WO2018057960A1

WO2018057960A1 - Downhole motor-pump assembly

Info

Publication number: WO2018057960A1
Application number: PCT/US2017/053059
Authority: WO
Inventors: Mark Krpec; David Tilley
Original assignee: Mark Krpec; David Tilley
Priority date: 2016-09-23
Filing date: 2017-09-22
Publication date: 2018-03-29

Abstract

A downhole motor-pump assembly disposed within a tubular string includes a rotor and a stator. The rotor has a first rotor portion and a second rotor portion. The first rotor portion has a first geometrical shape and the second rotor portion has a second geometrical shape. The first geometrical shape differs from the second geometrical shape. The stator has a first stator section and a second stator section. The first stator section is spaced from the second stator section by a gapped region. The first rotor portion is located within the first stator section and the second rotor potion is located within the second stator section. The differing geometry causes a difference in displacement in the first and second sections per revolution of the rotor. Therefore the difference in displacement must be made up and is induced into the tool at the gap or drillings between sections, and this additional volume is effectively pumped.

Description

DOWNHOLE MOTOR-PUMP ASSEMBLY

BACKGROUND

Field

[0001] Embodiments of the present disclosure generally relate to a downhole motor-pump assembly.

Description of the Related Art

[0002] It is known within the prior art to use a downhole motor {e.g., a drilling motor) and/or a downhole pump disposed within a drill string. In many situations, however, the design of the downhole motor is complex and contains numerous components in addition to a stator and a rotor, such as long torsional shaft drives, plungers, wobble shafts, bearings, and/or couplings. Additionally, the downhole pump is usually a separate component from the downhole motor. Consequently, there is a need for a simpler downhole motor-pump assembly, especially where the motive and pumped fluids can be combined before the pump discharge.

SUMMARY

[0003] A first embodiment of the present disclosure is a downhole motor-pump assembly disposed within a tubular string including a rotor and a stator. The rotor has a first rotor portion and a second rotor portion. The first rotor portion has a first geometrical shape and the second rotor portion has a second geometrical shape. The first geometrical shape differs from the second geometrical shape. The stator has a first stator section and a second stator section. The first stator section is spaced from the second stator section by a gapped region. The rotor is located within the stator and configured to be rotated by fluid flowing downstream within the tubular string.

[0004] Another embodiment of the present disclosure is a tubular string including a downhole motor-pump assembly and a string body. The downhole motor-pump assembly includes a stator and a rotor. The stator has a first stator section and a second stator section. The first stator section is spaced from the second stator section by a gapped region. The rotor is configured to rotate freely within the stator. The downhole motor-pump assembly is disposed within the string body and configured such that the rotor rotates within the stator when fluid is urged downstream within the tubular string.

[0005] Another embodiment of the present disclosure is a downhole motor-pump assembly including a stator and a single rotor. The stator has a first stator section and a second stator section. The single rotor is positioned within the first and second stator sections. The downhole motor-pump assembly is devoid of any wobble shafts or couplings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

[0007] Figure 1 illustrates a first embodiment of a downhole motor-pump assembly disposed within a tubular string in accordance with the present disclosure.

[0008] Figure 2 illustrates fluid flow paths associated with the downhole motor- pump assembly shown in Figure 1 .

[0009] Figure 3 illustrates a second embodiment of a downhole motor-pump assembly disposed within a tubular string in accordance with the present disclosure.

[0010] Figure 4 illustrates fluid flow paths associated with the downhole motor- pump assembly shown in Figure 3.

[0011] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. DETAILED DESCRIPTION

[0012] Embodiments described herein relate to a downhole motor-pump assembly disposed within a tubular string. The downhole motor-pump assembly may comprise a rotor and a stator. The rotor may have a first rotor portion and a second rotor portion. The first rotor portion may have a first geometrical shape, and the second rotor portion may have a second geometrical shape. The first geometrical shape may differ from the second geometrical shape. The rotor may be configured to rotate freely within the stator. The stator may have a first stator section and a second stator section. The first stator section may be spaced from the second stator section by a gapped region. The rotor may be located within the stator and configured to be rotated by fluid flowing downstream within the tubular string. In operation of the assembly, the first rotor portion and the first stator section may collectively function as a motor, and the second rotor portion and the second stator section may collectively function as a pump.

[0013] Figures 1 and 2 illustrate a first embodiment of the present disclosure in which a downhole motor-pump assembly 100 is disposed within a tubular string 102 (e.g., Work or Drill String) for the purpose of downhole debris removal. In well drilling and completion operations, there are applications requiring the picking up of debris in a wellbore. At times, fluid within the well cannot be pumped at a high enough flow rate to flush out the debris and circulate the debris back to a sea surface. For example, the physical limits of the wellbore may prevent fluid from being pumped at a flow rate that flushes out the debris without damaging the wellbore from the resulting pressures. The downhole motor-pump assembly 100 may be utilized to address some of these problems.

[0014] The downhole motor-pump assembly 100 includes a rotor 104 and a stator 106. The downhole motor-pump assembly includes an inlet opening 105 and an outlet opening 107. The rotor 104 has a first rotor portion 108 and a second rotor portion 1 10. In the embodiment shown in Figure 1 , the second rotor portion 1 10 is downstream of the first rotor portion 108. The first rotor portion 108 has a first geometrical shape and the second rotor portion 1 10 has a second geometrical shape. The first geometrical shape differs from the second geometrical shape. As seen in Figure 1 , the first geometrical shape has a pitch P, with the pitch P being the distance between two adjacent profile peaks within the first rotor portion 108. The pitch P is substantially constant throughout the first rotor portion 108. A pitch of the second geometrical shape is greater than pitch P. For example, as seen in Figure 1 , the pitch of the second geometrical shape is about three times the pitch P of the first geometrical shape. In other words, the pitch of the second geometrical shape is 3P. The pitch 3P of the second geometrical shape is the distance between two adjacent profile peaks within the second rotor portion 1 10. The pitch 3P is substantially constant throughout the second rotor portion 1 10. Because the first geometrical shape differs from the second geometrical shape, the volume of fluid displaced per revolution of the rotor 104 by the first rotor portion 108 differs from the volume of fluid displaced per revolution of the rotor by the second rotor portion 1 10. In the embodiment shown in Figure 1 , the volume of fluid displaced per revolution of the rotor by the second rotor portion 1 10 is greater than the volume of fluid displaced per revolution of the rotor by the first rotor portion 108. Revolution of the first rotor portion 108 defines a first orbital path and revolution of the second rotor portion 1 10 defines a second orbital path, the first and second orbital paths being substantially similar to each other. It is to be understood geometrical shapes other the ones shown in Figure 1 may be used for the first rotor portion 108 and the second rotor portion 1 10.

[0015] In one embodiment, the rotor 104 may be a single, one-piece element. It is to be understood, however, that the rotor 104 may be comprised of two or more elements coupled together. For example, the first rotor portion 108 may be a first element and the second rotor portion 1 10 may be a second element, with the first and second elements being coupled together. It is also to be understood that rotor 104 may include more than two rotor sections. For example, the rotor 104 may include a third rotor section positioned between the first and second rotor sections, with the third rotor section being of a third geometrical shape. In such a situation, the third geometrical shape may differ from the first geometrical shape, from the second geometrical shape, or from both the first and second geometrical shapes.

[0016] The stator 106 has a first stator section 1 12 and a second stator section 1 14. The first stator section 1 12 is spaced from the second stator section 1 14 by a gapped region 1 16. The rotor 104 is located within the stator 106 and configured to be rotated by fluid flowing downstream within the tubular string 102. More specifically, the first rotor portion 108 is located within the first stator section 1 12 and the second rotor portion 1 10 is located within the second stator section 1 14. The first stator section 1 12 has a first internal profile that is substantially similar to the first geometrical shape of the first rotor portion 108 and the second stator section 1 14 has a second internal profile that is substantially similar to the second geometrical shape of the second rotor portion 1 10. The rotor 104 is freely orbiting within the stator 106 and need not be coupled to any further device to perform its function, thereby eliminating the need of any wobble shafts, radial bearings, and/or couplings. A downstream end of rotor 104 rests on a platform 120 of the tubular string 102. Platform 120 may include a thrust bearing or collar to transfer any thrust load of the rotor 104. Note that the common rotor and the port arrangement cause a substantial balancing of thrust forces within the pump and motor assembly, lessening the requirements of the thrust bearing.

[0017] The tubular string 102 includes a pump opening 1 18 located downstream of the downhole motor-pump assembly 100. The tubular string 102 is configured such that the outlet opening 107, the pump opening 1 18, and the gapped or ported region 1 16 are fluidly connected to each other to form a localized circulation loop. The gapped or ported region 1 16 creates a suction force as fluid is pumped downstream through the second stator section 1 14. The suction force pulls wellbore fluid and debris particles DP located within the well into the tubular string 102 via the pump opening 1 18. As can be seen in Figure 1 , the tubular string 102 may further include a filter 121 . The filter 121 is located downstream of the gapped region 1 16 and is configured to enable wellbore fluid to pass therethrough while preventing passage of debris particles DP. The tubular string 102 may further include a oneway valve (not shown) positioned adjacent the pump opening 1 18. The one-way valve may open inwardly and be configured to enable wellbore fluid and debris particles to enter the tubular string 102 as a result of the suction force generated by fluid flowing downstream through the stator 106 while preventing the debris particles from being expelled from the pump opening 1 18 on shut-down.

[0018] In operation, the first rotor portion 108 and the first stator section 1 12 collectively function as a motor of the downhole motor-pump assembly 100, and the second rotor portion 1 10 and the second stator section 1 14 collectively function as a pump of the downhole motor-pump assembly. The tubular string 102 is first lowered to a desired depth within the wellbore. A driving fluid may then be urged downstream through the tubular string 102 at a flow rate of, for example, approximately 3 barrels per minute (i.e., BPM), and a pressure of approximately 1000 psi at inlet opening 105. As the driving fluid is urged downstream, it causes the rotor 104 to freely rotate within the stator 106, as the rotor is not connected to the stator via any wobble shafts, bearings, and/or couplings. As the rotor 106 rotates, the second rotor portion 1 10 within the second stator section 1 14 displaces a larger volume of fluid per revolution of the rotor than the first rotor portion 108 within the first stator section 1 12. Consequently, the second rotor portion 1 10 and the second stator section 1 14 would generate a suction force at the gapped or ported region 1 16 to induce the necessary additional flow to satisfy this section's additional flow requirement. The pressure at the gapped region 1 16 is then for example, approximately 0 psi. The suction force generated at the gapped region 1 16 creates a flow of wellbore fluid through the gapped region 1 16 and into the second stator section 1 14. Because the outlet opening 107, the pump opening 1 18, and the gapped region 1 16 are fluidly connected to each other, it generates the previously discussed localized circulation loop that can be seen in Figure 2.

[0019] For example, during operation of the downhole motor-pump assembly 100, the flow of additional wellbore fluid passing through the gapped region 1 16 could have a flow rate of approximately 6 BPM. Consequently, the flow rate of fluid flowing through the second stator section 1 14 will be greater than the flow rate of fluid flowing through the first stator section 1 12. For example, the flow rate of fluid flowing through the first stator section 1 12 may be approximately 3 BPM while the flow rate of fluid flowing through the second stator section 1 14 may be approximately 9 BPM. The driving fluid urged downstream through the tubular string 102 from, for example, a surface pump is combined with fluid pumped through the gapped region 1 16. As discussed above, the driving fluid entering the inlet opening 105 may exert a pressure of approximately 1000 psi while the combined fluid exiting the outlet opening 107 may have a lower pressure of approximately 300 psi, but with an inversely proportionate volume increase. [0020] As can be seen in Figure 2, some of the fluid exiting the outlet opening will flow upstream to the surface and some of the fluid will flow downstream because of the suction force and flow requirement at the gapped region 1 16 and generate the localized circulation loop. For example, fluid exiting the outlet opening 107 may have a flow rate of approximately 3 BPM to the surface and a flow rate of approximately 6 BPM downstream. Because of the suction force generated at the gapped region 1 16 and the localized circulation loop, wellbore fluid and debris particles DP will be pulled into the tubular string 102. As discussed above, the filter 121 will then permit passage of wellbore fluid therethrough while preventing passage of debris particles DP pulled into the tubular string 102.

[0021] In this manner, the tubular string 102 and the downhole motor-pump assembly 100 enable the removal of debris from the wellbore. Moreover, the tubular string 102 and the downhole motor-pump assembly 100 provide for the ability to control and monitor downhole performance within the well from a sea surface as a result of the pressures and flow rates seen at the surface correlating to those of the pumped fluid by the downhole pump. This is only possible with such positive displacement pumps. Another advantage of the downhole motor-pump assembly 100 is the reduced fluid pressure of a localized flow loop. The alternative requires flow to surface and a correspondingly higher pressure to drive such a flow path, which can be detrimental to the well. In addition, the progressive cavity pump does not shear the fluid as centrifugal pumps or eductors do. This allows for viscous fluids and gels that are required for certain downhole operations to be pumped downstream without being damaged.

[0022] Figures 3 and 4 illustrate a second embodiment in which the downhole motor-pump assembly 100 is disposed within a tubular string 202 (e.g., drill string) for the purpose of downhole production pumping. Tubular string 202 is substantially similar to tubular string 102, with the exception that tubular string 202 does not include a filter. Moreover, a sealing element 204 is positioned within the wellbore adjacent the pump opening 1 18. In this situation, the outlet opening 107, the pump opening 1 18, and the gapped region 1 16 are not fluidly connected to each other to create a localized circulation flow loop, as was the situation in Figure 1 . Instead, sealing element 204 isolates the outlet opening 107 from the pump opening 1 18. A suction force is still generated at the gapped region 1 16 as a result of the rotation of the second rotor portion 1 10 within the second stator section 1 14. As can be seen in Figure 4, the suction force generated at the gapped region 1 16 produces a production flow of gas and/or liquid hydrocarbons from the wellbore region downstream of the sealing element 204. For example, if fluid is urged downstream into the stator 106 through inlet opening 105 at a flow rate of approximately 3 BPM at a pressure of approximately 1000 psi, a combined flow through the pump section of 9 bpm, would be generated and consequently the difference would produce a production flow with a flow rate of approximately 6 BPM.

[0023] The produced flow will flow upstream into the tubular string 202 via pump opening 1 18 and through the gapped region 1 16 at the flow rate of approximately 6 BPM and combine with the driving fluid being urged downstream through the inlet opening 105 at a flow rate of approximately 3 BPM. Consequently, the combined fluid will exit the stator 106 via the outlet opening 107 at a flow rate of approximately 9 BPM and at a pressure of approximately 300 psi. The combined fluid will then flow upstream, for example, to a surface, at the flow rate of 9 BPM because sealing element 204 prevents fluid from flowing downstream. Combining the production flow with the driving fluid can be particularly beneficial when another well's higher pressure, higher temperature, or less viscous product can be used as the driving fluid urged downstream through the inlet opening 105. Doing so may reduce the viscosity of the combined fluids and enhance the production flow of the well in which the tubular string 202 is disposed.

[0024] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

What is claimed is:

1 . A downhole motor-pump assembly disposed within a tubular string, the motor-pump assembly comprising:

a rotor, the rotor having a first rotor portion and a second rotor portion, the first rotor portion having a first geometrical shape and the second rotor portion having a second geometrical shape, the first geometrical shape differing from the second geometrical shape; and

a stator having a first stator section and a second stator section, the first stator section being spaced from the second stator section by a gapped region, wherein the first rotor portion is located within the first stator section and the second rotor portion is located within the second stator section.

2. The downhole motor-pump assembly of claim 1 wherein the rotor is configured such that the first geometrical shape displaces a first volume of fluid upon rotation of the rotor and the second geometrical shape displaces a second volume of fluid upon rotation of the rotor.

3. The downhole motor-pump assembly of claim 2 wherein the second volume of fluid is greater than the first volume of fluid.

4. The downhole motor-pump assembly of claim 1 wherein the rotor is configured such that the first rotor section defines a first orbital path upon rotation of the rotor and the second rotor section defines a second orbital path upon rotation of the rotor, the first orbital path and second orbital path being substantially similar to each other, allowing the rotor sections to be common and rigid.

5. The downhole motor-pump assembly of claim 1 wherein the rotor freely rotates within the stator.

6. The downhole motor-pump assembly of claim 1 wherein the first stator section has a first internal profile that is substantially similar to the first geometrical shape and the second stator section has a second internal profile that is substantially similar to the second geometrical shape.

7. The downhole motor-pump assembly of claim 1 wherein the rotor is a single, one-piece member.

8. The downhole motor-pump assembly of claim 1 wherein the rotor is configured to be rotated by fluid flowing through the tubular string.

9. A tubular string comprising:

a downhole motor-pump assembly, the downhole motor-pump assembly including:

a stator, the stator having a first stator section and a second stator section, the first stator section being spaced from the second stator section by a gapped region; and

a rotor, wherein the rotor is configured to rotate freely within the stator; and

a string body, wherein the downhole motor-pump assembly is disposed within the string body and configured such that the rotor rotates within the stator when fluid is urged downstream within the tubular string.

10. The tubular string of claim 9 wherein the rotor has a first rotor portion and a second rotor portion, the first rotor portion having a first geometrical shape and the second rotor portion having a second geometrical shape, the first geometrical shape differing from the second geometrical shape.

1 1 . The tubular string of claim 10 wherein the rotor is a single, one-piece member.

12. The tubular string of claim 10 wherein the string body includes a pump opening fluidly connected to the gapped region, the pump opening located downstream of the downhole motor-pump assembly.

13. The tubular string of claim 12 wherein the pump opening is configured to enable wellbore fluid and debris to be pumped therethrough.

14. The tubular string of claim 13 wherein the tubular string includes a filter positioned between the gapped region and the pump opening.

15. The tubular string of claim 14 wherein the filter is configured to enable wellbore fluid to pass therethrough while preventing passage of debris particles.

16. The tubular string of claim 12 wherein the downhole motor-pump assembly comprises an inlet opening and an outlet opening,

17. The tubular string of claim 16 wherein the gapped region is located between the inlet and outlet openings.

18. A downhole motor-pump assembly comprising:

a stator having a first stator section and a second stator section; and a single rotor;

wherein the single rotor is positioned within the first and second stator sections, the downhole motor-pump assembly being devoid of any wobble shafts or couplings.

19. The downhole motor-pump assembly of claim 18 further comprising a thrust bearing.

20. The downhole motor-pump assembly of claim 19 wherein the thrust bearing is configured to transfer any unbalanced thrust load associated with rotation of the single rotor.