US20170183948A1 - Preconditioning flow to an electrical submersible pump - Google Patents

Abstract

A system and method of producing fluid from a wellbore by pressurizing the fluid and then directing the pressurized fluid to a centrifugal pump. Pressurizing the fluid compresses gas or vapor within the fluid, thereby decreasing the volume ratio of the gas or vapor within the fluid, which in turn increases operating efficiency of the centrifugal pump. A positive displacement pump, such as a gerotor pump, is used for pressurizing the fluid prior to sending it to the centrifugal pump.

Description

BACKGROUND OF THE INVENTION
• 1. Field of Invention
• The present disclosure is directed to a system for artificially lifting fluid from a wellbore. More specifically, the present disclosure concerns pumping fluid from the wellbore with an electrical submersible pump (“ESP”), and pressurizing the fluid upstream of the ESP with a positive displacement pump.
• 2. Description of Prior Art
• Electrical submersible pumping (“ESP”) systems are deployed in some hydrocarbon producing wellbores to provide artificial lift to deliver fluids to the surface. ESP systems are also sometimes used to transfer fluids from a wellsite to other equipment or facility for further processing. The fluids are usually made up of hydrocarbon and water. When installed, a typical ESP system is suspended in the wellbore at the bottom of a string of production tubing. Sometimes, ESP systems are inserted directly into the production tubing. In addition to a pump, ESP systems usually include an electrically powered motor for driving the pump, and a seal section for equalizing pressure in the motor to ambient. Centrifugal pumps usually have a stack of alternating impellers and diffusers coaxially arranged in a housing along a length of the pump. The impellers each attach to a shaft that couples to the motor; rotating the shaft and impellers forces fluid through passages that helically wind through the stack of impellers and diffusers. The produced fluid is pressurized as it is forced through the helical path in the pump. The pressurized fluid is discharged from the pump and into the production tubing, where the fluid is then conveyed to surface for distribution downstream for processing.
• On occasion, the fluid being pressurized by ESP systems has some percentage of gas or vapor entrained therein. However, with increasing gas or vapor content in the downhole fluid, ESP systems generally produce less head and become less efficient. Lowering pump head results in reduced pump discharge pressure and a drop in fluid being pumped by the ESP system. Additionally, a high amount of gas or liquid in the produced fluid increases fluid pressure drop when flowing through the tubing, which further contributes to a reduction in the produced fluid flow rate. Moreover, ESP systems are operationally limited by how much gas or vapor can be present in the downhole fluid being pressurized; and can experience vapor lock when the percentage of gas or vapor exceeds a threshold value. Occasionally, the upper limit of gas or vapor percentage in the produced fluid can approach around 30% by weight.
• Some of the conventional methods of tackling ESP gas problems include the use of gas separators, gas handlers, and helico-axial multiphase pumps. Some gas separators remove gas from the gas-liquid mixture into the tubing-casing annulus by centrifugal means, thereby reducing the amount of gas or vapor that actually enters the ESP system. Devices known as advanced gas handlers use centrifugal action to compress the gas before feeding the entire fluid into the ESP system. Helico-axial multiphase pumps have specially designed rotating impellers and diffusers that homogenize the gas and liquid phases prior to directing the coalesced gas-liquid mixture to the ESP system for pressurization. A limitation of conventional gas-handling systems is a high incremental cost to the total cost of the ESP string; and some systems have many internal components with moving parts, resulting in a complex system.
SUMMARY OF THE INVENTION
• Disclosed herein are examples of a method and system for artificially lifting fluid from a wellbore where the fluid is pre-pressurized upstream of a pump. In one example, disclosed is an electrical submersible pumping (“ESP”) system disposable in a wellbore that includes a gerotor pump with an inlet in communication with fluid in the wellbore, and an exit through which fluid pressurized in the gerotor pump is directed away from the gerotor pump. Also included with the ESP system is a centrifugal pump having an inlet in fluid communication with the exit of the gerotor pump, and a discharge in which fluid pressurized in the centrifugal pump is directed away from the centrifugal pump. Production tubing is included that is in fluid communication with the discharge of the centrifugal pump. In one example the gerotor pump includes a body, an idler in the body having an axis, planar upper and lower surfaces, a curved outer side surface, and a chamber having profiled sidewalls that lobes at designated locations along a circumference of the chamber, and a rotor disposed in the chamber and having an axis, an outer circumference profiled to define gears that project radially outward, so that when the rotor is rotated about its axis, the gears contact the sidewall of the chamber at various locations to define sealing interfaces and define high and low pressure sides in the chamber. In one example, the rotor has n gears and the idler has n+1 lobes. In one embodiment, the centrifugal pump is equipped with a series of diffusers, impellers disposed between adjacent diffusers, and a flow path extending through the diffusers and impellers, so that when the impellers are rotated, fluid is urged through the flow path and is pressurized with distance through the flow path. In one example, an end of the production tubing distal from the centrifugal pump couples with a wellhead assembly disposed at an opening of the wellbore. The fluid being pressurized by the gerotor pump can include a fluid having phases of liquid and gas or vapor. The ESP system optionally includes a motor section mechanically coupled with the gerotor pump and the centrifugal pump, a seal section in pressure communication with the motor so that a pressure in the motor section remains at substantially ambient pressure, and a monitoring sub coupled with the motor section. The centrifugal pump operates at an increased efficiency when pressurizing fluid from the discharge of the gerotor pump than when pressurizing fluid received from the wellbore.
• Also disclosed herein is an example of an electrical submersible pumping (“ESP”) system disposable in a wellbore that is made up of a positive displacement pump with a suction port in communication with fluid in the wellbore, a pressurization chamber in communication with the inlet, and a discharge port in communication with the pressurization chamber and that is at a pressure that is greater than a pressure of the suction port of the positive displacement pump; and a centrifugal pump having a suction port in communication with the discharge of the positive displacement pump and a discharge port that is at a pressure greater than a pressure of the suction port of the centrifugal pump. The ESP system can further have production tubing with an end in communication with the discharge port of the centrifugal pump, and a distal end coupled to a wellhead assembly disposed at an opening of the wellbore. In one alternative, the positive displacement pump is a gerotor pump. The ESP system can include a motor mechanically coupled to the positive displacement pump and to the centrifugal pump, and a seal section in pressure communication with the motor, so that pressure in the motor is maintained substantially at ambient pressure when the motor is in the wellbore. When fluid in the wellbore includes liquid and vapor or gas, a ratio of vapor or gas volume to liquid volume of the fluid is greater at the suction port of the positive displacement pump than at the suction port of the centrifugal pump, thereby increasing the operating efficiency of the centrifugal pump.
• Also disclosed herein is a method of pumping fluid produced from within a wellbore, where the method includes pressurizing an amount of the fluid having phases of liquid and gas or vapor, so that the gas or vapor in the fluid is compressed to thereby reduce a ratio of gas or vapor volume to liquid volume, directing the pressurized amount of the fluid to a centrifugal pump, and further pressurizing the pressurized amount of the fluid with the centrifugal pump. The step of pressurizing the amount of fluid having phases of liquid and gas or vapor can be performed using a positive displacement pump. Optionally, the positive displacement pump is a gerotor pump. The fluid further pressurized by the centrifugal pump can be directed to a wellhead assembly disposed at an opening of the wellbore. Both the positive displacement pump and the centrifugal pump can be powered with a single motor.
BRIEF DESCRIPTION OF DRAWINGS
• Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:
• FIG. 1 is a partial sectional view of an example of an ESP system disposed in a wellbore.
• FIGS. 2A and 2B are sectional views of an example of a portion of the ESP system ofFigure 1 having a positive displacement pump in combination with an centrifugal pump.
• FIG. 3 is a sectional view of an alternate example of positive displacement pump ofFigure 2.
• While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF INVENTION
• The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude.
• It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.
• One example of an electrical submersible pump (“ESP”)system10 is shown in a partial side sectional view inFIG. 1. TheESP system10 is illustrated disposed in awellbore12 which intersects asubterranean formation14.Tubular casing16 lines thewellbore12 andtubing18 is inserted coaxially within thecasing16. TheESP system10 includes amotor20, aseal system22 mounted on an upper end ofmotor20, whereinseal system22 equalizes pressure withinmotor20 to ambient. Also included withESP system10 is apositive displacement pump24 mounted on an end ofseal system22 distal frommotor20. Further in the example of FIG.1, acentrifugal pump26 is shown mounted on an end ofpositive displacement pump24 distal fromseal system22. Optionally, amonitoring sub28 is included withESP system10, where monitoring sub may include sensors for sensing one or more of temperature, pressure, and vibration withinwellbore12. Alternatively, monitoringsub28 may include a controller for sending and receiving control signals for controlling operations ofESP system10.
• Perforations30 are shown projecting radially outward fromwellbore12 throughcasing16, and intoformation14.Perforations30 provide a flow path for fluid entrained in the formation to make its way into thewellbore12. Further in this example,openings32 are formed through sidewalls oftubing18 to allow wellbore fluid F produced fromformation14 to flow intotubing18. After being directed into thetubing18, the fluid F can be pressurized by artificial lift byESP system10. Optionally, apacker34 is shown formed in theannulus36 betweentubing18 andcasing16, and is used for directing the flow of fluid F intotubing18. Fluid F enters intoESP system10 via aninlet38 formed onpositive displacement pump24. Frompositive displacement pump24, fluid F can then be directed to acentrifugal pump26. A string ofproduction tubing40 is shown coupled to a discharge end ofcentrifugal pump26. Around production tubing40 apacker42 is disposed and which forms a flow barrier in the annular space44 betweenESP system10 and the inner surface oftubing18.Packer42 thus forces fluid F flowing upwards withintubing18 to make its way intoinlet38.
• Still referring toFIG. 1, further illustrated is that an upper end ofproduction tubing40 terminates within awellhead assembly46 depicted positioned at an opening ofwellbore12 onsurface47. Piping withinwellhead assembly46 defines aproduction circuit48 for selectively directing the fluid F withinproduction tubing40 to designated destinations. In one example, fluid F withinproduction circuit48 is directed to atransfer line50 shown having a distal end terminating at aprocessing facility52. Examples ofprocessing facilities52 include refineries, olefins plants, and other facilities that process the fluid F for transport. Examples of processing for transport includes removing constituents from the fluid F such as water, sulfur, and other undesirable elements. Optionally,valves54 are provided withinproduction circuit40 andtransfer line50 for selectively directing the flow of fluid F therethrough.
• Referring now toFIGS. 2A and 2B, shown in a side sectional view is one example of an embodiment of thepositive displacement pump24A coupled withcentrifugal pump26A. As shown, included withinpositive displacement pump24A is ahousing56 which defines acavity58 therein. Apiston60 is disposed withincavity58, and as shown by the double-headed arrow reciprocates axially in thecavity58. Apiston rod62 connects to an end ofpiston60, and selectively provides a motive force to reciprocatepiston60 withincavity58. Acompression chamber64 is defined withincavity58 on a side ofpiston60 opposite frompiston rod62. In the illustrated example, fluid F from within wellbore12 (FIG. 1) is withincompression chamber64. Fluid F ofFIGS. 2A and 2B includes a two-phase mixture of liquid L and vapor V, where vapor V can include gas, vapor, or a mixture of both. As shown, fluid F is directed intocompression chamber64 via aninlet line66, which has a distal end connecting toinlet38 illustrated disposed on an outer surface ofpositive displacement pump24A. Optionally,inlet line66 can be equipped with acheck valve68, so that during a compression cycle, fluid F cannot escape fromcavity58 back intoinlet line66. In an alternative, fluid F can have up to around 75% gas by volume or by mass, and examples exist wherein fluid F is around 100% vapor.
• Depicted inFIG. 2B is thepositive displacement pump24A operating during a compression phase; whereinpiston60 is moved into the portion ofcavity58 occupied by fluid F thereby compressing fluid F. Pressurizing fluid F withpump24A compresses the vapor V in the fluid F, thereby reducing the ratio of gas or vapor volume with respect to liquid volume of the fluid F. The compressed and pressurized fluid F is directed tocentrifugal pump26A viadischarge line70 shown having one end coupled with adischarge71 on the outer housing ofpositive displacement pump24A. In the examples ofFIGS. 2A and 2B,centrifugal pump26A includes amain body72 through which a fluid flow path P helically courses from aninlet space74 to anoutlet space76. Inlet andoutlet spaces74,76 and pumpbody72 are encased within apump housing78.Impellers80 are shown disposed withinpump body72 and are intersected bypath P. Diffusers82 are sequentially spaced betweenimpellers80 and are also intersected by path P. Ashaft84 is shown that connects to theimpellers80, rotatingshaft84 correspondingly rotatesimpellers80, that in turn exert a force on the fluid F that urges fluid F through the path P and pressurizes fluid F. An advantage of pressurizing the fluid F before directing it to thecentrifugal pump26A is that the gas or vapor volume in the fluid F is decreased, which increases thecentrifugal pump26A operating efficiency. When feeding “prepressurized” fluid F having a reduced gas or vapor volume ratio to thecentrifugal pump26A, the resulting pressure differential imparted on the fluid F (pump head) by thecentrifugal pump26A is greater than when fluid F from the wellbore12 (FIG. 1) is fed directly to thecentrifugal pump26A. Further illustrated in the example ofFIG. 2B is that the pressurized fluid F exits path P intooutlet space76, and then is routed into production tubing44 for transfer to the wellhead assembly46 (FIG. 1).
• FIG. 3 shows in a plan sectional view one example of thepositive displacement pump24B, wherein thepump24B is the same as or similar to what is commonly referred to as a gerotor pump. As shown,pump24B has anouter housing56B and in which an idler86 is disposed.Idler86 ofFIG. 3 has generally planar upper and lower surfaces, and a curved outer circumference.Idler86 is selectively rotated about an axis A_X1with respect tohousing56B and as illustrated by arrow A₁. Provided within idler86 is arotor88 shown rotatable about axis A_X2, and in a direction illustrated by arrow A₂. Discharge line70 intersects a side ofhousing56B distal frominlet66. Formed axially through a middle portion of idler86 is anidler chamber90 which has an undulating curved profile and which forms lobes92_1-5at spaced apart angular locations around axis A_X1. Although five lobes92_1-5are shown inFIG. 3, the number of lobes92_1-5is not limited to five, but instead can be any other number. The outer circumference ofrotor88 is also profiled but semi-complementary to theidler chamber90. The curved undulating circumference of therotor88 defines gears94_1-4that selectively fit into the lobes92_1-5. As shown, the number of gears94_1-4is one less than the number of lobes92_1-5. An inner surface ofchamber90 forms achamber wall96.
• Strategic formation and synchronization of the lobes92_1-5and gears94_1-4causes interaction between the outer periphery of the gears94_1-4and various locations alongchamber wall96. Shown in the example ofFIG. 3, gear94₂is in sealing contact with a location on thewall96 proximate lobe92₂, and gear94₃is in sealing contact with a location on thewall96 proximate lobe92₃. Further shown is that gear94₄is in sealing contact with a location on thewall96 proximate lobe92₄. The sealing contact between gears94₂,94₃andwall96 forms an enclosed space inidler chamber90 to define alower pressure side98. Similarly the sealing contact between gears94₄,94₃andwall96 forms another enclosed space inidler chamber90 to define ahigher pressure side100.Lower pressure side98 is in fluid communication withinlet line66 andhigher pressure side100 is in fluid communication withdischarge line70. Continuous rotation of both the idler86 androtor88 causes the fluid initially trapped within thelower pressure side98 to be compressed between the gears94_1-4andsidewall96 thereby pressurizing the fluid F prior to being discharged through thedischarge line70. One advantage of the gerotor pump illustrated inFIG. 3, is that multiple phased fluids, i.e., those having a mixture of liquid and vapor and/or gas, can be efficiently pressurized irrespective of how compressible is the fluid F. As is known, the presence of gas, vapor, or both in the fluid F can increase compressibility of the fluid F. Accordingly, significant advantages are realized by incorporating the gerotor pump assembly with a centrifugal pump to increase the efficiency of the centrifugal pump. In one example, during gerotor rotation, due to the difference between the gears94_1-4and lobes92_1-5, enlarging and decreasing cavities are created, such as illustrated by the higher pressure and lower pressure sides98,100. As the cavities enlarge and decrease, fluid suction and compression occur continuously, and as the gas mixture is compressed by the gerotor the gas volume is reduced considerably due to compressibility effects of the gas or vapor. This results in a more homogenized mixture as it is fed to the centrifugal pump26 (FIG. 1). Embodiments exist where the gerotor pump includes two or more stages, and is powered bymotor20.
• The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results.Inlet line66 as shown is a single conduit topumps24A,24B (FIGS. 2A, 2B, and 3); in an example, multiple lines are provided to thepumps24A,24B, and thepumps24A,24B have multiple ports. In an alternate embodiment, the high pressure side of thepumps24A,24B communicates directly into a discharge chamber (not shown), which directly feeds into the suction ofcentrifugal pump26A,26B; in this alternateembodiment discharge line70 is not included. Optionally, a progressive cavity pump can be used as a pre-conditioning device, in lieu of a gerotor pump, and for conditioning fluid upstream of a centrifugal pump. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.

Claims (18)

What is claimed is:

1. An electrical submersible pumping (“ESP”) system disposable in a wellbore comprising:

a gerotor pump having,

an inlet in communication with fluid in the wellbore, and

an exit through which fluid pressurized in the gerotor pump is directed away from the gerotor pump;

a centrifugal pump having,

an inlet in fluid communication with the exit of the gerotor pump, and

a discharge in which fluid pressurized in the centrifugal pump is directed away from the centrifugal pump; and

production tubing in fluid communication with the discharge of the centrifugal pump.

2. The ESP system ofclaim 1, wherein the gerotor pump comprises

a body,

an idler in the body having an axis, planar upper and lower surfaces, a curved outer side surface, and a chamber having profiled sidewalls that lobes at designated locations along a circumference of the chamber, and

a rotor disposed in the chamber and having an axis, an outer circumference profiled to define gears that project radially outward, so that when the rotor is rotated about its axis, the gears contact the sidewall of the chamber at various locations to define sealing interfaces and define high and low pressure sides in the chamber.

3. The ESP system ofclaim 2, wherein the rotor comprises n gears, and the idler comprises n+1 lobes.

4. The ESP system ofclaim 1, wherein the centrifugal pump comprises a series of diffusers, impellers disposed between adjacent diffusers, and a flow path extending through the diffusers and impellers, so that when the impellers are rotated, fluid is urged through the flow path and is pressurized with distance through the flow path.

5. The ESP system ofclaim 1, wherein an end of the production tubing distal from the centrifugal pump couples with a wellhead assembly disposed at an opening of the wellbore.

6. The ESP system ofclaim 1, wherein the fluid being pressurized by the gerotor pump comprises a fluid having phases of liquid and gas or vapor.

7. The ESP system ofclaim 1, further comprising a motor section mechanically coupled with the gerotor pump and the centrifugal pump, a seal section in pressure communication with the motor so that a pressure in the motor section remains at substantially ambient pressure, and a monitoring sub coupled with the motor section.

8. The ESP system ofclaim 1, wherein the centrifugal pump operates at an increased efficiency when pressurizing fluid from the discharge of the gerotor pump than when pressurizing fluid received from the wellbore.

9. An electrical submersible pumping (“ESP”) system disposable in a wellbore comprising:

a positive displacement pump with a suction port in communication with fluid in the wellbore, a pressurization chamber in communication with the inlet, and a discharge port in communication with the pressurization chamber and that is at a pressure that is greater than a pressure of the suction port of the positive displacement pump; and

a centrifugal pump having a suction port in communication with the discharge of the positive displacement pump and a discharge port that is at a pressure greater than a pressure of the suction port of the centrifugal pump.

10. The ESP system ofclaim 9, further comprising production tubing having an end in communication with the discharge port of the centrifugal pump and a distal end coupled to a wellhead assembly disposed at an opening of the wellbore.

11. The ESP system ofclaim 9, wherein the positive displacement pump comprises a gerotor pump.

12. The ESP system ofclaim 9, further comprising a motor mechanically coupled to the positive displacement pump and to the centrifugal pump, and a seal section in pressure communication with the motor, so that pressure in the motor is maintained substantially at ambient pressure when the motor is in the wellbore.

13. The ESP system ofclaim 9, wherein when fluid in the wellbore comprises liquid and vapor or gas, a ratio of vapor or gas volume to liquid volume of the fluid is greater at the suction port of the positive displacement pump that at the suction port of the centrifugal pump, thereby increasing the operating efficiency of the centrifugal pump.

14. A method of pumping fluid produced from within a wellbore comprising:

pressurizing an amount of the fluid having phases of liquid and gas or vapor, so that the gas or vapor in the fluid is compressed to thereby reduce a ratio of gas or vapor volume to liquid volume;

directing the pressurized amount of the fluid to a centrifugal pump; and

further pressurizing the pressurized amount of the fluid with the centrifugal pump.

15. The method ofclaim 14, wherein the step of pressurizing the amount of fluid having phases of liquid and gas or vapor is performed using a positive displacement pump.

16. The method ofclaim 15, wherein the positive displacement pump comprises a gerotor pump.

17. The method ofclaim 14, further comprising directing the fluid further pressurized by the centrifugal pump to a wellhead assembly disposed at an opening of the wellbore.

18. The method ofclaim 15, further comprising powering both the positive displacement pump and the centrifugal pump with a single motor.

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