Method of forming stators for downhole motors

A stator for a downhole motor configured for use in a downhole environment. includes an inner tubular member formed from a first metallic material having an outer surface and a helically lobed inner surface, and an outer tubular member comprising a second metallic material that is different from the first metallic material. The inner tubular member is connected to the outer tubular member by compressive force passing from the outer tubular member through the inner tubular member to a rigid mandrel removably disposed within the inner tubular member. The inner tubular member and the outer tubular member form the stator of the downhole motor.

BACKGROUND

Downhole operations often include a downhole string that extends from an uphole system into a formation. The uphole system may include a platform, pumps, and other systems that support resource exploration, development, and extraction. During resource exploration operations, a drill bit is guided through the formation to form a well bore. The drill bit may be driven directly from the platform or both directly and indirectly through a flow of downhole fluid, which may take the form of drilling mud passing through a motor.

A motor, such as a downhole motor, includes a stator housing having a plurality of lobes and a rotor having another plurality of lobes. The stator is rotated by the downhole string and the rotor by the flow of fluid. The number of lobes on the rotor is one fewer than the number of lobes on the stator. In this manner, the flow of fluid drives the rotor eccentrically while the motor drives the drill bit concentrically. The stator housing may be made by installing a mandrel having a selected outer profile within a tubular member. Force application members are urged against the tubular member with a selected pressure. Internal surfaces of the tubular member take on the selected outer profile. Stator housings may also be formed by pouring molten metal over a mandrel having a selected outer profile.

SUMMARY

Disclosed is a stator for a downhole motor configured for use in a downhole environment. The stator includes an inner tubular member formed from a first metallic material having an outer surface and a helically lobed inner surface, and an outer tubular member comprising a second metallic material that is different from the first metallic material. The inner tubular member is connected to the outer tubular member by compressive force passing from the outer tubular member through the inner tubular member to a rigid mandrel removably disposed within the inner tubular member. The inner tubular member and the outer tubular member form the stator of the downhole motor.

DETAILED DESCRIPTION

A downhole motor, in accordance with an exemplary embodiment, is illustrated generally at10inFIGS. 1A and 1B. Downhole motor10may take the form of a positive displacement motor, following the Moineau Principle, having a power section12(FIG. 1A) operatively coupled to a bearing assembly14(FIG. 1B). That is, downhole motor10may take the form of a Moineau system configured for use in a downhole environment. Power section12includes an elongated composite metal housing16that defines a stator18. The term “composite” should be understood to describe that stator18may be formed with multiple layers of material as will be detailed below. Stator18includes an interior20having a selected inner contour in the form of a helically lobed inner surface22that may be defined by an elastomeric layer24or by a pre-contoured metal housing. It is to be understood that in the case of a pre-contoured metal housing, helically lobed inner surface22may be covered by an elastomeric material, a non-elastomeric material, referred to as a lined stator, or remain uncovered depending upon operating conditions of downhole motor10.

Downhole motor10also includes a rotor28arranged in interior20. Rotor28includes a helically lobed outer surface30that engages with helically lobed inner surface22of stator18. Helically lobed outer surface30includes one less lobe than helically lobed inner surface22. Rotor28includes a first end portion32, a second end portion33, and an intermediate portion34.

In operation, rotor28with helically lobed outer surface30rotates within stator18with helically lobed inner surface22to form a plurality of axial fluid chambers or cavities40which may be filled with pressurized drilling fluid37flowing through interior20in a direction43from an uphole end44toward a downhole end46of stator18. Bearing assembly14illustrated inFIG. 1Bincludes a flexible shaft50coupled to a rotatable drive shaft52which carries a bit box54. It is to be understood that additional components (not shown) may be arranged between power section12and bearing assembly14. Bit box54may operatively connect to a drill bit (not shown).

In accordance with an exemplary aspect illustrated inFIG. 2, composite metal housing16which defines stator18includes an outer tubular member60formed from a first material (not separately labeled) operatively connected with an inner tubular member62formed from a second material (also not separately labeled) that may be distinct from the first material. The term “composite” should be understood to describe that stator18may be formed from multiple layers of material. Inner tubular member62may be connected to outer tubular member60through various processes as will be discussed more fully below. In accordance with an aspect of an exemplary embodiment, inner tubular member62may extend an entire longitudinal length of outer tubular member60. However, it is to be understood that inner tubular member62may extend over only a portion of outer tubular member60. Inner tubular member62is shown to include the helically lobed inner surface22. It should be understood however that helically lobed inner surface22may extend into outer tubular member60.

In accordance with an aspect of an exemplary embodiment, the first material forming outer tubular member60includes selected material properties such as strength properties, chemical resistance, corrosion resistance, and/or brittleness, selected to support drilling loads and conditions associated with downhole environments.

In accordance with another aspect of an exemplary embodiment, the second material forming inner tubular member62may be selected for other desirable material properties. For example, the second material may be selected to include particular surface properties with respect to mechanical, material and chemical properties, e.g. friction, roughness, hardness, and/or brittleness, heat conductivity, ductility, electrical conductivity, wear resistance and chemical resistance or chemical reactivity. For example, the second material may include a low coefficient of friction. The term “low coefficient of friction” should be understood to mean a material that allows rotor28to rotate within stator18with limited wear. The use of a low coefficient of friction material may preclude a need for an inner layer in composite metal housing16.

In another example, the second material may be selected for improved bonding properties with an elastomeric material if used for as an inner layer, a non-elastomeric material if used for an inner layer, or another material having other desirable properties. Examples of desirable materials for inner tubular member62may include Copper and copper alloys, Molybdenum and Molybdenum alloys, Nickel and Nickel alloys, steel with various properties (corrosion resistive, hardenable, temperable), duplex steel, materials that are suitable for chemical and/or electro-chemical etching to create a specific surface roughness. In another example, the second material may be softer and more flowable in order to easier form lobes with high accuracy.

In accordance with an aspect of an exemplary embodiment, outer tubular member60and inner tubular member62may possess similar radial thicknesses. In accordance with another aspect of an exemplary embodiment, outer tubular member60and inner tubular member62may possess different radial thicknesses. In accordance with another aspect of an exemplary embodiment, outer tubular member60may be formed with a radial thickness that is greater than a radial thickness of inner tubular member62. Conversely, inner tubular member62may be formed with a radial thickness that is greater than a radial thickness of outer tubular member60.

In accordance with another aspect of an exemplary embodiment, various methods may be used to position an inner layer (not shown) also referred to as a lining, or to finish inner surface22of inner tubular member62such as, for example, physical vapor deposition (PVD), chemical vapor deposition (CVD), injection molding, a plasma spray process, spray coating, chemical deposition, nitriding, carburizing, plasma polymer coating, nitro-carburizing, boriding/boronizing, thermo-set process, baking process, aging. Examples of desirable materials for inner layers may include elastomeric material, thermo-plastic material, metallic material, ceramic material, chrome, graphite, diamond-like carbon (DLC) and alternative suitable materials.

Reference will now follow toFIGS. 3-6in describing various processes for forming composite metal housing16.FIG. 3depicts a short stroke rolling process110. Outer tubular member60is positioned about inner tubular member62. A rigid mandrel132may be arranged in interior20of inner tubular member62. In accordance with an aspect of an exemplary embodiment, rigid mandrel132may take the form of a contour forming member. Rigid mandrel132includes a first end134, a second end135, and an intermediate portion136. Intermediate portion136includes a contoured outer surface138defining a selected contour that corresponds to helically lobed inner surface22. The particular shape, form, and/or overall geometry of contoured outer surface138may vary depending upon a desired shape, form, and/or geometry of helically lobed inner surface22. Rigid mandrel132defines an axis of rotation139for composite metal housing16.

Inner and outer tubular members62and60are positioned between a first force application member, depicted as a first roller140and a second forced application member depicted as a second roller141. As each roller140,141is substantially similarly formed, a detailed description will follow with respect to roller140with an understanding that roller141may include a similar structure. Roller140includes a roller die143that strokes or reciprocates over outer tubular member60in a direction shown by arrow145. Rollers140and141urge outer tubular member60radially inwardly toward inner tubular member62. Both outer and inner tubular members60and62are urged radially inwardly toward rigid mandrel132applying a compressive force. By way of non-limiting embodiment rigid mandrel132may be tapered from first end134to second end135with the second end having an outer dimension (not separately labeled) that is less than an outer dimension (also not separately labeled) of first end134. The taper facilitates easy removal of the rigid mandrel132from composite metal housing16.

Roller140incudes a caliper section148that defines a travel depth of roller die143toward outer tubular member60and inner tubular member62. A clearance150between roller die143and an outer surface153or roller die143increases along a stroke path154defined between a first end section155and a second end section156. In operation, rollers140and141urge against outer tubular member60and reciprocate along stroke path154along an axis of movement160. Roller die143travels to greater depths along stroke path154applying a compressive force. At the same time, composite metal housing16rotates about an axis162as shown by arrow163. As the process continues, inner tubular member62takes on a shape corresponding to contoured outer surface138of rigid mandrel132forming helically lobed inner surface22. In addition to forming helically lobed inner surface22, compressive forces applied by rollers140and141compress outer tubular member60onto inner tubular member62. In another embodiment rigid mandrel132may not have a contoured outer surface and may be used only to compress outer tubular member60and inner tubular member62without forming an inner contoured surface.

In accordance with another aspect of an exemplary embodiment, outer tubular member60and/or inner tubular member62may comprises multiple material layers that be connected through an application of compressional forces to form composite metal housing16of stator18. Alternatively, in lieu of compressive forces, other connecting methods such as adhesion, forging, cold welding, hot welding, chemical connection, a mechanical connection like a form fit, may be employed to join outer tubular member60and inner tubular member62. The term “form fit” should be understood to describe an interlocking of at least two connecting partners. As a result, the connecting partners cannot detach themselves without or during intermittent force transmission. Thus, in the case of a form-fit or “form locking connection” of one connecting partner, the other connecting partner is in the way. Further, when applying compressive forces, heat may be applied to further enhance connecting characteristics (cold rolled) (hot rolled). Cold may be temperatures up to around 100 Centigrade, intermediate temperatures may be from around 100 Centigrade to 600 Centigrade, hot temperatures may be from 900 Centigrade and above.

Reference will now follow toFIG. 4, wherein like reference numbers represent corresponding parts in the respective views in describing a long stroke rolling process170employing a first force application member shown as a first roller172and a second force application member shown as a second roller173. As each roller172,173is substantially similarly formed, a detailed description will follow with respect to roller172with an understanding that roller173may include similar structure. Roller172includes a roller die177having a stroke path180that is longer than stroke path154(FIG. 3). Stroke path180extends between a first end182and a second end183.

In operation, two rollers, e.g., rollers172and173urge against outer tubular member60applying a compressive force and reciprocate along stroke path180along an axis of movement185. Roller177travels to greater depths along stroke path180. At the same time, composite metal housing16(FIG. 2) rotates about axis162as shown by arrow163inFIG. 4. As the process continues, inner tubular member62takes on a shape corresponding to contoured outer surface138of rigid mandrel132forming helically lobed inner surface22(FIG. 1A). In addition to forming helically lobed inner surface22, compressive forces applied by rollers172and173compress outer tubular member60onto inner tubular member62.

Reference will now follow toFIG. 5, wherein like reference numbers represent corresponding parts in the respective views in describing a rolling process190employing a first force application member shown as a first roller192, a second force application member shown as a second roller193, and a third force application member shown as a third roller194which rotate about a corresponding central axis (not separately labeled) in a direction identified by arrows196a-196c. A rigid mandrel200having a contoured outer surface202is arranged in interior (not separately labeled) of inner tubular member62. In operation, rollers192-194rotate and are urged radially inwardly in a direction identified by arrows206a-206capplying a compressive force to outer tubular member60and inner tubular member62. At the same time, outer and inner tubulars members60and62rotate in a direction identified by arrow209opposite first, second, and third rollers192,193, and194. As the process continues, inner tubular member62takes on a shape corresponding to contoured outer surface202of rigid mandrel200forming helically lobed inner surface22. In addition to forming helically lobed inner surface22, compressive forces applied by rollers192-194compress outer tubular member60onto inner tubular member62.

Reference will now follow toFIG. 6wherein like reference numbers represent corresponding parts in the respective views in describing a rotary swaging process212. Rotary swaging process212employs a plurality of force application members shown in the form of swaging devices or conforming blocks214a,214b,214c, and214darranged about outer tubular member60and inner tubular member62. Each conforming block214a-214dincludes a corresponding concave inner surface216a-216d. Conforming blocks214a-214dare urged radially inwardly in a direction identified by corresponding arrows218a-218dapplying a compressive force to outer tubular member60and inner tubular member62. A rigid mandrel224having a contoured outer surface226is arranged within interior20of inner tubular member62.

In operation, conforming blocks214a-214dare urged radially inwardly. At the same time, outer and inner tubulars60and62of composite metal housing16rotate in a direction identified by arrow228. As the process continues, inner tubular member62takes on a shape corresponding to contoured outer surface226of rigid mandrel224forming helically lobed inner surface22such as shown inFIG. 2. In addition to forming helically lobed inner surface22, compressive forces applied by conforming blocks214a-214dforce outer tubular member60onto inner tubular member62forming a connection.

Once composite metal housing16of stator18(FIG. 1A) is formed, one or more channels, one of which is indicated at250inFIG. 7may be formed in helically lobed inner surface22. Channels250may promote cooling of downhole motor10. Additionally, it is understood that composite metal housing16forming stator18may include one or more channels and/or passages that may serve as conduits for electrical cabling, hydraulic lines, and the like. Channels250may be achieved by placing a third material which could take the form of a massive material (not shown) in between outer tubular member60and inner tubular member62prior to forming helically lobed inner surface22. The massive material may later be dissolved by one of a variety of known processes such as by heating, etching, applying a chemical, a subtractive a machining method or the like such as shown inFIG. 7. By non-limiting example the massive material may take the form of a round bar member, a non-round bar member, a folded bar member and/or a non-folded bar member.

It is also to be understood that composite metal housing16forming stator18may be formed by any of the above described methods and/or other suitable processes. The use of different materials to form composite metal housing16provides better strength characteristics as well as enhances wear and corrosion resistance. For example, outer tubular member60may be formed from a first material having desired strength characteristics while inner tubular member62may be formed from a second material suitable for a selected forming operation. The second material may also be selected for desired finishing characteristics including hard facing, corrosion protection without compromising other desired properties such as strength and formability.

It should be understood that additional layers (not shown) may exist between outer tubular member60and inner tubular member62that promote connecting inner and outer tubulars and/or provide a desired heat barrier, electrical insulating layer, material diffusion layer, or the like. Such an intermediate layer may cover all or a portion of the inner surface of outer tubular member60. Further, it is to be understood that outer tubular member60may be pre-contoured.

Although, the method described herein is employed to form a stator of a progressive cavity motor, the method may also be employed to form other stators, such as a stator for a progressive cavity pump following the Moineau principle.

Embodiment 1. A stator for a downhole motor configured for use in a downhole environment comprising: an inner tubular member formed from a first metallic material having an outer surface and a helically lobed inner surface; and an outer tubular member comprising a second metallic material that is different from the first metallic material, wherein the inner tubular member is connected to the outer tubular member by compressive force passing from the outer tubular member through the inner tubular member to a rigid mandrel removably disposed within the inner tubular member, wherein the inner tubular member and the outer tubular member form the stator of the downhole motor.

Embodiment 2. The downhole motor according to any prior embodiment, wherein the first metallic material is more pliable than the second metallic material.

Embodiment 3. The downhole motor according to any prior embodiment, further comprising: one or more channels extending between the inner tubular member and the outer tubular member.

Embodiment 4. The downhole motor according to any prior embodiment, wherein the one or more channels is formed in a third material defined between the inner tubular member and the outer tubular member.

Embodiment 5. The downhole motor according to any prior embodiment, wherein the one or more channels define a conduit for one of an electrical cable and a hydraulic line.

Embodiment 6. The downhole motor according to any prior embodiment, further comprising: an inner layer provided on the helically lobed inner surface.

Embodiment 7. The downhole motor according to any prior embodiment, wherein the inner layer comprises an elastomeric material.

Embodiment 8. The downhole motor according to any prior embodiment, wherein the third material includes a round bar member.

Embodiment 9. The downhole motor according to any prior embodiment, wherein the third material includes a non-round bar member.

Embodiment 10. The downhole motor according to any prior embodiment, wherein the third material includes a folded bar member.

Embodiment 11. The downhole motor according to any prior embodiment, wherein the third material includes a non-folded bar member.

Embodiment 12. The downhole motor according to any prior embodiment, wherein the inner tubular member is formed from a metal alloy.

Embodiment 13. The downhole motor according to any prior embodiment, wherein the first metallic material comprises Copper.

Embodiment 14. The downhole motor according to any prior embodiment, wherein the first metallic material comprises Nickel.

Embodiment 15. The downhole motor according to any prior embodiment, wherein the first metallic material comprises Molybdenum.

Embodiment 16. The downhole motor according to any prior embodiment, wherein the first metallic material comprises Steel.

Embodiment 17. The downhole motor according to any prior embodiment, wherein the inner layer is formed from one of a metallic material, and ceramic.

Embodiment 18. The downhole motor according to any prior embodiment, wherein the inner layer is formed from one of graphite, and diamond-like carbon.

Embodiment 19. The downhole motor according to any prior embodiment, wherein the inner layer is formed from a thermo-plastic material.

Embodiment 20. The downhole motor according to any prior embodiment, further comprising an additional layer between the inner tubular and the outer tubular.