Drilling tool

Abstract

The present disclosure is directed to a drilling tool (1) for underground drilling in a borehole (5). The drilling tool (1) comprises a housing (10) comprising a longitudinal 5 axis (12). Further, the drilling tool (1) comprises a drill head (20) being arranged to drill along a drilling direction (22). Moreover, the drilling tool (1) comprises a first retention means (30) being radially extendable from the housing (10) with respect to the longitudinal axis (12). Said first retention means (30) is configured to anchor the drilling tool (1) in the borehole (5) by radially extending the first retention means (30). 10 Even further, the drilling tool (1) comprises a second retention means (40) being radially extendable from the housing (10) with respect to the longitudinal axis (12). Said second retention means (40) is configured to anchor the drilling tool (1) in the borehole (5) by radially extending the second retention means (40). Furthermore, the drilling tool (1) comprises a displacement device (50) being configured to change the 15 axial distance along the longitudinal axis (12) between the first retention means (30) and the second retention means (40).

Description

[0001] DRILLING TOOL

[0002] 1. Technical field

[0003] The present disclosure relates to a drilling tool for underground drilling in a borehole, a method for underground drilling, a power generation device for generating electric power inside a borehole, a method for generating electric power by means of said power generation device, and an underground drilling system.

[0004] 2. Prior art

[0005] It is known that in order to produce hydrocarbons, such as oil and / or gas, a borehole that extends into the hydrocarbon reservoir must first be drilled. This borehole can then be used to transport the oil and / or gas to the earth’s surface. Various techniques are used for drilling boreholes into hydrocarbon reservoirs, wherein two existing techniques are mentioned below.

[0006] A first technique is the use of drill pipes. This regularly involves connecting a plurality of drill pipes one after the other to move a drilling tool into the earth in the direction of a hydrocarbon formation. A second technique is the use of a coiled tubing at the end of which a drilling tool is attached. The coiled tubing serves to move the drill head into the earth in the direction of a hydrocarbon formation.

[0007] However, the known techniques for drilling boreholes and especially the two mentioned techniques have various limitations and / or disadvantages. For example, it is often not possible to achieve a desired horizontal and / or vertical depth of boreholes in order to realize an improved penetration of the hydrocarbon formation and thus a larger and / or more complete yield.

[0008] A first reason for this can be that above a certain insertion depth, retraction of the drill pipes or coiled tubing becomes impossible, since due to the dead weight such a high force would be required for retraction that the drill pipes or coiled tubing would be damaged during removal. Accordingly, an insertion above such insertion depths needs to be avoided. A second reason may be that, when using both drill pipes and / or coiled tubing, a lock-up occurs above a specific essentially horizontal insertion length, whereby the drill head cannot be moved any further. The particular reason for this may be that friction within the borehole prevents further movement of the drill pipes or the coiled tubing. A third reason can be that the drilling depth is regularly limited by the fact that, in the case of drill pipes driven at the earth’s surface, buckling of the rotating drill pipes occurs at increased drilling depths.

[0009] Thus, it is a first object of the present disclosure to provide a drilling tool and a respective method for underground drilling that overcome the aforementioned drawbacks at least partially. Particularly, it is an object of the present disclosure to provide a drilling tool and a respective method which allow longer horizontal and / or vertical drill holes.

[0010] Furthermore, for the underground operation of drill heads, power supply is often a critical aspect. Regularly complex conduit systems up to the earth’s surface are required, wherein these systems are prone to error and / or are complex to install.

[0011] Hence, a second object addressed by the present disclosure is to provide a power generation device and a respective method for generating electric power by means of said power generation device that overcome these drawbacks at least partially. In particular, the object is to provide power generation that is reliable and / or independent of the earth’s surface. . Summary of the invention

[0012] The first object is achieved, at least partly, by a drilling tool for underground drilling in a borehole, a method for underground drilling, a power generation device for generating electric power inside a borehole, a method for generating electric power by means of said power generation device, and an underground drilling system, as defined in the independent claims. Further aspects of the present disclosure are defined in the dependent claims.

[0013] In particular, the first object is achieved by a drilling tool for underground drilling in a borehole. The drilling tool comprises a housing comprising a longitudinal axis. Further, the drilling tool comprises a drill head being arranged to drill along a drilling direction. Moreover, the drilling tool comprises a first retention means being radially extendable from the housing with respect to the longitudinal axis, wherein the first retention means is configured to anchor the drilling tool in the borehole by radially extending the first retention means. Even further, the drilling tool comprises a second retention means being radially extendable from the housing with respect to the longitudinal axis, wherein the second retention means is configured to anchor the drilling tool in the borehole by radially extending the second retention means. It is to be understood that the term “radial extension” does not exclude an extension that is also partially along the longitudinal axis or along a circumferential direction. Furthermore, the drilling tool comprises a displacement device being configured to change the axial distance along the longitudinal axis between the first retention means and the second retention means.

[0014] The housing may comprise a plurality of housing segments. Further, it is understood that the longitudinal axis of the housing may correspond to an axis along which the drilling tool is configured to be guided in the borehole.

[0015] The drill head maybe arranged to drill along the longitudinal axis. Hence, the drilling direction may correspond with the direction of the longitudinal axis. Further, it is understood that for drilling the drill head may rotate relative to the housing. Moreover, the drill head maybe tilted relative to the housing. For example, for changing the drilling direction. In particular, the drill head maybe a steering drill head. Moreover, the drilling tool maybe used within a rotary steerable system (RSS). Exemplarily, the drill head may be configured to be steered preferably in real-time while rotating. Hence, the need for multiple trips in and out of the wellbore to change the drilling trajectory maybe eliminated. Furthermore, the drill head may comprise a variety of different drilling bits. For example, the drill head may comprise a drag bit, a roller cutter bit, a milled tooth bit, an insert bit, a polycrystalline diamond compact bit, a polycrystalline diamond compact core bit, a roller cone core bit, a diamond core bit, and / or combinations thereof. Further in this regard it is to be noted that the drill head may be adapted such that said drilling bits can be exchanged.

[0016] The first retention means and / or the second retention means may each comprise respective anchoring elements. Further details hereon are described throughout the following. When the first retention means anchors the drilling tool in the borehole this may refer to the aspect that the first retention means is immobile with respect to an axial extension direction of the borehole. Accordingly, when the second retention means anchors the drilling tool in the borehole this may refer to the aspect that the second retention means is immobile with respect to an axial extension direction of the borehole. It is understood that the drilling tool may comprise more than two retention means. That the first retention means and the second retention means are each radially extendable from the housing with respect to the longitudinal axis may also include a radial extension with an axial movement component with respect to the longitudinal axis. For example, the first retention means and / or the second retention means may comprise an elongated element being rotatably attached to the housing and being configured to be tilted outwards with respect to the longitudinal axis. In addition, it is to be noted that the radial extension may function similar to an aperture mechanism, i.e., that there is also a movement component in the circumferential direction.

[0017] The displacement device may be configured to change the axial distance along the longitudinal axis between the first retention means and the second retention means when the first retention means is anchored in the borehole and the second retention means is not. Further, the displacement device may be configured to change the axial distance along the longitudinal axis between the first retention means and the second retention means when the second retention means is anchored in the borehole and the first retention means is not. The displacement device may be an integrally formed unit. Alternatively, the displacement device may comprise subunits. For example, a first displacement subunit may serve to change an axial position of the first retention means with respect to the longitudinal axis and a second displacement subunit may serve to change an axial position of the second retention means with respect to the longitudinal axis.

[0018] The drilling tool according to the present disclosure has different advantages, particularly when compared to existing drilling tools. For example, by being provided with the first and second retention means and the displacement device the drilling tool can perform, or at least support, a forward movement and / or a backward movement in the borehole. Thus, a lock-up during substantially horizontal drilling maybe prevented. In detail, said lock-up may refer to a condition that may occur when a coiled tubing or a drill pipe is run into a substantially horizontal or highly deviated borehole. Lock-up occurs when the frictional force encountered by the coiled tubing or the drill pipe running inside the borehole reaches a critical point. Accordingly, the end of the coiled tubing or the drill pipe cannot be moved farther into the borehole. This problem may be at least partially overcome by the drilling tool according to the present disclosure.

[0019] Further, by being provided with the first and second retention means the drill head may be supported against the borehole. Thus, a rotation of the drill head relative to the housing can be prevented to cause a twisting of a coiled tubing or a drill pipe being attached to the housing. Further advantages of the drilling tool described herein will become apparent in light of the following description.

[0020] The first retention means may be extendable from the housing independently of the second retention means, and / or wherein the second retention means maybe extendable from the housing independently of the first retention means. Particularly, the first retention means may be controlled independently from the second retention means and / or the second retention means may be controlled independently from the first retention means. This allows particularly flexible control of the drilling process so that it can be adapted to different conditions.

[0021] The first retention means and / or the second retention means may comprise at least two, preferably at least three, and further preferably at least four anchoring elements respectively, wherein each of said anchoring elements is radially extendable from the housing with respect to the longitudinal axis and wherein each of said anchoring elements is preferably configured to form-fittingly and / or force-fittingly engage with the borehole. For example, the first retention means may comprise at least two, preferably at least three, and further preferably at least four anchoring elements. As a further example, the second retention means may comprise at least two, preferably at least three, and further preferably at least four anchoring elements. Said anchoring means may comprise a pointed rod element being configured to penetrate the earth material and / or rock material of a borehole. Further, the anchoring means may comprise a curved plate element configured to be supported against an interior wall of a borehole. For example, a radius of the curved plate element may match the radius of the borehole. Said pointed rod element may substantially allow for a form-fitting engagement with the borehole, whereas said curved plate element may substantially allow for a force-fitting engagement with the borehole. Nevertheless, it is understood that combinations of a form-fitting engagement and a force-fitting engagement are possible and maybe desired.

[0022] The first retention means and / or the second retention means may be configured to center the drilling tool in the borehole when being radially extended from the housing respectively. For example, the first retention means may comprise four anchoring elements, wherein the drilling tool may be centered in the borehole by radially extending each anchoring element from the housing by the same distance. Centering the drilling tool in the borehole allows for accurate and / or predictable drilling operations. The drilling tool may be electrically and / or hydraulically powered. For example, the drilling tool may comprise an electric motor. Said electric motor may be powered by an energy storage inside the drilling tool and / or by an electric supply line. Moreover, the drilling tool may be hydraulically powered by means of a hydraulic supply line.

[0023] The housing may comprise attachment means being adapted to attach the drilling tool to a coiled tubing and / or a drill pipe. For example, the attachment means may comprise a thread and / or a hole for a bolt and / or hook connection. By said attachment means the drilling tool may be used together with conventional technologies so that logistical and / or modification efforts can be reduced.

[0024] A drill pipe as described herein maybe a tubular steel conduit fitted with special threaded ends called tool joints. Regularly, drill pipes connect a rig surface equipment with drilling tools, for example to pump drilling fluid to the drilling tool, to be able to raise / lower, and / or to rotate the drilling tool and / or the drill head.

[0025] A coiled tubing as described herein maybe a continuous pipe wound on a spool. Regularly, said pipe is straightened prior to pushing into a borehole and rewound to coil the pipe back onto the transport and storage spool. Depending on the pipe diameter and the spool size, coiled tubing usually allows for depth ranges from 6oo to 5000 m.

[0026] The displacement device may comprise a pressure cylinder, wherein the pressure cylinder preferably is a hydraulic cylinder, wherein further preferably the pressure cylinder is arranged substantially parallel to the longitudinal axis. It has been shown that said pressure cylinder can provide sufficient force to push the drill head forward also during drilling. This can ensure a continuous drilling process. In this regard hydraulic cylinders are particularly advantageous as they allow precise drilling speed control.

[0027] The drill head may be axially displaceable relative to the housing along the longitudinal axis, wherein preferably the drill head is axially displaceable relative to the housing along the longitudinal axis while drilling. This allows deviations in the drilling speed, which can be caused for example by the retraction and extension of a displacement device, to be effectively compensated. As a result, a more uniform drilling process can be achieved, which can be advantageous for wear of the drill head, for example. Preferably the housing comprises a first housing segment which comprises the first retention means, and a second housing segment which comprises the second retention means, wherein the displacement device is configured to change the axial distance between the first housing segment and the second housing segment relative to the longitudinal axis. This design has proven to be particularly robust. One aspect of this can be that the retention means themselves do not necessarily have to be moved axially relative to the longitudinal axis and the housing. In other words, a separation of functions can be achieved, and the components concerned can be better adapted to one particular function.

[0028] The first housing segment may be slidably arranged within the second housing segment or the second housing segment may be slidably arranged within the first housing segment. For example, the first housing segment and the second housing segment may each comprise a substantially cylindrical shape, wherein the diameter of the second housing segment is smaller than the diameter of the first housing segment so that it can slide within the first housing segment. This embodiment is advantageous in that with a simple design, penetration of dirt and / or liquids into the drilling tool can be prevented.

[0029] The drill head may be attached to the second housing segment. It is understood that the drill head may be rotatably attached to the second housing segment. Particularly, the drill head may be attached to the second housing segment via a drill head displacement cylinder. This drill head displacement cylinder may be a pressure cylinder. Moreover, said drill head displacement cylinder may ensure that the drill head is axially displaceable relative to the housing along the longitudinal axis. Respective advantages are set out above.

[0030] The first housing segment may comprise the attachment means as described above. The respective advantages described with regards to the attachment means apply.

[0031] The drilling tool may further comprise a refrigeration element. This refrigeration element maybe operated electrically, e.g., by means of an energy storage within the drilling tool. Moreover, the refrigeration element maybe operated by a cooling fluid which is provided via a supply line. Said refrigeration element can provide cooling of the drill head. This can extend the service life of the drill head. In addition, the refrigeration element can enable greater drilling depths to be reached, where the naturally prevailing temperature would otherwise cause damage to the drilling tool and / or the drill head. The drilling tool may further comprise a pressure sensor. From this pressure sensor information can be obtained, which can be used to implement more accurate drilling. Preferably, the information is processed in the drilling tool. Accordingly, an error- prone signal line to the earth’s surface can be avoided or at least be designed redundantly.

[0032] The drill head may be electrically powered. This can eliminate the need for a linkage that transmits rotation from the earth’s surface to the drilling tool. Consequently, a simpler drilling process can be achieved.

[0033] The drilling tool may further comprise a seismic sensor and / or a seismic signal generator. With the help of the seismic sensor, the drilling tool may receive control commands from the earth’s surface, for example. Moreover, by means of the seismic signal generator the drilling tool may send information to the earth’s surface. Accordingly, an error-prone signal line to the earth’s surface can be avoided or at least be designed redundantly.

[0034] Moreover, the drilling tool may comprise transporting means for transporting one or more components inside the borehole by means of the drilling tool. The transporting means maybe configured to receive, retain, and / or dispense at least one component. Exemplarily the transporting means may comprise respective latching hooks which are configured to receive, retain, and / or dispense at least one component, such as a tube segment or a sensor. The drilling tool may be configured such that transporting can be performed while operating the drill head. Further, the drilling tool may be configured such that transporting can be performed when the drill head is not operated. The drilling tool comprising the transporting means could be operated without the drill head, e.g. after a drilling operation is already completed to transport a component needed in the borehole. Thus, in such embodiments the drilling tool may but does not have to comprise the drill head.

[0035] Further, the first object is achieved by a method for underground drilling. The method comprises the following steps (a) to (g):

[0036] (a) Arranging a drilling tool as described herein in a borehole.

[0037] (b) Operating the drill head to drill in the drilling direction of the drill head.

[0038] Further the method comprises the following steps in the given order: (c) Radially extending the first retention means from the housing with respect to the longitudinal axis. Thereby the first retention means maybe anchored in the borehole. The first retention means can be the retention means being further away from the drill head.

[0039] (d) Actuating the displacement device to increase the axial distance between the first retention means and the second retention means along the longitudinal axis. For example, if the displacement device comprises a pressure cylinder, as described above, then the displacement device may be actuated to increase the axial distance between the first retention means and the second retention means along the longitudinal axis by introducing an overpressure into the pressure cylinder.

[0040] (e) Radially extending the second retention means from the housing with respect to the longitudinal axis. Thereby the second retention means maybe anchored in the borehole. The second retention means can be the retention means being closer to the drill head.

[0041] (f) Radially retracting the first retention means towards the housing. Thereby the anchoring of first retention means in the borehole may be reversed.

[0042] (g) Actuating the displacement device to reduce the axial distance between the first retention means and the second retention means relative to the longitudinal axis. For example, if the displacement device comprises said pressure cylinder, then the displacement device may be actuated to reduce the axial distance between the first retention means and the second retention means along the longitudinal axis by introducing a negative pressure into the pressure cylinder.

[0043] It is understood that the drill head may rotate while any of the steps (c) to (g) are performed. Further, it is to be noted that the drill head can also be idle during any of steps (c) to (g).

[0044] The method for underground drilling according to the present disclosure has different advantages, particularly when compared to existing drilling methods. It is to be noted that the advantages described above with regards to the drilling tool may also apply for the method since the drilling tool is utilized for the drilling method. In detail, the method for underground drilling may allow that a lock-up during substantially horizontal drilling can be prevented. Moreover, the method may prevent a rotation of the drill head relative to the housing to cause a twisting of a coiled tubing or a drill pipe being attached to the housing.

[0045] The method may further comprise the step of radially retracting the second retention means towards the housing, wherein this step is preferably performed directly before, directly after, and / or while radially extending the first retention means from the housing. In this regard the term “directly” may refer to the aspect that no additional method step is performed between the respective method steps. Particularly preferred, said step is performed directly after radially extending the first retention means from the housing. This is as thereby an instability of the drilling tool inside the borehole may be reliably avoided.

[0046] Moreover, the method may comprise the step of transporting one or more components inside the borehole by means of the drilling tool. The step of transporting may comprise receiving, retaining, and / or dispensing at least one component. Exemplarily the drilling tool may comprise respective latching hooks which are configured to receive, retain, and / or dispense at least one component, such as a tube segment. Transporting maybe performed while operating the drill head.

[0047] Moreover, transporting may also be performed while the drill head is not operated and when the drilling tool does not comprise a drill head. Hence, the method may alternatively also be a method for underground transportation. The method may comprise the following steps (a) to (h):

[0048] (a) Arranging a drilling tool as described herein in a borehole.

[0049] (b) Transporting one or more components inside the borehole by means of the drilling tool, wherein transporting preferably comprises receiving, retaining, and / or dispensing at least one component.

[0050] (c) Optionally operating the drill head to drill in the drilling direction of the drill head.

[0051] Further the method comprises the following steps in the given order:

[0052] (d) Radially extending the first retention means from the housing with respect to the longitudinal axis. Thereby the first retention means maybe anchored in the borehole. The first retention means can be the retention means being further away from the drill head. (e) Actuating the displacement device to increase the axial distance between the first retention means and the second retention means along the longitudinal axis. For example, if the displacement device comprises a pressure cylinder, as described above, then the displacement device may be actuated to increase the axial distance between the first retention means and the second retention means along the longitudinal axis by introducing an overpressure into the pressure cylinder.

[0053] (f) Radially extending the second retention means from the housing with respect to the longitudinal axis. Thereby the second retention means maybe anchored in the borehole. The second retention means can be the retention means being closer to the drill head.

[0054] (g) Radially retracting the first retention means towards the housing. Thereby the anchoring of first retention means in the borehole may be reversed.

[0055] (h) Actuating the displacement device to reduce the axial distance between the first retention means and the second retention means relative to the longitudinal axis. For example, if the displacement device comprises said pressure cylinder, then the displacement device may be actuated to reduce the axial distance between the first retention means and the second retention means along the longitudinal axis by introducing a negative pressure into the pressure cylinder.

[0056] Moreover, the second object is achieved by a power generation device for generating electric power inside a borehole that extends into a subterranean hydrocarbon reservoir. The power generation device comprises a housing comprising a first pressure chamber and a second pressure chamber. The first pressure chamber is airtightly sealable within the housing. That the chamber is airtightly sealable may further include that the chamber is sealable against natural gas, oil, water, or mixtures thereof. The second pressure chamber comprises a pressure equalization opening which is configured such that the pressure inside the second pressure chamber is equal to the ambient pressure outside of the second pressure chamber in a proximity of the pressure equalization opening. Further, the power generation device comprises an electrically conductive coil, and a rigid, movable device which separates the first pressure chamber from the second pressure chamber. The movable device is configured such that if the first pressure chamber is airtightly sealed, the movable device moves when the ambient pressure changes. Moreover, the movable device comprises a magnet being configured to induce an electrical voltage in the electrically conductive coil when it moves. It is understood that a subterranean hydrocarbon reservoir may also be a reservoir tapped from the seabed. Thus, the term “subterranean” does not limit the claimed tool and method to onshore applications. Instead, offshore applications are also possible.

[0057] The power generation device allows for an independent generation of electric energy within a borehole. Particularly, by means of the power generation device energy may be produced in the borehole without a supply line. This enables drilling processes that are independent of the earth’s surface, for example.

[0058] The rigid, movable device may be slidably guided inside the housing along a sliding direction. Due to a sliding arrangement, rolling bearing elements can be dispensed with, so that the number of wear components is kept low.

[0059] The coil may comprise a substantially cylindrical shape. A longitudinal axis of the coil maybe parallel to the sliding direction. This increases the induce voltage.

[0060] A magnetic North-South axis of the magnet may be substantially parallel to the sliding direction. This increases the induce voltage. “Substantially parallel” may mean that the North-South axis is within at most 20°, preferably at most io°, more preferably at most 5° axial deviation from the sliding direction.

[0061] The movable device may be arranged to linearly move between the first pressure chamber and the second pressure chamber. A linear movement has proven to be advantageous in that it allows particularly simple designs to be realized. For example, this allows a hollow cylindrical container to serve as the housing and a movable device in the shape of a cylinder arranged therein.

[0062] The pressure equalization opening of the second pressure chamber may be covered by a screen filter and / or a balloon. The screen filter can be designed as a wire mesh. Alternatively, a membrane can be used as the screen filter. The balloon may be designed as a rubber balloon. Further, the balloon may be housed by a wire frame being attached to the outside of the housing of the power generation device. Thus, the balloon maybe protected against environmental influences. If the pressure equalization opening is covered by a balloon, then second pressure chamber and the balloon may be filled with a fluid such as oil, water, and or gas. Thus, when the ambient pressure outside of the second pressure chamber in the proximity of the pressure equalization opening increases, e.g., when the power generation device is transferred into a borehole, then the size of the balloon is reduced, and the fluid is urged into the second pressure chamber. The screen filter and / or the balloon can prevent impurities from entering the power generation device.

[0063] The magnet may be movably arranged inside the electrically conductive coil. Further, the electrically conductive coil maybe fixedly attached to the housing. For example, the coil may be integrally formed with the housing. It has shown that fixedly attaching the coil to the housing allows for particularly robust designs of the power generation device.

[0064] Even further, the above object is achieved by a method for generating electric power by means of a power generation device according to one of the preceding claims. The method comprises the following steps in the given order: (i) providing the power generation device; (ii) pressurizing the first pressure chamber to a first pressure and airtightly sealing the first pressure chamber; (iii) introducing the power generation device into a borehole such that the power generation device is in contact with a fluid inside the borehole, and (iv) controlling a flow of the fluid through the borehole such that pressure changes are introduced in the second pressure chamber.

[0065] The features and / or advantages described above with regards to the power generation device may also apply for the method for generating electric power and vice versa.

[0066] It is understood that controlling the fluid flow through the borehole may be performed on the earth’s surface, e.g., by means of respective valves. Moreover, controlling the fluid flow through the borehole may be performed by means of valves inside the borehole, e.g., by means of flapper valves and / or aperture valves.

[0067] The power generation device may be introduced to a depth inside the borehole wherein the ambient pressure at the depth and thus a second pressure in the second pressure chamber exceeds the first pressure which was introduced in the first pressure chamber. This results in an equalization of the pressures within the two chambers, so that the movable device reaches an equilibrium between the chambers and a pressure change in the second pressure chamber directly leads to a displacement of the magnet, which induces a voltage in the electrically conductive coil.

[0068] Further, controlling the fluid flowthrough the borehole may comprise a repeated throttling and / or interrupting of the fluid flow. This can generate ambient pressure changes in the proximity of the pressure equalization opening, wherein those pressure changes are introduced in the second pressure chamber and cause the movable device to move so that the magnet induces an electrical voltage in the coil. Accordingly, energy maybe produced in the borehole, for example even without a supply line.

[0069] The energy may be stored in a battery. This may provide a more constant supply of energy, for example to a drilling tool.

[0070] The first pressure lies in the range from 7 MPa to 35 MPa, preferably from 13 MPa to 27 MPa, and further preferably from 17 MPa to 24 MPa. It has been shown that these pressures are suitable for efficiently operating the power generation device at a variety of drilling depths.

[0071] The power generation device for generating electric power inside a borehole that extends into a subterranean hydrocarbon reservoir may alternatively be used in underwater applications to enable self-sufficient power generation underwater. For example, pressure changes generated by waves underwater can create pressure changes within the second pressure chamber. Thus, the magnet being configured to induce an electrical voltage in the electrically conductive coil may move and induce a respective electrical voltage. Specific underwater applications may comprise subsea navigation devices being powered by the power generation device in order to provide navigation signals, e.g., to ships. Moreover, the power generation device may be arranged inside a black box of an aircraft. Thus, if the aircraft has crashed over the ocean, signals can then be sent from the black box over an extended period of time. Accordingly, better traceability of the aircraft is possible.

[0072] Further, the above objects are achieved by an underground drilling system comprising the drilling tool described herein, and the power generation device described herein, wherein the power generation device is configured to provide the drilling tool with electric power.

[0073] 4. Brief description of the accompanying figures

[0074] In the following, the accompanying figures are briefly described:

[0075] Fig. 1 shows a schematic first drilling tool according to the present invention in lateral sectional view;

[0076] Fig. 2 shows the first drilling tool in top view; Fig. 3 shows a schematic second drilling tool according to the present invention in lateral sectional view;

[0077] Fig. 4 shows a schematic third drilling tool according to the present invention in lateral sectional view;

[0078] Figs. 5a-d illustrate the steps of a method for underground drilling according to the present invention;

[0079] Fig. 6 shows a diagram of the method for underground drilling;

[0080] Fig. 7 shows a schematic power generation device according to the present invention in lateral sectional view;

[0081] Fig. 8 shows another schematic power generation device according to the present invention in lateral sectional view, and

[0082] Fig. 9 shows a diagram of a method for generating electric power according to the present invention. . Detailed description of the figures

[0083] Figs. 1, 3, and 4 show different drilling tools 1 according to the present invention. However, apart from the differences described, the features described for the drilling tool 1 of the first embodiment may also apply to the drilling tool 1 of the second embodiment and the third embodiment.

[0084] Fig. 1 shows a drilling tool 1 for underground drilling in a borehole 5. The drilling tool 1 comprises a housing 10 comprising a longitudinal axis 12. From Fig. 1 together with Fig. 2 it is understood that the longitudinal axis 12 is also an axis of rotational symmetry for several components of the drilling tool 1.

[0085] Moreover, the depicted drilling tool 1 comprises a drill head 20 being arranged to drill along a drilling direction 22. In Fig. 1 the drilling direction 22 and the longitudinal axis 12 are parallel to one another. As depicted, the drill head 20 is axially displaceable relative to the housing 10 along the longitudinal axis 12 by means of a drill head displacement cylinder 24. Particularly, the drill head 20 is axially displaceable relative to the housing 10 along the longitudinal axis 12 while drilling. Further, the drilling tool 1 comprises a first retention means 30 being radially extendable from the housing 10 with respect to the longitudinal axis 12. The first retention means 30 is configured to anchor the drilling tool 1 in the borehole 5 by radially extending the first retention means 30, whereas in Fig. 1 the first retention means 30 is not radially extended. Even further, the drilling tool 1 comprises a second retention means 40 being radially extendable from the housing 10 with respect to the longitudinal axis 12. The second retention means 40 is configured to anchor the drilling tool 1 in the borehole 5 by radially extending the second retention means 40, wherein in Fig. 1 the second retention means 40 anchors the drilling tool 1 in the borehole 5 by being radially extended. The first retention means 30 is extendable from the housing 10 independently of the second retention means 40, and the second retention means 40 is extendable from the housing 10 independently of the first retention means 30.

[0086] Furthermore, the drilling tool 1 comprises a displacement device 50 being configured to change the axial distance along the longitudinal axis 12 between the first retention means 30 and the second retention means 40.

[0087] Fig. 2 shows that the second retention means 40 comprises four anchoring elements 42a, 42b, 42c, 42b, wherein each of said anchoring elements 42a, 42b, 42c, 42b is radially extendable from the housing 10 with respect to the longitudinal axis 12. Further, each of said anchoring elements 42a, 42b, 42c, 42b is configured to form- fittingly engage with the borehole 5. Said form-fit is achieved by penetrating the sidewall of the borehole.

[0088] Fig. 3 shows a drilling tool 1, wherein the first retention means and the second retention means are each configured to force-fittingly engage with the borehole 5. Said force-fit is achieved by pressing anchoring elements with a plate geometry against the sidewall of the borehole 5. As also illustrated in Fig. 3, the first retention means 30 and the second retention means 40 are configured to center the drilling tool 1 in the borehole 5 when being radially extended from the housing 10 respectively. Moreover, the housing 10 comprises attachment means 60 being adapted to attach the drilling tool 1 to a coiled tubing and / or a drill pipe.

[0089] Moreover, as also depicted in Fig. 1 and Fig. 3, the housing 10 comprises a first housing segment 14 which comprises the first retention means 30, and a second housing segment 16 which comprises the second retention means 40. The displacement device 50 is configured to change the axial distance between the first housing segment 14 and the second housing segment 16 relative to the longitudinal axis 12. Particularly, the displacement device 50 comprises a pressure cylinder 52, which maybe a hydraulic cylinder. As depicted, the pressure cylinder 52 is arranged substantially parallel to the longitudinal axis 12. The drill head 20 is attached to the second housing segment 16 and the first housing segment 14 comprises the attachment means 60.

[0090] Fig. 4 shows a drilling tool 1 according to a third embodiment of the present invention. Unlike in Figs. 1 and 3, the housing 10 of the drilling tool 1 of the third embodiment has an integral design. Accordingly, the displacement device 50 is configured such that the first retention means 30 and the second retention means 40 can be moved independently of each other with respect to the longitudinal axis 12. Furthermore, the drilling tool 1 of the third embodiment is configured to allow flow through the drilling tool 1 along the longitudinal axis 12. Thus, it is possible to convey a fluid and / or solid parts, such as oil, already during the drilling process. Moreover, by means of the drilling tool as depicted in Fig. 4, a core sample may be taken. It is understood that for taking a core sample further technical means may need to be provided which allow the core sample to be retained inside the drilling tool 1. An example of this may be interlocking doors that close the opening, i.e., the through hole, of the drilling tool 1 from the side of the drill head 20 so that a corresponding core sample can be held within the drilling tool 1.

[0091] Fig. 6 shows a diagram of a method too for underground drilling. Figs. 5a-d illustrate steps of this method too. As depicted in Fig. 6, the method too comprises the steps of

[0092] (a) Arranging 110 a drilling tool 1 as described herein in a borehole 5.

[0093] (b) Operating 120 the drill head 20 to drill in the drilling direction 22 of the drill head 20. Further, the method too further comprises the following steps in the given order:

[0094] (c) Radially extending 130 the first retention means 30 from the housing 10 with respect to the longitudinal axis 12. This step corresponds to Fig. 5a, where the first retention means 30 is radially extended.

[0095] (c’) The method further comprises the step of radially retracting 140 the second retention means 40 towards the housing 10. It is understood that this step needs to be performed in order to move from the state in Fig. 5d to the state in Fig. 5a. In particular, if a continuous movement of the drilling tool 1 is to be achieved.

[0096] (d) Actuating 150 the displacement device 50 to increase the axial distance between the first retention means 30 and the second retention means 40 along the longitudinal axis 12. This step corresponds to Fig. 5b, where the displacement device 50 has increased the axial distance between the first retention means 30 and the second retention means 40 along the longitudinal axis 12 compared to Fig. 5a.

[0097] (e) Radially extending 160 the second retention means 40 from the housing 10 with respect to the longitudinal axis 12. This step corresponds to Fig. 5c, where the second retention means 40 has been extended from the housing 10 with respect to the longitudinal axis 12 compared to Fig. 5b.

[0098] (f) Radially retracting 170 the first retention means 30 towards the housing 10. This step corresponds to Fig. 5c, where the first retention means 30 has been retracted towards the housing 10 compared to Fig. 5b.

[0099] (g) Actuating 180 the displacement device 50 to reduce the axial distance between the first retention means 30 and the second retention means 40 relative to the longitudinal axis 12. This step corresponds to Fig. 5d, where the displacement device 50 has reduced the axial distance between the first retention means 30 and the second retention means 40 relative to the longitudinal axis 12 compared to Fig. 5c.

[0100] Fig. 7 shows a power generation device 500 for generating electric power inside a borehole 5 that extends into a subterranean hydrocarbon reservoir. The power generation device 500 comprises a housing 510 comprising a first pressure chamber 512 and a second pressure chamber 514. Said first pressure chamber 512 is airtightly sealable within the housing 510. Further, the second pressure chamber 514 comprises a pressure equalization opening 515 which is configured such that the ambient pressure is present in the second pressure chamber 514. This pressure equalization opening 515 of the second pressure chamber 514 is covered by a screen filter 516. Moreover, the power generation device 500 comprises an electrically conductive coil 520, wherein the electrically conductive coil 520 is fixedly attached to the housing 510. Even further, the power generation device 500 comprises a rigid, movable device 530 which separates the first pressure chamber 512 from the second pressure chamber 514. The movable device 530 is configured such that if the first pressure chamber 512 is airtightly sealed, the movable device 530 moves when the ambient pressure changes. In addition, the movable device 530 comprises a magnet 532 being configured to induce an electrical voltage in the coil 520 when it moves. Particularly, the magnet 532 is movably arranged inside the electrically conductive coil 520. Further, the movable device 530 is arranged to linearly move between the first pressure chamber 512 and the second pressure chamber 514. The rigid, movable device 530 is slidably guided inside the housing 510 along a sliding direction 550. Particularly, the movable device 530 comprises a first sliding plate 534 and a second sliding plate 536. Both sliding plates are rigidly attached to the magnet 532. Moreover, the sliding plates 534, 536 seal and separate the first pressure chamber 512 from the second pressure chamber 514. It is understood that alternatively the sliding plates 534, 536 may be integrally formed with each other, for example as a housing structure in which the magnet 532 is received.

[0101] Further, the coil 520 comprises a substantially cylindrical shape. A longitudinal axis 522 of the coil 520 is parallel to the sliding direction 550. Further, a magnetic North- South axis 533 of the magnet 532 is substantially parallel to the sliding direction 550.

[0102] Fig. 8 shows the power generation device 500 of Fig. 7, wherein the pressure equalization opening 515 of the second pressure chamber 514 is not covered by a screen filter 516 but by a balloon 517 being housed by a wire frame 518 being attached to the outside of the housing 510 of the power generation device 500. As depicted the balloon 517 has a substantially spherical shape and is at least partially inflated.

[0103] Fig. 9 shows a diagram of a method 1000 for generating electric power by means of a power generation device 500 as described herein. The method 1000 comprises the following steps in the given order: (i) providing 1100 the power generation device 500; (ii) pressurizing 1200 the first pressure chamber 512 to a first pressure and airtightly sealing the first pressure chamber 512; (iii) introducing 1300 the power generation device 500 into a borehole 5 such that the power generation device 500 is in contact with a fluid inside the borehole 5, and (iv) controlling 1400 a flow of the fluid through the borehole 5 such that pressure changes are introduced in the second pressure chamber 514. Controlling the fluid flow through the borehole 5 such that pressure changes are introduced in the second pressure chamber 514 may comprise a repeated throttling and / or interrupting of the fluid flow. List of reference signs

[0104] 1 drilling tool

[0105] 5 borehole io housing

[0106] 12 longitudinal axis

[0107] 14 first housing segment

[0108] 16 second housing segment

[0109] 20 drill head

[0110] 22 drilling direction

[0111] 24 drill head displacement cylinder

[0112] 30 first retention means

[0113] 40 second retention means

[0114] 42a-42d anchoring elements

[0115] 50 displacement device

[0116] 52 pressure cylinder

[0117] 60 attachment means

[0118] 100 method for underground drilling

[0119] 110 arranging a drilling tool in a borehole

[0120] 120 operating the drill head

[0121] 130 radially extending the first retention means

[0122] 140 radially retracting the second retention means

[0123] 150 actuating the displacement device to increase the axial distance

[0124] 160 radially extending the second retention means

[0125] 170 radially retracting the first retention means

[0126] 180 actuating the displacement device

[0127] 500 power generation device

[0128] 510 housing

[0129] 512 first pressure chamber

[0130] 513 sealing

[0131] 514 second pressure chamber

[0132] 515 pressure equalization opening

[0133] 516 screen filter

[0134] 517 balloon

[0135] 518 wire frame

[0136] 520 electrically conductive coil

[0137] 522 longitudinal axis of the coil 530 rigid, movable device

[0138] 532 magnet

[0139] 533 magnetic North-South axis of the magnet

[0140] 540 proximity of the pressure equalization opening

[0141] 550 sliding direction of the rigid, movable device IOOO method for generating electric power noo providing the power generation device 1200 pressurizing the first pressure chamber

[0142] 1300 introducing the power generation device into a borehole 1400 controlling a flow of the fluid through the borehole

Claims

CLAIMS1. A drilling tool (1) for underground drilling in a borehole (5), wherein the drilling tool (1) comprises a housing (10) comprising a longitudinal axis (12); a drill head (20) being arranged to drill along a drilling direction (22); a first retention means (30) being radially extendable from the housing (10) with respect to the longitudinal axis (12), wherein the first retention means (30) is configured to anchor the drilling tool (1) in the borehole (5) by radially extending the first retention means (30); a second retention means (40) being radially extendable from the housing (10) with respect to the longitudinal axis (12), wherein the second retention means (40) is configured to anchor the drilling tool (1) in the borehole (5) by radially extending the second retention means (40), and a displacement device (50) being configured to change the axial distance along the longitudinal axis (12) between the first retention means (30) and the second retention means (40).

2. The drilling tool (1) according to the preceding claim, wherein the first retention means (30) is extendable from the housing (10) independently of the second retention means (40), and / or wherein the second retention means (40) is extendable from the housing (10) independently of the first retention means (30).

3. The drilling tool (1) according to any one of the preceding claims, wherein the first retention means (30) and / or the second retention means (40) comprises at least two, preferably at least three, and further preferably at least four anchoring elements (42a, 42b, 42c, 42b) respectively, wherein each of said anchoring elements (42a, 42b, 42c, 42b) is radially extendable from the housing (10) with respect to the longitudinal axis (12) and wherein each of said anchoring elements (42a, 42b, 42c, 42b) is preferably configured to form-fittingly and / or force-fittingly engage with the borehole (5).

4. The drilling tool (1) according to any one of the preceding claims, wherein the first retention means (30) and / or the second retention means (40) are configured to center the drilling tool (1) in the borehole (5) when being radially extended from the housing (10) respectively.

5. The drilling tool (1) according to any one of the preceding claims, wherein the drilling tool (1) is electrically and / or hydraulically powered.

6. The drilling tool (1) according to any one of the preceding claims, wherein the housing (10) comprises attachment means (60) being adapted to attach the drilling tool (1) to a coiled tubing and / or a drill pipe.

7. The drilling tool (1) according to any one of the preceding claims, wherein the displacement device (50) comprises a pressure cylinder (52), wherein the pressure cylinder (52) preferably is a hydraulic cylinder, wherein further preferably the pressure cylinder (52) is arranged substantially parallel to the longitudinal axis (12).

8. The drilling tool (1) according to any one of the preceding claims, wherein the drill head (20) is axially displaceable relative to the housing (10) along the longitudinal axis (12), wherein preferably the drill head (20) is axially displaceable relative to the housing (10) along the longitudinal axis (12) while drilling.

9. The drilling tool (1) according to any one of the preceding claims, wherein the housing (10) comprises a first housing segment (14) which comprises the first retention means (30), and a second housing segment (16) which comprises the second retention means (40), wherein the displacement device (50) is configured to change the axial distance between the first housing segment (14) and the second housing segment (16) relative to the longitudinal axis (12).

10. The drilling tool (1) according to the preceding claim, wherein the first housing segment (14) is slidably arranged within the second housing segment (16) or the second housing segment (16) is slidably arranged within the first housing segment (14).

11. The drilling tool (1) according to any one of claims 9 or 10, wherein the drill head (20) is attached to the second housing segment (16).

12. The drilling tool (1) according to any one of claims 9 to 11, wherein the first housing segment (14) comprises the attachment means (60) according to claim 6.

13. The drilling tool (1) according to any one of the preceding claims, wherein the drilling tool (1) further comprises a refrigeration element.

14. The drilling tool (1) according to any one of the preceding claims, wherein the drilling tool (1) further comprises a pressure sensor.

15. The drilling tool (1) according to any one of the preceding claims, wherein the drill head (20) is electrically powered.

16. The drilling tool (1) according to any one of the preceding claims, wherein the drilling tool (1) further comprises a seismic sensor and / or a seismic signal generator.

17. A method (too) for underground drilling, wherein the method (too) comprises the steps of- arranging (110) a drilling tool (1) according to any one of the preceding claims in a borehole (5);- operating (120) the drill head (20) to drill in the drilling direction (22) of the drill head (20), wherein the method (too) further comprises the following steps in the given order:- radially extending (130) the first retention means from the housing (10) with respect to the longitudinal axis (12);- actuating (150) the displacement device (50) to increase the axial distance between the first retention means (30) and the second retention means (40) along the longitudinal axis (12);- radially extending (160) the second retention means (40) from the housing (10) with respect to the longitudinal axis (12);- radially retracting (170) the first retention means (30) towards the housing (10), and- actuating (180) the displacement device (50) to reduce the axial distance between the first retention means (30) and the second retention means (40) relative to the longitudinal axis (12).

18. The method (loo) according to the preceding claim, wherein the method further comprises the step of radially retracting (140) the second retention means (40) towards the housing (10), wherein this step is preferably performed directly before, directly after, and / or while radially extending (130) the first retention means (30) from the housing (10).

19. A power generation device (500) for generating electric power inside a borehole (5) that extends into a subterranean hydrocarbon reservoir, wherein the power generation device (500) comprises a housing (510) comprising a first pressure chamber (512) and a second pressure chamber (514), wherein the first pressure chamber (512) is airtightly sealable within the housing (510); wherein the second pressure chamber (514) comprises a pressure equalization opening (515) which is configured such that the pressure inside the second pressure chamber (514) is equal to the ambient pressure outside of the second pressure chamber (514) in a proximity (540) of the pressure equalization opening (515); an electrically conductive coil (520), and a rigid, movable device (530) which separates the first pressure chamber (512) from the second pressure chamber (514), wherein the movable device (530) is configured such that if the first pressure chamber (512) is airtightly sealed, the movable device (530) moves when the ambient pressure changes, and wherein the movable device (530) comprises a magnet (532) being configured to induce an electrical voltage in the coil (520) when it moves.

20. The power generation device (500) according to the preceding claim, wherein the rigid, movable device (530) is slidably guided inside the housing (510) along a sliding direction (550).

21. The power generation device (500) according to the preceding claim, wherein the coil (520) comprises a substantially cylindrical shape, wherein a longitudinal axis (522) of the coil (520) is substantially parallel to the sliding direction (550).

22. The power generation device (500) according to one of the claims 20 to 21, wherein a magnetic North-South axis (533) of the magnet (532) is substantially parallel to the sliding direction (550).

23. The power generation device (500) according to one of the claims 19 to 22, wherein the movable device (530) is arranged to linearly move between the first pressure chamber (512) and the second pressure chamber (514).

24. The power generation device (500) according to one of the claims 19 to 23, wherein the pressure equalization opening (515) of the second pressure chamber (514) is covered by a screen filter (516) and / or a balloon (517).

25. The power generation device (500) according to one of the claims 19 to 24, wherein the magnet (532) is movably arranged inside the electrically conductive coil (520).

26. The power generation device (500) according to one of the claims 19 to 25, wherein the electrically conductive coil (520) is fixedly attached to the housing (510).

27. A method (1000) for generating electric power by means of a power generation device (500) according to one of the preceding claims 19 to 26, wherein the method (1000) comprises the following steps in the given order: providing (1100) the power generation device (500); pressurizing (1200) the first pressure chamber (512) to a first pressure and airtightly sealing the first pressure chamber (512); introducing (1300) the power generation device (500) into a borehole (5) such that the power generation device (500) is in contact with a fluid inside the borehole (5), and controlling (1400) a flow of the fluid through the borehole (5) such that pressure changes are introduced in the second pressure chamber (514).

28. The method (1000) according to the preceding claim, wherein the power generation device (500) is introduced to a depth inside the borehole (5) wherein the ambient pressure at the depth and thus a second pressure in the second pressure chamber (514) exceeds the first pressure which was introduced in the first pressure chamber (512).

29. The method (1000) according to one of the preceding claims 27 to 28, wherein controlling the fluid flow through the borehole (5) comprises a repeated throttling and / or interrupting of the fluid flow to cause ambient pressure changes.

30. The method (1000) according to one of the preceding claims 27 to 29, wherein the first pressure lies in the range from 7 MPa to 35 MPa, preferably from 13 MPa to 27MPa, and further preferably from 17 MPa to 24 MPa.

31. An underground drilling system comprising the drilling tool (1) according to any one of claims 1 to 17, and the power generation device (500) according to any one of the claims 19 to 26, wherein the power generation device (500) is configured to provide the drilling tool (1) with electric power.

Images