Downhole electrical submersible pump with upthrust balance

In accordance with embodiments of the present disclosure, a electrical submersible pump includes a pump housing, a shaft extending at least partially through the pump housing and adapted to be driven by a submersible motor, an impeller attached to the shaft and having an impeller passage for fluid to flow therethrough, and a diffuser that is stationary relative to the pump housing and having a diffuser passage, wherein the diffuser is disposed corresponding to the impeller to form a pump stage such that fluid can flow between the impeller passage and the diffuser passage. The electrical submersible pump also includes a labyrinth seal formed between the impeller and the diffuser, wherein the labyrinth seal selectively seals the impeller passage from a cavity formed between the impeller and the diffuser to maintain the impeller in a floating condition relative to the diffuser.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a U.S. National Stage Application of International Application No. PCT/US2014/047975 filed Jul. 24, 2014, which is incorporated herein by reference in its entirety for all purposes.

TECHNICAL FIELD

The present disclosure relates generally to well drilling and hydrocarbon recovery operations and, more particularly, to systems and methods for balancing the upthrust exerted on components of an electrical submersible pump.

BACKGROUND

Hydrocarbons, such as oil and gas, are commonly obtained from subterranean formations that may be located onshore or offshore. The development of subterranean operations and the processes involved in removing hydrocarbons from a subterranean formation typically involve a number of different steps such as, for example, drilling a wellbore at a desired well site, treating the wellbore to optimize production of hydrocarbons, and performing the necessary steps to produce and process the hydrocarbons from the subterranean formation.

When producing and processing the hydrocarbons from the subterranean formation, an underground pump is often used to force fluids toward the surface. More specifically, an electrical submersible pump (ESP) may be installed in a lower portion of the wellbore and used to pressurize fluids, thereby sending the fluids toward the surface. Such ESPs typically include a series of alternating impellers and diffusers, the impellers being designed to rotate as rotors relative to the stationary diffusers. The rotating impellers increase the pressure of the fluids flowing therethrough. When fluids are pumped in this manner against relatively high pressure differentials, the momentum of the fluid may push the individual impellers against downstream diffusers in the series, which applies an undesirable upward thrust to various components of the ESP. This upward thrust, known herein as “upthrust”, can reduce the overall lifespan of the ESP.

DETAILED DESCRIPTION

Certain embodiments according to the present disclosure may be directed to an electrical submersible pump (ESP) that may be specifically designed for balancing an upward thrust (upthrust) on the impellers of the pump caused by pumping downhole fluids through the pump. Certain embodiments may include an ESP that has an electric motor for driving a shaft having centrifugal impellers distributed therealong. Each impeller is located adjacent a diffuser, which is stationary with regard to the pump wall, to form a multi-stage pump. Certain embodiments of the ESP may be useful in the petroleum industry, and especially useful for highly pressurized downhole pumping of fluid from wells drilled to produce fluid in the energy industry.

Certain embodiments may include a labyrinth seal formed between the impeller and corresponding diffuser of a pump stage. The labyrinth seal may reduce an amount of upthrust on the impeller from the pressurized fluid flowing therethrough. In certain embodiments, each pump stage can be coupled with other pump stages to increase dynamic lift of the centrifugal pump as required to meet the volumetric and total dynamic head requirements of each individual well. In such embodiments, labyrinth seals may be formed between an impeller and the diffusers on one or both sides of the impeller to reduce the amount of upthrust on the impeller from the pressurized fluid. The labyrinth seals and their effect on impeller upthrust in ESPs will be discussed in further detail below.

Turning now to the drawings,FIG. 1illustrates a schematic partial cross-sectional view of one example pumping system100, in accordance with certain embodiments of the present disclosure. The pumping system100may be disposed within a wellbore105, which may be cased or uncased according to a particular implementation, in a formation110. The pumping system100may be an electrical submersible pump (ESP). The ESP may include a centrifugal pump120coupled to an intake section125, a seal section130, and a motor section135. In general, the pumping system100may be suspended by a production tubular115in a suitable manner known in the art, with a submersible electrical cable extending from a power supply on the surface (not shown) to the motor of the motor section135. The pump120may have one or more intakes in the vicinity of the intake section125. The pump120may have a pump outlet located and attached for flow to a conduit for receiving pumped fluid in the vicinity of an upper end of the pump120. From this upper end, the pump120may be connected to a conduit for carrying the fluid to the surface or into the casing of another submersible pump.

FIG. 2is a schematic diagram illustrating in greater detail the components that make up the pumping system100. More specifically, the illustrated pumping system100includes the pump120described above, the intake section125, the seal section130, and the motor section135. As illustrated, each of these sections may be separate tool components that are coupled together axially to form the pumping system100described above. Each of these sections120,125,130, and135is designed to carry out a specific function.

For example, the motor section135is used to convert electrical energy into mechanical energy to urge rotation of a shaft150extending at least partially through the pump120. The seal section130includes a thrust bearing designed to cushion a downward thrust (downthrust) output from the pump120to the lower components of the pumping system100. In this manner, the seal section130functions as a protector for the lower portions of the pumping system100. In some embodiments, the intake section125may include a gas separator152used to ensure that relatively little gas travels through the pump120and up to the surface.

As illustrated, the pump120includes a pump housing154, the shaft150, and several pump stages156that are stacked one over the other along the length of the pump120. Each of the pump stages156is made up of an impeller158and a diffuser160. The impellers158are coupled to the shaft150and are designed to rotate as rotors relative to the diffusers160. The diffusers160remain stationary with respect to the pump housing154, and the motor section135rotates the shaft150to rotate the impellers158, which pump fluids through the pumping system100. In certain embodiments, the motor section135may rotate the impellers158relative to the diffusers160at a speed of approximately 3600 revolutions per minute, although this speed could be higher or lower. As the impellers158rotate, they pressurize downhole fluids, urging them up the pump through passages formed into the impellers158and the diffusers160. Specifically, each rotating impeller draws the fluid up through fluid passages in the impeller and directs the fluid into fluid passages of the downstream diffuser.

In the pump120, one or more impellers158may be designed to move up and down relative to the diffusers160along a direction of the axis162. This movement may be based on a number of different forces being applied to the impellers158. For example, certain forces applied to an impeller158in a downward (e.g., upstream) direction may exert a downward thrust (downthrust) on the impeller158, thereby pushing the impeller158downward. Such downward forces may include a force acting on the impeller158due to gravity as well as a pressure differential between the lower pressure upstream end of the impeller158and the higher pressure downstream end of the impeller158. Similarly, certain forces applied to the impeller158in an upward (e.g., downstream) direction may exert an upthrust on the impeller158, pushing the impeller158upward. Such upward forces may come from the momentum of the pressurized fluid flowing upward through the passages of the impeller158, as well as the pressure differential.

It is desirable to maintain a particular balance between the upthrust and downthrust forces on the impellers158of the pump120, in order to increase the efficiency of operation of the ESP. For example, it may be desirable to maintain the impellers158in a slight net downthrust condition relative to the diffusers160such that each impeller158is forced downward toward the next upstream diffuser160in the pump120. In other embodiments, the impellers158may be in a no net thrust condition relative to the diffusers160, such that the forces on the impeller158are balanced and the impeller158does not directly contact either one of its neighboring diffusers160. The net downthrust condition is acceptable because the pumping system100includes the seal section130, which as noted above includes a thrust bearing configured to dissipate any additional downward forces received from the pump120(e.g., due to downthrust). For example, the protector thrust bearing within the seal section130may be able to handle up to 12,000 lbs of force in the downward direction. However, the only component in conventional centrifugal pumping systems able to dissipate upthrust forces are individual washers disposed on the impellers158. These washers do little to dissipate the forces applied thereto when the impeller158is thrust up against the downstream diffuser160, and as a result they wear out relatively quickly. Accordingly, in order to maximize the lifetime of the pumping system100, it is desirable to maintain the impellers158in a net downthrust or no net thrust condition so the impellers158do not contact the downstream diffusers160. As discussed in detail below, present embodiments of the pumping system100include pump stages156that utilize labyrinth seals to balance out the upthrust forces on the impellers158.

FIGS. 3-5illustrate three different configurations of the pump120that may employ the disclosed labyrinth seals between the impellers158and their respective diffusers160.FIG. 3shows the pump120in a float configuration, where a hub170A of one impeller158A is not in contact with a hub170B of the adjacent impeller158B. In this configuration, one impeller158A may move up and down along the axis162of the shaft150without the other impeller158B moving in the same way.FIG. 4shows the pump120in a compression configuration, where the hubs170of each of the impellers158of the pump120are in contact with one another along the length of the pump120. In this configuration, all of the impellers158move up and down along the axis162of the shaft together relative to the diffusers160.

FIG. 5shows the pump120in a hybrid configuration, where the hubs170of some adjacent impellers158are in contact with each other while the hubs170of other adjacent impellers158are not in contact with each other. For example, the pump120may include a first group172A of the impellers158with hubs all contacting one another. There may be multiple groups (e.g.,172A and172B) each with the same number of impellers158in a compression configuration. Between each of these groups172A and172B, the hubs170of adjacent impellers158are not in contact. Thus, the hybrid configuration illustrated inFIG. 5is a hybrid version of the pump stage configurations shown inFIGS. 3 and 4. As noted above, any of the above described pump stage configurations (e.g., float, compression, or hybrid) may utilize the disclosed labyrinth seals disposed between the impellers158and diffusers160.

FIG. 6is a cross sectional view of an embodiment of certain components of the pump120. More specifically, the illustrated pump120includes one impeller158disposed between two adjacent diffusers160A and160B. The impeller158and the diffuser160A disposed above the impeller158may form one of the pump stages156of the pump120. The impeller158includes a balance ring190formed along a portion of the impeller158that interfaces with the diffuser160A. The balance ring190includes an upwardly extending outer edge192that is disposed in close proximity with, but not touching, a corresponding downwardly extending inner edge194of the diffuser160A.

As illustrated, a washer196may be pressed into a lower portion of the balance ring190. The washer196, which may be a phenolic washer, is used to absorb forces caused by the pump stage156running in an upthrust condition. That is, if the force on the impeller158in an upward direction is greater than the force on the impeller158in a downward direction, the impeller158may move upward and into contact with the diffuser160A. In the illustrated embodiment, this contact would occur between a hub198of the diffuser160A and the washer196on the impeller158. Such contact between the impeller158and the diffuser160A may lead to undesirable wear on the washer196, thereby reducing the pump lifetime.

As noted above, the pump120includes a labyrinth seal200positioned between the impeller158and the corresponding diffuser160A to reduce the upward movement of the impeller158relative to the diffuser160A. In the illustrated embodiment, the labyrinth seal200is formed into the balance ring of the impeller158, specifically positioned along the upwardly extending outer edge192that faces the downwardly extending inner edge194of the diffuser160A. In other embodiments, the labyrinth seal200may be formed into an inner edge of the impeller158facing a corresponding outer edge of the diffuser160A. It should also be noted that, in other embodiments, the labyrinth seal200may be formed into the diffuser160A (e.g., along the edge194) instead of the impeller158, as illustrated inFIG. 7. In still further embodiments, the labyrinth seal200may be formed into both the impeller158and the diffuser160A.

The labyrinth seal200is a series of grooves formed into the impeller158(and/or the diffuser160A) that provides a circuitous path between the impeller158and the diffuser160A so that leakage of fluid through the labyrinth seal200is reduced or eliminated. As fluid flows toward the labyrinth seal200, the fluid may form vortexes within the grooves of the labyrinth seal200. This prevents the fluid from passing through the seal toward the next groove and eventually out of the seal.

In present embodiments, the labyrinth seal200provides such a tortuous path between a fluid passage of the pump stage156(e.g., an impeller passage) and a cavity202formed between the impeller158and the diffuser160A. As the net forces on the impeller158reach an upthrust condition, pushing the impeller158toward the diffuser160A (as shown by an arrow204), the labyrinth seal200seals the cavity202off from the fluid passage. Thus, pressurized fluid that previously entered the cavity202cannot flow out of the cavity through the labyrinth seal200. As a result, the fluid trapped in the cavity202presses downward against the impeller158, balancing the forces on the impeller158so that the impeller158does not come into direct contact with the diffuser160A. In this manner, the labyrinth seal200seals the impeller passage from the cavity202to maintain the impeller158in a stable, floating condition relative to the diffuser160A.

In the illustrated embodiment, the labyrinth seal200includes four grooves each with a square or rectangular profile formed into the impeller158. However, it should be noted that different types and numbers of grooves may be utilized as labyrinth seals200in other embodiments. For example, the labyrinth seal200may include an increased or decreased number of grooves between the impeller158and the diffuser160A (e.g., 2, 3, 5, 6, 7, 8, 9, 10, or more grooves). In some embodiments, the impeller158may be formed so that the upwardly extending edge192of the balance ring190(and/or downwardly extending edge194of the diffuser160A) is longer than in the illustrated embodiment in order to accommodate an increased number of labyrinth seal grooves. In addition, the labyrinth seal200may include any desirable shape of grooves formed into the impeller158, the diffuser160A, or both. These different shapes of grooves may include at least square (as illustrated), rectangular, round, helical, threaded, or some other design. In embodiments where a threaded labyrinth seal200is provided, the labyrinth seal200may include corresponding threaded grooves formed in both the impeller158and the diffuser160A.

The disclosed labyrinth seal200reduces the possibility of the impeller158coming into direct contact with the diffuser160A as a result of an upthrust condition. This may increase the stability of operation and the efficiency of the pump stage156since no impacts occur between the impeller158and the diffuser160A. In addition, the labyrinth seal200may extend the overall lifespan of the pump120, since the washer196does not have to endure the wear it would if the labyrinth seal200was not present. Further, the labyrinth seal200may be formed into an already existing portion of the impeller158and/or the diffuser160A, making it relatively easy to manufacture.

It may be desirable to maintain the impeller158in a slight downthrust condition relative to both the diffuser160A above the impeller as well as the diffuser160B below the impeller. Even though the pump120generally includes the seal section130(shown inFIG. 2) for absorbing any force in the downward direction due to a net downthrust on the impellers158of the pump120, reducing this downthrust may be desirable in order to maintain the seal section for longer than would be available using a conventional pump. To that end,FIG. 8illustrates an embodiment of the pump120having two labyrinth seals200A and200B, one between the impeller158and the upper diffuser160A and the other between the impeller158and the lower diffuser160B.

InFIG. 8, the upper labyrinth seal200A is formed between the impeller158and the diffuser160A, while the lower labyrinth seal200B is formed between the impeller158and the diffuser160B. Both of the labyrinth seals200A and200B, in the illustrated embodiment, are formed into extensions of the impeller158. However, it should be noted that one or both of the labyrinth seals200A and200B may be formed directly into the diffusers160A and160B, respectively, as illustrated inFIG. 7. This two-seal configuration is particularly useful in the context of pumping downhole fluids through an ESP since the pump120is generally aligned and maintained in a vertical orientation, so that the pump120can compensate for downthrust conditions of the impeller158due to gravity.

The labyrinth seal200B at the bottom may be formed between similar components of the impeller158and/or the diffuser160B as the above labyrinth seal200A. For example, the labyrinth seal200B may be formed into a downwardly extending outer edge210of the impeller158, adjacent a corresponding upwardly extending inner edge212of the diffuser160B. In other embodiments, however, the labyrinth seal200B may be formed into an inner edge of the impeller158adjacent a corresponding outer edge of the diffuser160B.

The labyrinth seal200B may separate a fluid passage of the pump120from a cavity214formed between the impeller158and the diffuser160B. Thus, the labyrinth seal200B provides a tortuous path between the fluid passage and the cavity214. As the net forces on the impeller158reach a downthrust condition, pushing the impeller158toward the diffuser160B (as shown by arrow216), the labyrinth seal200B seals the cavity214off from the fluid passage. Thus, pressurized fluid that previously entered the cavity214cannot flow out of the cavity through the labyrinth seal200B. The fluid trapped in the cavity214presses upward against the impeller158, balancing the forces on the impeller158so that the impeller158does not come into direct contact with the diffuser160B. In this manner, the labyrinth seal200B seals the impeller passage from the cavity214to maintain the impeller158in a stable, floating condition relative to the diffuser160B.

When two labyrinth seals200A and200B are utilized, as inFIG. 8, the labyrinth seals200A and200B may be configured to balance the net forces on the impeller158such that the impeller158does not come into contact with either of the two adjacent diffusers160A and160B. When the impeller158is in a downthrust condition, based on the forces applied thereto, the impeller158moves downward. As this happens, the labyrinth seal200A moves downwards relative to the stationary diffuser160A. As a result of this movement, some of the fins that define the grooves of the labyrinth seal200A may become exposed to the fluid passageway, being no longer directly across from the diffuser160A. In addition, the fins of the labyrinth seal160A may bend slightly, thereby breaking the seal caused by the labyrinth seal200A and releasing the downthrust condition. The fluid from the cavity202that would otherwise be pushing downward on the impeller158is released to the passage of the pump120, reducing at least a portion of the downward force on the impeller158. At the same time, the other labyrinth seal200B is sealing off the cavity214from the passages of the pump120so that fluid within the cavity214exerts an upward force on the impeller158.

A more detailed view of an embodiment of the pump120with two labyrinth seals200A and200B on a single impeller158is shown inFIG. 9in an upthrust condition. When the impeller158is in the upthrust condition, the impeller158moves upward (as shown by the arrow204). Consequently, the labyrinth seal200B moves upwards relative to the stationary diffuser160B. As a result of this movement, some of the fins of the labyrinth seal200B may become exposed to a fluid passageway230, since they are no longer directly across from the diffuser160B. Any of the fins of the labyrinth seal160B that are not exposed to the passageway230may bend slightly, thereby breaking the seal caused by the labyrinth seal200B and releasing the upthrust condition. The fluid from the cavity214that would otherwise be pushing upward on the impeller158is released to the passageway230of the pump120, reducing at least a portion of the upward force on the impeller158. At the same time, the upper labyrinth seal200A is sealing off the cavity202from the passageway230of the pump120so that fluid within the cavity202exerts a downward force on the impeller158. The passageway230may include a fluid passage through the impeller158and corresponding fluid passages through the diffusers160A and160B.

It should be noted that different arrangements or combinations of the disclosed labyrinth seals200may be implemented in different embodiments of the presently disclosed pump120. For example, in some pumps120, the labyrinth seal200B may formed between the impeller158and the diffuser160B below the impeller158, without the above labyrinth seal. In other embodiments, the labyrinth seal200A may be present between the impeller158and the diffuser160A above the impeller158, without the below labyrinth seal. In still further embodiments, both labyrinth seals200A and200B may be present, as illustrated inFIGS. 8 and 9. It may be desirable to at least include the labyrinth seal200A at the top of the impeller158, in order to seal off the cavity202and thus keep the top of the impeller158from impacting the diffuser160A. However, any desirable combination may be utilized and configured to provide the desired force balance to the impeller158.

As illustrated inFIGS. 8 and 9, embodiments of the pump120having two labyrinth seals200A and200B for a given impeller158may have different numbers of grooves for the different labyrinth seals200A and200B. For example, in both illustrated embodiments, the labyrinth seal200A between the impeller158and the above diffuser160A is longer and has a greater number of grooves than the labyrinth seal200B between the impeller158and the below diffuser160B. This may be because a net upthrust generally occurs when the flow rate of the fluid through the impeller158is higher than the pump120was designed to handle, and therefore a more robust seal is desirable at the upper portion of the impeller158. This may also be because a net upthrust is less desirable from a lifetime standpoint, since the washer196used to absorb the upward impact forces wears out more quickly than the seal section130(shown inFIG. 2) of the pump120used to absorb the downward impact forces. Thus, any desirable number of grooves may be used to form the labyrinth seals200A and200B at the top and bottom of the impeller158, and these numbers may be the same or different between the two labyrinth seals200A and200B, based on the expected forces and the desired net thrust on the impeller158.

FIG. 10is a process flow diagram illustrating a method250of operating the pumping system100(e.g., ESP) disclosed inFIGS. 1-9above. The method250includes rotating (block252) the shaft via the motor section and, as a result, rotating (block254) the impeller relative to the diffuser to urge fluid through the impeller passage of the impeller and into a corresponding diffuser passage of the diffuser. The method250also includes pressurizing (block256) fluid flowing through the impeller passage via the impeller. Further, the method250includes sealing (block258) the impeller passage from a cavity formed between the impeller and the diffuser via the labyrinth seal when the impeller moves toward the diffuser in an axial direction of the shaft. This applies both when the impeller is in an upthrust condition moving toward the diffuser above the impeller and when the impeller is in a downthrust condition moving toward the diffuser below the impeller. Indeed, as described above, the method may apply to an impeller with two labyrinth seals between the impeller and the diffusers on either side.