Drilling tool comprising shock reducers

Abstract

The present invention relates to a drilling tool (1) comprising a body (2) to which a plurality of raised blades (3) are fitted, wherein at least some the blades comprise a plurality of cutting teeth (4) arranged at the front edge (5) of the blade in the direction of rotation (R) of the drilling tool, each cutting tooth being positioned radially with respect to the central axis (6) of the drilling tool, and wherein, according to the invention, at least one cutting tooth is associated with a front shock reducer (7) arranged in the same radial position as the cutting tooth, the front shock reducer being on another blade that precedes the blade to which the cutting tooth is fitted, in the direction of rotation of the drilling tool.

Description

[0001] Drilling tool including shock reducers

[0002] Domain

[0003] The present invention relates to a well drilling tool. More particularly, the drilling tool comprises a body on which a plurality of raised blades are provided, wherein at least a portion of the blades comprise a plurality of cutters arranged at the leading edge of the blade in the direction of rotation of the drilling tool, each cutter being positioned at a radial position relative to the central axis of the drilling tool.

[0004] State of the

[0005] Different types of drilling tools are available for cutting a formation in a wellbore and include, for example, drill bits, reamers, or coring tools. Well drilling bits include fixed cutter bits, tapered roller bits, percussion bits, and hybrid bits that combine fixed cutters and tapered rollers. Each type of bit has its own advantages and disadvantages, and the parameters to consider for their design vary greatly from one type of bit to another.

[0006] Fixed cutter bits generally include a threaded connection and a tool body coaxially aligned with a central axis. The bit includes an internal plenum extending axially through the connection and partially into the bit body. The threaded connection connects the bit to a drill string. The tool body includes a plurality of blades that rise from the tool body and form a gap therebetween. The blades carry a plurality of cutters including a cutting face oriented in the direction of rotation of the bit. The cutters are generally arranged in a row extending radially from the leading edge of the blades, thereby defining a cutting structure. The leading face of the bit is defined as the portion of the bit that faces down the wellbore and includes the blades and the cutting structure engaging the earth formation.The drill bit further includes a plurality of nozzles incorporated into the tool body and extending from the plenum of the tool body through a location in the gap formed between the blades. During drilling, a drilling fluid or drilling mud is pumped through the drill string to which the drill bit is attached, so as to jet the drilling fluid through the plurality of nozzles. The nozzles are oriented to jet the drilling fluid to clean the cutting structure and remove debris from the bottom hole. The drilling fluid further assists in cooling the cutting structure.

[0007] Cutters typically comprise an elongated, generally cylindrical substrate made of tungsten carbide bearing a cutting layer of polycrystalline diamond or a superabrasive material such as cubic boron nitride, thermally stable diamond, polycrystalline cubic boron nitride, ultra-hard tungsten carbide, or a combination of these materials. Such cutters are well known in the state of the art. The cutters typically used in fixed-cutter bits are polycrystalline diamond compact cutters, commonly referred to as PDG cutters for short, and may have various types of shapes depending on the drilling application. The cutters may be welded, brazed, or pressed into machined dimples typically at the leading edge of the blades, or in other words, on the edge of the blade facing the direction of rotation of the bit. PDG cutters are extremely hard and abrasion-resistant materials.However, the main problem with PDC knives is that they are brittle and impact can lead to cracking, breakage and premature failure.

[0008] To improve bit durability, manufacturers design their bits with the goals of minimizing stick slip, torsional vibration, and torque oscillations that damage PDC cutters. One approach is to limit the maximum depth of cut (DOC) of the cutters with one or more domed inserts mounted on the blades behind the cutters. The cutters engage the rock formation before the domed inserts. The cutters cut the formation with a certain depth of cut that is limited to a maximum depth of cut by the domed inserts that engage with the formation and bear against the formation.

[0009] WO2018 / 144762 describes a drill bit that includes a plurality of DOC (Depth of Etch) inserts. Each blade of the drill bit includes a row of cutters adjacent to each other and arranged on the front edge of the blade and a plurality of DOC inserts arranged in a row at a rearward position relative to the cutters of the same blade. The DOC inserts on each blade are rearward of the cutters on the same blade relative to the direction of rotation of the drill bit. Each DOC insert on each blade is positioned immediately behind and following a cutter on the same blade. Thus, the DOC inserts are arranged in the same radial position as the cutting face of the cutters. The DOC inserts are designed to have a larger contact surface with the rock, and are therefore particularly suitable for use in soft formations.DOC inserts are designed to limit the maximum cutting depth of the cutter's cutting faces as they engage the formation. The surface of these DOC inserts is designed to slide over the formation, and these inserts are not designed to penetrate and shear the formation. Despite their larger contact area, DOC inserts of this type have a complex elongated shape that increases the cost of the bit. In addition, because an elongated insert is in greater contact with the formation, it does not wear much. If a cutter begins to break or wear, the insert can reduce cutting efficiency and decrease the penetration rate by reducing the DOC depth of cut.

[0010] WO2021126898 addresses the problem of tool erosion, particularly cutter erosion, due to certain drilling fluids by providing drill bits in which a portion of the drilling fluid bypasses the leading face of the bit. Such a bit includes an orifice or nozzle formed in a guard position and in fluid communication with the central passage through a passageway oriented in a direction away from the face of the bit, substantially in the opposite direction to the direction of drilling. Such an auxiliary opening reduces stress and erosion on the face of the bit as well as on the cutters disposed thereon. Further, the bit may include a plurality of inserts on the plurality of blades, wherein at least some of the inserts are positioned behind the plurality of PDC cutters between the leading edge and the trailing edge of the plurality of blades. No further details are given on the positioning of these inserts.

[0011] Document US2021 / 270089 discloses a drill bit comprising a tool body having defined thereon a plurality of blades supporting a first plurality of cutters, which are PDC cutters, and wherein at least one of the plurality of blades supports at least one pointed cutter and one donut-shaped cutter such that the sharper pointed cutter cuts directly into the rock and the donut-shaped cutter grinds the formation against the following rock face.

[0012] Document US2014 / 102798 discloses fixed cutter bits provided with stabilizing elements for the purpose of improving bit stability, rate of penetration (ROP) and tool durability.The drill bit comprises a blade having a cutter-supporting surface and extending radially along the tool face, and a stabilizing element mounted on the blade-supporting surface at a position behind a cutter of a same blade, wherein the stabilizing element has a longitudinal axis and a concave end spaced from the blade-supporting surface, the concave end comprising a first formation-facing surface extending to a first tip spaced from the blade-supporting surface, and a second formation-facing surface extending to a second tip spaced from the blade-supporting surface, wherein the first tip and the second tip are totally eclipsed by the cutting face of a single cutter in a profile view rotated about an axis.Alternatively, the stabilizing members are provided in the form of a pair of cylindrical members having a dome-shaped top, and in which such inserts have a central axis, the stabilizing members being arranged in pairs adjacent to each other so that their central axis forms an angle with each other and with the knife support surface in a profile view turned around an axis, the pair of stabilizing members being positioned at a position behind a knife on the same blade and totally eclipsed by the cutting face of a single knife with which they are associated in a profile view turned around the axis.

[0013] Document US2007 / 0151770 discloses a rotary drill bit comprising a body including a crown, at least one cutter on the crown and a rolling element rotatably positioned behind at least one cutter, the rolling element being configured to reduce the exposure of at least one cutter behind which it is positioned without adversely affecting the hydraulics of the drill bit. The rolling element shown in the document appears bulky and is only positioned in a cone area of ​​the crown.

[0014] US Patent No. 6,883,623 describes a protective structure at the front and rear of guard knives that are centrally disposed on a blade in a guard region. Such a structure would decrease knife cleaning efficiency and cutting efficiency if applied to other blade regions such as the taper region, nose region, and shoulder region.

[0015] U.S. Patent No. 6,408,958 discloses two embodiments of drill bits. In a first embodiment, the drill bit has a blade structure comprising a plurality of first cutting elements having a cutting face with an edge oriented to engage and cut the formation, and a plurality of second cutting elements behind the first cutting elements and slightly inclined relative to a perpendicular to the profile of the tool face at the location of the second cutting element. These second cutting elements serve as less aggressive backup cutting elements in the event of a first cutting element breakage.In the second embodiment, the second cutting elements are positioned at a radially intermediate level between two first cutting elements in order to provide protection against wear of the material of the tool body or the blades, such as the formation of a wear ring (O-ring in English) in the tool body or grooves on the blades.

[0016] In some drilling applications, field conditions often force drillers to deviate from the ideal stabilized bottom hole assembly design and steady-state drilling procedures. This typically affects drill string dynamics and inevitably creates conditions such as vertical, lateral, and torsional shocks and vibrations on the cutters that negatively affect fixed-cutter bits. With today's highly wear-resistant cutters, it is essential to protect the cutters from breakage. It is necessary to provide fixed-cutter bits suitable for harsh operating conditions, in which the cutting structure is effectively protected against axial impacts, lateral or torsional shocks, and vibrations.There is also a need to provide a fixed-blade bit with improved tool face control, particularly for applications with bent motors.

[0017] Summary of the invention.

[0018] The present invention aims to provide a downhole cutting tool comprising cutters and shock reducers, arranged in such a way as to prevent or minimize damage to the cutters. In particular, the present invention aims to provide a drilling tool in which the cutters are better protected against vertical, lateral and torsional shocks and vibrations.

[0019] Advantageously, the present invention aims to provide a drilling tool made of relatively conventional components minimizing its manufacturing cost. Examples of conventional components include dome-shaped inserts, truncated dome-shaped inserts or dome-shaped structures obtained by molding the blades of the drill bit. Another objective of the present invention is to provide a drilling tool that can be used in a poorly stabilized bottom hole assembly, such as for example in a bottom hole assembly without stabilizers or in a bottom hole assembly comprising a motor such as a positive displacement motor (sparrow motor). These objectives are achieved by the present invention.

[0020] The present invention relates to a drilling tool comprising a body on which a plurality of raised blades are provided, wherein at least a portion of the blades comprises a plurality of knives arranged at the front edge of the blade in the direction of rotation of the drilling tool, each knife being positioned in a radial position relative to the central axis of the drilling tool, and wherein, according to the invention, at least one knife is associated with a front shock reducer arranged in the same radial position as said knife, said front shock reducer being on another blade which precedes the blade on which said knife is provided, in the direction of rotation of the drilling tool.

[0021] Preferably, the knives disposed on the front edge of each blade are provided next to each other, preferably with a gap between them, and each having a respective radial position. Preferably, the knives at the front edge of each blade are provided in a row extending substantially in a radial direction.

[0022] Preferably, the anterior shock reducer and associated knife are positioned on adjacent blades.

[0023] Preferably, each knife of the plurality of knives comprises an apex, and in a profile folded about the central axis of the drilling tool, a cutting profile line passing through said apexes of said knives is defined, and each anterior shock reducer has an apex positioned recessed relative to said cutting profile line.

[0024] The term "top" in relation to a knife or shock reducer refers to the top of a knife or shock reducer furthest from the upper surface of the blade on which the knife or shock reducer is positioned. Preferably, the front shock reducer is made of polycrystalline diamond.

[0025] Preferably, the anterior shock reducer has a width less than or equal to the width of the knife.

[0026] Preferably, the blades comprise:

[0027] • at least one main blade extending from a cone region of the drilling tool to a guard region of the drilling tool, and on which extends a plurality of anterior shock reducers; and

[0028] • at least one secondary blade extending at least from a nose region of the drilling tool to a guard region of the drilling tool, and on which a plurality of anterior shock reducers extend.

[0029] In the context of the present invention, the term "leading" refers to a position ahead or preceding another element, in the direction of rotation of the drilling tool.

[0030] Preferably, the tool according to the invention is such that at least one knife is associated with a front shock reducer arranged in the same radial position as said knife, said front shock reducer being on another blade which precedes in the direction of rotation of the drilling tool.

[0031] Preferably, the anterior shock absorbers are provided on the blades in the form of cylindrical inserts fixed on the upper surface of the blades or in the form of structures protruding from the upper surface of the blades and molded with the blades.

[0032] In some embodiments of the drilling tool according to this invention, the drilling tool further comprises a rear shock reducer associated with a cutter, disposed on the same blade as said cutter, and disposed at a rear position and at the same radial position as said cutter.

[0033] The term "trailing" refers to a position backward or following another element, in the direction of rotation of the drilling tool. The terms "front blade" and "back blade" and "front shock reducer" and "back shock reducer" therefore refer to the relative positions of the blades and shock reducers.

[0034] Thus, an anterior blade can include:

[0035] • a posterior shock reducer associated with a knife of said anterior blade and;

[0036] • an anterior shock reducer associated with a knife of a posterior blade. Also, a posterior blade can include:

[0037] • a rear shock reducer associated with a knife of the rear blade and a front shock reducer associated with a knife of a blade even further back in the direction of rotation of the tool.

[0038] Preferably, at least one knife is associated with:

[0039] • a front shock reducer which is arranged in the same radial position as said knife, said front shock reducer being on another blade which precedes in the direction of rotation of the drilling tool, and;

[0040] • is also associated with a rear shock reducer, arranged at the same radial position as said knife, said rear shock reducer being on the same blade as said knife and arranged at a position behind said knife.

[0041] Preferably, the rear shock reducer associated with a knife has a top positioned set back from the cutting profile line.

[0042] Preferably, the rear shock absorber has a width less than or equal to the width of the knife.

[0043] Preferably, the drilling tool comprises:

[0044] • at least one main blade extending from a cone region of the drilling tool to a guard region of the drilling tool, and having thereon a plurality of front shock reducers and a plurality of rear shock reducers, wherein each rear shock reducer is at a position behind its associated cutter on the same blade, and wherein each front shock reducer is at a position behind and radially offset from the rear shock reducers; and

[0045] • at least one secondary blade extending at least from a nose region of the drilling tool to a guard region of the drilling tool, and on which extends a plurality of anterior shock reducers and a plurality of posterior shock reducers, in which each posterior shock reducer is at a position behind its associated cutter on the same blade, and in which each anterior shock reducer is at a position behind and radially offset from the posterior shock reducers.

[0046] Preferably, the rear shock absorbers are provided on the blades in the form of cylindrical inserts fixed on the upper surface of the blades or in the form of structures protruding from the upper surface of the blade and molded with the blades.

[0047] In one embodiment, the drilling tool comprises:

[0048] • at least two main blades, extending radially from a taper region of the drilling tool to a guard region of the drilling tool, wherein each of the cutters has a unique radial position when considering only the main blades; and

[0049] • a number of secondary blades being the same or a multiple of the number of said main blades, said secondary blades extending radially at least from a nose region of the drilling tool to a guard region of the drilling tool, wherein each of the knives of the secondary blades has a redundant radial position with a knife of a main blade.

[0050] In the context of the present invention, the term "redundant" refers to elements such as a knife, anterior shock reducer or posterior shock reducer having the same radial position relative to the central axis as another knife, another anterior shock reducer or another posterior shock reducer, respectively.

[0051] In one embodiment, the drilling tool includes six blades, including three primary blades and three secondary blades, wherein the cutters are arranged in a "track set" configuration such that each of the cutters and front shock reducers of a secondary blade has a redundant radial position with a respective cutter and front shock reducer of a primary blade positioned at 180° relative to the central axis of the bit.

[0052] In one embodiment, the blades of the drilling tool comprise: • at least two main blades extending radially from a cone region of the drilling tool to a guard region of the drilling tool; and

[0053] • at least two secondary blades extending radially from a nose region of the drilling tool to a guard region of the drilling tool; wherein each cutter of the main blades and the secondary blades has a unique radial position when considering all the blades.

[0054] In one of the preceding embodiments, the drilling tool has a drilling tool body comprising a front face on which the blades carrying cutters are arranged, preferably the innermost cutter being spaced from the central axis of the drilling tool so as to form a space for forming a core sample with a diameter less than or equal to 15%, preferably less than or equal to 10% of the diameter of the tool body, the space being located at the central axis of the drilling tool, and a cavity for discharging the core sample towards the periphery of the drilling tool, the cavity being delimited by two lateral surfaces of two adjacent blades and a clearance surface set back from the front face of the tool body.

[0055] In another aspect, the present invention relates to the use of a drilling tool according to one of the embodiments described herein in directional drilling or in drilling through an interbedded lithology or in a poorly stabilized downhole assembly.

[0056] Description of the drawings.

[0057] The drawings are presented for illustrative purposes only and are not intended to limit the scope of the present invention. The drawings are not necessarily to scale; in some cases, certain features have been enlarged or omitted from the drawings to facilitate understanding of some of the concepts of the present invention.

[0058] Figure 1 shows a superposition view of the cutters and shock reducers of a drill bit according to an embodiment of the present invention in a profile folded around the central axis of the drill bit.

[0059] Fig. 2A shows a single-plane rotational view of the radial positions of the cutters and shock absorbers of two adjacent blades in a comparative example of a drill bit.

[0060] Fig. 2B shows a single-plane rotational view of the radial positions of the cutters and shock absorbers of two adjacent blades of a drill bit according to one embodiment of the present invention.

[0061] Fig. 3A shows a perspective view of a formation portion and a track set of two blade cutters of a drill bit with shock reducers according to an embodiment of the present invention in which the cutters engage and cut the formation.

[0062] Fig. 3B shows a perspective view of a portion of a formation and a single set arrangement of two blade cutters of a drill bit with shock reducers according to one embodiment of the present invention, wherein the cutters engage and cut the formation.

[0063] Fig. 4A shows a single position arrangement of cutters of a drill bit and a position of a shock reducer according to one embodiment of the present invention.

[0064] Fig. 4B shows an alternative single-position arrangement of cutters of a drill bit and a position of a shock reducer according to one embodiment of the present invention.

[0065] Figure 5 shows a top view of a drill bit according to one embodiment of the present invention.

[0066] Detailed description.

[0067] According to a first aspect, the present invention relates to a drilling tool for formation cutting in a wellbore. The drilling tool comprises a shock reducer arrangement as described below which protects the cutters from vertical, lateral and torsional shocks and vibrations, thereby extending the life of the cutters and the drilling tool.

[0068] In the accompanying description, the term "downhole cutting tool" may refer to a drill bit, preferably a fixed cutter bit, or to a core drill bit or an enlarger or to any type of drilling tool provided with fixed cutters.

[0069] In the description herein, the term "fixed cutter bit" may be referred to equivalently as "drill bit" or "tool". In the present description, the present invention will be presented for one embodiment in the form of a fixed cutter bit. Those skilled in the art will appreciate that the concept of the present invention may also be applied to an expander, a core drill bit, or any type of drilling tool provided with fixed cutters.

[0070] In the context of the present invention, the drilling tool is a fixed cutter bit comprising a threaded connection and a tool body coaxially aligned with a central axis. The bit comprises an internal plenum extending axially through the connection and partially into the bit body. The threaded connection connects the bit to a drill string. The tool body comprises a plurality of blades which rise from the tool body and form a gap therebetween. The blades carry a plurality of cutters comprising a cutting face oriented at an angle of inclination in the direction of rotation of the bit. The cutters are preferably arranged in a row extending radially on the leading edge of the blades, thereby defining a cutting structure. The leading face of the bit is defined as the portion of the bit which faces down the wellbore and which comprises the blades and the cutting structure engaging the earth formation.In this specification, the term "bit face" or "bit face" refers to the face of the bit facing down the borehole during drilling. The term "blade top surface" refers to the surface of the blade facing down the wellbore hole during drilling.

[0071] The drill bit further includes a plurality of nozzles incorporated in the bit body and extending from the plenum of the bit body through a location in the gap formed between the blades. During drilling, a drilling fluid or drilling mud is pumped through the drill string to which the drill bit is attached so as to jet the drilling fluid through the plurality of nozzles. The nozzles are oriented to jet the drilling fluid to clean the cutting structure and remove debris from the bottom hole. The drilling fluid further assists in cooling the cutting structure. The tool body and blades may be made of steel or a tungsten carbide composite material, referred to by those skilled in the art as a tool die. When made from a tungsten carbide composite material, the tool body and blades are typically formed by casting in a graphite mold.In this description, the term "blades" refers to a structure that rises axially from the tool body and radially relative to the central axis of the tool. The blades may extend radially in a straight or curved manner along the tool body.

[0072] The drill bit according to the present invention further comprises shock reducers provided on at least two blades. The term "shock reducer" is equivalent to "shock absorber", "damper", "impact arrestor", "retarder", "depth of cut (DOC) controller", "low vibe", or any other terminology of a person skilled in the art suitable for an insert or structure provided on a blade to reduce shocks on the cutters. The shock reducers are protruding elements from the upper surface of the blades with an upper portion at a height less than or equal to, preferably less than, the height of the top of an associated cutter relative to the upper surface of the blade. Advantageously, the width of the shock reducers is less than or equal to the diameter of the cutters.More preferably, the shock reducers have an upper surface having the shape of a dome, a truncated dome, or a torus. In some embodiments, the shock reducers are inserts having an elongated longitudinal portion, for example, a cylindrical portion or a prismatic portion, inserted into machined pockets on the blades of the drill bit. The shock reducers may be inserts made from a hard material such as tungsten carbide. The shock reducers may be secured in the pockets provided in the blades by interference fitting, welding, or brazing. The shape of the shock reducers is not limiting to the present invention, and other shapes than those described herein may be provided.Alternatively, the shock absorbers may be dome-shaped structures or truncated dome-shaped structures forming part of the blades and obtained by molding the blades, when the blades are made of a tungsten carbide matrix.

[0073] In the context of the present invention, the term "knife" may refer to a cutting element such as polycrystalline diamond compact knives, abbreviated herein as "PDC knives".

[0074] PDC cutters comprise an elongated, generally cylindrical, tungsten carbide substrate carrying a cutting layer of polycrystalline diamond or superabrasive material such as cubic boron nitride, thermostable polycrystalline diamond (TSP), polycrystalline cubic boron nitride, ultra-hard tungsten carbide, or a combination of these materials. Such cutters are well known in the art. PDC cutters may have various types of shapes. In one embodiment of the present invention, the PDC cutters have a circular cutting face with a chamfer. The cutters may be welded, brazed, or press-fitted into machined pockets generally at the leading edge of the blades, or in other words, at the edge of the blade oriented in the direction of rotation of the bit.

[0075] In the context of the present invention, the term "leading" refers to a position forward in the direction of rotation of the bit. The term "trailing" refers to a position rearward relative to a leading member in the direction of rotation of the bit.

[0076] The drill bit of the present invention may include from three to sixteen blades. The number of blades is limited by the fact that there is not enough space to accommodate them. The larger the diameter of the drill bit, the more room there is to have a higher number of blades. Some drill bits may have twelve blades, for example in a 12" (311 mm) diameter size and up to sixteen in a 17" (444 mm) diameter size. For tools with a diameter of 8" (215 mm), the minimum number of blades would be three, but unusually, preferably at least four to nine or ten blades in general. For tools with a diameter of 6" (152 mm), these tools generally include a maximum of eight to nine blades. For the same diameter, the more blades the drill bit includes, the more cutters and inserts it requires, which increases the cost of the drill bit and the complexity of the drill bit design.A drill bit generally requires a design with optimal positions of cutters, shock reducers, nozzles, blade shape and spacing between blades to provide a well-balanced bit with an efficient cutting structure, effective cooling and cleaning of the cutting structure and efficient evacuation of rock pieces. The bit may advantageously comprise six blades or seven blades or eight blades or nine blades. In a more suitable embodiment, the bit comprises six blades.

[0077] The blades may be arranged on the tool body so as to form a space for forming a core sample, preferably of diameter less than or equal to 15%, more preferably less than or equal to 10% of the tool body diameter, the space for forming the core sample passing through the central axis of the tool, and a cavity for discharging the core sample towards the periphery of the tool, the cavity being defined by two side surfaces of two adjacent blades and a clearance surface set back from the front face of the bit. Such an arrangement of the blades is described in US Pat. No. 8,960,335. In the present specification, such an arrangement of the blades may be referred to as a "microcoring" feature. The term "side surface of the blade" refers to a surface of the blade rising from the tool body.

[0078] Alternatively, the blades may be arranged on the tool body such that a first blade extends radially from the central axis or from a position close to the central axis of the tool body with a first knife positioned with its cutting portion intersecting the central axis of the tool or very close to the central axis of the tool, preferably within 5 mm of the axis.

[0079] In this description, the term "near the central axis" refers to a radial position about the central axis at a radial distance from the central axis less than 2 times the diameter of the radially innermost cutter of the tool, preferably less than 1.5 times the diameter of the radially innermost cutter of the tool.

[0080] Figure 1 shows a non-limiting example of a tool profile as it would appear with all the blades, cutters 4 and associated shock reducers 7, 15 rotated in a single plane about a central axis 6. The profile rotated about the axis makes it possible to define different areas of the tool face profile:

[0081] • a cone region 11 which is the most central region of the tool face, the cone region 11 extending radially from the central axis 6 of the tool at a first axial position 31 relative to the central axis 6 to a second radial position at a second axial position 32 further forward in the direction of the tool face to form an inverted cone;

[0082] • a nose region 12 having a first radius of curvature 33, forming a circular portion extending radially from an innermost point tangent to the cone region at the second axial position 32, towards a radially outermost point 34 forming an angle of between 35° to 55°, preferably 40° to 50°, for example 45° with the central axis in the forward direction of the tool;

[0083] • a shoulder region 13 extending radially from the outermost point 34 of the nose region 12 to a guard point 35 forming an angle of 90° with the central axis in the forward direction of the tool;

[0084] • a guard region 14 which extends substantially parallel to the central axis of the tool from the shoulder region 13 at the guard point 35 to an end 36.

[0085] In some embodiments, the cone region 11 may be replaced by a flat region extending substantially perpendicular to the central axis. In some embodiments, such as for drill bits including a microcoring feature, the innermost cutter may be some distance from the central axis, for example a distance of 5 mm to 20 mm.

[0086] The cutters 4 disposed in the shoulder region 13 and the guard region 14 are more susceptible to wear and breakage due to vibration and shock during rotation of the bit, due to their higher circumferential speed compared to the circumferential speed of the cutters disposed in the cone region 11. The cutters disposed in the nose region 12 are more subject to wear from axial shocks because they are axially at the most forward position of the bit face. The cutters 4 in the cone region 11 experience less vibrational shocks or axial shocks and therefore do not require as many shock reducers 7, 15 in the cone region as in the nose region, shoulder region and guard region.

[0087] Fig. 2A represents a simplified schematic view of:

[0088] • front blade portion (not shown) carrying knives 4' and a rear shock reducer 15 radially behind a knife 4' and;

[0089] • rear blade portion (not shown) carrying 4" knives radially offset from the 4' knives of the front blade; in which the two portions of the front blade and the rear blade are presented in a profile rotated around the central axis 6 of the tool.

[0090] Fig. 2B represents a simplified schematic view of: • front blade portion (not shown) carrying knives 4' and a front shock reducer 7 radially offset from the knives 4' and;

[0091] • rear blade portion (not shown) carrying 4" knives radially offset from the 4' knives of the front blade; in which the two portions of the front blade and the rear blade are presented in a profile rotated around the central axis 6 of the drill bit and in which the front shock reducer 7 has the same radial position as a 4" knife of the rear blade.

[0092] As shown in Fig. 2A and 2B, each knife 4', 4" on a blade has a vertex 10', 10" furthest from the upper surface 9 of the blade. For convenience, in this description, a vertex of a knife or shock absorber furthest from the upper surface 9 of a blade will be referred to herein as a "vertex". A shock absorber 7, 15 also has a vertex 8, 18. The vertices 10', 10" of each knife 4', 4" make it possible to define, in a profile folded around the central axis, a cutting profile line 50 which is a line passing through each vertex 10', 10" of the knives 4', 4" comprising a straight portion and a curved portion like that seen in Fig. 1. It is understood that Fig. 2A and 2B are conceptual figures.

[0093] The radial position of a knife 4 is defined as the radial position of the apex 10 of the knife 4 relative to the central axis 6 of the tool, and the radial position of a shock reducer 7, 15 is defined as the radial position of the apex 8, 18 of the shock reducer 7, 15 relative to the central axis 6 of the tool.

[0094] Shock absorbers prevent the cutters from engaging the formation too deeply. If a sudden shock occurs, the reactive force is not only absorbed by the cutters, but the shock absorber also helps prevent excessive shock to the cutters. By protecting the cutters from behind, as in state-of-the-art bits, the protection of the cutters is limited. The shock absorbers located behind the cutters apply a reaction force to the rock formation that has just been cut. The value of the cutting depth does not have much influence on the effectiveness of the shock absorbers. However, the greater the cutting depth, the greater the forces on the cutters and the greater the risk that a shock will induce a crack or break it. The cutting depth indicates how deeply the cutters engage the formation.During drilling, the cutters cut helical grooves 16 and ridges 17 into the rock with a pitch equal to the cutting depth. The ridges 17 may have a profile with a concave upper portion resulting from the prior passage of the cutters. To limit the cutting depth, the practice was to place the shock reducers in a position such that they would bear on the groove in the rocks created by the cutter as conceptually shown in Fig. 2A. The closer the shock reducer 15 is located behind the cutter, the smaller the offset between the apex 10' of the cutter 4' and the apex 18 of the shock reducer 15 must be to allow the shock reducer to slide over the groove in the rock.To make a shock reducer more effective at the rear of a cutter, its exposure relative to the cutter could be minimized, so that the apex 18 of the shock reducer 15 is close to or at the same level as the apex 10' of the cutter 4'. Since the shock reducer 15 is placed behind the cutter, the offset of the apex 18 of the shock reducers 15 must be very small. For example, if the depth of cut is 1 mm made over one full rotation of the bit, or 360°, then a shock reducer placed behind the cutter, for example 10° behind the apex of the cutter relative to the centerline of the bit, then the offset must be equal to 1 mm*10 / 360, i.e. 0.02 mm. But this would cause another problem as the cutter wears. As the cutter wears, the shock reducer slides on the rock formation and limits the cutting depth, slowing the bit down and possibly preventing it from drilling.Such a small offset of 0.02 mm also raises the issue of difficulty in manufacturing such tight tolerances.

[0095] The inventors have surprisingly found that a knife 4 positioned in a radial position on a first blade can be effectively protected by a shock reducer 7 positioned in the same radial position as the knife 4, but on another blade, preferably a blade anterior in the direction of rotation of the tool, preferably an adjacent blade anterior to the first blade in the direction of rotation R of the tool. One advantage of placing the 7" shock reducer on the main blade versus a 4" cutter on a rear blade, is that the shock reducer can now be positioned for example 50° to the centerline of the bit in front of the 4" cutter, which is equivalent to 310° behind that same 4" cutter. The offset can now be 1mm*310 / 360, i.e. 0.86mm for a 1mm depth of cut. With this higher offset, a small amount of PDC wear does not have such a negative impact on the depth of cut.It also facilitates the manufacturing process by avoiding tight tolerances.

[0096] For convenience, in this description, a "leading" or "front" element such as a shock reducer or a blade refers to an element being in a forward or leading position relative to another element, in the direction of rotation R of the tool. Also in this description, a "trailing" or "back" element refers to an element being in a rearward or trailing position relative to another element in the direction of rotation R of the tool.

[0097] At least one knife 4 is associated with a front shock reducer 7, the term "associated" meaning in the context of the present document that the knife 4 and the front shock reducer 7 associated therewith have the same radial position relative to the central axis 6 of the tool 1. In the context below, the term "front shock reducer" refers to a shock reducer arranged on a front blade and associated with a knife 4 of a rear blade. More particularly, a front shock reducer 7 associated with a knife 4 is located on a blade other than the knife associated therewith, in a position forward relative to the associated knife 4, at an angle of less than 180° relative to the central axis 6 of the tool 1.

[0098] As shown in Fig. 2B, in order to sufficiently protect a 4" knife on a posterior blade, while maintaining a sufficient cutting depth and a good penetration rate, a front shock reducer 7 on a front blade, associated with the 4" knife of the posterior blade has a top 8 set back from the cutting profile line 50 at the same radial position of the 4" knife. The distance between the top of the front shock reducer 7 and the cutting profile line 50 can be selected from 1% to 99%, preferably from 5% to 90%, preferably from 5% to 70%, or more preferably from 5% to 30% of the height between the cutting profile line 50 and the upper surface 9 of the blade in the same radial position.

[0099] The front shock reducer is advantageously made of a hard material such as tungsten carbide or polycrystalline diamond, in order to prevent wear of this front shock reducer. Preferably, the front shock reducer has a width less than or equal to the width of the knives.

[0100] Preferably, the drilling tool comprises:

[0101] • at least one main blade MB extending from a cone region 11 of the tool to a guard region 14 of the tool, and on which extends a plurality of knives 4 and front shock reducers 7; and

[0102] • at least one secondary blade SB extending at least from a nose region 12 of the tool to a guard region 14 of the tool, and on which extends a plurality of knives 4 and front shock reducers 7.

[0103] In this description, the term "primary blade" refers to a blade 3 extending radially from a position at or near the central axis 6 in the region of the cone 11 through a nose region 12, a shoulder region 13, to the guard 14 of the tool. The term "secondary blade" refers to a blade 3 extending radially from a position in the region of the cone 11 near the nose region 12 or from the nose region 12 to the guard 14 of the bit. Typically, the secondary blades SB extend to the guard region 14 from a radial region more outward than the innermost region of the main blades MB. The secondary blades SB are shorter than the main blades MB and include fewer cutters 4 and fewer shock absorbers 7 than on the main blades MB.

[0104] The shock reducers have been described above. In some embodiments, the anterior shock reducers 7 may be provided on the blades 3 as cylindrical inserts fixed to the blades 3 and protruding from the upper surface 9 of the blades 3, or as structures protruding from the upper surface 9 of the blades and molded with the blades as described above.

[0105] The cutting structure of the drill bit comprises knives 4 which are positioned on the front edge 5 of each blade 3. Each blade further comprises at least one front shock reducer associated with a respective knife of another blade, preferably the adjacent rear blade.

[0106] Preferably, at least one main blade MB comprises a row of front shock reducers 7, in which each front shock reducer 7 is associated with a cutter 4 of a rear blade, so that the radial position of each front shock reducer 7 is the same as the radial position of its associated cutter 4 on the rear blade. Since the torque on the cutters is lower in the innermost region of the bit, the front shock reducers can be omitted in the region close to the central axis 6 of the bit, as shown for example in Figures 1 and 5, while it is preferable to protect each of the cutters 4 of the front blade at least in the shoulder region 13 and in the guard region 14 by front shock reducers 7.

[0107] Preferably, at least one secondary blade SB comprises a row of front shock reducers 7, in which each front shock reducer 7 is associated with a knife 4 of a rear blade, so that the radial position of each front shock reducer is the same as the radial position of its associated knife on the rear blade. One or two front shock reducers may be omitted in the innermost radial region of the secondary blade, while it is preferable to protect each of the knives 4 of the rear blade at least in the shoulder region 13 and in the guard region 14 by front shock reducers 7.

[0108] Advantageously, the features related to the shock reducers described above may be combined with a particular arrangement of blades and cutters in which the drill bit comprises:

[0109] • at least two main blades MB, extending radially from a cone region 11 of the bit to a guard region 14 of the bit, wherein each cutter 4 has a unique radial position when considering the main blades MB only; and

[0110] • a number of secondary blades SB being the same or a multiple of the number of said main blades MB, said secondary blades SB extending radially from a nose region 11 of the bit to a guard region 14 of the bit, wherein each knife 4 of the secondary blades has a redundant radial position with a knife 4 of a main blade MB.

[0111] Such an arrangement is referred to herein as a "track set". In other words, in a track set arrangement, the knives 4 of the secondary blades SB have a redundant radial position with some of the knives 4 of the main blades MB. As a result, each front shock reducer 7 of a secondary blade SB has a redundant radial position with the radial position of a front shock reducer 7 of a main blade MB.

[0112] Figures 2A and 2B show a conceptual view of the knives of an anterior blade and a posterior blade engaging rock formation 20 (the hatched area).

[0113] Fig. 2A shows a schematic view of a portion of a cutting structure of a prior art drill bit in which the 4' knives of a front blade and the 4" knives of a rear blade are superimposed in a swung profile. The front blade (not shown) is the first blade in the direction of rotation R of the tool engaging and cutting the formation, and the rear blade (not shown) is the second blade in the direction of rotation of the tool engaging and cutting the formation after the front blade. Each of the knives has a rounded cutting surface. The knives of each blade are positioned radially next to each other and generally have some space between them. In the swung profile, the 4" knives of the rear blade partially overlap the 4' knives of the front blade. On a single front blade, a rear shock absorber 15 (only one being shown in Fig.2A) is associated with a cutter 4' and positioned radially behind the cutter 4'. During drilling, the cutters 4' of the main blade engage the formation with a certain cutting depth and form a plurality of grooves 16 and ridges 17 in the formation. The ridges 17 generally have a profile with an upper concave portion resulting from the forward passage of the cutters. As shown in Fig. 2A, the furthest ends 10" of the cutters 4" of the rear blade are radially offset from the furthest ends 10' of the cutters 4' of the front blade. The cutters 4" of the rear blade cut at least a portion of the uncut formation, i.e. the ridge 17 left after the passage of the cutters 4' of the front blade.

[0114] Fig. 2B shows a schematic view of a portion of a cutting structure of a drill bit according to an embodiment of the present invention in which the knives 4' of a front blade and the knives 4" of a rear blade are superimposed in a single folded profile. The front blade is the first blade in the direction of rotation R of the drill bit engaging and cutting the formation, and the rear blade is the second blade in the direction of rotation of the drill bit engaging and cutting the formation after the front blade. Each of the knives has a rounded cutting surface. The knives of each blade are positioned radially next to each other, preferably with a gap between the two. In the folded profile, the knives 4" of the rear blade partially overlap the knives 4' of the front blade. On a single front blade, a front shock reducer 7 (only one shown in Fig.2B for convenience) is positioned radially offset between two 4' cutters and has the same radial position as a 4" cutter of a later blade. During drilling, the 4' cutters of the main blade engage the formation with a certain cutting depth and form a plurality of grooves 16 and ridges 17 in the formation. The ridges 17 generally have a profile with an upper concave portion resulting from the forward passage of the cutters. As shown in Fig. 2B, the outermost ends 10" of the 4" cutters of the later blade are radially offset from the outermost ends 10' of the 4' cutters of the earlier blade. The 4" cutters of the later blade cut at least a portion of the uncut formation after the passage of the 4' cutters of the earlier blade.The anterior shock reducer 7 associated with a 4" knife of the posterior blade can rest against the ridge 17, advantageously against the concavity of the ridge 17.

[0115] Fig. 3A shows a perspective view of a portion of a formation 20 during drilling and a redundant cutter arrangement of two blades of a six-blade bit with shock reducers, in which the cutters engage and cut the formation 20. For clarity, the blades are not shown. A first anterior blade (not shown) includes cutters 4', anterior shock reducers 7' and optionally, posterior shock reducers 15' positioned behind the cutters 4' and in front of the anterior shock reducers 7'.

[0116] A second posterior blade (not shown) includes 4" cutters, 7" anterior shock reducers, and optionally, 15" posterior shock reducers positioned behind the 4" cutters and in front of the 7" anterior shock reducers. During drilling, the cutters 4' of the anterior blade cut into the formation 20 a plurality of grooves 16 with ridges 17 therebetween, wherein the grooves 16 and ridges 17 have a helical path. In the context herein, a ridge 17 refers to the uncut formation left after the passage of two adjacent cutters 4' of a prior blade. The ridges 17 generally have a profile with an upper portion comprising a concavity resulting from the anterior passage of cutters.The ridges 17 provide a helical contact surface for the anterior shock reducers 7' of the anterior blade to bear against, thereby protecting the 4" knives of the posterior blade engaging the uncut formation and which are in the same helical path as their associated anterior shock reducer 7', by providing a reactive force to limit the cutting depth of the 4" knife of the posterior blade. The helical contact surfaces of the ridges are also grooved due to the previous passage of other prominent (more anterior) knives in the formation. As shown in Fig. 3A the helical contact surfaces of the ridges 17 are relatively wide and the grooves 16 formed by two adjacent knives 4' of a previous blade are shallow.

[0117] In one embodiment, when the cutters are arranged in a redundant configuration and the tool includes six blades including primary and secondary blades, the cutters and front shock reducers of a secondary blade may be positioned 180° from the centerline of the bit to the cutters and front shock reducers of a primary blade. In another embodiment, when the cutters are arranged in a redundant configuration and the tool includes four blades, including two primary and two secondary blades, the two primary blades must be 180° from each other from the centerline of the bit and the cutters and front shock reducers of a primary blade may be positioned at a redundant radial position with the cutters and front shock reducers of a secondary blade positioned 90° or 270° from a primary blade.

[0118] Preferably, each knife 4 associated with a front shock reducer 7 as described above is further associated with a rear shock reducer 15 as shown in FIG. 3A. The term "associated" means in the context of the present document that the knife 4 and the rear shock reducer 15 associated therewith have the same radial position relative to the central axis 6 of the tool. In the context below, the term "rear shock reducer" refers to a shock reducer disposed on a blade 3, the rear shock reducer 15 being associated with a knife 4 and disposed at a rear position relative to the knife 4 of the same blade 3.Therefore, in such an embodiment, each blade 3 comprises at least one knife 4 disposed at the front edge 5 of the blade 3, a rear shock reducer 15 associated with the knife 4 of the same blade 3 and a front shock reducer 7 associated with another knife of another rear blade, in which the front shock reducer is radially offset from the knife of the same blade and the rear shock reducer of the same blade. The front shock reducer is preferably at the rear and offset from the rear shock reducer on the same blade. As shown in Fig. 3A, a knife 4" is associated with a pair of shock reducers 15", 7' in which:.

[0119] • a 15" rear shock reducer is positioned at a position to the rear of said 4" knife on the same blade and at the same radial position; and

[0120] • a 7' front shock reducer is positioned at a front position relative to said 4" knife on another front blade and at the same radial position.

[0121] The combination of the cutters 4 with the front shock reducers 7 and the rear shock reducers 15 provides better stabilization of the bit during drilling, reduces shock to the cutters and extends the life of the bit, particularly when the bit is used in difficult conditions such as use in a poorly stabilized downhole assembly or in combination with a positive displacement motor, for example in directional drilling applications.

[0122] The rear shock absorbers 15 may be made from a hard material such as polycrystalline diamond or tungsten carbide. Since wear of the rear shock absorbers is less critical than for the front shock absorbers 7, the rear shock absorbers 15 are preferably made of tungsten carbide.

[0123] Preferably, the rear shock absorbers have a width equal to or less than the width of the knives.

[0124] Preferably, a plurality of rear shock reducers 15 extends radially along the main blades MB from a cone region 11 of the tool to a guard region 14 of the tool and a plurality of rear shock reducers 15 extends radially along the secondary blades SB from at least a nose region 12 of the tool to a guard region 14 of the tool. Preferably, each blade comprises:

[0125] • a first row of rear shock reducers 15 associated with the knives 4 of the same blade and at a position at the rear of said knives 4; and

[0126] • a second row of front shock reducers 7 preferably arranged behind the rear shock reducers 15 and radially offset from the rear shock reducers 15 on the same blade and associated with the knives 4 of another rear blade. At least one main blade MB comprises a row of rear shock reducers 15, in which each rear shock reducer 15 is associated with a knife 4 of the same blade, so that the radial position of each rear shock reducer is the same as the radial position of its associated knife. However, due to the lack of space in the central region of the tool, near the central axis 6, not all knives are associated with a rear shock reducer 15. At least one of the radially inner knives of the cone region 11 is not associated with a rear shock reducer 15.During drilling, the torque applied to the radially innermost cutters of the drill bit is smaller than the torque applied to the radially outermost cutters. Therefore, the rear shock reducers can be omitted near the central axis, while it is preferable to protect each of the cutters at least in the region of the shoulder 13 and in the guard region 14 by rear shock reducers 15.

[0127] At least one secondary blade SB comprises a row of rear shock reducers 15, in which each rear shock reducer 15 is associated with a knife 4 of the same blade, so that the radial position of each rear shock reducer is the same as the radial position of its associated knife. Some of the most radially inner knives of a secondary blade may not be associated with a rear shock reducer. However, since the majority of the knives 4 of the secondary blades SB are located at least in the shoulder region 13 and in the guard region 14, each of these knives 4 in the shoulder region 13 and the guard region 14 is protected by rear shock reducers 15.

[0128] In a drill bit having a cutting structure arranged in a redundant configuration, having main blades MB and secondary blades SB, and including rear shock reducers 15 and front shock reducers 7, each cutter 4 on a secondary blade SB has a radial position redundant with that of a cutter on a main blade MB, each rear shock reducer 15 of a secondary blade SB has a radial position redundant with the radial position of a rear shock reducer 15 of a main blade MB and each front shock reducer 7 of a secondary blade SB has a radial position redundant with the radial position of a front shock reducer 7 of a main blade MB. In another embodiment, a drill bit may have a cutting structure arranged in a "single set" configuration, instead of a redundant configuration.The term "single-position" refers to a cutter arrangement on the blades including the main blades and the secondary blades, in which each cutter of the main blades and the secondary blades has a unique radial position when considering all the blades. In a drill bit with a single-position cutter arrangement including front shock reducers, each front shock reducer also has a unique radial position when considering all the blades. In a single-position configuration, a front shock reducer associated with a cutter of a first blade may be positioned on a front blade that is not necessarily adjacent to the first blade in the direction of rotation of the tool. FIG.3B shows a perspective view of a portion of a formation 20 during drilling and a cutter arrangement of two blades (not shown) of a drill bit in which the cutters are arranged in a unique configuration with shock reducers according to one embodiment of the present invention, and in which the cutters engage and cut the formation 20. For bits according to this alternative embodiment, the cutting structure is such that in a folded profile of all the blades, the radial overlap between the cutters of adjacent blades is generally greater, resulting in a more advantageous contact area between the rock formation and the cutter and a better penetration rate. As can be seen in FIG.3B, the cutters of each blade dig helical grooves 16 and form ridges 17 therebetween, in which the width of the groove and ridges appears narrower compared to a formation cut by cutters with a redundancy arrangement. In the present context, the ridges 17 are an uncut formation left by the passage of two adjacent cutters of a prior blade. The ridges formed by the cutters of a first prior blade provide a narrow helical contact surface on which the anterior shock reducers of a non-adjacent subsequent blade can bear. Therefore, with a single-position cutter arrangement, the anterior shock reducers may have a narrower contact surface with uncut formation portions previously formed by the cutters during drilling, but the cutting structure is more efficient.The grooves 16 cut by the cutters are generally deeper and the ridges 17 formed therebetween are generally narrower and higher, as seen in Fig. 3B. The top of the shock reducers may be set back a greater distance from the cutting profile line 50. The bits according to this alternative embodiment may also include posterior shock reducers, each of which also has a unique radial position when considering all the blades.

[0129] Fig. 4A shows a top view of the knife positions of a six-blade bit comprising three main blades MB1, MB2, MB3 and three secondary blades SB1, SB2, SB3 and in which the knives are arranged in a reverse spiral single-position configuration. The term "reverse spiral single-position configuration" refers to a knife arrangement in which, starting from the innermost knife of the tool, each subsequent knife in the direction of rotation of the tool is positioned radially at an incremental distance from the central axis 6 of the bit. The knives may alternatively be arranged in a direct spiral configuration, in which starting from the innermost knife of the bit, each subsequent knife in the direction opposite the direction of rotation of the bit is positioned radially at an incremental distance from the central axis 6 of the bit. In fig.4A, for convenience, only the cutters and a single anterior shock reducer are shown, and the first 25 cutters of the bit are numbered according to their radial position relative to the central axis. Starting from the innermost cutter of the bit, each of the following cutters in the direction of rotation of the bit is radially offset from one another. When looking at, for example, the fifteenth cutter of the secondary blade SB1 and the sixteenth cutter of the main blade MB3, their respective radial positions are offset but relatively close to one another.Therefore, the radial position of the front shock reducer on the main blade MB3 associated with the fifteenth knife of the secondary blade SB1 and the radial position of the sixteenth knife of the main blade MB3 are also offset and relatively close to each other, resulting in a poorer contact area between the front shock reducer and the uncut formation. In order to provide a better contact area between the front shock reducer and the uncut formation, the front shock reducer 7 may be provided on another blade further forward in the direction of rotation, but at an angle less than 180° relative to its associated knife.

[0130] Fig. 4B shows a top view of the knife positions of a six-blade tool comprising three main blades MB1, MB2, MB3 and three secondary blades SB1, SB2, SB3 and in which the knives are arranged in a swapped single-position configuration. The term "swapped single-position configuration" refers to a single-position knife configuration in which, after designing a first model in a reverse spiral single-position arrangement of knives as described above, a second model of a tool has been generated by rotatingly swapping the secondary blades with each other and their knives. Fig. 4B shows an example of a swapped single-position arrangement of knives on a tool, in which the secondary blades SB1, SB2 and SB3 and their knives have been rotated through an angle of 120° around the central axis of the tool. In Fig.4B, for convenience, only the knives and a single shock reducer are shown and the radial positions of the first 25 knives are numbered according to their radial position relative to the central axis. In this configuration of Fig. 4B, the fifteenth knife is at a forward position relative to the sixteenth knife in the direction of rotation of the tool and is at a rearward position relative to the twelfth and eighteenth knives. The fifteenth knife and its associated front shock reducer are at an intermediate radial position between the twelfth and eighteenth knives. Therefore, in this configuration, the front shock reducer associated with the fifteenth knife has a better contact surface with the uncut formation left by the twelfth and eighteenth knives, on which it can bear, thus providing better protection for the fifteenth knife.

[0131] Figure 5 shows a top view of a drill bit 1 according to an embodiment of the present invention. The drill bit comprises blades 3, including three main blades MB1, MB2, MB3 and three secondary blades SB1, SB2, SB3. The drill bit 1 of this embodiment comprises a central cavity 40 for forming a core sample and a clearance surface 41 on the drill bit body 2 for discharging the core sample to the periphery of the drill bit, the clearance surface being formed between a main blade MB1 and a secondary blade SB3. Such a "microcoring function" is shown for illustrative purposes only, is optional and not limiting for the present invention.

[0132] The three main blades MB1, MB2, MB3 extend radially along the bit body 2 from a central region near the central axis 1 of the bit through a cone region 11, a nose region 12, a shoulder region 13 and a guard region 14 of the bit.

[0133] The three secondary blades SB1, SB2, SB3 extend radially along the body 2 of the tool from a region near the nose region 12 through a shoulder region 13 and a guard region 14 of the tool. The secondary blades are shorter than the main blades and include fewer cutters 4 and fewer shock absorbers 7, 15 than on the main blades.

[0134] The drill bit further comprises nozzles 42 disposed in the space between the blades 3. Advantageously, the shape of the blades and the positions of the nozzles are optimized to provide a well-balanced drill bit. The nozzles extend from the plenum of the drill bit to the face of the drill bit so as to spray drilling fluid to flush out cuttings formed during drilling and advantageously clean and cool the cutting structure.

[0135] Each blade 3 comprises a row of knives 4, advantageously PDC knives of cylindrical shape and each positioned at the front edge 5 of each blade 3.

[0136] Each of the knives of the three main blades MB1, MB2, MB3 has a unique radial position when considering the knives of the three main blades only. For example, a first main blade MB1 includes a first knife being the single innermost knife of the tool. A second main blade MB2 includes a second blade placed radially further than the first and along the cutting profile. A third main blade MB3 includes a third blade placed radially further from the first and second. The first main blade MB1 further includes a fourth knife placed radially further from the second knife and the third knife, and so on.

[0137] Each of the secondary blades SB1, SB2, SB3 is positioned at 180° from a main blade MB1, MB2, MB3 relative to the central axis, so that three pairs of opposing blades (MB1, SB1; MB2, SB2; MB3, SB3) can be defined, each pair of opposing blades comprising a main blade and a secondary blade. For each pair of opposing blades, the radial position of each blade 4 of the secondary blades is the same as the radial position of the blades 4 of the main blades. The secondary blades are shorter than the main blades and therefore comprise fewer knives than the main blades. Each knife of the secondary blades has a unique position when considering the knives of the secondary blades only, but is redundant with a knife of an opposing main blade. The arrangement of the cutters of the drill bit according to this embodiment is referred to as a redundancy arrangement.Each main blade MB1, MB2, MB3 comprises a first row of rear shock reducers 15 extending from the cone region to the guard region of the bit and arranged at the rear of the knives 4. Due to the lack of space on the main blades near the central axis 6 of the tool, the innermost knives of these main blades are not associated with any rear shock reducers.

[0138] Each main blade MB1, MB2, MB3 further comprises a second row of front shock reducers 7 extending from the cone region to the guard region of the tool and arranged to the rear of the first row of rear shock reducers 15, at the same radial position as the knives 4 of their respective rear secondary blade SB2, SB1, SB3. Due to the lack of space on the main blades near the central axis of the bit, the innermost knives of these main blades may not be associated with a front shock reducer.

[0139] Each secondary blade SB1, SB2, SB3 includes a first row of rear shock reducers 15 extending from the nose region to the guard region of the bit and arranged at the rear of the cutters 4. Due to the lack of space on the secondary blades near the innermost cutter of the secondary blades, some of these innermost cutters of these secondary blades may not be associated with a rear shock reducer. For example, in the present embodiment shown in Figure 4, the innermost cutter 4 of the secondary blade SB3 is protected only by a rear shock reducer 15. This arrangement does not constitute a limitation of the present invention.

[0140] Each secondary blade SB1, SB2, SB3 further comprises a second row of anterior shock reducers 7 extending from the nose region to the guard region of the bit and arranged behind the first row of posterior shock reducers 15, at the same radial position as the knives 4 of their respective posterior main blade MB2, MB3, MB1. Due to the lack of space on the secondary blades near the innermost knife of the secondary blades, some of these innermost knives of these secondary blades may not be associated with an anterior shock reducer 7.

[0141] In another embodiment, pairs of secondary and main blades having redundant cutters and shock absorbers may have been positioned at an angle of 60° or 120° relative to the central axis. In this case, there are two main blades MB and four secondary blades SB on a 6-blade tool.

[0142] In one embodiment, the drill bit may comprise three main blades MB and three secondary blades SB and wherein the cutting structure is arranged such that a first cutter of a first main blade crosses or touches or is close to within 5 mm of the central axis of the drill bit, and such that the first main blade extends from a central area of ​​the drill bit through a cone region, a nose region, a shoulder region and a guard region. In this embodiment, the cavity for forming a core and a clearance surface for evacuating a core to the periphery of the drill bit, i.e. the "microcoring" feature, are therefore not present. The redundant arrangement of cutters and the arrangement of the rear shock reducers and the front shock reducers on the main blades and on the secondary blades follow the same principle as that described for the embodiment of FIG. 4A.

[0143] In other embodiments, the drill bit may comprise eight blades, including four main blades and four secondary blades or two main MB blades and six secondary SB blades. Alternatively, the drill bit may comprise nine blades, including three main blades and six secondary blades. Alternatively, the drill bit may comprise twelve blades, including three main blades and nine secondary blades or four main blades and eight secondary blades. The arrangement of the cutter redundancy and the arrangement of the rear shock reducers and the front shock reducers on the main blades and on the secondary blades follow the same principle as described above. Alternatively, the drill bit comprises seven blades, including three main MB blades and four secondary SB blades.

[0144] In one embodiment, the drill bit may include a prime number of blades, e.g., five blades or seven blades, with a unique position arrangement of cutters. In such an embodiment, each blade includes a row of cutters having a unique radial position and positioned at the leading edge of the blades, a first row of rear shock reducers, and a second row of front shock reducers, wherein each cutter is associated with a rear shock reducer on a single blade and a front shock reducer on an adjacent front blade. The shape of the blades and the positions of the nozzles are advantageously optimized to provide good balance of the tool. Due to space constraints, some cutters near the central axis or some of the innermost cutters of the blades may not be associated with a rear shock reducer and / or a front shock reducer.

[0145] Other embodiments of drill bits in which the cutters are associated with a front shock reducer and optionally a rear shock reducer can be designed by those skilled in the art, for example by varying the number of main blades and secondary blades, the shape of the blades, the shape of the cutters, the shape of the shock reducers, the desired arrangement of the cutters, i.e., single-position or redundant, the diameter and / or shape of the cutters, the angle of inclination of the cutters, the diameter and / or shape of the shock reducers, the number and shape of the nozzles, the presence or absence of a microcoring functionality, etc.

[0146] A comparative bit comprising six blades and a microcoring feature was tested in a field in which significant downhole fracture conditions and highly interbedded lithology resulted in significant downhole vibration. The comparative bit had a cutting structure in which the PDG cutters were arranged at the edge of the blades with a single-position configuration and protected by back shock reducers associated with most of the cutters. The downhole conditions induced vibration on the bit that caused significant damage to the PDG bit.

[0147] The drill bit according to the embodiment described in connection with Figure 5 was tested in the same field and surprisingly reached the target depth with good performance and minimal wear conditions. The drill bit was still usable after this test.

[0148] The drill bit according to the embodiment described in connection with Figure 5 was then tested in a geothermal application in which the exceptional control of the tool face allowed for more efficient and therefore fewer trajectory corrections, which resulted in drilling the planned section with a record penetration rate in a systematic manner. In the present description, the drilling tool has been described for one embodiment as a drill bit, but the arrangement of the cutters, for example in a redundant configuration or in a single-position configuration, the positioning of the anterior shock reducers and, optionally, the positioning of the posterior shock reducers, the features related to the shock reducers as described above, can be applied to other embodiments of drilling tools such as an expander, or a coring crown.

[0149] List of references in the figures

[0150] 1 drill bit

[0151] 2 tool bodies (drill body)

[0152] 3 blade

[0153] 4 knife

[0154] 4' Knives of the front blade

[0155] 4” Back Blade Knives

[0156] 5 front edge of the blades

[0157] 6 central axis of the tool (trapan)

[0158] 7 front shock reducer

[0159] 8 anterior shock reducer summit

[0160] 9 upper surface of the blades

[0161] 10 knife tops

[0162] 10' knife tip of a front blade

[0163] 10” knife tip of a posterior blade

[0164] 11 cone region

[0165] 12 Nose region

[0166] 13 shoulder region

[0167] 14 guard region

[0168] 15 rear shock reducer

[0169] 15' anterior blade rear shock reducer

[0170] 15” Rear Blade Shock Reducer

[0171] 16 grooves

[0172] 17 crests

[0173] 18 posterior shock reducer summit

[0174] 31 first point in first axial position in the cone region 32 second point in second axial position further forward in the cone region

[0175] 33 radius of curvature of the nose region

[0176] 34 outermost point of the nose region

[0177] 35 guard point 36 guard end point

[0178] 40 central cavity

[0179] 41 clearance area

[0180] 42 nozzle

[0181] 50 cutting profile line

Claims

Claims 1. A drilling tool (1) comprising a body (2) on which a plurality of raised blades (3) are provided, wherein at least a portion of the blades (3) comprises a plurality of knives (4) arranged at the front edge (5) of the blades in the direction of rotation (R) of the drilling tool (1), each knife (4) being positioned at a radial position relative to the central axis (6) of the drilling tool (1), characterized in that at least one knife (4) is associated with a front shock reducer (7) arranged in the same radial position as said knife (4), said front shock reducer (7) being located on another blade (3) which precedes the blade on which the knife (4) is provided in the direction of rotation (R) of the drilling tool.

2. A drilling tool according to claim 1 wherein each of the plurality of knives (4) comprises a top (10), and wherein in a profile folded around the central axis (6) of the drilling tool (1), a cutting profile line (50) passing through said tops (10) of the knives is defined, and wherein each anterior shock reducer (7) has a top (8) positioned set back from said cutting profile line (50).

3. A drilling tool according to claim 1 or 2 wherein the front shock reducer (7) is made of polycrystalline diamond.

4. A drilling tool according to any preceding claim, wherein the front shock reducer (7) has a width less than or equal to the width of the cutter (4).

5. A drilling tool according to any preceding claim, wherein the blades (3) comprise: • at least one main blade (MB) extending from a cone region (11) of the drilling tool to a guard region (14) of the drilling tool, and on which extends a plurality of anterior shock reducers (7); and • at least one secondary blade (SB) extending at least from a nose region (12) of the drilling tool to a guard region (14) of the drilling tool, and on which a plurality of anterior shock reducers (7) extend.

6. A drilling tool according to any preceding claim, wherein the front shock reducers (7) are provided on the blades in the form of cylindrical inserts fixed on the upper surface (9) of the blades (3) or in the form of structures protruding from the upper surface (9) of the blades (3) and molded with the blades (3).

7. A drilling tool according to any preceding claim further comprising at least one rear shock reducer (15) associated with a knife (4) and arranged on the same blade as said knife (4), at a rear position relative to said knife (4) and at the same radial position as said knife (4).

8. A drilling tool according to any preceding claim further comprising at least one knife which is associated with a front shock reducer arranged in the same radial position as said knife, said front shock reducer being on another blade which precedes the blade on which the knife (4) is provided in the direction of rotation of the drilling tool, and said knife (4) also being associated with a rear shock reducer (15) arranged in the same radial position as said knife (4), said rear shock reducer being on the same blade as said knife and arranged at a rear position relative to said knife (4).

9. A drilling tool according to claim 7 or 8 wherein the rear shock reducer (15) associated with a knife (4) has a top (18) positioned set back from the cutting profile line (50).

10. A drilling tool according to any one of claims 7 to 9, wherein the rear shock reducer (15) has a width less than or equal to the width of the knife.

11. A drilling tool according to any one of claims 7 to 10, wherein: • at least one main blade (MB) extending from a cone region (11) of the drilling tool to a guard region (14) of the drilling tool, and on which extends a plurality of front shock reducers (7) and a plurality of rear shock reducers (15), wherein each rear shock reducer (15) is at a position behind its associated cutter (4) on the same blade, and wherein each anterior shock reducer (7) is at a position behind and radially offset from the posterior shock reducers (15); and • at least one secondary blade (SB) extending at least from a nose region (12) of the drilling tool to a guard region (14) of the drilling tool, and on which extends a plurality of front shock reducers (7) and a plurality of rear shock reducers (15), in which each rear shock reducer (15) is at a position behind its associated knife (4) on the same blade, and in which each front shock reducer (7) is at a position behind and radially offset relative to the rear shock reducers (15).

12. A drilling tool according to any one of claims 7 to 11, wherein the rear shock reducers (15) are provided on the blades (3) in the form of cylindrical inserts fixed on the upper surface (9) of the blades (3) or in the form of protruding structures from the upper surface (9) of the blade (3) and molded with the blades (3).

13. A drilling tool according to any preceding claim comprising: • at least two main blades (MB), extending radially from a cone region (11) of the drilling tool to a guard region (14) of the drilling tool, wherein each of the cutters (4) has a unique radial position when considering only the main blades; and • a number of secondary blades (SB) being the same or a multiple of the number of said main blades (MB), said secondary blades (SB) extending radially at least from a nose region (12) of the drilling tool to a guard region (14) of the drilling tool, wherein each of the knives (4) of the secondary blades (SB) has a redundant radial position with a knife (4) of a main blade (MB).

14. A drilling tool according to any preceding claim wherein the drilling tool comprises six blades (3) comprising three main blades (MB) and three secondary blades (SB) in which the knives (4) are arranged in a track set configuration such that each of the knives and front shock reducers of a secondary blade (SB) has a redundant radial position with a respective knife and an anterior shock reducer of a main blade (MB) positioned at 180° relative to the central axis (6) of the drilling tool.

15. A drilling tool according to any one of claims 1 to 11, wherein the blades (3) comprise: o at least two main blades (MB) extending radially from a cone region (11) of the drilling tool to a guard region (14) of the drilling tool; and o at least two secondary blades (SB) extending radially from a nose region (11) of the drilling tool to a guard region (14) of the drilling tool; wherein each cutter (4) of the main blades (MB) and the secondary blades (SB) has a unique radial position when considering all the blades (3).

16. Drilling tool according to one of the preceding claims wherein the body of the drilling tool (2) comprises a front face on which the blades (3) carrying knives (4) are arranged, the innermost knife being spaced from the central axis (6) of the drilling tool so as to form a space (40) for forming a core sample with a diameter less than or equal to 15%, preferably less than or equal to 10% of the diameter of the body (2) of the tool, the space (40) being located at the central axis (6) of the drilling tool, and a cavity for evacuating the core sample towards the periphery of the drilling tool, the cavity being delimited by two lateral surfaces of two adjacent blades (MB1, SB3) and a clearance surface (41) set back from the front face of the body (2) of the tool.

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