Low surface friction drill bit body for use in wellbore formation

A low surface friction body for a drill bit includes a matrix drill bit body. The body includes a particulate phase having a friction-reducing additive, and a binding material that bonds the particulate phase using a suitable manufacturing process such as selective laser sintering. The particulate phase may include tungsten carbide, the friction-reducing additive may be polytetrafluoroethylene, and the binder material may be copper or cobalt. The friction-reducing additive is distributed throughout at least a portion of the drill bit body that includes the surface that will come into contact with drill cuttings and drilling fluid during operation. The molecular properties of the friction-reducing additive result in a drill bit body having a surface that is resistant to sticking even after enduring chipping and other types of wear.

RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/US2014/024926 filed Mar. 12, 2014, which designates the United States, and which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to tooling and equipment used to form wellbores for extracting hydrocarbons from a geological formation and, more particularly, to drill bit bodies that include low friction surfaces.

DESCRIPTION OF RELATED ART

Wells are drilled to access and produce oil, gas, minerals, and other naturally-occurring deposits from subterranean geological formations. The drilling of a well typically is accomplished with a drill bit that is rotated to advance the wellbore by removing topsoil, sand, clay, limestone, calcites, dolomites, or other materials from a formation. Pieces of such materials removed from the formation by the drill bit are generally referred to as “cuttings” or “drill cuttings.”

A drill bit is typically classified as either a fixed cutter drill bit or a rotary cone drill bit, which may also be referred to as a roller cone drill bit. Generally, a rotary cone drill bit includes a drill bit body having multiple rotating cones (i.e., “roller cones”) with cutting elements. The roller cones rotate relative to the bit body as the drill bit is rotated downhole. In contrast, a fixed cutter drill bit includes a drill bit body having cutting elements at fixed locations on the exterior of the drill bit body. The cutting elements remain at their fixed locations relative to the bit body as the drill bit is rotated downhole.

During drilling, the drill bit experiences some of the most intense strains and pressures of any component in the drill string. Some of the focus in bit design is to strengthen and increase the durability of drill bits. In some cases, material selection drives the durability of the drill bit, and steel bits and tungsten carbide bits have become popular because of their durability.

Fixed cutter and roller cone bit bodies are often formed of matrix materials, and referred to, accordingly, as a matrix bit body. The materials used to form a matrix bit body may include a powder, which is typically a hard and durable material, and a binder material that holds the powder together to form the bit. Since the resulting matrix in many cases does not chemically bond the powder component and the binder together, the matrix drill bit may be susceptible to fracturing or other types of damage if it experiences sufficient chipping or other types of wear.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Unless otherwise specified, any use of any form of the terms “connect,” “engage,” “couple,” “attach,” or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion and, thus, should be interpreted to mean “including, but not limited to.” Unless otherwise indicated, as used throughout this document, “or” does not require mutual exclusivity.

Disclosed herein are systems, tools, and methods for improving the performance of a drill bit, including by selectively applying particular low-friction coatings to strategic locations on the surface of the drill bit. In one aspect, the particular materials and their selective placement on the bit expose the materials to friction from drill bit rotation, and allow such materials to “grow” and bond when exposed to frictional forces. This may provide “self-healing” properties to drill bit, such as to resist further damage when minor damage such as small chips occur. The coating may be applied to matrix drill bits, in particular, but may also be suitable for application to other types of drill bits. In the case of a matrix drill bit, the powder component of the matrix drill bit, which may also be referred to as a “particulate phase”, may be coated with low friction material following fabrication of the drill bit. In many cases, the low friction material may be polytetrafluoroethylene or other suitable material. The matrix drill bit may be a roller cone drill bit, a fixed cutter drill bit, or any other type of drill bit.

The systems and methods described herein provide for the introduction of a friction-reducing additive material into the particulate phase (or powder component) of a matrix drill bit during fabrication of the drill bit body. The introduction of friction-reducing additive to the drill bit particulate phase may reduce the propensity for drill cuttings to stick to the surface of the drill bit during drilling. Low friction coatings may also be applied to the outer portion of the drill bit with the same goal in mind. Such coatings, however, tend to wear away during operation, resulting in a drill bit that is unprotected from cuttings, muds, or other materials that may stick to the drill bit. Such wear may happen quickly during drilling because the drill bit is operating in an extreme environment, sometimes removing very hard materials from the well-bore at high temperatures and pressures. Operation in this type of extreme environment increases the likelihood that the drill bit will experience chips and nicks that would penetrate a low-friction layer of material that coats only the outermost surface of the drill bit.

In an illustrative embodiment, a friction-reducing additive is combined with a substrate material of a matrix drill bit in the early stages of fabrication. This combined material is placed in a mold, and binding material is added with heat to form the matrix drill bit. The friction-reducing additive may be polytetrafluoroethylene powder or nano-powder, or a similar type of low friction material with high heat resistance. The substrate material is typically a tungsten carbide in powder, casted particle, or mono-crystalline form. In an embodiment, the friction-reducing additive includes tungsten carbide particles coated with polytetrafluoroethylene prior to mixing or compounding with additional tungsten carbide to form particulate phase. The friction-reducing additive may be mixed with the substrate material of the matrix drill bit to provide consistent friction characteristics throughout the body of the drill bit so that as the drill bit erodes, newly exposed surfaces of the drill bit will have a similarly low friction coefficient.

The friction-reducing additive may be used to reduce the static friction coefficient of the body of a drill bit body relative to the friction coefficient of a drill bit body that does not include the friction-reducing additive. For example, a matrix drill bit that includes tungsten carbide as a particulate phase and copper as a binding material may have a friction coefficient of, for example, 0.2-0.35. The friction-reducing additive may have much lower friction coefficient of, in the case of polytetrafluoroethylene, for example, 0.04. The static friction coefficient of the surface of a drill bit body may be substantially reduced by including a friction-reducing additive component in the particulate phase of a matrix drill bit that would otherwise be composed of tungsten carbide and copper or cobalt.

The lower coefficient of friction on the surface provides for a lower chance of drill cuttings to adhere or stick to the matrix material in the junk slot area, which is the area of the drill bit between cutting surfaces where cuttings migrate away from the cutting surfaces of the drill bit. The lower coefficient of friction also reduces the loss due to wear on the drill bit surface by reducing friction between the drill bit and solids suspended in the fluid surrounding the drill bit during drilling.

Referring now to the figures,FIG. 1indicates a cross-section through section line A-A′ of an embodiment of a roller cone drill bit that includes a friction-reducing additive. The roller cone drill bit100is a common type of drill bit used in wellbore drilling, but is merely an example of a commonly used type of drill bit. The concepts, systems and methods described herein may be used in a variety of drill bits such as, for example, fixed cutting element drill bits. In the roller cone drill bit100, rotating cones102have teeth104, which may be carbide inserts or milled type teeth, on their outer surface. Each tooth is mounted on an arm106of the drill bit body.

FIG. 2depicts such a drill bit200operating in a drill string to form a wellbore. During drilling, as illustrated inFIG. 2, a drill rig208uses sections of pipe210to transfer rotational force to the drill bit200and a pump212to circulate drilling fluid (as illustrated by flow arrows A) to the bottom of the wellbore through sections of the pipe210. As the drill bit200rotates, the applied weight-on bit (“WOB”) forces the downward pointing teeth of the rotating cones into the formation being drilled. The WOB, applied through the points of the teeth, applies a compressive stress to the formation that exceeds the yield stress of the formation and induces fracturing of formation material under the drill bit. The fracturing results in fragments (also referred to as cuttings) that are flushed away from the cutting surfaces of the drill bit200by the drilling fluid, which may also be referred to as drilling mud.

Despite the flushing away, cuttings contained in the drilling mud may adhere to the surface of a traditional bit, which may cause the drill bit to not function properly or to stall. To keep the bit in proper operation, the drilling fluid adds lubrication to prevent sticking and carries cuttings away from the bit. The drill bit may also include a lubricating outer layer to further reduce the chance for cuttings to adhere to the drill bit. The outer layer of the bit may be worn away through use, however, which may result in the outermost layer of the bit losing the lubricating element. In an illustrative embodiment, a friction-reducing material may be added to a powder component of the matrix drill bit to provide a wear-resistant low-friction drill bit. The friction-reducing additive may be polytetrafluoroethylene (hereinafter “PTFE”) powder or another suitable low-friction material, as noted above.

When interacting with an opposing surface such as a wellbore wall, PTFE embedded in the drill bit may undergo the molecular process of scission, creating active PTFE groups that chemically react with the bit surface on which the PTFE is deployed. This scission results in strong adhesion to the bit surface and causes growth in, as well as reorientation of, PTFE crystallites in a very thin subsurface region of the bulk polymer PTFE embedded in the drill bit. Such structural rearrangement assists in joining adjacent aligned PTFE crystallites to form films and ribbons that emerge as debris. The PTFE debris is also a low-friction material that may be useful as lubricator. Thus, PTFE dispersed within the powder component of a matrix drill bit may, in response to chipping and wear, effectively grow a new low friction surface when previously unexposed portions of PTFE infused drill bit material becomes exposed to the drilling environment after damage to the drill bit in the form of cracking, chipping, or other types of wear.

When included in a matrix-type drill bit, the PTFE may be mixed in with the powder ingredient of, for example, a tungsten carbide, steel, ceramic, or other matrix drill bit. Despite the low friction characteristics of PTFE (typically associated with resistance to adhesion), the powder portion of the drill bit still sufficiently holds together because at low sliding speeds, the PTFE demonstrates good adhesion. This adhesion, combined with the surface layer adhesion resulting from the scission-related chemical changes noted above result in a drill bit body that has a low-friction surface along with a high degree of toughness and resistance to fracture.

In an illustrative embodiment of a PTFE impregnated drill bit, PTFE is incorporated into the powder component of the bit, which is typically tungsten carbide or a similarly hard material. The PTFE may be incorporated in the powder component, either by bonding it to the powder component or mixing it with the powder component to form a PTFE impregnated or infused powder. The PTFE impregnated powder may be (i) inserted in a mold or otherwise suspended so that it will remain diffused throughout the drill bit, or (ii) added to a drill bit matrix such that PTFE only diffuses in the outer most portion of the drill bit. This outermost portion is the portion of the drill that may be exposed to a well-bore wall over the life of the drill bit, and may range from a couple of millimeters to tens of centimeters thick or more depending on the size and design of the drill bit. In these embodiments, the outer surface of the drill bit may also be lubricated with a separate coating of PTFE or a similar friction-reducing material.

The PTFE impregnated materials may reduce the tendency of clay particles and larger, agglomerated masses of cuttings from sticking to a drill bit surface. This holds true even as the drill bit experiences wear. The ability of PTFE to effectively grow and bond when exposed to frictional forces results in the drill bit functioning as a self-healing drill bit when small chips occur to expose new areas of PTFE impregnated material.

Referring again to the figures,FIG. 3illustrates a cross-sectional diagram of a portion of a roller cone bit302having a matrix drill bit head including PTFE for friction reduction. The roller cone bit302includes a roller cone304joined to a support arm308, respectively. The roller cone304is supported on bearings334and a spindle336. A compressible sealing element318is included to seal a gap300between the roller cone304and spindle336. The roller cone304may be composed of tungsten carbide360(indicated by an “x” particle), friction-reducing material350(indicated by an “o” particle), and a binder material, which may be (copper, cobalt, or another binder). In some configurations, the friction-reducing material350is PTFE. In this case, the friction-reducing material350may encounter frictional forces at the surface of roller cone304when exposed to frictional forces during operation of the drill bit. The rubbing of wellbore materials on exposed friction-reducing material350A causes growth in the friction-reducing material350, causing a more complete and smooth layer of friction-reducing material350to be formed. The exposed friction-reducing material350may be a PTFE coating layer applied after the sintering and formation of the drill bit, or a layer occurring as a result of friction-reducing material350being sintered into the drill bit.

FIG. 4illustrates a cross-section through A-A′ of a second illustrative embodiment of a roller cone drill bit402that is analogous to the roller cone drill bit302shown inFIG. 3, which also includes a friction-reducing additive. In this embodiment, the roller cone is a multi-layer roller cone404that is subdivided into two areas, outer area410and inner area420. The outer area410includes the friction-reducing material350and the inner area420does not include the friction-reducing material350, resulting in an enhanced matrix drill bit402. The outer area410and inner area420may be joined together using selective laser sintering (SLS) or any other suitable bonding mechanism to create the multilayer roller cone404.

In an embodiment, to lubricate the multilayer roller cone404, a material matrix containing tungsten carbide360, friction-reducing additive350, and a binder (e.g., copper) may be placed into a mold. This may be a single mold or a mold containing an inner portion and an outer portion such that the material to be molded is held against the sides of the mold while leaving a cavity or hollow inner portion that may be later filled with the inner area420. The material matrix is placed in the boundary layer of the outer area410and sintered. The remaining area, which corresponds to the inner area420, is then filled with tungsten carbide360and a binder (such as copper or cobalt) and sintered as well. SLS may be used to only heat specific areas of the multi-layer roller cone404to a temperature sufficient for diffusion to occur. In this way, a rough barrier may be maintained between the outer area410and the inner area420, although some diffusion may occur between the layers such that particulates may be found in those areas. Alternatively, the mold may be completely filled in a method that will provide for tungsten carbide360, friction-reducing material350, and the binder in outer area410and tungsten carbide360and a binder (copper) in the inner area420. The areas then may be selectively sintered using SLS. Again, in operation, the sliding of wellbore materials on the exposed friction-reducing material360A causes growth in the friction-reducing material, causing a more complete and smooth surface layer to be formed. The exposed friction-reducing material may be an initial coating layer applied after the sintering and formation of the drill bit or a layer occurring as a result of PTFE being sintered into the drill bit.

FIGS. 5A and 5Billustrate detail views of the chipping of a drill bit cutting element500, as indicated inFIG. 3. The illustration is a conceptual representation of the chipping or wearing away process of the drill bit cutting element500and the reformation of an outer layer of friction-reducing material350A. Initially, the existing outer layer of friction-reducing material350A is exposed to the drilling environment while lubricating elements350and powder component360are interior to the drilling environment and held together by a binding component. When a chip510occurs, as shown inFIG. 5B, new friction-reducing material350is exposed and grows under friction to reform lubricating layer350A resulting from the scission reactions described previously. The ability of the friction-reducing material to grow and bond under friction, as noted above, effectively makes the lubricating layer “self-healing” because the friction-reducing material350reforms the lubricating layer350A as the friction-reducing material350is exposed to frictional forces in the wellbore.

FIG. 6illustrates a cross-section of a third illustrative embodiment of a roller cone drill bit602that is analogous to the roller cone drill bits described above. The roller cone drill bit602includes a cone604and is similar to the roller cone bit402ofFIG. 4, primarily differing in that the friction-reducing material650is rebounded to the tungsten carbide powder or particles. In this embodiment, roller cone604is again subdivided into two areas, outer area610and inner area620. The outer area610, includes a particulate phase651of pre-bonded groupings651of friction-reducing material650and tungsten carbide660, and the inner area620includes tungsten carbide660and binder material without a friction-reducing material650. Alternatively, in some embodiments, tungsten carbide may be left out of the inner layer620in favor of the binder material or another substrate material.

A purpose of the particulate phase is to provide for hardness to the matrix drill bit. Similarly, the purpose of the binder is to provide durability to the matrix drill bit. Since hardness is not as necessary for unexposed areas, however, the particulate phase may be omitted or reduced in concentration in the inner area620. Selective Laser Sintering (SLS) may be utilized to create the multilayer roller cone604, as described previously with regard toFIG. 4.

FIG. 7illustrates a cross-section of a fourth embodiment of a roller cone drill bit702that includes a friction-reducing additive750and roller cone704. The roller cone drill bit702ofFIG. 7is similar to that ofFIG. 6, primarily differing in that a lubricating outer layer of the friction-reducing material750A is added after sintering using, for example, sintering or a primer and topcoat process. In this embodiment, roller cone704is subdivided into two areas, outer area710and inner area720. The outer area710, includes tungsten carbide760with friction-reducing material750and the inner area720includes a tungsten carbide760without the friction-reducing material750. The formation of the roller cone of drill bit702may be nearly identical to the formation of the collar cone drill bit602described with regard toFIG. 6, except that the outer lubricating layer750A may be added by sintering a layer of friction-reducing material750to the outer area710or adding an additional layer of friction-reducing material750using, for example, a primer and topcoat process. As with the roller cone drill bits described above, when chips occur, friction-reducing material750that is bonded to the underlying tungsten carbide760will grow together with the outer layer of friction-reducing material750A.

FIG. 8is a cross-section of an alternative embodiment of a drill bit804showing a cross-section of a fixed cutter drill bit804similar to that of the roller cone cross-section shown inFIG. 7. The drill bit804, however, is a fixed cutter drill bit804. In this embodiment, fixed cutter drill bit804is subdivided into two areas, outer area810and inner area820. The outer area810includes tungsten carbide860with friction-reducing material850and the inner area820includes tungsten carbide860without the friction-reducing material850. Alternatively in some embodiments, tungsten carbide860may be left out of the inner area820altogether in favor of an alternative substrate material, such as the binder material. The drill bit804may be constructed using, for example, the SLS fabrication method described above, or any other suitable fabrication method. Like the roller cone bit embodiments described above, the areas810and820then may be selectively sintered via SLS or a similar process. After formation, an outer layer of the friction-reducing material850A may be, for example, added. As chips occur, friction-reducing material that is bonded to the tungsten carbide will grow together with the outer layer of friction-reducing material850A. It is noted that the concepts described herein may be applied to the fixed cutter bit depicted inFIG. 8in any of the example drill bits described herein, and in other types of drill bits that incorporate a matrix drill bit portion.

The erosion resistance of a drill bit, such as a roller cone or fixed cutter drill bit, is an important factor to consider in selecting a drill bit that is able to continuously perform under drilling conditions. Drill bits that erode quickly may need to be replaced frequently, interrupting and addition expense to the drilling process. Increased erosion resistance of the drill bit, however, may allow for more continuous and efficient drilling operations. This disclosure describes systems, tools, and methods for providing a drill bit using a friction-reducing additive in the body of the drill bit. The friction-reducing additive increases erosion resistance. In addition to the embodiments described above, many examples of specific combinations are within the scope of the disclosure, some of which are detailed in the following examples:

A drill bit including:a molded matrix drill bit body comprising a particulate phase and a binder material; andat least one cutting element;wherein the particulate phase comprises a tungsten carbide component and a friction-reducing additive component, the friction reducing additive component having a lower coefficient of friction than the tungsten carbide component; andwherein the friction-reducing additive component comprises polytetrafluoroethylene and is dispersed within at least a portion of the matrix drill bit body.

The drill bit of example 1, wherein the friction-reducing additive component comprises polytetrafluoroethylene-coated tungsten carbide particles.

The drill bit of example 1 or 2, wherein:the matrix drill bit body comprises an outer area and an inner area;the outer area comprises the particulate phase having polytetrafluoroethylene dispersed therein; andthe inner area comprises a second particulate phase that does not include polytetrafluoroethylene.

The drill bit of example 3, further comprising a surface coating of polytetrafluoroethylene applied to the outer area.

The drill bit of example 3 or 4, wherein the outer area has a thickness of more than two millimeters.

The drill bit of example 3 or 4, wherein the outer area has a thickness of more than ten centimeters.

The drill bit of example 1 or 2, wherein:the matrix drill bit body comprises an outer area and an inner area;the outer area comprises the particulate phase having polytetrafluoroethylene dispersed therein; andthe inner area comprises a second particulate phase that does not include tungsten carbide.

The drill bit of any of examples 1-7, wherein the matrix drill bit body further comprises a surface coating of polytetrafluoroethylene.

The drill bit of example 1, wherein the binder material comprises copper.

The drill bit of example 1, wherein friction-reducing additive component embedded in the matrix drill bit body is operable to grow and bond an outer surface comprising the friction-reducing additive component in response to exposure to frictional forces following damage to the surface of the drill bit body.

A method of forming a matrix drill bit body, the method comprising:placing particulate phase and a binding material in a mold, the particulate phase comprising a tungsten carbide particulate and a polytetrafluoroethylene particulate; andsintering the particulate phase and binding material to form the matrix drill bit body;wherein sintering the particulate phase and binding material includes causing polytetrafluoroethylene to diffuse into the tungsten carbide particulate.

The method of example 11, further comprising bonding polytetrafluoroethylene to tungsten carbide particles to form the polytetrafluoroethylene particulate prior to placing particulate phase and a binding material in a mold.

The method of example 11 or 12, wherein sintering the particulate phase and binding material to form the matrix drill bit body comprises sintering the particulate phase and binding material to form an outer area of the matrix drill bit body, the method further comprising:placing a second particulate phase that does not include polytetrafluoroethylene in a cavity formed by the outer area of the matrix drill bit body; andsintering the second particulate phase to form an inner area of the matrix drill bit body; andusing selective laser sintering to form a barrier between the inner area and the outer area that prevents diffusion of polytetrafluoroethylene into the inner area.

The method of example 11 or 12, wherein sintering the particulate phase and binding material to form the matrix drill bit body comprises sintering the particulate phase and binding material to form an outer area of the matrix drill bit body, the method further comprising:

placing a second particulate phase that does not include tungsten carbide in a cavity formed by the outer area of the matrix drill bit body; and

sintering the second particulate phase to form an inner area of the matrix drill bit body; and

using selective laser sintering to form a barrier between the inner area and the outer area that prevents diffusion of polytetrafluoroethylene into the inner area.

The method of example 13 or 14, further comprising applying a low friction coating to an outer surface of the outer area.

The method of example 15, wherein the low friction coating comprises a topcoat of polytetrafluoroethylene.

The method of any of examples 11-16, further comprising forming a friction-reducing layer on an outer surface of the matrix drill bit body by operating a drill bit that includes the matrix drill bit body to form a wellbore.

The method any of examples 11-16, further comprising forming an outer surface comprising polytetrafluoroethylene by exposing the matrix drill bit body to frictional forces.

The method of example 17 wherein forming the friction-reducing layer further comprises regenerating a portion of the outer lubricating layer by continuing to operate the drill bit after the drill bit is chipped to remove a portion of the outer lubricating layer.

A well formation system comprising a drill string, the drill string having a low surface friction drill bit, wherein the low surface friction drill bit comprises:at least one cutting element and a molded matrix drill bit body comprising a particulate phase and a binding material, the particulate phase including tungsten carbide and polytetrafluoroethylene;wherein the polytetrafluoroethylene is dispersed throughout at least a portion of the matrix drill bit body.

The well formation system of example 20, wherein:the matrix drill bit body further comprises an inner area and an outer area;the outer area comprises the particulate phase and the binding material;the inner area consisting of a material that does not include polytetrafluoroethylene; and

a barrier that prevents diffusion of the polytetrafluoroethylene to the inner area.

The well formation system of claim20or21, wherein the matrix drill bit body comprises a roller cone drill bit body having a low friction coating applied to an outer surface of the roller cone drill bit body.

It should be apparent from the foregoing that the various features embodied in the disclosed example embodiments are not limited to only those example embodiments. Various changes and modifications are possible without departing from the spirit thereof.