the circumference are electromagnets. Wherein, the difference between the magnetic field directions in the first time period and the second time period can be achieved by reversing the current therein and / or its individual mobility, e.g., its rotatability about an axis perpendicular to the cross-section, or its common mobility along the circumference, and / or by running current through different selected magnets among the plurality of magnets. The current reversal and / or the selective running of the current can be established by the electrical wires based on signals from a control unit and the mobility of the mechanical drive means.

[0146] In an embodiment of the present invention, the difference between the flow resistances of the drilling fluid mixed with abrasive particles in the first channel and the second channel is determined by the differences between the respective lengths, the respective cross-sections, the surface roughnesses of the respective inner wall surfaces of the first channel and the second channel in the longitudinal direction, and / or the changes of the respective cross-sections and / or the surface roughnesses of the inner wall surfaces along the respective lengths, for example, in the form of surface profiles, obstacles, indentations, and / or protrusions, and / or the changes of the channel shapes, for example, along the length, for example, in the form of curvature or bend. In an embodiment, these resistances can be adjusted along the process, for example, by adding, adjusting, or removing surface roughness, obstacles, or, for example, by adding, adjusting, or removing the bend or curvature of the channel.

[0147] During the process of passing through the first outlet and the second outlet from the first inlet and the second inlet respectively, the total flow resistances felt by the drilling fluid mixed with abrasive particles must be coordinated with each other to achieve the combination of most abrasive particles downstream of the outlet.

[0148] In a specific embodiment, the difference between the flow resistances of the drilling fluid mixed with abrasive particles in the first channel and the second channel is determined by the differences in their respective cross-sections, and the respective lengths and the surface roughnesses of the inner wall surfaces and the changes along the respective lengths are equal to each other.

[0149] In an embodiment, the lengths of the first channel and the second channel are equal to each other. In an embodiment, the first inlet, the second inlet, the first outlet, and the second outlet are arranged on the same cross-section along the flow - that is to say, the first channel and the second channel start and end at the same position along the drill string. In an embodiment, the flow resistance of the first channel and / or the second channel for the drilling fluid mixed with abrasive particles is constant along the length. In an embodiment, the first channel and / or the second channel is completely straight in length. In an embodiment, the cross-section of the first channel and / or the second channel is constant along the length. In an embodiment, the first channel and / or the second channel includes a local reduction in the cross-sectional area along the length. In an embodiment, the first time period and the second time period are equal to each other.

[0150] In an embodiment, the first channel and the second channel together have a circular cross-section and are straight in the flow direction of the flow, for example, together form a cylinder. The channels are separated from each other only by a straight wall within the cylinder. In one of these embodiments, the cross-section and the surface roughness of the channel are constant along its length, the lengths are equal to each other, and the flow resistance is basically determined by the difference in the cross-sectional area, which is achieved by extending the wall away from the central axis of the cylinder.

[0151] In one embodiment, the first channel is disposed within the second channel. Preferably, the first channel is concentrically disposed with the second channel. In another embodiment, the second channel is disposed within the first channel, e.g., concentrically.

[0152] In one embodiment, the system is configured to move abrasive particles in the flow towards the wall of the channel through which the flow passes. By bringing the particles closer to the wall of the channel, the particles can be better manipulated by magnets located outside the channel. In one embodiment, the system is configured to provide a vortex in the flow, thereby moving the abrasive particles in the flow to the outside of the flow, i.e., closer to the wall of the channel through which the flow passes. For example, the channel through which the flow passes can be provided with vanes that generate a vortex in the flow. The centrifugal force generated by the vortex moves the abrasive particles to the perimeter of the flow, thereby closer to the channel wall where the magnetic field of the magnetic deflector is strongest and where deflection is most easily established.

[0153] In a preferred embodiment, the vanes are configured to generate a vortex that makes a complete rotation within the length of the magnetic separator placed along the channel through which the flow passes.

[0154] In one embodiment, substantially axial grooves or channels are provided on the inner surface of the wall of the channel, the grooves or channels preferably extending along the length of the deflection portion, i.e., the portion where the particles are deflected into the first or second channel, to guide the particles to the entrance of the channel.

[0155] Preferably, once the abrasive particles have moved past the edge of the flow, the vortex is removed from the flow. Thus, in one embodiment, downstream of the vanes that generate the vortex, other vanes can be provided that are shaped to moderate the vortex of the flow, preferably removing the rotational motion of the drilling fluid and the abrasive particles carried by the drilling fluid. Thus, before entering the channel, the flow is substantially axial.

[0156] In an embodiment, the lengths of the first and second channels are between 2 meters and 3 meters. For ease of operation, it is desirable to have a component including a drill bit, adjustment means, and orientation sensors and other sensors used in the first and second channels, such as a final shaping evaluation sensor within a swivel joint, an optional recirculation unit, such as within a stabilizer joint within a recirculation joint, and ultimately a pulse generator or electromagnetic telemetry joint within a 9.5-meter length range. As long as any orientation sensor is placed downstream within a rigid section connected to the drill bit, the portions of the first and second channels do not have to be rigid.

[0157] In an embodiment, the diameter along the length (e.g., in the case of a non-circular channel, the effective diameter) is greater than five times the diameter of the abrasive particles to avoid channel blockage. For example, in the case of abrasive particles with a diameter of 1 mm, it is at least 0.2 cm². In an actual embodiment, the maximum cross-sectional area of the second channel is limited by these factors, namely the internal cross-section of a typical drill string (e.g., an oil drill string, component) (usually up to 0.6 times the borehole diameter), the cross-sectional area required for the first channel, and the cross-sectional area occupied by any walls between the channels, which may be part of the cross-sectional area, such as the wiring between sensors, the control unit, (a part of) the deflection device, and / or any additional intermediate space. The sum of the cross-sectional areas of the two channels is preferably as large as possible to avoid overly restricting the flow rate and causing unnecessary pressure loss and wear. For example, in a 10 cm borehole, the inner diameter may be approximately 6 cm, and the space for the channels is approximately 30 cm².

[0158] In an embodiment, the pressure drop over the entire length is typically less than 50 kPa. In an embodiment, the flow rate ratio in the first channel and the second channel is typically between 1 and 10, and the velocity ratio is typically between 1, 2, and 3. In an embodiment, both the first time period and the second time period are between 0 and 1.5 seconds. For example, the first time period and the second time period can be 0.5 seconds to synchronize with a drill bit rotation speed of 60 revolutions per minute.

[0159] In an exemplary embodiment where the component drills a 10.5 cm diameter borehole, the first channel and the second channel have equal inlet positions and outlet positions along the drill string, have a constant flow resistance along the length, and the lengths of both the first channel and the second channel are equal to 2 meters. Among them, the cross-section of the first channel is approximately 7 cm², and the cross-section of the second channel is approximately 23 cm². The pressure drop along the channel length is approximately 5 kPa, the inlet flow rate is approximately 0.50 m³ / min, the flow rate ratio in the first channel and the second channel is approximately 5, the respective velocities are approximately 1.8 m / s and 3.0 m / s, the first time period and the second time period are approximately 0.5 seconds. The rotation speed of the drill bit is approximately 60 revolutions per minute, so every half rotation, the first major portion or the second major portion enters the first channel or the second channel respectively, and the starting time for the first major portion to deflect into the second channel is approximately 0.5 seconds. The starting time consists of the second major portion that deflects into the first channel 0.5 seconds later, and both major portions flow out from the first outlet and the second outlet approximately 1.15 seconds after the first major portion passes through the first inlet.

[0160] Generally, the diameter of the abrasive particles is approximately 0.6 mm - 1.0 mm. According to the drill bit pressure drop and the rock removal balance of the drill bit, an abrasive particle concentration of approximately 0.2 vol% is usually sufficient for normal steering operations.

[0161] In an envisaged embodiment, during rotation of the drill bit, the first flow resistance and / or the second flow resistance of the first channel and the second channel can be adjusted by adjusting one or more of the quantities determining the flow resistance (e.g., based on a signal from a control unit). For example, by adjusting or increasing a local reduction of the cross-section within one or both channels, e.g., by moving an obstacle into the channel, or by adjusting the length (e.g., telescopically). The adjustability can contribute to further penetration into the object while predicting changing conditions within the drill hole.

[0162] In the case where the drill bit is a mechanical drill bit, preferably, the drilling fluid for the cleaning nozzles comes from the flow through the channels. In order to pass abrasive particles from the same flow together with the drilling fluid from the flow through the abrasive jet nozzles, the abrasive particles are filtered on one side of the abrasive jet nozzles.

[0163] In an embodiment of the method according to the invention, the method further comprises, simultaneously with the impact of the flow on the bottom of the wellbore,

[0164] - filtering the abrasive particles in the first and second flow portions upstream of the abrasive jet nozzles and the cleaning nozzles, e.g., in the intermediate space of the drill bit, and

[0165] - deflecting the filtered abrasive particles into the abrasive jet nozzles, while

[0166] - allowing the drilling fluid in the first and second flow portions of the flow to flow into both the abrasive jet nozzles and the cleaning nozzles.

[0167] In an embodiment of the system according to the invention, the drill bit further comprises a filter for the same purpose, which is arranged in the intermediate space of the drill bit and rotates with the drill bit. The filter is configured to direct the abrasive particles received in the flow through the drill bit fluid inlet in the flow to the abrasive nozzles, while allowing the drilling fluid in the flow to flow into both the abrasive jet nozzles and the cleaning nozzles.

[0168] In an alternative embodiment, for the same purpose, the drill bit comprises a deflector, e.g., a magnetic deflector or a chute directed towards the abrasive jet nozzles, which is configured to direct the abrasive particles towards the abrasive jet nozzles. The abrasive particles mixed with the drilling fluid have a higher density and thus a greater inertia compared to the drilling fluid without abrasive particles. Therefore, the abrasive particles have a longer memory of the flow direction in which they are released into the fluid, and thus, during any distribution of the drilling fluid on both the cleaning nozzles and the abrasive jet nozzles, the direction and the concentration in the first region are relatively increased.

[0169] In the case where the drill bit is a mechanical drill bit and there are no cleaning nozzles, the flow generally all enters the abrasive jet nozzles. In an embodiment, one or more abrasive jet nozzles consist only of a single abrasive jet nozzle.

[0170] In an embodiment, the drill bit rotates relative to a drill string section that remains stationary relative to the longitudinal axis of rotation of the drill bit and further slides into the wellbore as the drill bit deepens.

[0171] In an embodiment, the drill bit rotates with the drill string, and the drill bit is fixed to the drill string by a sub. In other embodiments, the drill bit rotates relative to the drill string, and the drill string rotates at different rotational speeds, such as at a higher speed, to mitigate stick-slip vibrations. For such relative rotation, a motor, such as a downhole motor, is provided between the sub-bit and the drill bit, which is well known in the art.

[0172] For a pure AJD drill bit, high rotational speeds do not increase the rate of penetration and increase the wear of the drill bit. The preferred rotational speed for a drill bit for steering purposes is from 40 to 150 revolutions per minute. The rotational speed should not be too low so as not to excite stick-slip vibrations.

[0173] Preferably, in view of the robustness of the system, the channels rotate with the sub, as described above, which depends on the number of downhole rotating components relative to the drill string. In an embodiment of the system, the first and second channels are fixedly mounted within the sub, for example, a regulating device including these channels is fixedly mounted within the sub to rotate with the sub, such as to rotate with the drill bit.

[0174] In an embodiment of the method according to the present invention, the method includes downhole recycling of abrasive particles that impinge on the bottom of the wellbore through an abrasive jet nozzle. Such downhole recycling includes:

[0175] - capturing at least a portion of the abrasive particles present in the flow downstream of the impingement on the bottom of the wellbore, such as at a substantially constant flow rate, and

[0176] - introducing the captured abrasive particles into the flow upstream of the abrasive jet nozzle, such as upstream of the drill bit, such as upstream of the first and second channels.

[0177] Wherein, the abrasive particles may be magnetic abrasive particles, such as steel shots, and introducing the abrasive particles into the flow includes transporting the abrasive particles into the flow using a magnetic field.

[0178] In an embodiment of the system according to the present invention, the system further includes a recirculation unit, the downhole recirculation unit being adapted to recirculate magnetic abrasive particles passing through an abrasive jet nozzle for impact with the bottom of the wellbore. Such a downhole recirculation unit includes one or more magnets, such as one or more movable magnets, the one or more magnets being arranged such that one or more of their magnetic fields attract abrasive particles downstream of the impact with the bottom of the wellbore and convey the attracted particles to a mixing chamber at a substantially constant flow rate, the flow passing through the mixing chamber upstream of the abrasive jet nozzle. Examples of such recirculation units are disclosed in the previously discussed WO2008 / 119821, WO2005 / 005767, and WO2005 / 05766.

[0179] When using an abrasive jet bit, the capture of abrasive particles entering the flow towards the abrasive jet nozzle advantageously occurs downstream of the first and second channels and without passing through a regulating device.

[0180] In a practical example, abrasive particles are typically recirculated at the bit 5 to 10 times within a fraction of a second over a full rotation range of the bit. In this case, abrasive recirculation can be regarded as a concentration amplifier at the abrasive jet bit downstream of the dual-channel section of the swivel joint. Recirculation will make the transition along the flow from the first flow portion to the second flow portion and back less abrupt, however, if one considers that the recirculated particles extend the first high-concentration flow portion during the time period in which the first flow portion passes through the abrasive jet nozzle, then as long as the rotational speed of the bit does not exceed approximately 150 revolutions per minute and the frequency of the flow portions is synchronized with the rotational speed, this extension of the time period generally does not exceed 0.1 second and has a minimal impact on the steering.

[0181] Adding the captured particles does reduce the difference between the concentrations along subsequent flow portions, so a larger portion of the total number of abrasive particles entering the channels must deflect into the channels to achieve the same concentration difference and thus the same difference in erosion force along the bottom of the wellbore. Recirculation can be used to fine-tune the hole-making difference and thus adjust the steering action.

[0182] In these recirculation units, the abrasive particles are typically recirculated very quickly relative to a first time period and a second time period, i.e., on a time scale of approximately 0.01 seconds, and then escape after an average of 8 rounds of recirculation. After escaping, the abrasive particles return to the surface through the annulus of the drill string.

[0183] When using a mechanical bit in combination with recirculation, considering the high concentration differences achieved along subsequent flow portions, preferably as close as possible to 200%, the captured abrasive particles preferably enter the flow upstream of the first and second channels, in which case a large portion of the deflection must be 100% of the abrasive particles received from the supply channel.

[0184] The concentration range of the abrasive particles supplied from the surface is typically from 0.1% in mechanical drilling without downhole recirculation to 1% in AJD drilling with downhole recirculation.

[0185] In an embodiment of the method according to the invention, the durations of the first time period and the second time period are set and / or adjusted based on downhole measurements, such as during the rotation of the drill bit. These measurements may include one or more of the following:

[0186] - Detecting particles immediately downstream of the first outlet and the second outlet,

[0187] - Detecting the location of impact with the bottom of the wellbore, such as the azimuthal location,

[0188] - Detecting the geometric direction of wellbore deepening.

[0189] Other measurements may also be included, such as those commonly used in MWD units.

[0190] An embodiment of the system according to the invention includes one or more sensors. These sensors may include one or more of the following:

[0191] - One or more position sensors configured and arranged on the drill bit to provide a signal to the control unit indicating the position (e.g., azimuthal position) at which impact occurs with the bottom of the wellbore,

[0192] - One or more presence detection sensors, such as high-frequency acoustic sensors or magnetic sensors, arranged at a position downstream of the deflection device, such as at the first inlet and the second inlet and / or at the first outlet and the second outlet and / or near the drill bit, the one or more presence detection sensors being configured to provide a signal to the control unit indicating the presence of abrasive particles at the position, e.g., indicating that the first flow portion or the second flow portion passes by the sensor,

[0193] - One or more navigation sensors configured and arranged on the drill bit to provide a signal indicating the geometric direction of wellbore deepening.

[0194] The control unit is configured to control the actuator of the particle deflection device based on the signals from the sensors.

[0195] In one embodiment, one or more presence detection sensors are disposed at one or both of the first and second channels. For example, the presence detection sensors are disposed near or at the channel inlet to monitor the particles entering the channel, and / or near or at the channel outlet to monitor the particles leaving the channel, e.g., to verify the end result of the conditioning unit generating the first and second flow portions, and / or elsewhere along the channel.

[0196] In one embodiment, one or more of the presence detection sensors are configured to provide a signal indicative of the number of abrasive particles present, e.g., the number of abrasive particles passing through the sensor, e.g., per unit time, e.g., per unit flow of drilling fluid.

[0197] In one embodiment, one or more (e.g., one) presence detection sensors are disposed at one of the first and second channels (e.g., only at the first channel).

[0198] In one embodiment, one or more presence detection sensors are disposed at the supply channel, e.g., near its outlet. In one embodiment, one or more presence detection sensors are disposed at the drill bit, e.g., at or near the drill bit fluid inlet, intermediate space, or nozzle.

[0199] In an embodiment where the abrasive particles are magnetic abrasive particles (e.g., steel shot), one or more of the presence detection sensors are magnetic sensors of a specific form of inductive magnetic sensor or magnetometer, the presence detection sensors being configured to provide a signal indicative of the number of abrasive particles present in the flow passing through the sensor. Inductive magnetic sensors are known in the art, e.g., for measuring the static level of magnetic particles in a container (e.g., a pipe) by measuring the self-inductance in a coil, as described in US2010243240. The self-inductance of the coil varies with the number of magnetic abrasive particles present within the coil and is determined by the ratio of the voltage and current varying over time. When a varying AC current flows through the coil, the self-inductance can be determined by precise voltage and current measurements during the process. Alternatively, the magnetic field induced by the coil can be measured to determine the number of particles, the magnetic field increasing with the number of particles within the coil. For this purpose, e.g., a Hall probe can be arranged at or near the sensor location, which is known in the art, e.g., used in linear variable differential transformers (LVDTs) and linear motors. In the case of magnetic field measurement, e.g., by a Hall probe, the Earth's magnetic field can be corrected during the processing and interpretation of the measurement.

[0200] In addition to the prior art, in this embodiment of the present invention, an induction coil is arranged around the flow of abrasive particles for determining the concentration and / or flow rate of the abrasive particles, the abrasive particles passing through the drilling system in the flow of drilling fluid towards the nozzle.

[0201] In one embodiment, one or more induction coils are arranged around the supply channel, such as at or near the supply channel outlet. In one embodiment, one or more induction coils are arranged around the first channel of the regulating unit, such as at or near the first inlet, in the axial central portion of the first channel, and / or at or near the first outlet. In one embodiment, one or more coils are arranged around the second channel of the regulating unit, such as at or near the second inlet, in the axial central portion of the second channel, and / or at or near the second outlet. In one embodiment, one or more coils are arranged at or near the drill fluid inlet, the drill intermediate space, and / or the nozzles.

[0202] In one embodiment, at least one coil is arranged at a position along the flow of abrasive particles for determining the concentration of abrasive particles passing through the coil.

[0203] In one embodiment, at least two coils are arranged at axially spaced positions along the flow of abrasive particles for determining the flow rate of abrasive particles passing through the two coils by comparing the measurements of the number of particles passing through the coils and the timing of particle passage through the two coils.

[0204] In one embodiment, at least two coils are arranged at axially spaced positions along the flow of abrasive particles for determining the change in concentration along the flow (e.g., along a channel or between channels).

[0205] In one embodiment, at least one coil is arranged in the drill for measuring the concentration of abrasive particles passing through over time during drill rotation, for determining the time for a first flow portion and a second flow portion to pass through the nozzle, in combination with the determination of the angular position of the nozzle, in order to synchronize the passage of the first flow portion and the second flow portion through the nozzle with angular sectors at the bottom of the wellbore that require enhanced erosion to direct the wellbore in a direction away from the portion.

[0206] In a particular embodiment, an induction magnetometer is arranged at or near the inlet of one of the channels (e.g., the first channel) and at or near the outlet of the same channel, and not around the flow at the other of the channels (e.g., the second channel). If the particles are deflected in the first channel and the second channel, then during a first time period and a second time period respectively, the velocity of the particles in one of the channels (e.g., the first channel) is lower than the velocity in the other of the channels (e.g., the second channel). For measurement accuracy, the induction magnetometer is preferably arranged around the flow at the channel where the velocity is lower. In the embodiment where the first channel under discussion is arranged within the second channel, the coil can advantageously be arranged at the first channel.

[0207] In certain embodiments, one induction magnetometer is arranged around the flow at the supply channel, e.g., near or at its outlet, two induction magnetometers are around the first channel, i.e., at or near its inlet and at or near its outlet, and one induction magnetometer is at or near the drill bit, e.g., at or near the fluid inlet, e.g., directly upstream of the fluid inlet. In embodiments where the particle deflection device includes a particle concentration device, the induction magnetometer around the supply flow can be arranged at the concentration device, e.g., near its outlet, e.g., directly downstream of its outlet.

[0208] In practical embodiments, the coils arranged at one or more of the channels are embedded in the walls of their respective channels. Axial ferromagnetic guides can be arranged outside the coils.

[0209] According to any of the above embodiments, the invention further relates to the use of one or more induction magnetometers for measuring the concentration and / or flow rate of abrasive particles in a drilling fluid mixed with abrasive particles in a directional drilling system.

[0210] The control unit can be connected to one or more sensors of the directional drilling system to receive the signals provided by them, compare the values represented by the signals with a predetermined reference value of the quantity thus measured, and / or with previous values and / or the values of other sensors, and generate the control signals for different actuators of the system according to the results of the comparison. In practical embodiments, the control unit employs a control loop for controlling the regulating unit to generate a first flow portion and a second flow portion. In particular, the control unit can adjust the timing and duration of the deflection into either channel by the particle deflection device based on the sensor measurement values. In addition, the concentration of the supply flow and / or the flow resistance of the channels of the regulating unit can be changed.

[0211] Particle detection can be used, for example, by the control unit to calculate the speed (e.g., flow rate) of the abrasive particles through the channel and the expected arrival time of the abrasive at the bottom of the wellbore, and adjust the timing and duration of the first and second cycles to match the rotational speed of the drill bit, so that when the abrasive jet nozzle is aligned with a selected angular sector at the bottom of the wellbore, the high-concentration flow portion reaches the selected angular sector.

[0212] In particular, particle detection can be used, for example, by the control unit to determine the concentration difference between subsequent flow portions in order to obtain feedback and control the hole-making difference. The sensors used by the control unit for detecting the concentration difference, such as HF acoustic sensors or magnetic sensors, are preferably arranged along the flow inside, on, or near the drill bit for this purpose.

[0213] Position sensors and navigation sensors can be used to obtain feedback on the direction and rotational position of the drill bit, the inclination angle, the azimuth angle, and the front cutting face relative to the local geomagnetic field and the gravity vector g. This feedback can be used, for example, to control an adjustment device to adjust the drilling direction if necessary.

[0214] The adjustment device may be several meters away from the drill bit. However, the measurement sensors and / or the direction sensors are preferably located near the drill bit. All relevant distances are known to the control unit of the system. Advantageously, in a pure AJD drilling system, the direction sensors may be located closer to the drill bit, which may contribute to more precise steering.

[0215] The control unit can use simple or complex orientation targets for drilling. By applying model-based process control, the functions of the control unit can be upgraded. Preferably, an algorithm for deriving the rotational speed of the string of the abrasive jet nozzle through which the abrasive jet passes and the front cutting face angle is provided.

[0216] In one embodiment, the control loop includes a large control loop with an orientation controller and a small control loop with a concentration adjustment controller.

[0217] In the large control loop, the orientation controller takes the orientation target as input. The measurements of the sensors at the drill bit and / or the geographical data are input into the orientation controller, which controls the orientation action, rotation, phase, and radius of the drill bit based on the measurements and the orientation target. The sensors include, for example, position sensors, such as accelerometers in three directions, gyro sensors in three directions, magnetic sensors in three directions (e.g., magnetometers, especially for detecting the direction of the drill bit relative to the geomagnetic field), and particle presence detection sensors (e.g., three). The orientation controller further stores this data in a memory and outputs to the surface whether the orientation target has been reached and to what extent it has been reached. The orientation controller further uses the response of the concentration adjustment controller of the small control loop as the basis for its actions.

[0218] In the small control loop, the concentration adjustment controller takes the output of the orientation controller of the large loop and the sensor measurements including temperature, flow rate, pressure, and particle presence detection (especially in the form of the measurement of the number of abrasive particles) as its input. The concentration adjustment controller controls the adjustment actions of the adjustment unit, including the deflection of the particle inlet channels. The response of the adjustment unit is fed back into the controller to verify whether the control target has been reached. As described above, the control actions of the controller are also fed back into the orientation controller of the large control loop. The control actions are also stored in the memory.

[0219] For example, the large control loop is executed over a time span of several minutes, usually more than 10 minutes. The small control loop is usually faster than one minute.

[0220] According to any of the foregoing embodiments, the present invention further relates to a method and a system for controlling the concentration and / or flow rate of abrasive particles in a flow of drilling fluid mixed with abrasive particles in a directional drilling system based on a presence detection sensor (e.g., in particular an inductive magnetometer).

[0221] The present invention can integrate mud pulse telemetry technology, which is commonly used in drilling systems for drilling into soil layers. A typical mud pulse telemetry system includes sending and receiving facilities and downhole sending and receiving equipment. The sending and receiving facilities are at the surface while drilling into the underground soil layer as an object, and the downhole sending and receiving equipment is generally integrated with the measurement while drilling (MWD) equipment downhole. For example, an important message sent from the surface to the downhole equipment can be a signal to change from a first directional target (e.g., drilling at a 70-degree inclination) to a second control target (e.g., drilling 30 degrees to the left). For example, an important message sent to the surface can be an alarm confirming that a new setting has been received, a directional target has been achieved, a new rock type has been detected while drilling, or a hardware failure has been triggered. In the present invention, communication between the downhole information and the surface can be achieved by utilizing hardware components near the first channel and the second channel, such as in a downhole steering joint having the first channel and the second channel. This advantageously eliminates the need to add a downhole pulse generator and separate downhole telemetry control electronics to the drilling assembly. The remaining part of the mud pulse telemetry system can be in the manner commonly used in drilling systems for drilling into soil layers.

[0222] In the present invention, mud pulse telemetry can be used, for example, to transmit signals from sensors (if any) to a control unit, for example, when the control unit is arranged outside the wellbore, for example, at the surface of the soil layer when the object is a soil layer. In the present invention, mud pulse telemetry can be particularly advantageously implemented within the first channel and the second channel, thereby deliberately partially blocking the channels to generate pressure pulses, and thus advantageously utilizing the reduced diameter through which the abrasive particles pass. The telemetry mode is preferably used only in the tangent steering stage, for example, when steering correction is limited, in which no deflection occurs in the tangent steering stage, and the loss of steering time during the generation of telemetry pulses is more easily achieved. However, according to the present invention, the telemetry mode can also be used when drilling a curved section and performing the method.

[0223] In an embodiment of the method according to the present invention, where the abrasive particles are magnetic particles, for this purpose, the method further comprises:

[0224] - Activating a magnetic field in the first channel and / or the second channel for a time interval to cause local accumulation of magnetic abrasive particles in the first channel and / or the second channel, thereby generating a pressure pulse within the channel,

[0225] - Subsequently, eliminating the magnetic field,

[0226] Wherein, the activation and elimination are repeated to generate a series of pressure pulses over time, and the amplitude and timing of the pressure pulses are determined such that the series of pressure pulses represents one of the downhole measurements for a mud pulse telemetry system. For example, if the object is a subsurface soil layer, downhole information is transmitted to a receiver of a telemetry device of a borehole unit at the surface.

[0227] In an embodiment of the system according to the present invention, wherein the abrasive particles are magnetic particles, for the same purpose, the system further includes a mud pulse telemetry unit. The mud pulse telemetry unit includes:

[0228] - A telemetry control unit, which is generally connected to the swivel joint having the first channel and the second channel by wire, or for example, forms an integrated component of such a swivel joint. The telemetry control unit is configured to receive one or more of the signals provided by the one or more sensors from downhole electronics (for example, in the case where the object is a subsurface soil surface, deriving information to be sent to the surface therefrom), and encode them into a series of pulses having a predetermined timing and amplitude, and

[0229] - A switchable magnet, which is arranged to generate a magnetic field in the first channel and / or the second channel. The switchable magnet is configured to cause local accumulation of the magnetic abrasive particles in the first channel and / or the second channel during activation, thereby generating a pressure pulse within the channel, and when the switchable magnet is deactivated, stop causing the local accumulation.

[0230] Wherein, the telemetry control unit is configured to control the activation and deactivation of the switchable magnet, whereby the switchable magnet repeatedly generates the pressure pulses to form a series of pressure pulses, and the timing and amplitude of the series of pressure pulses correspond to the encoded series of pulses, for example, if the object is a subsurface soil surface, it is detected by a receiver of a telemetry system on a borehole unit at the surface.

[0231] The mud pulse telemetry unit may further include conversion means connected to the control unit downstream of the first channel and the second channel (for example, outside the wellbore, for example, at the surface of the soil layer when the object is a soil layer). The conversion means is adapted to record the timing and amplitude of the series of the pressure pulses and generate a corresponding signal to the control unit, for example, a series of voltages having corresponding timing and amplitude. The control unit (for example, also arranged outside the wellbore, for example, at the surface of the soil layer when the object is a soil layer, near the conversion means) is configured to decode the corresponding signal generated by the conversion means into the quantity measured by the one or more sensors, compare the value with a predetermined reference value of the quantity, and generate the control signal to the particle deflection means according to the result of the comparison.

[0232] It is believed that although the above discussion only relates to the first channel and the second channel, the concept allows the use of more channels. For example, the first channel, the second channel, and the third channel can be used to divide a flow into a first sub-flow, a second sub-flow, and a third sub-flow. In one such method, the three sub-channels each have different flow resistances, and abrasive particles are deflected into at least two of the first channel, the second channel, and the third channel during at least two of the first time period, the second time period, and the third time period. The differences in the flow resistances of the drilling fluid mixed with the abrasive particles result in differences in the velocities of the drilling fluid mixed with the abrasive particles flowing through the respective channels. The differences between the three velocities and thus the three flow resistances cause, downstream of the exits of the three channels, during the respective first time period, second time period, and third time period, most of the abrasive particles deflected into the first channel and / or most of the abrasive particles deflected into the third channel to at least partially overlap because they combine with the drilling fluid passing through these channels during the time period to form a first flow portion. The few abrasive particles that are not deflected during the first time period, the second time period, and / or the third time period, i.e., the abrasive particles entering the channels (other than the channels into which most of the abrasive particles are deflected during the time period), form a second flow portion together with the drilling fluid passing through these channels during the respective time periods. In one embodiment, one of the sub-flows is a main sub-flow that does not adjust the particle concentration. This method includes dividing a flow into three or more sub-flows. For example, a first channel, a second channel, and a third channel are provided to divide a flow into a first sub-flow, a second sub-flow, and a third sub-flow, where the first sub-flow among the sub-flows is the main sub-flow that does not adjust the particle concentration, and the second sub-flow and the third sub-flow are used to produce alternating particle concentrations. In this method, the flow is first subdivided into a sub-flow passing through the first channel and a sub-flow passing through the second channel and the third channel. In this method, the latter flow is the flow exiting the supply channel. Thus, in this method, the supply channel exit is located downstream of the position where the flow is divided, and the flow is divided into a sub-flow in which the particle concentration is not adjusted and a sub-flow in which the particle concentration is adjusted by passing the flow through two sub-channels. The flow to be directed through the second channel and the third channel is controlled by a deflection device. The deflection device is configured to alternately deflect most of all the abrasive particles in the flow exiting the supply channel into the second channel during a first time period, and not deflect most of all the abrasive particles in the flow exiting the supply channel into the second channel during a second time period after the first time period. Preferably, during the second time period, most of all the abrasive particles in the flow exiting the supply channel are deflected into the third channel. Thus, the flow of the drilling fluid is divided into two sub-flows. A first sub-flow passing through the second channel and a second sub-flow passing through the third channel. The second channel and the third channel have different flow resistances, so one sub-flow takes longer to pass through the channel than the other sub-flow.

[0233] Differences between the respective flow resistances of the drilling fluid mixed with abrasive particles result in differences in the velocities of the drilling fluid mixed with abrasive particles flowing through the respective channels. The difference between the two velocities and thus between the two flow resistances causes, downstream of the outlets of the second and third channels, a substantial portion of the abrasive particles deflected into the second channel and a substantial portion of the abrasive particles deflected into the third channel to at least partially overlap as they combine downstream of the outlets of the second and third channels with the drilling fluid passing through these channels during the said time period. In addition, the flows leaving the outlets of the second and third channels also combine with the main flow (i.e., the flow through the first channel). The three sub-flows together form a flow that alternately includes a first flow portion and a second flow portion, the first flow portion including the increased flow concentration generated in the second and third channels, and the second flow portion including the decreased flow concentration generated in the second and third channels.

[0234] In a system employing three channels, the control system and the deflection device are configured to deflect abrasive particles into the first, second, and third channels during a first time period, a second time period, and a third time period. In an alternative system, a first channel, a second channel, and a third channel are provided to divide the flow into a first sub-flow, a second sub-flow, and a third sub-flow, where one of the three sub-flows is a main sub-flow and the particle concentration in the main sub-flow is not adjusted. In such a system, the flow is first subdivided into a sub-flow passing through the first channel and a sub-flow passing through the second and third channels. In such a system, the latter flow is the flow through the supply channel outlet. Thus, in the said system, the supply channel outlet is located downstream of the position where the flow is divided, and the flow is divided into a sub-flow in which the particle concentration is not adjusted and a sub-flow in which the particle concentration is adjusted by passing the flow through two sub-channels.

[0235] The invention also relates to the joint according to claim 23 and the abrasive particle pulse generator according to claim 24. It should be noted that the embodiments related to the system discussed herein also relate to the said joint and the said abrasive particle pulse generator to provide the same or similar advantages when providing the same or similar features.

[0236] Throughout the present invention, the term "fluid", similar to "fluid communication", "fluid connection", "fluid inlet", "fluid outlet", should be interpreted as including a fluid mixed with abrasive particles. That is, for example, a "fluid inlet" is adapted to allow a drilling fluid mixed with abrasive particles to enter. BRIEF DESCRIPTION OF THE DRAWINGS

[0237] The present invention will now be described with reference to the accompanying drawings. In the drawings:

[0238] Figure 1 A system according to the present invention is schematically shown, the system being for directional drilling of a curved wellbore in a subterranean formation,

[0239] Figure 2 Schematically shows an embodiment of the system according to the present invention, as well as an enlarged view of its mechanical drill bit and an enlarged view of the interior of its steerable joint.

[0240] Figure 3 Schematically shows the use of the system according to the present invention during a first time period.

[0241] Figure 4a Schematically shows Figure 3 of the system during the Figure 3 in a top view represented as section A - A.

[0242] Figure 4b Schematically shows Figure 3 of the system during a second time period Figure 3 in a top view represented as section A - A.

[0243] Figure 5a Schematically shows the use of the system according to the present invention during a first time period.

[0244] Figure 5b Schematically shows Figure 5a the operation of the deflection device in the system of

[0245] Figure 6 Schematically shows the use of the system according to the present invention during a first time period and the operation of the deflection device.

[0246] Figure 7 Schematically shows a recirculation joint and a drill bit used within the system according to the present invention. Detailed Description

[0247] The drawings show an embodiment of a directional drilling system 1 according to the present invention.

[0248] Figure 1 Highly schematically shows an embodiment of the system 1 when directionally drilling a curved wellbore 4a in a subterranean formation 2. The drilling has progressed through a limestone layer 2a and a sandstone layer 2b into the rock layer 2c of the subterranean formation. As can be clearly seen in the enlarged view of the system 1, the system 1 is connected to a drill string 40, which is rotated by a top drive 3b of a derrick 3a at the surface 2d. Within the cement casing of the main vertical wellbore 4, an anchor 3c and a whipstock 3d are arranged, and the whipstock 3d guides the drill string 40 to deviate through the casing into the wellbore 4a. The wellbore 4a is the last of four curved wellbores 4a, 4b, 4c, 4d that deviate from the drilled main wellbore 4. All the deviated curved wellbores 4a, 4b, 4c, 4d include a curved section and a subsequent straight section. The system 1 is currently deepening the straight section of the wellbore 4a. The wellbore 4a has a wellbore bottom 4a'.

[0249] Except for the tower 3a and the top drive 3b, a pump 98 is provided at the surface 2d. The pump 98 pumps the drilling fluid 91 through a particle injection device 99. In the particle injection device 99, magnetic abrasive particles 92 from an abrasive particle supply device 95 are combined with the drilling fluid 91 to form a flow 90 of the drilling fluid 91 mixed with the abrasive particles 92. The flow rate and concentration of the abrasive particles 92 in the flow 90 are substantially constant. The flow 90 enters the system 1 through a supply passage passing through the drill string 40, and then flows through the steerable joint 20, the recirculation joint 50, and the drill bit 10 within the system 1. In this case, the drill bit 10 is an abrasive jet drill bit. After passing through the drill bit 10, the flow 90 impacts the bottom 4a' of the wellbore in the form of an abrasive jet of the flow 90, thereby eroding the bottom 4a' of the wellbore. After the impact, the flow 90 travels upward again towards the surface 2d, moving between the annular space between the cylindrical wellbore wall and the system 1. When passing through the recirculation joint 50, a part of the abrasive particles 92 in the flow are captured by the recirculation joint 50 and recirculated as a recirculation flow 93 into the flow 90 within the recirculation joint. After the recirculation joint captures the abrasive particles 92 from the flow 90, the abrasive particles travel further towards the surface as a return flow 94. The particles 92 remaining in the recirculation flow 94 are filtered at the surface 2d to merge into the supply 95 of the abrasive particles.

[0250] Figure 2 Two possible embodiments of the system 1 according to the present invention are schematically shown. Both have the same steerable joint 20, and its interior is schematically shown in an enlarged view on the right side of the two embodiments. In the system 1 on the far left, the drill bit 10 is a mechanical drill bit. In the system 1 on the far right, the drill bit 10 is an abrasive jet drill bit, and the system includes a recirculation unit 50. The recirculation unit 50 and the AJD drill bit of the system are shown in more detail in Figure 7 which.

[0251] As shown in the enlarged view of the mechanical drill bit 10, the drill bit 10 includes a drill bit face facing the bottom 4a' of the wellbore during use, a drill bit fluid inlet 10i, one or more abrasive jet nozzles 17a, and an intermediate space between the drill bit fluid inlet 10i and the one or more abrasive jet nozzles 17a. The abrasive jet drill bit of the rightmost embodiment also includes these components, as shown in Figure 7 which.

[0252] The abrasive jet nozzles 17a are configured to eject a flow 90 of the drilling fluid 91 mixed with the abrasive particles 92 in the form of an abrasive jet 90 into an impact with the bottom 4a' of the wellbore. The mechanical drill bit includes a plurality of abrasive jet nozzles 17a arranged at different azimuthal positions. The AJD drill bit has only one abrasive jet nozzle 17a, as shown in Figure 7 which.

[0253] Each abrasive jet nozzle 17a has a nozzle inlet for fluid communication with the intermediate space, each nozzle inlet extending from said intermediate space at least during rotation of the drill bit 10 .

[0254] Mechanical drill bit 10 further comprises cleaning nozzle 17w, mechanical cutter 18 and filter 19. The filter is configured and arranged in drill bit 10 so that abrasive particles from stream 90 are deflected only into abrasive jet nozzle 17a and drilling fluid 91 from stream 90 enters both abrasive jet nozzle and cleaning nozzle 17w.

[0255] Both embodiments of the system 1 further include an identical joint 20 , the downhole end of which is connected to the drill bit 10 for rotation therewith, and the other end of which is connected to the tubular drill string 40 .

[0256] The joint 20 includes a joint fluid inlet 20i that can be fluidly connected to a supply channel through the drill string 40 to receive a flow 90 of drilling fluid 91 mixed with abrasive particles 92 from the supply channel when the system 1 is connected to the drill string 40. The joint further includes a joint fluid outlet 20o that is fluidly connected or can be connected to the drill bit fluid inlet 10i.

[0257] The joint 20 further comprises a regulating unit fluidly connected to the joint drill bit inlet 20i at its downstream, the regulating unit being configured to vary the concentration of abrasive particles 92 along the flow portions 90h, 90l of the flow 90 received from the supply channel, which flow portions subsequently enter the drill bit fluid inlet 10i through the joint drill bit fluid outlet 20o.

[0258] The regulating unit includes a first channel 21 and a second channel 22. The first channel 21 has a first flow resistance to the drilling fluid 91 mixed with the abrasive particles 92, a first inlet 21i, and a first outlet 21o fluidly connected to the joint drill bit fluid outlet 20o. The second channel 22 is arranged in parallel with the first channel 21, and has a second flow resistance to the drilling fluid 91 mixed with the abrasive particles 92, a second inlet 22i, and a second outlet 22o fluidly connected to the joint drill bit fluid outlet 20o.

[0259] The conditioning unit further comprises a particle deflection device 23 between the sub-drill fluid inlet 20i and the first and second inlets 21i, 22i. Figure 2 and Figure 3 4. Figure 3 The particle deflection device comprises one or more actuators 23m and is connected to a control unit (not shown) of the system 1 .

[0260] The particle deflection device 23 is configured to periodically deflect a first major portion 92m1 of all the abrasive particles 92 received through the adapter bit fluid inlet 20i from the supply channel to the first inlet 21i during a first time period based on a control signal received from the control unit, and to deflect a second major portion 92m2 of all the abrasive particles 92 in the flow 90 received through the adapter bit fluid inlet 20i from the supply channel to the second inlet 22i during a second time period after the first time period.

[0261] Figure 3 The particle deflection device 23 that deflects the first major portion 92m1 to the first channel 21 is shown.

[0262] The first channel and the second channel 21, 22 are straight channels with equal internal surface roughness and both have a constant cross-section along their lengths, that is Figure 4a and Figure 4b the cross-section shown. The first channel and the second channel 21, 22 together form a cylinder. Since the first channel and the second channel 21, 22 are separated by a plate-like wall, their lengths are equal and they start and end at the same position along the flow. Since the cross-sectional areas of the channels 21 and 22 are not equal to each other, there is a difference between the first flow resistance and the second flow resistance. This difference in flow resistance results in a velocity difference between the first major portion 92m1 of the abrasive particles 92 passing through the first channel 21 and the second major portion 92m2 of the abrasive particles 92 passing through the second channel 22. The flow resistance of the first channel 21 is greater than the flow resistance of the second channel 22 because the cross-sectional area of the first channel 21 is smaller than the cross-sectional area of the second channel 22. Therefore, the first major portion 92m1 moves through the first channel 21 more slowly than the second major portion 92m2 moves through the second channel 22.

[0263] The velocity difference causes the first major portion and the second major portion 92m1, 92m2 to combine with any of the drilling fluid 91 entering the first channel and the second channel 21, 22 during the first time period and the second time period respectively into a first flow portion 90h in the combined section downstream of the first outlet and the second outlet 21o, 22o. A small amount of the non-deflected abrasive particles 92 combine with any of the drilling fluid 91 entering the first channel and the second channel 21, 22 during the second time period and the first time period respectively into a subsequent second flow portion 90l. In Figure 3 it, the first major portion and the second major portion will combine immediately downstream of the outlets 21, 22.

[0264] In Figure 3 it, the drill bit 10 is an abrasive jet drill (AJD drill bit). The drill bit has an abrasive jet nozzle 17a. There are no cleaning nozzles and mechanical cutters on the drill bit face.

[0265] The control unit is configured such that the signal from the control unit received by the deflection device 23 causes the actuator 23m of the deflection device 23 to deflect the first major portion and the second major portions 92m1, 92m2 of the abrasive particles 92 into the first and second channels 21, 22 during a period synchronized with the rotational speed of the AJD bit 10, whereby the first flow portion 90h passes through the abrasive jet nozzle 17a and is guided, together with any of the drilling fluid 91 entering the first and second channels 21, 22 during the first and second time periods respectively, to a selected angular sector 4a” at the bottom of the wellbore 4a'. And then the subsequent second flow portion 90l passes through the abrasive jet nozzle 17a without being guided to the selected angular sector 4a”. In Figure 3 In it, the first flow portion jets out from the abrasive jet nozzle 17a and is guided to the selected angular sector 4a” so as to impact the selected angular sector 4a”. The selected angular sector 4a” will form the outer bend of the curved wellbore section being drilled.

[0266] For the sake of most clearly illustrating the principle, the difference between the concentration of the first flow portion 90h and that of the second flow portion is shown as 100%. That is to say, there are no abrasive particles 92 in the second flow portion 90l. In practice, when using the AJD bit 10, this difference will be less than 100% to still achieve a certain erosion of the wellbore 4a' outside the selected portion 4a” as well, that is to say, to deepen the inner bend of the curved wellbore section to at least a certain extent. The concentration of the abrasive particles determines the erosion force of the ejected abrasive jet 90. Therefore, the radius of the curved wellbore section increases as the concentration difference between the flow portions 90h, 90l decreases.

[0267] The abrasive particles 92 are magnetic abrasive particles 92, that is, ferromagnetic abrasive particles, and the actuator 23m of the deflection device 23 includes a magnetic switch. The magnetic switch is as shown in the top view of the cross-section A-A Figure 4a and Figure 4b immediately upstream of the first inlet and the second inlet 21i, 22i in Figure 3 . Figure 4a Shows the magnetic switch during the first time period (that is, in the case of Figure 3 ). Figure 4b Shows the magnetic switch during the second time period.

[0268] The magnetic switch is configured to establish, during the first time period, a non-uniform magnetic field 23B on the shown cross-section that guides the abrasive particles 92 to the first inlet 21i, and during the second time period, to establish a non-uniform magnetic field 23B on the shown cross-section that guides the abrasive particles 92 to the second inlet 22i.

[0269] The magnetic switch includes a plurality of magnets 23m which are arranged at different azimuthal positions along the outer circumference of the flow 90 in the shown cross-section, i.e., along the circumference of the channel accommodating the flow 90 at different azimuthal positions. The plurality of magnets 23m together generate a non-uniform magnetic field 23B.

[0270] There are seven magnets 23m along the circumference. The arrows within the magnets 23m indicate the direction of their N poles. The arrows are oriented relative to each other such that elliptical magnetic field lines are generated in the cross-section. The magnets 23m are not uniformly distributed along the circumference: during a first time period, most of the magnets 23m are located on one side of the circumference of the first channel 21, see Figure 4a whereas during a second time period, most of the magnets are located on one side of the circumference of the second channel 22, see Figure 4b . Accordingly, the density of the magnetic field 23B generated during the first time period is higher in the part of the cross-section covering the first channel 21 than in the part covering the second channel 22. As Figure 4b shown, the density of the magnetic field 23B generated during the second time period is higher in the part of the cross-section covering the second channel 22 than in the part covering the first channel 21.

[0271] To achieve the different positions of the magnets 23m along the circumference, the magnets 23m are movable permanent magnets 23m, and the actuator further includes drive means (not shown) which are connected to the magnets 23m and configured to move the magnets 23m as a whole along the circumference when switching between the respective time periods based on a signal received from the control unit. The curved arrows along the circumference show the movement: in Figure 4a the first time period is shown, the magnets 23m have just rotated clockwise to direct the particles to the first channel 21, while in Figure 4b the second time period is shown, the magnets 23m have just rotated counterclockwise to direct the particles to the second channel 22.

[0272] The rightmost embodiment of the system 1 is equipped with the Figure 2 shown AJD bit 10. The system 1 further includes a recirculation unit 50 for recirculating the abrasive particles 92 passing through the abrasive jet nozzle 17a for impact with the wellbore bottom 4a'. The recirculation unit 50 is shown in more detail in Figure 7 . The downhole recirculation unit 50 includes a magnet 51 which is arranged such that one or more magnetic fields generated thereby attract the abrasive particles 92 from the flow 90 downstream of the impact with the wellbore bottom 4a'. Thereafter, the flow conveys the attracted particles 92 in the recirculation flow 93 to the mixing section 52c of the channel 52 of the recirculation unit 50 at a substantially constant flow rate. After the flow 90 passes through the steerable joint 20, it flows through the recirculation unit to the abrasive jet nozzle 17a.

[0273] AsFigure 3 As shown, system 1 further includes one or more sensors 81, 82. These sensors include a position sensor 82, which is configured and directly arranged above the drill bit 10 to provide a signal to the control unit to indicate the position where the flow 90 impacts the bottom 4a' of the wellbore. These sensors further include a navigation sensor 82, which is configured and arranged on or directly above the drill bit to provide a signal to indicate the geometric direction of the deepening of the wellbore 4a.

[0274] These sensors also include presence detection sensors 81 in the form of high-frequency acoustic sensors or magnetic sensors, which are arranged at a position directly downstream of the first outlet and the second outlet 21o, 22o. These presence detection sensors 81 are configured to provide a signal to the control unit to indicate the presence of abrasive particles 92 at the position. These signals at least indicate which of the first flow portion 90h or the second flow portion 90l passes through the sensor 81.

[0275] The control unit is configured to control the actuator 23m of the particle deflection device 23 based on the signals from the sensors 81, 82.

[0276] The control unit is connected to one or more sensors 81, 82 to receive the signals provided by them, and is configured to compare the values represented by the signals with a predetermined reference value of the quantity measured thereby, and generate a control signal for the particle deflection device 23 according to the result of the comparison.

[0277] Figure 5a , Figure 5b and Figure 6 Embodiments with different particle deflection devices 24 and different arrangements of the first and second channels are shown. The first channel 21 is arranged within the second channel 22 instead of being radially adjacent to the second channel 22, so that the first channel is radially surrounded by the second channel. In addition, the deflection of the particles entering the channels 21, 22 is achieved by mechanical rather than magnetic deflection means. A particle concentrating device 25 is arranged directly upstream of the first and second inlets 21i, 22i, between the outlet of the supply channel and the first and second inlets 21i, 22i. Through the concentrating device 25, the supply concentration of the abrasive particles in the first cross-sectional portion 25o1 of the outlet 25o is higher than that in the second cross-sectional portion 25o2 of the outlet. The radial movement of the first inlet 21i relative to the first and second portions 25o1, 25o2 causes a smaller or larger cross-sectional portion of the first inlet 21i to be located within the profiles of the first and second portions 25o1, 25o2, so that the corresponding inlet receives a higher or lower concentration of abrasive particles 92. The relative radial movement is driven by the actuator mechanism of the deflection device 24.

[0278] The particle concentrating device 25 includes an inlet and an outlet 25o. The inlet is fluidly connected to the supply channel outlet for receiving a flow 90 of drilling fluid 91 mixed with abrasive particles 92 from the supply channel. The concentrating device 25 is configured to direct most of the abrasive particles 92 of the supply flow 90 to a first portion 25o1 of the outlet 25o and a minority of the abrasive particles 92 to a second portion 25o2 of the outlet, such that the concentration (and thus the flow rate) of the abrasive particles 92 is higher in the first portion 25o1 and lower in the second portion 25o2. In this example, the concentrating device 25 is a filter. In fact, the concentrating device 25 forms an extension of the supply channel.

[0279] As Figure 5b shown, the first channel 21 is movable such that its inlet 21i is in a first position 21i'. In the first position, the first channel is radially coincident and axially aligned within the profile of the first portion 25o1 of the outlet 25o of the concentrating device 25 during a first time period, so that the first inlet 21i receives abrasive particles 92 of the supply flow 90 at a high concentration (and thus a high flow rate). The position is as Figure 5a and Figure 5b both shown. The first channel 21 is further movable such that during a second time period, the inlet 21i of the first channel 21 is in a second position 21i''. In the second position, the first channel is radially outside the profile of the first portion 25o1 of the outlet 25 during the second time period and is not axially aligned therewith, such that the first inlet does not receive or receives fewer abrasive particles 92 of the supply flow 90 at a high concentration (and thus a high flow rate), thereby receiving abrasive particles at a lower concentration. In Figure 5b the dashed line of the outer profile of the first channel 21 shows the second position. During the second time period, the first inlet 21i is in a second position 21i'' radially inside the profile of the second portion 25o2 of the outlet 25o of the concentrating device 25 in order to receive abrasive particles 92 of the supply flow 90 at a lower concentration.

[0280] To move the first inlet 21 into the first and second positions 21i', 21i'', the first channel 21 is pivotable about a pivot 24p that extends radially away from the inlet 21i of the first channel and towards the outlet 21o. The actuator mechanism of the deflecting device 24 is arranged in the second channel 22 and is configured to move the first channel 21 between the first and second positions 21i', 21i'' of the inlet of the first channel by pivoting the first channel 21 about the pivot 24p.

[0281] From Figures 5a to 5bIt can be verified that by the movement of the first inlet 21i, the second inlet 22i simultaneously enters and exits the profile of the first part 25o1 of the outlet 25. At the second position 21i” of the first inlet 21i, the second inlet 22i is radially within the profile of the first part 25o1 and axially aligned with the first part 25o1 during the second time period, and is radially within the profile of the second part 25o2 during the first time period. The effect of this is that the first channel and the second channel 21, 22 alternately - during the first time period and the second time period - receive abrasive particles 92 of the high-concentration supply stream 90.

[0282] From Figure 5b The detailed view of the cross-section B-B at the interface between the outlet 25o and the inlets 21i, 22i in can verify that the first part 25o1 of the concentrator outlet 25o is radially surrounded by the second part 25o2. The first part and the second part 25o1, 25o2 are concentric.

[0283] The first channel 21 is arranged within the second channel 22 such that the inlet 21i of the first channel 21 is concentric with the second channel 22 at the first position 21i' of the first inlet 21i. Thus, at the first position 21i' of the first inlet 21i, the first channel is axially aligned with the first part of the outlet of the concentrator. At the second position 21i” of the inlet 21i of the first channel 21i, the first channel 21 is eccentrically arranged within the second channel 22 and is not axially aligned with the first part 25o1.

[0284] The actuator mechanism of the deflection device 24 includes a linear motor 24m controllable by a control unit. The motor 24m is fixed to the second channel 22 and is indirectly connected to the first channel via a cable 24c to drive the movement of the first channel 21 within the second channel 22. The actuator mechanism includes a transfer mechanism to convert the output movement of the motor 24m into the relative movement of the first channel 21. In the present embodiment, the transfer mechanism includes a cable 24c and a cable guide 24cg fixed to the second channel 22. The cable 24c extends from the linear motor 24m to the first channel 21 through the cable guide 24cg. The cable 24c engages with the first channel 21 near the first inlet 21i to effect a pivoting movement. The linear output movement of the motor 24m is in the axial direction (as indicated by the double arrow in Figure 5a ), and the cable guide 24cg guides the cable 24c to engage with the first channel 21 in the radial direction, whereby the operation of the linear motor 24m causes the cable 24c to pull the first channel 21 in the radial direction. Figure 5bThe single arrow in [Figure] indicates this pulling motion. The transfer mechanism further includes an elastic element in the form of a spring 24s, which is engaged with the cable 24c at a radial position exactly opposite to the first channel 21. The transfer mechanism is fixed to both the first channel and the second channel, so as to extend and contract when moving towards the second position 21i”( Figure 5b as shown by the double arrow in [Figure]) to achieve opposite motions to counteract the pulling effect of the cable 24c. The actuator mechanism includes two limiters 24l, which limit the movement range of the first channel 21 to Figure 5b the two positions shown in [Figure].

[0285] In Figure 6 the alternative embodiment shown in [Figure], the transfer mechanism includes a channel wall guide 24wg instead of a cable guide 24cg and a cable 24c. The motor 24m is fixed to the channel wall guide 24wg instead of the cable 24c. The channel wall guide 24wg cooperates with the outer wall of the first channel 21 to convert the output motion of the motor 24m into a pivoting motion of the first channel 21. The wall guide 24wg and the first channel wall are engaged at complementary inclined surfaces near the inlet 21i in the axial-radial direction, so that the axial motion caused by the motor 24c causes the inclined surfaces to slide relative to each other, thereby inducing a radial motion component of the first channel 21 and a consequent pivoting motion around the pivot 24p. The spring 24s is interconnected with the first channel and the second channel at the same radial position where the channel wall guide 24wg engages the first channel 21 to counteract the effect of the motor 24c at a certain axial distance. The limiter 24l limits the movement range of the first channel 21 and the wall guide 24wg in the radial direction.

Claims

1. A method for directional drilling of a wellbore (4a, 4b, 4c, 4d) in an object (2) using the bottom of the wellbore (4a'), the method comprising: - providing a drill bit (10) connected to the lower end of a drill string (40) and comprising: - a bit face that faces the bottom of the wellbore (4a') during use, - one or more abrasive jet nozzles (17a) configured to direct a flow (90) of drilling fluid (91) mixed with abrasive particles (92) to impact the bottom of the wellbore (4a') in the form of an abrasive jet, and if there are multiple ones of the one or more abrasive jet nozzles (17a), they are arranged at different adjacent azimuthal positions, - an intermediate space between the drill bit fluid inlet (10i) of the drill bit (10) and the one or more abrasive jet nozzles (17a), each of the one or more abrasive jet nozzles (17a) having a nozzle inlet for fluid communication with the intermediate space, each nozzle inlet extending from the intermediate space; - upstream of the drill bit fluid inlet (10i), passing a flow (90) of drilling fluid mixed with abrasive particles at a substantially constant supply rate through a supply channel having a supply channel outlet, - simultaneously, rotating the drill bit (10) at a rotational speed so as to rotate the one or more abrasive jet nozzles (17a), and causing the flow (90) of drilling fluid mixed with abrasive particles to continuously pass through the intermediate space, the one or more nozzle inlets, and the one or more abrasive jet nozzles (17a) through the supply channel outlet and the drill bit fluid inlet (10i) to impact the bottom of the wellbore (4a'), thereby deepening the wellbore (4a); and - during rotation of the drill bit (10) and while a flow (90) of drilling fluid mixed with abrasive particles passes through, varying the concentration of the abrasive particles (92) along a subsequent flow portion of the flow (90) passing through the abrasive jet nozzles (17a) of the drill bit (10) such that the concentration of the abrasive particles (92) is alternately higher in a first flow portion (90h) and lower in a subsequent second flow portion (90l), wherein varying the concentration of the abrasive particles (92) in the flow (90) of drilling fluid mixed with abrasive particles comprises: - upstream of the drill bit fluid inlet (10i), causing the flow (90) to pass parallelly through a first channel (21) and a second channel (22) from the supply channel outlet to a first outlet (21o) and a second outlet (22o) respectively, and then alternately entering the drill bit fluid inlet (10i) from the first outlet (21o) and the second outlet (22o), - during a first time period, deflecting a first major portion (92m1) of all the abrasive particles (92) in the flow (90) passing through the supply channel outlet into the first channel (21), and - during a second time period after the first time period, causing a second major portion (92m2) of all the abrasive particles (92) in the flow (90) passing through the supply channel outlet not to be deflected into the first channel (21), -Subsequently, the flow (90) is made to enter the one or more abrasive jet nozzles (17a) from the first outlet (21o) and the second outlet (22o). Wherein, the difference between the flow resistance of the drilling fluid (91) mixed with the abrasive particles (92) in the first channel (21) and the flow resistance of the drilling fluid (91) mixed with the abrasive particles (92) in the second channel (22) results in a difference between a first velocity when the drilling fluid (91) mixed with the abrasive particles (92) flows through the first channel (21) and a second velocity when the drilling fluid (91) mixed with the abrasive particles (92) flows through the second channel (22). Wherein, the difference between the first velocity and the second velocity causes, downstream of the first outlet (21o) and the second outlet (22o), a first major portion (92m1) of the abrasive particles (92) deflected into the first channel during a first time period and the abrasive particles (92) entering the second channel during a second time period, together with the drilling fluid (91) entering the first channel (21) and the second channel (22) during the first time period and the second time period respectively, to combine to form a first flow portion (90h), and the abrasive particles (92) entering the first channel during the second time period and the abrasive particles (92) entering the second channel during the first time period after the second time period, together with the drilling fluid (91) entering the first channel (21) and the second channel (22) during the second time period and the first time period after the second time period respectively, to combine to form a second flow portion (90l).

2. The method according to claim 1, wherein The change in the concentration of the abrasive particles (92) in the flow (90) of the drilling fluid mixed with the abrasive particles includes: -During a first time period, deflecting a first major portion (92m1) of all the abrasive particles (92) in the flow (90) flowing through the outlet of the supply channel into the first channel (21), and -During a second time period after the first time period, deflecting a second major portion (92m2) of all the abrasive particles (92) in the flow (90) flowing through the outlet of the supply channel into the second channel (22), and -Subsequently, the flow (90) is made to enter the one or more abrasive jet nozzles (17a) from the first outlet (21o) and the second outlet (22o). Wherein, the difference between the flow resistance of the drilling fluid (91) mixed with the abrasive particles (92) in the first channel (21) and the flow resistance of the drilling fluid (91) mixed with the abrasive particles (92) in the second channel (22) results in a difference between a first velocity when the first major portion (92m1) flows through the first channel (21) and a second velocity when the second major portion (92m2) flows through the second channel. Wherein, the difference between the first velocity and the second velocity causes, downstream of the first outlet (21o) and the second outlet (22o), A first major portion (92m1) deflected into a first channel during a first time period and a second major portion (92m2) deflected into a second channel during a second time period are combined with drilling fluid (91) entering the first channel (21) and the second channel (22) during the first time period and the second time period respectively to form a first flow portion (90h), and A small amount of undeflected abrasive particles (92) are combined with drilling fluid (91) entering the first channel (21) and the second channel (22) during the second time period and the first time period respectively to form a second flow portion (90l).

3. The method according to claim 1 or claim 2, wherein The first flow portion (90h) and the second flow portion (90l) pass through one or more abrasive jet nozzles (17a) at a frequency synchronized with the rotational speed of the drill bit (10), and the first time period and the second time period are timed such that - The first flow portion (90h) passes through the abrasive jet nozzle (17a), and the abrasive jet nozzle (17a) is directed towards a selected angular sector (4a'') of the bottom of the wellbore (4a'), and - The second flow portion (90l) passes through the abrasive jet nozzle (17a), and the abrasive jet nozzle (17a) is not directed towards the selected angular sector (4a'') of the bottom of the wellbore (4a').

4. The method according to claim 1 or 2, wherein The abrasive particles (92) are magnetic abrasive particles (92), and the deflection into the first channel (21) and the second channel (22) is achieved by alternately guiding a magnetic field (23B) on the cross-section of the flow (90) immediately upstream of the first channel (21) and the second channel (22) towards the first channel (21) and towards the second channel (22) during the first time period and the second time period respectively, wherein, during the first time period, the density of the magnetic field (23B) in the portion covering the cross-section of the first channel (21) is higher than the density in the portion covering the cross-section of the second channel (22), and during the second time period, the density of the magnetic field in the portion covering the cross-section of the second channel (22) is higher than the density in the portion covering the cross-section of the first channel (21).

5. The method according to claim 1 or 2, wherein The difference between the flow resistances of the drilling fluid (91) mixed with the abrasive particles (92) in the first channel (21) and the second channel (22) is determined by the differences between their respective lengths, their respective cross-sections, the surface roughness of their respective inner wall surfaces in the longitudinal direction, and / or the variations of their respective cross-sections and / or the surface roughness of their inner wall surfaces along their respective lengths.

6. The method according to claim 5, wherein The difference between the flow resistances of the drilling fluid (91) mixed with the abrasive particles (92) in the first channel (21) and the second channel (22) is determined by the differences in their respective cross-sections, and wherein, their respective lengths, the surface roughness of the inner wall surfaces, and the variations along their respective lengths are equal to each other.

7. The method according to claim 1 or 2, wherein The drill bit (10) is a mechanical drill bit (10), which further includes one or more cleaning nozzles (17w) on the drill bit face, and the rotation of the drill bit (10) includes mechanically cutting the bottom of the wellbore (4a') by the mechanical drill bit (10) to deepen the wellbore (4a), The method further includes, simultaneously with the impact of the bottom of the wellbore (4a') by the flow (90) in the form of the abrasive jet, - filtering abrasive particles (92) in the first flow portion (90h) and the second flow portion (90l) upstream of the abrasive jet nozzle (17a) and the cleaning nozzle (17w), and - deflecting the filtered abrasive particles (92) into the abrasive jet nozzle (17a), while - causing the drilling fluid (91) in the first flow portion (90h) and the second flow portion (90l) of the flow (90) to flow into both the abrasive jet nozzle (17a) and the cleaning nozzle (17w).

8. The method according to claim 1 or 2, wherein The method further includes downhole recycling of the abrasive particles (92) passing through the abrasive jet nozzle (17a) for impact with the bottom of the wellbore (4a'), and the downhole recycling includes: - capturing at least a portion of the abrasive particles (92) present in the flow (90) downstream of the impact with the bottom of the wellbore (4a'), and - causing the captured abrasive particles (92) to flow into the flow (90) upstream of the abrasive jet nozzle (17a).

9. The method according to claim 1 or 2, wherein Setting and / or adjusting the duration and / or timing of the first time period and the second time period based on downhole measurements, the downhole measurements including one or more of the following: - detecting abrasive particles downstream of the deflection, - detecting the location of impact with the bottom of the wellbore (4a'), - detecting the geometric direction of deepening of the wellbore (4a).

10. The method according to claim 9, wherein The abrasive particles (92) are magnetic abrasive particles (92), wherein the method further includes: - activating a magnetic field in the first channel (21) and / or the second channel (22) for a time interval to locally accumulate the magnetic abrasive particles (92) in the first channel (21) and / or the second channel (22), thereby generating a pressure pulse within the channel (21, 22), and - subsequently, eliminating the magnetic field, wherein the activation and elimination are repeated to generate a series of pressure pulses over time, and the amplitude and timing of the pressure pulses are determined such that the series of pressure pulses represents one of the downhole measurements for the mud pulse telemetry unit.

11. A directional drilling system (1) for drilling a directional wellbore (4a) in an object (2) using a wellbore bottom (4a'), wherein, The drilling system can be connected to a tubular drill string (40), The directional drilling system (1) includes: - a drill bit (10), which includes: - a drill bit face that faces the bottom of the wellbore (4a') during use, - a drill bit fluid inlet (10i), - one or more abrasive jet nozzles (17a) configured to eject a flow (90) of drilling fluid (91) mixed with abrasive particles (92) as an impact with the bottom of the wellbore (4a') in the form of an abrasive jet, and if there are multiple one or more abrasive jet nozzles (17a), they are arranged at different azimuthal positions, and - An intermediate space between the drill bit fluid inlet (10i) and the one or more abrasive jet nozzles (17a), each of the one or more abrasive jet nozzles (17a) having a nozzle inlet for fluid communication with the intermediate space, each of the nozzle inlets extending from the intermediate space; and - A joint (20) whose lower well end is connected to the drill bit (10), and the other end of the joint (20) is connected to the tubular drill string (40), the joint (20) comprising: - A joint fluid inlet (20i) which can be fluidly connected to a supply channel through the drill string (40) to receive a flow (90) of drilling fluid (91) mixed with abrasive particles (92) from the supply channel when the system (1) is connected to the drill string (40), and - A joint fluid outlet (20o) which is fluidly connected to the drill bit fluid inlet (10i), characterized in that the joint (20) further comprises a regulating unit fluidly connected downstream of the joint fluid inlet (20i), the regulating unit being configured to vary the concentration of abrasive particles (92) along a flow portion of the flow (90) received from the supply channel, which flow portion then enters the drill bit fluid inlet (10i) through the joint fluid outlet (20o), the regulating unit comprising: - A first channel (21) having a first flow resistance to the drilling fluid (91) mixed with abrasive particles (92), a first inlet (21i), and a first outlet (21o) fluidly connected to the joint fluid outlet (20o), - A second channel (22) arranged parallel to the first channel (21) having a second flow resistance to the drilling fluid (91) mixed with abrasive particles (92), a second inlet (22i), and a second outlet (22o) fluidly connected to the joint fluid outlet (20o), - Particle deflecting means (23, 24) between the joint fluid inlet (20i) and the first inlet (21i) and the second inlet (22i), the particle deflecting means (23, 24) comprising one or more actuators (23m, 24m) and being connected to the control unit of the system (1), wherein the particle deflecting means (23, 24) is configured to periodically, - During a first time period, deflect a first major portion (92m1) of all the abrasive particles (92) received from the supply channel through the joint fluid inlet (20i) into the first inlet (21i), and - During a second time period following the first time period, cause a second major portion (92m2) of all the abrasive particles (92) in the flow (90) received from the supply channel through the joint fluid inlet (20i) not to be deflected into the first inlet (21i), wherein the first channel (21) and the second channel (22) are constructed such that the difference between the first flow resistance and the second flow resistance results in a velocity difference between the drilling fluid (91) mixed with abrasive particles (92) passing through the first channel (21) and the drilling fluid (91) mixed with abrasive particles (92) passing through the second channel (22), Wherein, the speed difference causes, in the combined section downstream of the first outlet (21o) and the second outlet (22o), a first major portion (92m1) of the abrasive particles deflected into the first inlet during a first time period and the abrasive particles (92) entering the second inlet during a second time period, to be combined with any of the drilling fluid (91) entering the first inlet (21i) and the second inlet during the first time period and the second time period respectively, to form one of the flow portions, and the abrasive particles (92) entering the first inlet during the second time period and the abrasive particles entering the second inlet during the first time period after the second time period, to be combined with any of the drilling fluid (91) entering the first inlet during the second time period and entering the second inlet during the first time period after the second time period respectively, to form a subsequent one of the flow portions.

12. The directional drilling system (1) according to claim 11, wherein, The control unit and the particle deflection devices (23, 24) are configured to - during a first time period, deflect a first major portion (92m1) of all the abrasive particles (92) in the flow (90) flowing through the outlet of the supply channel into the first channel (21), and - during a second time period after the first time period, deflect a second major portion (92m2) of all the abrasive particles (92) in the flow (90) flowing through the outlet of the supply channel into the second channel (22), and - subsequently cause the flow (90) to enter the one or more abrasive jet nozzles (17a) from the first outlet (21o) and the second outlet (22o), wherein the speed difference causes, in the combined section downstream of the first outlet (21o) and the second outlet (22o), a first major portion (92m1) deflected into the first channel during a first time period and a second major portion (92m2) entering the second inlet during a second time period, to be combined with any of the drilling fluid (91) entering the first inlet (21i) and the second inlet during the first time period and the second time period respectively, to form one of the flow portions, and the abrasive particles (92) entering the first inlet during the second time period and the abrasive particles entering the second inlet during the first time period after the second time period, to be combined with any of the drilling fluid (91) entering the first inlet during the second time period and entering the second inlet during the first time period after the second time period respectively, to form a subsequent one of the flow portions.

13. The directional drilling system (1) according to claim 12, wherein, The control unit is configured such that the signals of the control unit received by the particle deflection devices (23, 24) cause the actuators (23m, 24m) of the particle deflection devices (23, 24) to deflect the first major portion (92m1) and the second major portion (92m2) of the abrasive particles (92) into the first channel (21) and the second channel (22) in a time period synchronized with the rotational speed of the drill bit (10), and timed such that the subsequent one of the flow portions passes through one or more abrasive jet nozzles (17a), while the abrasive jet nozzles (17a) are directed together with any of the drilling fluid (91) entering the first channel (21) and the second channel (22) in the first time period and the second time period respectively to a selected angular sector (4a'') of the wellbore bottom (4a'), and the subsequent one of the flow portions passes through one or more abrasive jet nozzles (17a), while the abrasive jet nozzles (17a) are not directed to the selected angular sector (4a'') of the wellbore bottom (4a').

14. The directional drilling system (1) according to any one of claims 11 - 13, wherein, The abrasive particles (92) are magnetic abrasive particles (92), and the actuators of the particle deflection devices include magnetic switches, the magnetic switches being configured to establish a non-uniform magnetic field (23B) in a cross-section immediately upstream of the first inlet (21i) and the second inlet (22i) in a first time period, the non-uniform magnetic field (23B) guiding the abrasive particles (92) towards the first inlet (21i) in the plane of the cross-section, and to establish a non-uniform magnetic field (23B) in a cross-section immediately upstream of the first inlet (21i) and the second inlet (22i) in a second time period, the non-uniform magnetic field (23B) guiding the abrasive particles (92) towards the second inlet (22i) in the plane of the cross-section, wherein the density of the magnetic field (23B) generated in the first time period is higher in the portion of the cross-section covering the first channel (21) than in the portion of the cross-section covering the second channel (22), and the density of the magnetic field (23B) generated in the second time period is higher in the portion of the cross-section covering the second channel (22) than in the portion of the cross-section covering the first channel (21), wherein the magnetic switch includes a plurality of magnets arranged at different azimuthal positions along the outer circumference of the flow (90) immediately upstream of the first inlet (21i) and the second inlet (22i), the plurality of magnets together generating the non-uniform magnetic field (23B).

15. The directional drilling system (1) according to claim 14, wherein, The magnets are movable permanent magnets, and the actuator further includes a drive device connected to the magnets and configured to move the magnets as a whole along a circumference when switching between respective time periods based on signals received from the control unit to determine that the magnetic field (23B) guides the abrasive particles to respective channels in respective time periods.

16. The directional drilling system (1) according to any one of claims 11-13, wherein, The difference between the flow resistances of the drilling fluid (91) mixed with abrasive particles (92) in the first channel (21) and the second channel (22) is determined by differences between their respective lengths, their respective cross-sections, the surface roughness of their respective inner wall surfaces, and / or changes in their respective cross-sections and / or the surface roughness of their inner wall surfaces along their respective lengths in the longitudinal direction.

17. The directional drilling system (1) according to claim 15, wherein, The difference between the flow resistances of the drilling fluid (91) mixed with abrasive particles (92) in the first channel (21) and the second channel (22) is determined by differences in their respective cross-sections, with their respective lengths, the surface roughness of the inner wall surfaces, and changes along their respective lengths being equal to each other.

18. The directional drilling system (1) according to any one of claims 11-13, wherein, The drill bit (10) is an abrasive jet drill bit, where the bit face has no cleaning nozzles and mechanical cutting tools.

19. The directional drilling system (1) according to any one of claims 11-13, wherein, The drill bit (10) is a mechanical drill bit and further includes: - one or more mechanical cutting tools (18) arranged on the bit face, - one or more cleaning nozzles (17w) arranged at respective adjacent azimuthal positions different from one or more abrasive jet nozzles (17a), - a filter (19) arranged in the intermediate space of the drill bit (10) and rotating with the drill bit (10), the filter (19) configured to direct abrasive particles (92) received in the flow (90) through the drill bit fluid inlet (10i) to the abrasive jet nozzles (17a), while allowing the drilling fluid (91) in the flow (90) to flow into both the abrasive jet nozzles (17a) and the cleaning nozzles (17w).

20. The directional drilling system (1) according to any one of claims 11-13, wherein, The abrasive particles (92) are magnetic abrasive particles (92), and the system further includes a downhole recirculation unit (50) for recirculating the abrasive particles (92) passing through the abrasive jet nozzles (17a) for impact with the bottom of the wellbore (4a'), the downhole recirculation unit (50) including one or more magnets (51) arranged such that the resulting one or more magnetic fields attract the abrasive particles (92) from the flow (90) downstream of the impact with the bottom of the wellbore (4a') and convey the attracted particles (92) in the recirculation flow (93) to the mixing section (52c) at a substantially constant flow rate, the flow (90) passing through the mixing section (52c) upstream of the abrasive jet nozzles (17a).

21. The directional drilling system (1) according to any one of claims 11 - 13, comprising one or more sensors (81, 82), the one or more sensors (81, 82) including one or more of the following: - one or more position sensors (82) configured to and arranged on or directly above the drill bit to provide a signal indicating position to the control unit, - one or more presence detection sensors (81) arranged at a downstream position of the deflection device, the one or more presence detection sensors (81) being configured to provide a signal to the control unit indicating the presence of abrasive particles (92) at the position, - one or more navigation sensors configured and arranged on or directly above the drill bit to provide a signal to the control unit indicating the geometric direction of deepening of the wellbore (4a), The control unit is configured to control the actuators (23m, 24m) of the particle deflection devices (23, 24) based on the signals from the sensors (81, 82).

22. The directional drilling system (1) according to claim 21, wherein, The abrasive particles (92) are magnetic abrasive particles (92), The system (1) further includes a mud pulse telemetry unit, including: - a telemetry control unit configured to receive one or more of the signals provided by one or more of the sensors (81) and encode these signals into a series of pulses having a predetermined timing and amplitude, - a switchable magnet arranged to generate a magnetic field in the first channel and / or the second channel, the switchable magnet being configured to, during activation, cause local accumulation of magnetic abrasive particles in the first channel (21) and / or the second channel (22), thereby generating a pressure pulse within the channels (21, 22), and the switchable magnet, when deactivated, ceases to cause the local accumulation, wherein the telemetry control unit is configured to control the activation and deactivation of the switchable magnet so that the switchable magnet repeatedly generates the pressure pulse to form a series of pressure pulses, the timing and amplitude of the series of pressure pulses corresponding to the encoded series of pulses.

23. A steerable sub (20) for a directional drilling system, the wellbore end of the steerable sub (20) being connectable to the drill bit (10) of the system (1), and the other end of the steerable sub (20) being connectable to the tubular drill string (40) of the system (1), the steerable sub (20) comprising: - a joint fluid inlet (20i) fluidly connectable through the tubular drill string (40) to a supply channel to receive, when the joint (20) is connected to the drill string (40), a flow (90) of drilling fluid (91) mixed with abrasive particles (92) from the supply channel, and - a joint fluid outlet (20o) fluidly connectable to the drill bit fluid inlet (10i) to pass the flow (90) through the drill bit when the joint (20) is connected to the drill bit (10), - an adjustment unit configured to cause a change in the concentration of abrasive particles (92) along a flow portion of the flow (90) received from the supply channel, the adjustment unit being fluidly connected to the downstream joint fluid inlet (20i), the adjustment unit including: - a first channel (21) having a first flow resistance to the drilling fluid (91) mixed with abrasive particles (92), a first inlet (21i), and a first outlet (21o) fluidly connected to the joint fluid outlet (20o), - A second channel (22) arranged parallel to the first channel (21), a second inlet (22i), and a second outlet (22o) fluidly connected to the joint fluid outlet (20o), having a second flow resistance to the drilling fluid (91) mixed with the abrasive particles (92). - Particle deflection devices (23, 24) arranged at a position along the flow (90) between the joint fluid inlet (20i) and the first inlet (21i) and the second inlet (22i), the particle deflection devices (23, 24) including one or more actuators (23m, 24m) capable of being connected to a control unit. wherein the particle deflection devices (23, 24) are configured to periodically. - In a first time period, deflect a first major portion (92m1) of all the abrasive particles (92) received from the supply channel through the joint fluid inlet (20i) into the first inlet (21i), and - In a second time period after the first time period, deflect a second major portion (92m2) of all the abrasive particles (92) in the flow (90) received from the supply channel through the joint fluid inlet (20i) into the second inlet (22i). wherein the first channel (21) and the second channel (22) are constructed such that the difference between the first flow resistance and the second flow resistance results in a velocity difference between the first major portion (92m1) of the abrasive particles (92) passing through the first channel (21) and the second major portion (92m2) of the abrasive particles (92) passing through the second channel (22). wherein the velocity difference causes, in a combined section downstream of the first outlet (21o) and the second outlet (22o), the first major portion (92m1) and the second major portion (92m2) to combine with any of the drilling fluid (91) that enters the first channel (21) and the second channel (22) during the first time period and the second time period respectively to form one of the flow portions, and the small amount of non - deflected abrasive particles (92) combine with any of the drilling fluid (91) that enters the first channel (21) and the second channel (22) during the second time period and the first time period respectively to form the subsequent one of the flow portions.

24. An abrasive particle pulsator for a directional drilling system, the abrasive particle pulsator being configured to vary the concentration of abrasive particles (92) along a flow portion of the flow (90) of abrasive particles (92) mixed with the drilling fluid (91) to pass through one or more abrasive nozzles (17a) of the system (1), the pulsator comprising: - A first channel (21) having a first flow resistance to the drilling fluid (91) mixed with the abrasive particles (92), a first inlet (21i), and a first outlet (21o). - A second channel (22) arranged parallel to the first channel (21), a second inlet (22i), and a second outlet (22o), having a second flow resistance to the drilling fluid (91) mixed with the abrasive particles (92). - Particle deflecting devices (23, 24), which are arranged at positions along the flow (90) immediately upstream of the first inlet (21i) and the second inlet (22i), the particle deflecting devices (23, 24) comprising one or more actuators (23m, 24m) connected to or connectable to a control unit, wherein the particle deflecting devices (23, 24) are configured to periodically, - during a first time period, deflect a first major portion (92m1) of all abrasive particles (92) of the flow (90) passing through said position into the first inlet (21i), and - during a second time period following the first time period, deflect a second major portion (92m2) of all abrasive particles (92) of the flow (90) passing through said position into the second inlet (22i), wherein the first channel (21) and the second channel (22) are constructed such that a difference between a first flow resistance and a second flow resistance results in a velocity difference between said first major portion (92m1) of abrasive particles (92) passing through the first channel (21) and said second major portion (92m2) of abrasive particles (92) passing through the second channel (22), wherein the velocity difference causes, in a combined section downstream of the first outlet (21o) and the second outlet (22o), the first major portion (92m1) and the second major portion (92m2) to combine with any of said drilling fluid (91) entering the first inlet (21i) and the second inlet (22i) during the first time period and the second time period, respectively, into one of said flow portions, and the small number of non-deflected abrasive particles (92) to combine with any drilling fluid (91) entering the first channel (21) and the second channel (22) during the second time period and the first time period, respectively, into a subsequent one of said flow portions.

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