WO2020028658A1 - Apparatus and method for assembling positive displacement devices - Google Patents

Abstract

A tool for assembling a positive displacement device includes an expandable core including an outer surface including a helical profile, and an expander configured to expand the expandable core radially outwards in response to displacing the expander in a first axial direction relative to the expandable core.

Description

APPARATUS AND METHOD FOR ASSEMBLING

POSITIVE DISPLACEMENT DEVICES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims benefit of U.S. provisional patent application No. 62/713,370 filed August 1, 2018, entitled“Apparatus and Method for Assembling Positive Displacement Devices,” which is incorporated herein by reference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND

[0003] The present disclosure relates generally to positive-displacement devices that include rotors rotatably disposed in stators. A progressive cavity pump (PC pump) transfers fluid by means of a sequence of discrete cavities that move through the pump as a rotor is turned within a stator. The transfer of fluid in this manner results in a volumetric flow rate proportional to the rotational speed of the rotor within the stator, as well as relatively low levels of shearing applied to the fluid. Consequently, progressive cavity pumps are typically used in fluid metering and pumping of viscous or shear sensitive fluids, particularly in downhole operations for the ultimate recovery of oil and gas. Progressive cavity pumps may also be referred to as PC pumps, progressing cavity pumps, "Moineau" pumps, eccentric screw pumps, or cavity pumps.

[0004] A PC pump may be used in reverse as a progressive cavity motor (PC motor) by passing fluid through the cavities between the rotor and stator to power the rotation of the rotor relative to the stator, thereby converting the hydraulic energy of a high pressure fluid into mechanical energy in the form of speed and torque output, which may be harnessed for a variety of applications, including downhole drilling. Progressive cavity motors may also be referred to as positive displacement motors (PD motors), eccentric screw motors, or cavity motors. PD motors, or simply mud motors, are used in the directional drilling of oil and gas wells.

[0005] Progressive cavity devices (e.g., progressive cavity pumps and motors) include a stator having a helical internal bore and a helical rotor rotatably disposed within the stator bore. Conventional stators often comprise a radially outer tubular housing and a radially inner component disposed within the housing. The inner component may include a cylindrical outer surface that is bonded to the cylindrical inner surface of the housing and a helical inner surface that defines the helical bore of the stator. Alternatively, the stator may comprise a single integral component. Conventional rotors often comprise a steel tube or rod having a helical- shaped outer surface, which may be chrome-plated or coated for wear and corrosion resistance. The helical internal bore defines lobes on the inner surface of the stator and the helical-shaped outer surface of the rotor defines at least one lobe on the outer surface of the rotor. In general, the rotor may have one or more lobes. To satisfy the fundamental gear tooth law, the stator will have one more lobe than the rotor.

[0006] When the rotor and stator are assembled, the rotor and stator lobes intermesh to form a series of cavities. More specifically, an interference fit between the helical outer surface of the rotor and the helical inner surface of the stator results in a plurality of circumferentially spaced hollow cavities in which fluid can travel. During rotation of the rotor, these hollow cavities advance from one end of the stator towards the other end of the stator. Each cavity is sealed from adjacent cavities by seals formed along contact lines between the rotor and the stator by said interference. For example, during downhole drilling operations, drilling fluid or mud is pumped through the PD motor as the sealed cavities progressively opening and closing to accommodate the circulating mud. Pressure differentials across adjacent cavities exert forces on the rotor that causes the rotor to rotate within the stator. The centerline of the rotor is typically offset from the center of the stator so that the rotor rotates within the stator on an eccentric orbit. The amount of torque generated by the power section depends on the cavity volume and pressure differential.

BRIEF SUMMARY OF THE DISCLOSURE

[0007] An embodiment of a tool for assembling a positive displacement device comprises an expandable core comprising an outer surface including a helical profile, and an expander configured to configured to expand the expandable core radially outwards in response to displacing the expander in a first axial direchon relative to the expandable core. In some embodiments, the expandable core is configured to contract radially inwards in response to displacing the expander in a second axial direchon opposite the first axial direchon. In some embodiments, the tool further comprises a rod extendable through a central passage of the expandable core, wherein the expander is coupled to the rod. In certain embodiments, the expander is configured to apply a radially directed force against the expandable core in response to receiving an axially directed force from the rod. In certain embodiments, the rod is configured to displace the expander axially relative to the expandable core in response to the application of a torque to the rod. In some embodiments, the expandable core comprises a central passage including a frustoconical inner surface and the expander comprises a frustoconical outer surface configured to matingly engage the frustoconical inner surface of the expandable core. In some embodiments, the expandable core comprises a plurality of circumferentially spaced grooves extending into the expandable core from the outer surface thereof. In certain embodiments, the expandable core comprises at least one of a polymeric and composite material.

[0008] An embodiment of a tool for assembling a positive displacement device having a stator comprises an expandable core comprising an outer surface including a helical profile and a central passage including a frustoconical inner surface, a rod extendable into a central passage of the expandable core, and an expander configured to couple to the rod and including a frustoconical outer surface, wherein the expandable core comprises an unexpanded position and an expanded position, and wherein the expander is configured to actuate the expandable core between the unexpanded and expanded positions. In some embodiments, the expandable core comprises a plurality of circumferentially spaced grooves extending into the expandable core from the outer surface thereof. In some embodiments, the expandable core comprises at least one of a polymeric and composite material. In certain embodiments, the frustoconical outer surface of the expander is configured to matingly engage the frustoconical inner surface of the expandable core. In certain embodiments, the rod is configured to displace the expander axially relative to the expandable core in response to the application of a torque to the rod. In some embodiments, the expander is configured to expand the expandable core radially outwards in response to displacing the expander in a first axial direction relative to the expandable core. In some embodiments, the expandable core is configured to contract radially inwards in response to displacing the expander in a second axial direction opposite the first axial direction. In certain embodiments, the tool further comprises an annular retainer coupled to the rod and configured to engage an annular shoulder of the expandable core.

[0009] An embodiment of a method for assembling a positive displacement device comprises

(a) inserting an assembly tool into a first section of a stator of the positive displacement device,

(b) actuating the assembly tool from an unexpanded position to an expanded position, and (c) inserting an end of at least one of the first section and a second section of the stator into at least one of the first and second sections with the assembly tool disposed in the first section. In some embodiments, the method further comprises (d) actuating the assembly tool from the expanded position to the unexpanded position, and (e) removing the assembly tool from the first section of the stator. In some embodiments, (b) comprises (bl) engaging a frustoconical outer surface of an expander of the assembly tool against a frustoconical inner surface of an expandable core of the assembly tool. In certain embodiments, (b) further comprises (b2) rotating a rod of the assembly tool, and (b3) axially displacing the expander of the assembly tool in response to (b2).

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a detailed description of disclosed embodiments, reference will now be made to the accompanying drawings in which:

[0011] Figure 1 is a schematic partial cross-sectional view of a production system in accordance with principles disclosed herein;

[0012] Figure 2 is a perspective, partial cut-away view of an embodiment of a pump of the production system of Figure 1 in accordance with principles disclosed herein;

[0013] Figure 3 is a cross-sectional end view of the pump of Figure 2;

[0014] Figure 4 is a perspective view of an embodiment of a tool for assembling a positive displacement device in accordance with principles disclosed herein;

[0015] Figure 5 is a side view of the assembly tool of Figure 4;

[0016] Figure 6 is a front view of the assembly tool of Figure 4;

[0017] Figure 7 is a side cross-sectional view of the assembly tool of Figure 4; and

[0018] Figures 8-11 are side cross-sectional views of an embodiment of a method for assembling a positive displacement device using the assembly tool of Figure 4 in accordance with principles disclosed herein.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

[0019] The following discussion is directed to various embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

[0020] 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... ." Also, the term "couple" or "couples" is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection as accomplished via other devices, components, and connections. In addition, as used herein, the terms "axial" and "axially" generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms "radial" and "radially" generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. Any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or“upstream” meaning toward the surface of the borehole and with“down”,“lower”,“downwardly”,“downhole”, or“downstream” meaning toward the terminal end of the borehole, regardless of the borehole orientation.

[0021] Referring to Figure 1, a well or production system 10 is shown. Production system 10 is generally configured for extracting hydrocarbon bearing reservoir fluid (indicated by arrow 12 in Figure 1) from a subsurface reservoir 3 via a wellbore 5 that extends through the subsurface reservoir 3 from the surface 7. Though shown as vertical in Figure 1, in general, wellbore 5 may have generally vertical portions or generally horizontal portions and may have curved portions between various portions. In the embodiment of Figure 1, production system 10 includes a tubular casing 14, which may be a metal pipe for example, is positioned and cemented in wellbore 5. Casing 14 has a set of perforations 16 at a location corresponding to subsurface reservoir 3 to provide for fluid communication between subsurface reservoir 3 and a central passage 18 of casing 14.

[0022] In this embodiment, production system 10 additionally includes production tubing 20 that extends into casing 14 from the surface 7, an extension shaft 25 that extends into and through production tubing 20 from a set of exterior surface equipment 30 positioned at the surface 7, and a positive displacement device or pump 40. Although in this embodiment positive displacement device 40 comprises a pump, in other embodiments, device 40 may comprise a fluid motor (e.g., a downhole motor used in drilling systems) or other types of positive displacement devices. Pump 40 is coupled to the lower ends of production tubing 20 and extension shaft 25 and is positioned within casing 14 and wellbore 5 at a selected depth below the surface 7. Production tubing 20 includes a lower end 21 within casing 14 and wellbore 5, and an upper end 23 opposite lower end 21 that may extend above the surface 7, where upper end 23 terminates at a discharge port 24. The discharge port 24 of production tubing 20 is routed to a convenient location to release an outlet stream 15 of fluid produced from subsurface reservoir 3.

[0023] Surface equipment 30 of production system 10 includes a source of rotational power, which is motor 32 in this embodiment, a shaft bearing 34, and other equipment known in the art. Shaft 25 may also be called a rod string and is coupled between pump 40 and motor 32 to transmit rotational power from motor 32 to pump 40. In this embodiment, motor 32 is positioned outside the production tubing 20 and outside the wellbore 5, and the fluid-tight shaft bearing 34 allows shaft 25 to extend into production tubing 20 without a loss of reservoir fluid 12. During operation of production system 10, fluid 12 from subsurface reservoir 3 enters casing 14 through perforations 12, where the reservoir fluid 12 enters pump 40 suspended within casing 14. Pump 40 discharges the reservoir fluid 12 into the lower end 21 of production tubing 20, though which the reservoir fluid 12 flows to the surface 7 and is discharged from the upper end 23 of production tubing 20 at discharge port 24 as outlet stream 15.

[0024] Referring to Figures 1-3, an embodiment of the pump 40 of Figure 1 is shown in Figures 2, 3. Pump 40 of production system 10 includes a generally cylindrical housing or stator 50 and a helical shaped rotor 80 rotatably disposed in stator 50. Pump 40 comprises a progressive cavity pump (PCP) 40. Additionally, in the embodiment of Figures 1-3, pump 40 comprises a metal-to-metal (MTM) PCP 40 in which stator 50 of pump 40 does not include an elastomeric liner, which may be susceptible to degradation and failure in at least some applications, including high temperature applications and applications where reservoir fluid 12 includes chemicals that may corrode or otherwise inhibit the performance of an elastomeric liner. As will be described further herein, stator 50 comprises a plurality of stator sections 50A-50C each having a pair of opposing axial ends 52 and an inner surface 54 extending between ends 52. Helical-shaped rotor 80 of pump 40 includes an outer surface 82 that defines a set of rotor lobes or helical profiles 84 that intermesh with a set of stator lobes or helical profiles 56 defined by the inner surface 54 of stator 50. Although in this embodiment pump 40 comprises a MTM PCP 40, in other embodiments, pump 40 may comprise an elastomeric PCP 40 including a stator 50 with an elastomeric liner.

[0025] As best shown in Figure 3, the rotor 80 has one fewer lobe 84 than the stator 50. When the rotor 80 and the stator 50 are assembled, a series of cavities 90 are formed between the outer surface 82 of the rotor 80 and the inner surface 54 of the stator 50. Each cavity 90 is sealed from adjacent cavities 90 by seals formed along the contact lines between the rotor 80 and the stator 50. Additionally, a central or longitudinal axis 85 of the rotor 80 is radially offset from a central or longitudinal axis 55 of the stator 50 by a fixed value known as the “eccentricity” of the rotor-stator assembly. Consequently, rotor 80 may be described as rotating eccentrically within stator 50. During operation of pump 40, rotor 80 is rotated by motor 32 via extension shaft 25 to force reservoir fluid 12 through a first set of open cavities 90. As the rotor 80 rotates inside the stator 50, adjacent cavities 90 are opened and filled with reservoir fluid 12. As this rotation and filling process repeats in a continuous manner, the fluid flows progressively down the length of pump 40 until the pressurized reservoir fluid 12 is discharged into the lower end 21 of production tubing 20.

[0026] In at least some applications, the capacity of pump 40 to generate sufficient discharge pressure to flow or“lift” reservoir fluid 12 upwards through production tubing 20 to discharge port 24 is dependent on the axial and angular alignment between the sections 50A- 50C of stator 50. In other words, axial and/or angular misalignment between the sections 50A-50C of stator 50 may inhibit the performance of pump 40. For example, axial and/or angular misalignment between sections 50A-50C of stator 50 during the assembly of pump 40 may produce discontinues in inner surface 54 of stator 50 that increase the wear of pump 40 and reduce the lift capacity of pump 40, thereby inhibiting the performance of production system 10. Thus, it may advantageous in at least some applications to maintain as much axial and angular alignment as possible between adjoining sections 50A-50C of stator 50 to thereby maximize the performance of pump 40 and production system 10.

[0027] Referring to Figures 4-7, an embodiment of a tool 100 for assembling positive displacement devices, such as pump 40 shown in Figures 1-3, is shown in Figures 3-6. Particularly, assembly tool 100 is configured for axially and rotationally synchronizing the sections of the stator of the positive displacement device. In the embodiment of Figures 4-7, assembly tool 100 has a central or longitudinal axis 105 and generally includes an expandable body or core 102, an actuator or rod 140, an annular retainer 150, an annular frustoconical expander 160, and a retaining pin 180. In the embodiment of Figures 4-7, expandable core 102 comprises polypropylene; however, in other embodiments, core 102 may comprise various flexible, polymeric, composite, and elastomeric materials. Expandable core 102 of assembly tool 100 has a first end 102A, a second end 102B opposite first end 102A, a central passage 104 (shown in Figure 7) defined by a generally cylindrical inner surface 106 extending between ends 102A, 102B, and an outer surface 108 extending between ends 102A, 102B. The inner surface 106 of expandable core 102 includes an inclined or frustoconical surface 110 extending axially from second end 102B. As will be described further herein, frustoconical inner surface 110 of expandable core 102 is configured to matingly engage with expander 160 to expand the outer surface 108 of core 102 radially outwards from central axis 105. Additionally, in this embodiment, the inner surface 108 of expandable core 102 includes a recess or counterbore that forms an annular shoulder 112 proximal first end l02A;however, in other embodiments, annular shoulder 112 may instead be located proximal second end 102B of expandable core 102.

[0028] The outer surface 108 of expandable core 102 includes a plurality of circumferentially spaced lobes or helical profiles 114 configured to matingly engage the stator lobes (e.g., stator lobes 56 of stator 50) of the pump assembly tool 100 is used to assemble. In this embodiment, expandable core 102 includes two lobes 114; however, in other embodiments, the number of lobes 114 of expandable core 102 may vary. Additionally, in this embodiment, expandable core 102 includes a plurality of circumferentially spaced grooves 116 extending between ends 102A, 102B. Grooves 116 extend radially into expandable core 102 from outer surface 108 and assist with permitting the radial expansion and contraction of outer surface 108 during the operation of assembly tool 100. In this embodiment, expandable core 102 includes four circumferentially spaced grooves 116; however, in other embodiments, the number of grooves 116 of expandable core 102 may vary.

[0029] Rod 140 of assembly tool 100 has a first end 140A, a second end 140B opposite first end 140 A, and a generally cylindrical outer surface 142 extending between ends 140 A, 140B. In this embodiment, at least a portion of the outer surface 142 of rod 140 comprises a releasable or threaded connector 144 extending axially from first end 140A. Additionally, rod 140 includes a radial aperture 146 configured to receive retaining pin 180. Retainer 150 of assembly tool 100 is generally cylindrical and includes a releasable or threaded connecter 152 disposed on an inner surface thereof. In this embodiment, a retainer clip or C-ring 156 is also included for securing retainer 150 with rod 140. Expander 160 of assembly tool 100 has an inclined or frustoconical outer surface 162 extending between opposing axial ends of expander 160 and a central bore or passage defined by a generally cylindrical inner surface that includes a releasable or threaded connector 164.

[0030] In this configuration, both retainer 150 and expander 160 are releasably or threadably connected to rod 140. Additionally, in this embodiment, expander 160 is tack welded (indicated by arrow 166) to rod 140 to lock expander 160 with rod 140 such that expander 160 is prevented from moving axially or rotationally relative to rod 140. Retainer 150 is disposed directly adjacent to the shoulder 112 of expandable core 102, limiting the movement of expandable core 102 in a first axial direction (indicated by arrow 153 in Figure 7) relative to retainer 150. Retaining pin 180, which is positioned between the first end 140A of rod 140 and retainer 150, prevents rod 140 from being inadvertently unthreaded or released from retainer 150 during the operation of assembly tool 100.

[0031] Referring to Figures 8-11, an exemplary method of assembling a metal-to-metal positive displacement device (e.g., a positive displacement pump, motor, etc.) including a housing or stator 200 using assembly tool 100 is shown. Similar to stator 50 shown in Figures 2, 3, stator 200 has a central or longitudinal axis 205 and comprises a plurality of stator sections 200A, 200B each having a pair of opposing axial ends 202 and an inner surface 204 extending between ends 202 that matches the profile of the outer surface 108 of the expandable core 102 of assembly tool 100. Additionally, each section 200A, 200B of stator 200 includes a male or pin end 206 positioned at one end 202 thereof and a female or box end 208 positioned at an opposing end 202 thereof. In the embodiment of Figures 8-11, to assemble a first stator section 200A with a second stator section 200B of stator 200, assembly tool 100 is inserted into an end 202 of first section 200A in a first or unexpanded state where the frustoconical outer surface 162 of expander 160 is axially spaced from the frustoconical inner surface 110 of the expandable core 102. As shown in Figure 8, assembly tool 100 is inserted into first section 200A of stator 200 such that a portion of the outer surface 108 of expandable core 102 is in mating engagement with the inner surface 204 of first section 200A while the first end 102A of expandable core 102 extends out axially from the end 202 of first section 200A.

[0032] As shown in Figure 9, in this embodiment, with assembly tool 100 partially received in first section 200A of stator 200, a torque is applied to rod 140 of assembly tool 100 to rotate (indicated by arrow 203 in Figure 9) rod 140 and expander 160 in a first rotational direction (e.g., clockwise in Figure 9) relative to expandable core 102, thereby displacing rod 140 and expander 160 axially relative to expandable core 102. The expandable core 102 is transformable between the unexpanded position and a second or expanded position. Particularly, the axial displacement of expander 160 forces the frustoconical outer surface 162 of expander 160 into mating engagement with the frustoconical inner surface 110 of expandable core 102, thereby forcing or expanding the outer surface 108 of core 102 radially outwards against the inner surface 204 of first section 200A such that assembly tool 100 is disposed in the expanded position. Thus, the inclined or frustoconical interface formed between the frustoconical outer surface 162 of expander 160 and the frustoconical inner surface 110 of expandable core 102 translates the axially directed force applied to expander 160 from rod 140 into a radially directed force applied to expandable core 102 from expander 160. [0033] Additionally, as the frustoconical outer surface 162 of expander 160 is compressed against the frustoconical inner surface 110 of expandable core 102, the annular shoulder 112 of core 102 is compressed against annular retainer 150. The expansion of expandable core 102 reduces or eliminates any clearance or radial gap between the outer surface 108 of core 102 and the inner surface 204 of first section 200A, thereby forcing the central axis 105 of assembly tool 100 into substantial alignment with the central axis 205 of first section 200 A while also angularly or rotationally aligning the lobes 114 of expandable core 102 with the lobes defined by the inner surface 204 of first section 200A. In other words, the expansion of expandable core 102 provides interference perfect or tight fit between the outer surface 108 of core 102 and the inner surface 204 of first section 200A.

[0034] As shown in Figures 10 and 11, in this embodiment, with assembly tool 100 disposed in the expanded position, second section 200B of stator 200 is angularly aligned with expandable core 102 and the pin end 206 of the second section 200B is extended over the first end 102A of expandable core 102 until the pin end 206 of second section 200B is fully received in the corresponding box end 208 of first section 200A. Particularly, second section 200B of stator 200 is rotated (indicated by arrow 205 in Figure 11) relative to expandable core 102 and first section 200 A, thereby permitting the inner surface 204 of second section 200B to follow the contour of the outer surface 108 of core 102 as second section 200B is threaded over core 102. Additionally, with assembly tool 100 disposed in the expanded state, the central axis 205 of second section 200B is forced into alignment with the central axes 105 and 205 of assembly tool 100 and first section 200 A, thereby axially and angularly aligning first section 200A with second section 200B such that any discontinuity between the inner surface 204 of first section 200A and the inner surface 204 of second section 200B is minimized. In this manner, assembly tool 100 may axially and rotationally synchronize first section 200A of stator 200 with second section 200B.

[0035] Once the pin end 206 of second section 200B is fully inserted into the box end 208 of first section 200A, first section 200A may be welded to second section 200B at the joint formed between ends 206, 208 thereof to securely attach first section 200A with second section 200B. In other embodiments, first section 200A may be secured to second section 200B via other mechanisms known in the art, including the use of releasable fasteners. Following the attachment of first section 200A to second section 200B, rod 140 may be rotated in a second rotational direction opposite the first rotational direction to return assembly tool 100 to the unexpanded position, permitting the assembly tool 100 to be unthreaded and removed from sections 200A, 200B of stator 200 upon the application of a force against rod 140 in a second axial direction (opposite first axial direction 153 shown in Figure 7). As assembly tool 100 is removed from stator 200, retaining pin 180 prevents the separation of expandable core 102 from rod 140. Alternatively, once assembly tool 100 is returned to the unexpanded position, assembly tool 100 may be displaced in the first axial direction 153 through second section 200B until the first end 102 A of expandable core projects from the box end 208 of second section 200B, at which time a third section of stator 200 may be attached to the box end 208 of second section 200B. In the manner described above, the central axes 205 of sections 200 A, 200B may be substantially aligned by radially expanding the outer surface 108 of expandable core 102, thereby maximizing the performance and reducing the wear of the positive displacement device comprising stator 200.

[0036] While disclosed embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.

Claims

CLAIMS What is claimed is:

1. A tool for assembling a positive displacement device, comprising:

an expandable core comprising an outer surface including a helical profile; and an expander configured to configured to expand the expandable core radially outwards in response to displacing the expander in a first axial direction relative to the expandable core.

2. The tool of claim 1, wherein the expandable core is configured to contract radially inwards in response to displacing the expander in a second axial direction opposite the first axial direction.

3. The tool of claim 1, further comprising a rod extendable through a central passage of the expandable core, wherein the expander is coupled to the rod.

4. The tool of claim 3, wherein the expander is configured to apply a radially directed force against the expandable core in response to receiving an axially directed force from the rod.

5. The tool of claim 3, wherein the rod is configured to displace the expander axially relative to the expandable core in response to the application of a torque to the rod.

6. The tool of claim 1, wherein the expandable core comprises a central passage including a frustoconical inner surface and the expander comprises a frustoconical outer surface configured to matingly engage the frustoconical inner surface of the expandable core.

7. The tool of claim 6, wherein the expandable core comprises a plurality of circumferentially spaced grooves extending into the expandable core from the outer surface thereof.

8. The tool of claim 1, wherein the expandable core comprises at least one of a polymeric and composite material.

9. A tool for assembling a positive displacement device having a stator, comprising:

an expandable core comprising an outer surface including a helical profile and a central passage including a frustoconical inner surface;

a rod extendable into a central passage of the expandable core; and

an expander configured to couple to the rod and including a frustoconical outer surface; wherein the expandable core comprises an unexpanded position and an expanded position, and wherein the expander is configured to actuate the expandable core between the unexpanded and expanded positions.

10. The tool of claim 9, wherein the expandable core comprises a plurality of circumferentially spaced grooves extending into the expandable core from the outer surface thereof.

11. The tool of claim 9, wherein the expandable core comprises at least one of a polymeric and composite material.

12. The tool of claim 9, wherein the frustoconical outer surface of the expander is configured to matingly engage the frustoconical inner surface of the expandable core.

13. The tool of claim 9, wherein the rod is configured to displace the expander axially relative to the expandable core in response to the application of a torque to the rod.

14. The tool of claim 9, wherein the expander is configured to expand the expandable core radially outwards in response to displacing the expander in a first axial direction relative to the expandable core.

15. The tool of claim 14, wherein the expandable core is configured to contract radially inwards in response to displacing the expander in a second axial direction opposite the first axial direction.

16. The tool of claim 9, further comprising an annular retainer coupled to the rod and configured to engage an annular shoulder of the expandable core.

17. A method for assembling a positive displacement device, comprising: (a) inserting an assembly tool into a first section of a stator of the positive displacement device;

(b) actuating the assembly tool from an unexpanded position to an expanded position; and

(c) inserting an end of at least one of the first section and a second section of the stator into at least one of the first and second sections with the assembly tool disposed in the first section.

18. The method of claim 17, further comprising:

(d) actuating the assembly tool from the expanded position to the unexpanded position; and

(e) removing the assembly tool from the first section of the stator.

19. The method of claim 17, wherein (b) comprises:

(bl) engaging a frustoconical outer surface of an expander of the assembly tool against a frustoconical inner surface of an expandable core of the assembly tool.

20. The method of claim 17, wherein (b) further comprises:

(b2) rotating a rod of the assembly tool; and

(b3) axially displacing the expander of the assembly tool in response to (b2).