Downhole positive displacement motor and associated systems and methods

Abstract

A downhole positive displacement motor (PDM) includes a power section, a bearing section, and a transmission section coupling the power and bearing sections. The power section has a rotor and a stator operable by a pressurized fluid flowing through the motor. The transmission section includes cutting edges configured to reduce a maximum dimension of debris within the pressurized fluid. A method for operating a PDM includes reducing a maximum dimension of debris within the pressurized fluid in a transmission section of the motor before entering a bearing section.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application 63 / 746,567, filed Jan. 17, 2025, and entitled “DOWNHOLE POSITIVE DISPLACEMENT MOTOR AND ASSOCIATED SYSTEMS AND METHODS,” which is hereby incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure generally relates to downhole motors and more particularly relates to downhole positive displacement motors used in drilling, completion, and rework of oil wells.BACKGROUND

[0003] In today's drilling industry, positive displacement motors (PDMs) are used for drilling, completing, and reworking oil wells. Drilling rigs use downhole motors to provide torque and revolutions per minute (RPM) to the drill bit, and any other drilling device in the drill string below the motor. Some examples of tools that run below the motor include rotary steerable tools, torque reduction tools, and measurement while drilling (MWD) tools. In addition, well service rigs, including coiled tubing rigs, use PDMs to drill out frac plugs and clean up the well bore.

[0004] The power section of a typical PDM has a cylindrical housing, a stator formed along the inner wall of the housing, and an elongated, helical rotor positioned within the stator. The stator includes an elastomer or rubber that seals against the rotor as the rotor contacts the stator. A high pressure, high flow rate drilling fluid pumped through the PDM causes the helically shaped rotor to roll against the stator, thus creating an eccentric rotation of the rotor that is used to drive the drill bit.

[0005] As the downhole motor power section wears, the stator can start tearing and chunking into pieces that travel down the drill string with the drilling fluid. In some cases the pieces can plug up components below the motor such as directional tools and the drill bit. Components becoming plugged in this way can result in, for example, trip, stuck pipe, and / or well control issues. Screens are sometimes used to capture and prevent pieces of the stator from clogging down string components, but pieces can spill over and continue moving down the drill string once screens become full. FIG. 1 depicts piles 100 of stator pieces captured from a drill string.BRIEF SUMMARY

[0006] One general aspect of the disclosed technology includes a downhole positive displacement motor, including a power section, a bearing section comprising a drive shaft, and a transmission section coupling the power section to the bearing section. The power section includes a rotor and a stator operable by a pressurized fluid flowing through the motor. The transmission section includes a plurality of cutting edges configured to reduce a maximum dimension of debris within the pressurized fluid.

[0007] Implementations according to this aspect of the disclosure may include one or more of the following features. In some cases the debris includes pieces of the stator. In some cases the motor has a single-piece housing for the transmission section and the bearing section. In some cases the plurality of cutting edges include a plurality of blades. In some cases the transmission section includes a flow diverter with an entry port and the plurality of blades are fixed across the entry port. In some cases the transmission section includes a plurality of cutters and each cutter includes a respective subset of the plurality of cutting edges.

[0008] In some cases the transmission section includes a coupling shaft and first and second couplings attached to first and second ends of the coupling shaft, and the plurality of cutters are fixed to and extend from at least one of the first and second couplings. In some cases the transmission section includes at least one abrasive coating. In some cases the transmission section includes a rotor extension coupled to the rotor, and the abrasive coating includes a carbide coating fixed to the rotor extension. In some cases the maximum dimension of the debris is no greater than 4 / 32 inch.

[0009] Another general aspect of the disclosed technology includes a downhole positive displacement motor that includes a stator with an outer tubular housing and an inner elastic layer and a rotor positioned within the stator. The rotor is configured to rotate in response to a pressurized fluid flowing through the motor. The motor also includes a bearing section with a drive shaft and a coupling shaft between the rotor and the bearing section. The motor also includes a flow diverter between the coupling shaft and the bearing section. The flow diverter has at least one entry port with a plurality of blades fixed across the at least one entry port to cut apart debris within the pressurized fluid. The debris can include pieces of the stator.

[0010] Implementations according to this aspect may include one or more of the following features. In some cases the motor is configured for use with a downhole string comprising a most restrictive opening and the plurality of blades have a maximum spacing no greater than the most restrictive opening. In some cases the maximum spacing is no more than 4 / 32 inch. In some cases the motor also includes a coupler coupling the flow diverter with the coupling shaft. The coupler includes a plurality of cutters and each cutter includes a plurality of cutting edges.

[0011] In some cases the motor also includes a single-piece housing, and the coupling shaft, the flow diverter, and the bearing section are positioned within the single-piece housing. In some cases the single-piece housing is a bent housing.

[0012] Another general aspect of the disclosure includes a method for operating a downhole positive displacement motor on a downhole string. The method includes pumping a pressurized fluid through a power section of a positive displacement motor. The power section includes a rotor and a stator. The method further includes directing the pressurized fluid from the power section through a transmission section of the motor and into a bearing section of the motor. The method further includes reducing a maximum dimension of debris within the pressurized fluid in the transmission section before the pressurized fluid enters the bearing section.

[0013] Implementations according to this aspect may include one or more of the following features. In some cases reducing the maximum dimension includes cutting pieces of the debris with a plurality of cutting edges within the transmission section. In some cases reducing the maximum dimension includes directing the pressurized fluid through an entry port of a flow diverter. In various cases the entry port includes a plurality of blades fixed across the entry port. In some cases the debris includes pieces of the stator.

[0014] While multiple implementations and aspects are disclosed, still other embodiments of the disclosure will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the disclosed apparatus, systems and methods. As will be realized, the disclosed apparatus, systems and methods are capable of modifications in various obvious aspects, all without departing from the spirit and scope of the disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a depiction of piles of pieces of a stator captured from a drill string.

[0016] FIG. 2 is a partial cross-section of a downhole positive displacement motor according to an implementation.

[0017] FIG. 3 is a representation of part of a PDM drive subassembly according to an implementation.

[0018] FIG. 4 is an enlarged view of the rotor crossover of the drive subassembly in FIG. 3.

[0019] FIG. 5 is an enlarged perspective view of a lower coupling of the drive subassembly in FIG. 3.

[0020] FIG. 6 is a partial view of a flow diverter and entry port of a drive subassembly according to an implementation.

[0021] FIG. 7 is a perspective view of a flow diverter and entry port of a drive subassembly according to an implementation.

[0022] FIG. 8 is a perspective view of a drive subassembly housing according to an implementation.

[0023] FIG. 9 is a flow chart of a method for operating a downhole positive displacement motor according to an implementation.DETAILED DESCRIPTION

[0024] Implementations of the disclosed technology involve downhole positive displacement motors (PDMs) and related devices, systems, and methods. Various examples described herein relate to drilling, though applications are not limited to drilling and may also include well completion, workover, and other applications. Implementations may involve a string of components deployed in a wellbore (e.g., a drill string, a work string, or any other suitable string of components), referred to herein as a “string” or “downhole string” for convenience. A pressurized fluid used to operate a PDM can include a drilling fluid, working fluid, or other fluid suitable for a particular implementation as will be appreciated.

[0025] FIG. 2 is a partial cross-section of a downhole positive displacement motor 200 for use in a downhole string (e.g., drill string, work string, etc.) within a wellbore, according to various implementations of the disclosed technology. The PDM 200 includes a power section 202, a transmission section 204, and a bearing section 206. At the top of the motor 200, the power section 202 includes a rotor 210 and a stator 212. A pressurized fluid (e.g., drilling fluid, working fluid, etc.) pumped through the motor moves the rotor with respect to the stator to convert hydraulic horsepower (e.g., flow rate and pressure) to mechanical horsepower (e.g., RPM and torque). The stator 212 includes an outer tubular housing 214 and an inner layer 216. According to various implementations, the inner layer 216 of the stator is formed from an elastic material such as rubber or one or more elastomers. In some cases the elastic material is nitrile butane rubber.

[0026] After prolonged use, the inner layer 216 of the stator 212 can begin to tear and break into pieces. In some cases, this problem can be the primary mode of failure for a typical PDM because the pressurized fluid carries the pieces of stator down the string where the pieces can clog or plug other equipment. As will be appreciated, rotary steerable tools, measurement while drilling tools, drill bits, and other components of the Bottom Hole Assembly have restricted openings and inner diameters (IDs) that can easily plug. If any one of the Bottom Hole Assembly components plug, the reduced circulation can create a stuck pipe and / or a well control issue.

[0027] Various implementations of the disclosed technology provide a positive displacement motor, such as the PDM 200 shown in FIG. 2, that is configured to reduce the size of debris in the fluid, including loose stator pieces, to enable the debris to pass more easily through the string below without clogging. In various cases a PDM is configured to cut or otherwise break apart broken bits of the stator and other debris so that the pieces have a maximum dimension that is less than the most restrictive opening in the down string equipment. In some cases the debris is reduced to pieces small enough to fit through one or more nozzles of an attached bit, which can have a diameter of just 10 / 32 inch.

[0028] According to various implementations, a PDM includes one or more cutting elements. The cutting elements have physical features designed to cut, wear down, and / or break apart stator pieces and other debris into smaller pieces. For example, a cutting element can have physical features such as one or more edges, corners, and / or projections. In some cases a cutting element includes an abrasive surface or coating that may cut or grind pieces of debris. According to various implementations, multiple cutting elements are placed in the transmission section of a PDM. This placement enables the cutting elements to cut and break up loose pieces of stator from the power section before the pressurized fluid enters the bearing section of the motor.

[0029] Continuing with reference to FIG. 2, the transmission section 204 of the PDM 200 is just below the power section 202 and transmits the mechanical horsepower from the power section 202 to the bearing pack 206, drive sub, and other components in the drill string below the motor 200. According to various implementations, the transmission section 204 includes an extension 220 of the rotor 210 that is connected to a coupling shaft 222 through an upper coupling 224. A lower coupling 226 connects the coupling shaft 222 to a flow diverter 228.

[0030] In some cases the coupling shaft 222 is also called a “flex shaft” because it can enable the bearing section to be angled relative to the power section. The flow diverter 228 includes one or more entry ports 230 through which the pressurized fluid continues to flow down the motor and the drill string. As shown in FIG. 2, the internal components of the transmission section are connected together within an outer housing 236, which in the depicted example is a single-piece flex housing that also houses the bearing section 206, angled relative to the power section. In some cases the outer housing 236 may be a straight housing.

[0031] The bearing pack or bearing section 206 is at the bottom of the motor 200. The bearing section 206 isolates the rotation and torque created by the power section 202 from the drill string and the motor housing. In the depicted example in FIG. 2, the bearing section 206 includes an upper rotating bearing 240, an upper stationary bearing 242, and a thrust bearing stack 244. The bearing section 206 also includes a safety retention nut 246 connected to a spacer 248 encircling part of the drive shaft 250. Lower stationary and rotating bearings 252, 254 are also provided as shown in FIG. 2.

[0032] As previously discussed, implementations of the disclosed technology include one or more cutting elements configured to cut, wear down, and / or break apart loose pieces of the stator 216 and other debris in the pressurized fluid. In various cases a cutting element has structural features such as one or more edges, corners, and / or projections. In some cases a cutting element includes an abrasive surface or coating that may grind or cut pieces of debris. In various cases the cutting elements are configured to cut and / or break apart stator pieces and debris into pieces with a maximum dimension of 4 / 32 inch or less. Other dimensions can also be implemented depending on the size of various down string restrictions.

[0033] Examples of cutting elements include, but are not limited to, blades, abrasive coatings (e.g., carbide coatings), and cutters. As used herein, a cutter is a physical structure or body including multiple edges and / or teeth oriented in one or more directions for cutting or breaking pieces of debris. In some cases a cutter includes one or more projections from the surface of a motor component into the fluid space within the motor housing. For example, a cutter may be fixed or attached to (e.g., welded) or integral with a surface of a motor component.

[0034] According to various implementations, multiple cutting elements are placed in the transmission section 204 of the PDM, downstream from the stator 212 and upstream from the bearings and drive shaft 250. For example, one or more cutting elements may be attached to at least one of the rotor extension 220, the coupling shaft 222, the flow diverter 228, and the upper and lower couplings 224, 226.

[0035] During operation, the internal components of the PDM turn faster than the surrounding housing. The rotation and speed of the motor can spin attached cutting element(s) into contact with debris suspended in the pressurized fluid, thus cutting, grinding, and otherwise breaking apart the debris. In addition, in various cases the velocity and pressure of the fluid within the motor housing forces the debris against the cutting element(s) prior to exiting the motor. According to various implementations the movement of the motor and cutting elements, and the velocity and pressure of the fluid within the restricted volume of the housing, combine to cut, chew, grind, and break up debris, including loose pieces of the stator, traveling through the motor.

[0036] FIG. 3 is a representation of a PDM drive subassembly 300 illustrating examples of various transmission components also shown in FIG. 2. Among other things, the drive subassembly 300 includes a rotor extension 220 (also referred to as a rotor crossover sub), a coupling shaft 222, upper and lower couplings 224, 226, and a flow diverter 228 with multiple entry ports 230. FIG. 3 also depicts the placement of cutting elements according to various implementations of the disclosed technology. As used herein, a cutting element includes one or more cutting edges, one or more abrasive surfaces, or both. In the example of FIG. 3, the cutting elements include an abrasive surface or coating 310 attached to the rotor extension / crossover 220, cutters 312 attached to the lower coupling 226, and cutting blades 314 (e.g., industrial strength blades) fixed (e.g., welded or integrally formed) across a flow diverter entry port 230. The drive subassembly 300 may include one or more additional cutting elements in these or different locations and / or a different combination of these locations. As just one possible example, in some cases cutters may be attached to the upper coupling 224 where it meets the coupling shaft 222.

[0037] FIG. 4 is an enlarged view of an example of a cutting element in the form of an abrasive coating or surface 310 according to various implementations. In this example, the abrasive surface is implemented as a carbide coating that is welded to the rotor crossover or extension 220. The abrasive surface can in some cases have a pattern. As shown in FIG. 4, in some implementations the abrasive surface / coating 310 includes end collar portions 400, 402 separated by one or more intermediate curving segments 404 of the coating.

[0038] FIG. 5 is an enlarged partial view of the PDM coupling shaft 222 attached to the lower coupling 226. Multiple cutting elements implemented as cutters 312 are attached to an end of the lower coupling 226, following the circumference of the coupling 226. In this example, each of the cutters 312 projects from the coupling 226 in a direction parallel to the coupling shaft axis. The cutters are spaced apart and include multiple ridges or edges 320 configured to cut and break apart debris within the pressurized fluid as the coupling 226 and other parts of the motor spin within the motor housing.

[0039] FIG. 6 is a partial view of a PDM flow diverter 228 depicting an entry port 230 according to various implementations. FIG. 7 is a perspective view of another PDM flow diverter 228 depicting an entry port 230 according to various implementations. As shown in FIGS. 6 and 7, in various implementations the entry ports 230 include multiple cutting blades 314 (e.g., industrial blades) mounted across the opening to ensure that pieces of the stator and other debris are cut to a size small enough to fit through subsequent openings in down string components. According to various implementations, the cutting blades 314 cut and break apart pieces of debris carried into the flow diverter entry port 230 at high velocity and pressure by the pressurized fluid.

[0040] In some cases the cutting blades 306 are spaced no more than 4 / 32 inch apart. In various cases the cutting blades 314 are formed from a metal or metal alloy. Further, while the figures illustrate one entry port 230, it should be appreciated that multiple diverter entry ports 230 may be used. For example, in some cases two, three, four, or more flow diverter entry ports 230 are present, each having multiple cutting blades 314 mounted across its opening.

[0041] In various cases the outer housing of a positive displacement motor may include multiple housing components coupled together. Among other things, the motor housing can include a power section housing, a stator adaptor, a fixed bend (or straight housing), and separate bearing housings. The power section housing may be referred to as the stator housing. As shown in FIGS. 2 and 8, various implementations of the disclosed technology provide a PDM with a single piece housing 236 that takes the place of the housings for the stator adaptor, fixed bend, and bearing. In various implementations the single piece housing 236 has a straight configuration without a bend.

[0042] In various cases the shape and configuration of the housing 236 controls the velocity and amount of pressurized fluid (including stator pieces and other debris) flowing within the housing to the mud lubricated bearing and motor drive shaft 250. In particular, the restricted volume of the integrated housing 236 further pressurizes the fluid and forces debris against the various cutting elements, thus cutting and breaking down the debris into smaller pieces. In some cases the housing 236 can improve the internal flow and pressure control within the motor because the single piece housing 236 lacks the intermediate connections and changing diameters and wall thicknesses sometimes present in multi-piece housings. The single piece design can also improve the strength of both straight and fixed bend housings. While the single piece housing 236 is believed to provide advantages over multi-piece housings in various implementations, it should be appreciated that the disclosed technology is not limited to these types of single-piece housings. Various implementations may instead include a combination of two or more housing pieces for, e.g., a stator adaptor, a fixed bend, the bearings, etc.

[0043] FIG. 9 is a flow chart of a method 500 for operating a downhole positive displacement motor according to various implementations of the disclosed technology. It will be appreciated that operating a downhole PDM involves many steps that will be well known to those skilled in the art and are thus omitted here for clarity. According to various implementations, the method 500 includes pumping a pressurized fluid through the PDM. This involves pumping 502 the pressurized fluid into the power section of the motor, directing 504 the pressurized fluid from the power section through the transmission section, and directing 506 the pressurized fluid from the transmission section to the bearing section. The method 500 also includes reducing 510 the maximum dimension of debris in the pressurized fluid before directing 506 the pressurized fluid into the bearing section of the motor. In various cases the debris includes broken or separated pieces of the motor's stator.

[0044] In various implementations, the step of reducing 510 the maximum dimension of debris in the fluid includes cutting, wearing down, and / or breaking up pieces of debris with one or more cutting elements. In some cases the reducing 510 includes cutting pieces of debris with blades mounted across one or more entry ports of a flow diverter. In some cases the size of the debris is reduced so that the maximum dimension of the debris is no greater than the size of the most restrictive opening down string. In various cases the debris is reduced to a maximum dimension of no more than 4 / 32 inch, though other dimensions are also possible.

[0045] According to various implementations, the method 500 of operating a downhole PDM includes moving the cutting elements through the pressurized fluid (e.g., drilling fluid, working fluid, etc.) at high speed. This brings the cutting elements into forceful contact with debris in the fluid thus cutting, grinding, and otherwise breaking apart the debris. For example, cutting elements can be fixed to internal components of the motor's transmission section, thus allowing the cutting elements to spin through the pressurized fluid as the transmission components rotate the motor drive shaft.

[0046] In various implementations pressurizing the fluid forces suspended debris against the cutting elements at high pressure and velocity, thus aiding in cutting and breaking up pieces of debris (including pieces of the stator). In various cases the method involves using the outer housing of the transmission section to pressurize and direct fluid, and suspended debris, against the cutting elements before exiting to the bearing section. In some cases the housing is configured to increase the speed and / or pressure of the fluid, thereby improving cutting performance. For example, the housing may provide a constriction or “choke point” to improve speed. In some cases the transmission housing is part of a single-piece housing for the transmission and bearing sections. The single-piece design lacks internal connections and discontinuities present in multi-piece housings, thus improving flow of the pressurized fluid.

[0047] Although the disclosure has been described with reference to certain implementations and embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosed apparatus, systems, and methods.

Examples

Embodiment Construction

[0024]Implementations of the disclosed technology involve downhole positive displacement motors (PDMs) and related devices, systems, and methods. Various examples described herein relate to drilling, though applications are not limited to drilling and may also include well completion, workover, and other applications. Implementations may involve a string of components deployed in a wellbore (e.g., a drill string, a work string, or any other suitable string of components), referred to herein as a “string” or “downhole string” for convenience. A pressurized fluid used to operate a PDM can include a drilling fluid, working fluid, or other fluid suitable for a particular implementation as will be appreciated.

[0025]FIG. 2 is a partial cross-section of a downhole positive displacement motor 200 for use in a downhole string (e.g., drill string, work string, etc.) within a wellbore, according to various implementations of the disclosed technology. The PDM 200 includes a power section 202, a...

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application 63 / 746,567, filed Jan. 17, 2025, and entitled “DOWNHOLE POSITIVE DISPLACEMENT MOTOR AND ASSOCIATED SYSTEMS AND METHODS,” which is hereby incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure generally relates to downhole motors and more particularly relates to downhole positive displacement motors used in drilling, completion, and rework of oil wells.BACKGROUND

[0003] In today's drilling industry, positive displacement motors (PDMs) are used for drilling, completing, and reworking oil wells. Drilling rigs use downhole motors to provide torque and revolutions per minute (RPM) to the drill bit, and any other drilling device in the drill string below the motor. Some examples of tools that run below the motor include rotary steerable tools, torque reduction tools, and measurement while drilling (MWD) tools. In addition, well service rigs, including coiled tubing rigs, use PDMs to drill out frac plugs and clean up the well bore.

[0004] The power section of a typical PDM has a cylindrical housing, a stator formed along the inner wall of the housing, and an elongated, helical rotor positioned within the stator. The stator includes an elastomer or rubber that seals against the rotor as the rotor contacts the stator. A high pressure, high flow rate drilling fluid pumped through the PDM causes the helically shaped rotor to roll against the stator, thus creating an eccentric rotation of the rotor that is used to drive the drill bit.

[0005] As the downhole motor power section wears, the stator can start tearing and chunking into pieces that travel down the drill string with the drilling fluid. In some cases the pieces can plug up components below the motor such as directional tools and the drill bit. Components becoming plugged in this way can result in, for example, trip, stuck pipe, and / or well control issues. Screens are sometimes used to capture and prevent pieces of the stator from clogging down string components, but pieces can spill over and continue moving down the drill string once screens become full. FIG. 1 depicts piles 100 of stator pieces captured from a drill string.BRIEF SUMMARY

[0006] One general aspect of the disclosed technology includes a downhole positive displacement motor, including a power section, a bearing section comprising a drive shaft, and a transmission section coupling the power section to the bearing section. The power section includes a rotor and a stator operable by a pressurized fluid flowing through the motor. The transmission section includes a plurality of cutting edges configured to reduce a maximum dimension of debris within the pressurized fluid.

[0007] Implementations according to this aspect of the disclosure may include one or more of the following features. In some cases the debris includes pieces of the stator. In some cases the motor has a single-piece housing for the transmission section and the bearing section. In some cases the plurality of cutting edges include a plurality of blades. In some cases the transmission section includes a flow diverter with an entry port and the plurality of blades are fixed across the entry port. In some cases the transmission section includes a plurality of cutters and each cutter includes a respective subset of the plurality of cutting edges.

[0008] In some cases the transmission section includes a coupling shaft and first and second couplings attached to first and second ends of the coupling shaft, and the plurality of cutters are fixed to and extend from at least one of the first and second couplings. In some cases the transmission section includes at least one abrasive coating. In some cases the transmission section includes a rotor extension coupled to the rotor, and the abrasive coating includes a carbide coating fixed to the rotor extension. In some cases the maximum dimension of the debris is no greater than 4 / 32 inch.

[0009] Another general aspect of the disclosed technology includes a downhole positive displacement motor that includes a stator with an outer tubular housing and an inner elastic layer and a rotor positioned within the stator. The rotor is configured to rotate in response to a pressurized fluid flowing through the motor. The motor also includes a bearing section with a drive shaft and a coupling shaft between the rotor and the bearing section. The motor also includes a flow diverter between the coupling shaft and the bearing section. The flow diverter has at least one entry port with a plurality of blades fixed across the at least one entry port to cut apart debris within the pressurized fluid. The debris can include pieces of the stator.

[0010] Implementations according to this aspect may include one or more of the following features. In some cases the motor is configured for use with a downhole string comprising a most restrictive opening and the plurality of blades have a maximum spacing no greater than the most restrictive opening. In some cases the maximum spacing is no more than 4 / 32 inch. In some cases the motor also includes a coupler coupling the flow diverter with the coupling shaft. The coupler includes a plurality of cutters and each cutter includes a plurality of cutting edges.

[0011] In some cases the motor also includes a single-piece housing, and the coupling shaft, the flow diverter, and the bearing section are positioned within the single-piece housing. In some cases the single-piece housing is a bent housing.

[0012] Another general aspect of the disclosure includes a method for operating a downhole positive displacement motor on a downhole string. The method includes pumping a pressurized fluid through a power section of a positive displacement motor. The power section includes a rotor and a stator. The method further includes directing the pressurized fluid from the power section through a transmission section of the motor and into a bearing section of the motor. The method further includes reducing a maximum dimension of debris within the pressurized fluid in the transmission section before the pressurized fluid enters the bearing section.

[0013] Implementations according to this aspect may include one or more of the following features. In some cases reducing the maximum dimension includes cutting pieces of the debris with a plurality of cutting edges within the transmission section. In some cases reducing the maximum dimension includes directing the pressurized fluid through an entry port of a flow diverter. In various cases the entry port includes a plurality of blades fixed across the entry port. In some cases the debris includes pieces of the stator.

[0014] While multiple implementations and aspects are disclosed, still other embodiments of the disclosure will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the disclosed apparatus, systems and methods. As will be realized, the disclosed apparatus, systems and methods are capable of modifications in various obvious aspects, all without departing from the spirit and scope of the disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a depiction of piles of pieces of a stator captured from a drill string.

[0016] FIG. 2 is a partial cross-section of a downhole positive displacement motor according to an implementation.

[0017] FIG. 3 is a representation of part of a PDM drive subassembly according to an implementation.

[0018] FIG. 4 is an enlarged view of the rotor crossover of the drive subassembly in FIG. 3.

[0019] FIG. 5 is an enlarged perspective view of a lower coupling of the drive subassembly in FIG. 3.

[0020] FIG. 6 is a partial view of a flow diverter and entry port of a drive subassembly according to an implementation.

[0021] FIG. 7 is a perspective view of a flow diverter and entry port of a drive subassembly according to an implementation.

[0022] FIG. 8 is a perspective view of a drive subassembly housing according to an implementation.

[0023] FIG. 9 is a flow chart of a method for operating a downhole positive displacement motor according to an implementation.DETAILED DESCRIPTION

[0024] Implementations of the disclosed technology involve downhole positive displacement motors (PDMs) and related devices, systems, and methods. Various examples described herein relate to drilling, though applications are not limited to drilling and may also include well completion, workover, and other applications. Implementations may involve a string of components deployed in a wellbore (e.g., a drill string, a work string, or any other suitable string of components), referred to herein as a “string” or “downhole string” for convenience. A pressurized fluid used to operate a PDM can include a drilling fluid, working fluid, or other fluid suitable for a particular implementation as will be appreciated.

[0025] FIG. 2 is a partial cross-section of a downhole positive displacement motor 200 for use in a downhole string (e.g., drill string, work string, etc.) within a wellbore, according to various implementations of the disclosed technology. The PDM 200 includes a power section 202, a transmission section 204, and a bearing section 206. At the top of the motor 200, the power section 202 includes a rotor 210 and a stator 212. A pressurized fluid (e.g., drilling fluid, working fluid, etc.) pumped through the motor moves the rotor with respect to the stator to convert hydraulic horsepower (e.g., flow rate and pressure) to mechanical horsepower (e.g., RPM and torque). The stator 212 includes an outer tubular housing 214 and an inner layer 216. According to various implementations, the inner layer 216 of the stator is formed from an elastic material such as rubber or one or more elastomers. In some cases the elastic material is nitrile butane rubber.

[0026] After prolonged use, the inner layer 216 of the stator 212 can begin to tear and break into pieces. In some cases, this problem can be the primary mode of failure for a typical PDM because the pressurized fluid carries the pieces of stator down the string where the pieces can clog or plug other equipment. As will be appreciated, rotary steerable tools, measurement while drilling tools, drill bits, and other components of the Bottom Hole Assembly have restricted openings and inner diameters (IDs) that can easily plug. If any one of the Bottom Hole Assembly components plug, the reduced circulation can create a stuck pipe and / or a well control issue.

[0027] Various implementations of the disclosed technology provide a positive displacement motor, such as the PDM 200 shown in FIG. 2, that is configured to reduce the size of debris in the fluid, including loose stator pieces, to enable the debris to pass more easily through the string below without clogging. In various cases a PDM is configured to cut or otherwise break apart broken bits of the stator and other debris so that the pieces have a maximum dimension that is less than the most restrictive opening in the down string equipment. In some cases the debris is reduced to pieces small enough to fit through one or more nozzles of an attached bit, which can have a diameter of just 10 / 32 inch.

[0028] According to various implementations, a PDM includes one or more cutting elements. The cutting elements have physical features designed to cut, wear down, and / or break apart stator pieces and other debris into smaller pieces. For example, a cutting element can have physical features such as one or more edges, corners, and / or projections. In some cases a cutting element includes an abrasive surface or coating that may cut or grind pieces of debris. According to various implementations, multiple cutting elements are placed in the transmission section of a PDM. This placement enables the cutting elements to cut and break up loose pieces of stator from the power section before the pressurized fluid enters the bearing section of the motor.

[0029] Continuing with reference to FIG. 2, the transmission section 204 of the PDM 200 is just below the power section 202 and transmits the mechanical horsepower from the power section 202 to the bearing pack 206, drive sub, and other components in the drill string below the motor 200. According to various implementations, the transmission section 204 includes an extension 220 of the rotor 210 that is connected to a coupling shaft 222 through an upper coupling 224. A lower coupling 226 connects the coupling shaft 222 to a flow diverter 228.

[0030] In some cases the coupling shaft 222 is also called a “flex shaft” because it can enable the bearing section to be angled relative to the power section. The flow diverter 228 includes one or more entry ports 230 through which the pressurized fluid continues to flow down the motor and the drill string. As shown in FIG. 2, the internal components of the transmission section are connected together within an outer housing 236, which in the depicted example is a single-piece flex housing that also houses the bearing section 206, angled relative to the power section. In some cases the outer housing 236 may be a straight housing.

[0031] The bearing pack or bearing section 206 is at the bottom of the motor 200. The bearing section 206 isolates the rotation and torque created by the power section 202 from the drill string and the motor housing. In the depicted example in FIG. 2, the bearing section 206 includes an upper rotating bearing 240, an upper stationary bearing 242, and a thrust bearing stack 244. The bearing section 206 also includes a safety retention nut 246 connected to a spacer 248 encircling part of the drive shaft 250. Lower stationary and rotating bearings 252, 254 are also provided as shown in FIG. 2.

[0032] As previously discussed, implementations of the disclosed technology include one or more cutting elements configured to cut, wear down, and / or break apart loose pieces of the stator 216 and other debris in the pressurized fluid. In various cases a cutting element has structural features such as one or more edges, corners, and / or projections. In some cases a cutting element includes an abrasive surface or coating that may grind or cut pieces of debris. In various cases the cutting elements are configured to cut and / or break apart stator pieces and debris into pieces with a maximum dimension of 4 / 32 inch or less. Other dimensions can also be implemented depending on the size of various down string restrictions.

[0033] Examples of cutting elements include, but are not limited to, blades, abrasive coatings (e.g., carbide coatings), and cutters. As used herein, a cutter is a physical structure or body including multiple edges and / or teeth oriented in one or more directions for cutting or breaking pieces of debris. In some cases a cutter includes one or more projections from the surface of a motor component into the fluid space within the motor housing. For example, a cutter may be fixed or attached to (e.g., welded) or integral with a surface of a motor component.

[0034] According to various implementations, multiple cutting elements are placed in the transmission section 204 of the PDM, downstream from the stator 212 and upstream from the bearings and drive shaft 250. For example, one or more cutting elements may be attached to at least one of the rotor extension 220, the coupling shaft 222, the flow diverter 228, and the upper and lower couplings 224, 226.

[0035] During operation, the internal components of the PDM turn faster than the surrounding housing. The rotation and speed of the motor can spin attached cutting element(s) into contact with debris suspended in the pressurized fluid, thus cutting, grinding, and otherwise breaking apart the debris. In addition, in various cases the velocity and pressure of the fluid within the motor housing forces the debris against the cutting element(s) prior to exiting the motor. According to various implementations the movement of the motor and cutting elements, and the velocity and pressure of the fluid within the restricted volume of the housing, combine to cut, chew, grind, and break up debris, including loose pieces of the stator, traveling through the motor.

[0036] FIG. 3 is a representation of a PDM drive subassembly 300 illustrating examples of various transmission components also shown in FIG. 2. Among other things, the drive subassembly 300 includes a rotor extension 220 (also referred to as a rotor crossover sub), a coupling shaft 222, upper and lower couplings 224, 226, and a flow diverter 228 with multiple entry ports 230. FIG. 3 also depicts the placement of cutting elements according to various implementations of the disclosed technology. As used herein, a cutting element includes one or more cutting edges, one or more abrasive surfaces, or both. In the example of FIG. 3, the cutting elements include an abrasive surface or coating 310 attached to the rotor extension / crossover 220, cutters 312 attached to the lower coupling 226, and cutting blades 314 (e.g., industrial strength blades) fixed (e.g., welded or integrally formed) across a flow diverter entry port 230. The drive subassembly 300 may include one or more additional cutting elements in these or different locations and / or a different combination of these locations. As just one possible example, in some cases cutters may be attached to the upper coupling 224 where it meets the coupling shaft 222.

[0037] FIG. 4 is an enlarged view of an example of a cutting element in the form of an abrasive coating or surface 310 according to various implementations. In this example, the abrasive surface is implemented as a carbide coating that is welded to the rotor crossover or extension 220. The abrasive surface can in some cases have a pattern. As shown in FIG. 4, in some implementations the abrasive surface / coating 310 includes end collar portions 400, 402 separated by one or more intermediate curving segments 404 of the coating.

[0038] FIG. 5 is an enlarged partial view of the PDM coupling shaft 222 attached to the lower coupling 226. Multiple cutting elements implemented as cutters 312 are attached to an end of the lower coupling 226, following the circumference of the coupling 226. In this example, each of the cutters 312 projects from the coupling 226 in a direction parallel to the coupling shaft axis. The cutters are spaced apart and include multiple ridges or edges 320 configured to cut and break apart debris within the pressurized fluid as the coupling 226 and other parts of the motor spin within the motor housing.

[0039] FIG. 6 is a partial view of a PDM flow diverter 228 depicting an entry port 230 according to various implementations. FIG. 7 is a perspective view of another PDM flow diverter 228 depicting an entry port 230 according to various implementations. As shown in FIGS. 6 and 7, in various implementations the entry ports 230 include multiple cutting blades 314 (e.g., industrial blades) mounted across the opening to ensure that pieces of the stator and other debris are cut to a size small enough to fit through subsequent openings in down string components. According to various implementations, the cutting blades 314 cut and break apart pieces of debris carried into the flow diverter entry port 230 at high velocity and pressure by the pressurized fluid.

[0040] In some cases the cutting blades 306 are spaced no more than 4 / 32 inch apart. In various cases the cutting blades 314 are formed from a metal or metal alloy. Further, while the figures illustrate one entry port 230, it should be appreciated that multiple diverter entry ports 230 may be used. For example, in some cases two, three, four, or more flow diverter entry ports 230 are present, each having multiple cutting blades 314 mounted across its opening.

[0041] In various cases the outer housing of a positive displacement motor may include multiple housing components coupled together. Among other things, the motor housing can include a power section housing, a stator adaptor, a fixed bend (or straight housing), and separate bearing housings. The power section housing may be referred to as the stator housing. As shown in FIGS. 2 and 8, various implementations of the disclosed technology provide a PDM with a single piece housing 236 that takes the place of the housings for the stator adaptor, fixed bend, and bearing. In various implementations the single piece housing 236 has a straight configuration without a bend.

[0042] In various cases the shape and configuration of the housing 236 controls the velocity and amount of pressurized fluid (including stator pieces and other debris) flowing within the housing to the mud lubricated bearing and motor drive shaft 250. In particular, the restricted volume of the integrated housing 236 further pressurizes the fluid and forces debris against the various cutting elements, thus cutting and breaking down the debris into smaller pieces. In some cases the housing 236 can improve the internal flow and pressure control within the motor because the single piece housing 236 lacks the intermediate connections and changing diameters and wall thicknesses sometimes present in multi-piece housings. The single piece design can also improve the strength of both straight and fixed bend housings. While the single piece housing 236 is believed to provide advantages over multi-piece housings in various implementations, it should be appreciated that the disclosed technology is not limited to these types of single-piece housings. Various implementations may instead include a combination of two or more housing pieces for, e.g., a stator adaptor, a fixed bend, the bearings, etc.

[0043] FIG. 9 is a flow chart of a method 500 for operating a downhole positive displacement motor according to various implementations of the disclosed technology. It will be appreciated that operating a downhole PDM involves many steps that will be well known to those skilled in the art and are thus omitted here for clarity. According to various implementations, the method 500 includes pumping a pressurized fluid through the PDM. This involves pumping 502 the pressurized fluid into the power section of the motor, directing 504 the pressurized fluid from the power section through the transmission section, and directing 506 the pressurized fluid from the transmission section to the bearing section. The method 500 also includes reducing 510 the maximum dimension of debris in the pressurized fluid before directing 506 the pressurized fluid into the bearing section of the motor. In various cases the debris includes broken or separated pieces of the motor's stator.

[0044] In various implementations, the step of reducing 510 the maximum dimension of debris in the fluid includes cutting, wearing down, and / or breaking up pieces of debris with one or more cutting elements. In some cases the reducing 510 includes cutting pieces of debris with blades mounted across one or more entry ports of a flow diverter. In some cases the size of the debris is reduced so that the maximum dimension of the debris is no greater than the size of the most restrictive opening down string. In various cases the debris is reduced to a maximum dimension of no more than 4 / 32 inch, though other dimensions are also possible.

[0045] According to various implementations, the method 500 of operating a downhole PDM includes moving the cutting elements through the pressurized fluid (e.g., drilling fluid, working fluid, etc.) at high speed. This brings the cutting elements into forceful contact with debris in the fluid thus cutting, grinding, and otherwise breaking apart the debris. For example, cutting elements can be fixed to internal components of the motor's transmission section, thus allowing the cutting elements to spin through the pressurized fluid as the transmission components rotate the motor drive shaft.

[0046] In various implementations pressurizing the fluid forces suspended debris against the cutting elements at high pressure and velocity, thus aiding in cutting and breaking up pieces of debris (including pieces of the stator). In various cases the method involves using the outer housing of the transmission section to pressurize and direct fluid, and suspended debris, against the cutting elements before exiting to the bearing section. In some cases the housing is configured to increase the speed and / or pressure of the fluid, thereby improving cutting performance. For example, the housing may provide a constriction or “choke point” to improve speed. In some cases the transmission housing is part of a single-piece housing for the transmission and bearing sections. The single-piece design lacks internal connections and discontinuities present in multi-piece housings, thus improving flow of the pressurized fluid.

[0047] Although the disclosure has been described with reference to certain implementations and embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosed apparatus, systems, and methods.

Examples

Embodiment Construction

[0024]Implementations of the disclosed technology involve downhole positive displacement motors (PDMs) and related devices, systems, and methods. Various examples described herein relate to drilling, though applications are not limited to drilling and may also include well completion, workover, and other applications. Implementations may involve a string of components deployed in a wellbore (e.g., a drill string, a work string, or any other suitable string of components), referred to herein as a “string” or “downhole string” for convenience. A pressurized fluid used to operate a PDM can include a drilling fluid, working fluid, or other fluid suitable for a particular implementation as will be appreciated.

[0025]FIG. 2 is a partial cross-section of a downhole positive displacement motor 200 for use in a downhole string (e.g., drill string, work string, etc.) within a wellbore, according to various implementations of the disclosed technology. The PDM 200 includes a power section 202, a...

Claims

1. A downhole positive displacement motor, comprising:a power section comprising a rotor and a stator operable by a pressurized fluid flowing through the motor;a bearing section comprising a drive shaft; anda transmission section coupling the power section to the bearing section, the transmission section comprising a plurality of cutting edges configured to reduce a maximum dimension of debris within the pressurized fluid.

2. The motor of claim 1, wherein the debris comprises pieces of the stator.

3. The motor of claim 1, further comprising a single-piece housing for the transmission section and the bearing section.

4. The motor of claim 1, wherein the plurality of cutting edges comprises a plurality of blades.

5. The motor of claim 4, wherein the transmission section comprises a flow diverter comprising an entry port and wherein the plurality of blades are fixed across the entry port.

6. The motor of claim 1, wherein the transmission section comprises a plurality of cutters, each cutter comprising a respective subset of the plurality of cutting edges.

7. The motor of claim 6, wherein the transmission section comprises a coupling shaft and first and second couplings attached to first and second ends of the coupling shaft, wherein the plurality of cutters are fixed to and extend from at least one of the first and second couplings.

8. The motor of claim 1, wherein the transmission section comprises at least one abrasive coating.

9. The motor of claim 8, wherein the transmission section comprises a rotor extension coupled to the rotor, wherein the abrasive coating comprises a carbide coating fixed to the rotor extension.

10. The motor of claim 1, wherein the maximum dimension of the debris is no greater than 4 / 32 inch.

11. A downhole positive displacement motor, comprising:a stator comprising an outer tubular housing and an inner elastic layer;a rotor positioned within the stator, the rotor configured to rotate in response to a pressurized fluid flowing through the motor;a bearing section comprising a drive shaft;a coupling shaft between the rotor and the bearing section;a flow diverter between the coupling shaft and the bearing section, the flow diverter comprising at least one entry port; anda plurality of blades fixed across the at least one entry port to cut apart debris within the pressurized fluid, the debris comprising pieces of the stator.

12. The motor of claim 11, wherein the motor is configured for use with a downhole string comprising a most restrictive opening, wherein the plurality of blades have a maximum spacing no greater than the most restrictive opening.

13. The motor of claim 12, wherein the maximum spacing is no more than 4 / 32 inch.

14. The motor of claim 11, further comprising a coupler coupling the flow diverter with the coupling shaft, the coupler comprising a plurality of cutters, each cutter comprising a plurality of cutting edges.

15. The motor of claim 11, further comprising a single-piece housing, wherein the coupling shaft, the flow diverter, and the bearing section are positioned within the single-piece housing.

16. The motor of claim 15, wherein the single-piece housing is a bent housing.

17. A method for operating a downhole positive displacement motor on a downhole string, comprising:pumping a pressurized fluid through a power section of a positive displacement motor, the power section comprising a rotor and a stator;directing the pressurized fluid from the power section through a transmission section of the motor and into a bearing section of the motor; andreducing a maximum dimension of debris within the pressurized fluid in the transmission section before the pressurized fluid enters the bearing section.

18. The method of claim 17, wherein reducing the maximum dimension comprises cutting pieces of the debris with a plurality of cutting edges within the transmission section.

19. The method of claim 17, wherein reducing the maximum dimension comprises directing the pressurized fluid through an entry port of a flow diverter, the entry port comprising a plurality of blades fixed across the entry port.

20. The method of claim 17, wherein the debris comprises pieces of the stator.

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