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.
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.
For a more complete understanding of the present disclosure and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
Illustrative embodiments of the present disclosure are described in detail herein. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation specific decisions must be made to achieve developers' specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of the present disclosure. Furthermore, in no way should the following examples be read to limit, or define, the scope of the invention.
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,
For example, the motor section 135 is used to convert electrical energy into mechanical energy to urge rotation of a shaft 150 extending at least partially through the pump 120. The seal section 130 includes a thrust bearing designed to cushion a downward thrust (downthrust) output from the pump 120 to the lower components of the pumping system 100. In this manner, the seal section 130 functions as a protector for the lower portions of the pumping system 100. In some embodiments, the intake section 125 may include a gas separator 152 used to ensure that relatively little gas travels through the pump 120 and up to the surface.
As illustrated, the pump 120 includes a pump housing 154, the shaft 150, and several pump stages 156 that are stacked one over the other along the length of the pump 120. Each of the pump stages 156 is made up of an impeller 158 and a diffuser 160. The impellers 158 are coupled to the shaft 150 and are designed to rotate as rotors relative to the diffusers 160. The diffusers 160 remain stationary with respect to the pump housing 154, and the motor section 135 rotates the shaft 150 to rotate the impellers 158, which pump fluids through the pumping system 100. In certain embodiments, the motor section 135 may rotate the impellers 158 relative to the diffusers 160 at a speed of approximately 3600 revolutions per minute, although this speed could be higher or lower. As the impellers 158 rotate, they pressurize downhole fluids, urging them up the pump through passages formed into the impellers 158 and the diffusers 160. 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 pump 120, one or more impellers 158 may be designed to move up and down relative to the diffusers 160 along a direction of the axis 162. This movement may be based on a number of different forces being applied to the impellers 158. For example, certain forces applied to an impeller 158 in a downward (e.g., upstream) direction may exert a downward thrust (downthrust) on the impeller 158, thereby pushing the impeller 158 downward. Such downward forces may include a force acting on the impeller 158 due to gravity as well as a pressure differential between the lower pressure upstream end of the impeller 158 and the higher pressure downstream end of the impeller 158. Similarly, certain forces applied to the impeller 158 in an upward (e.g., downstream) direction may exert an upthrust on the impeller 158, pushing the impeller 158 upward. Such upward forces may come from the momentum of the pressurized fluid flowing upward through the passages of the impeller 158, as well as the pressure differential.
It is desirable to maintain a particular balance between the upthrust and downthrust forces on the impellers 158 of the pump 120, in order to increase the efficiency of operation of the ESP. For example, it may be desirable to maintain the impellers 158 in a slight net downthrust condition relative to the diffusers 160 such that each impeller 158 is forced downward toward the next upstream diffuser 160 in the pump 120. In other embodiments, the impellers 158 may be in a no net thrust condition relative to the diffusers 160, such that the forces on the impeller 158 are balanced and the impeller 158 does not directly contact either one of its neighboring diffusers 160. The net downthrust condition is acceptable because the pumping system 100 includes the seal section 130, which as noted above includes a thrust bearing configured to dissipate any additional downward forces received from the pump 120 (e.g., due to downthrust). For example, the protector thrust bearing within the seal section 130 may 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 impellers 158. These washers do little to dissipate the forces applied thereto when the impeller 158 is thrust up against the downstream diffuser 160, and as a result they wear out relatively quickly. Accordingly, in order to maximize the lifetime of the pumping system 100, it is desirable to maintain the impellers 158 in a net downthrust or no net thrust condition so the impellers 158 do not contact the downstream diffusers 160. As discussed in detail below, present embodiments of the pumping system 100 include pump stages 156 that utilize labyrinth seals to balance out the upthrust forces on the impellers 158.
As illustrated, a washer 196 may be pressed into a lower portion of the balance ring 190. The washer 196, which may be a phenolic washer, is used to absorb forces caused by the pump stage 156 running in an upthrust condition. That is, if the force on the impeller 158 in an upward direction is greater than the force on the impeller 158 in a downward direction, the impeller 158 may move upward and into contact with the diffuser 160A. In the illustrated embodiment, this contact would occur between a hub 198 of the diffuser 160A and the washer 196 on the impeller 158. Such contact between the impeller 158 and the diffuser 160A may lead to undesirable wear on the washer 196, thereby reducing the pump lifetime.
As noted above, the pump 120 includes a labyrinth seal 200 positioned between the impeller 158 and the corresponding diffuser 160A to reduce the upward movement of the impeller 158 relative to the diffuser 160A. In the illustrated embodiment, the labyrinth seal 200 is formed into the balance ring of the impeller 158, specifically positioned along the upwardly extending outer edge 192 that faces the downwardly extending inner edge 194 of the diffuser 160A. In other embodiments, the labyrinth seal 200 may be formed into an inner edge of the impeller 158 facing a corresponding outer edge of the diffuser 160A. It should also be noted that, in other embodiments, the labyrinth seal 200 may be formed into the diffuser 160A (e.g., along the edge 194) instead of the impeller 158, as illustrated in
The labyrinth seal 200 is a series of grooves formed into the impeller 158 (and/or the diffuser 160A) that provides a circuitous path between the impeller 158 and the diffuser 160A so that leakage of fluid through the labyrinth seal 200 is reduced or eliminated. As fluid flows toward the labyrinth seal 200, the fluid may form vortexes within the grooves of the labyrinth seal 200. This prevents the fluid from passing through the seal toward the next groove and eventually out of the seal.
In present embodiments, the labyrinth seal 200 provides such a tortuous path between a fluid passage of the pump stage 156 (e.g., an impeller passage) and a cavity 202 formed between the impeller 158 and the diffuser 160A. As the net forces on the impeller 158 reach an upthrust condition, pushing the impeller 158 toward the diffuser 160A (as shown by an arrow 204), the labyrinth seal 200 seals the cavity 202 off from the fluid passage. Thus, pressurized fluid that previously entered the cavity 202 cannot flow out of the cavity through the labyrinth seal 200. As a result, the fluid trapped in the cavity 202 presses downward against the impeller 158, balancing the forces on the impeller 158 so that the impeller 158 does not come into direct contact with the diffuser 160A. In this manner, the labyrinth seal 200 seals the impeller passage from the cavity 202 to maintain the impeller 158 in a stable, floating condition relative to the diffuser 160A.
In the illustrated embodiment, the labyrinth seal 200 includes four grooves each with a square or rectangular profile formed into the impeller 158. However, it should be noted that different types and numbers of grooves may be utilized as labyrinth seals 200 in other embodiments. For example, the labyrinth seal 200 may include an increased or decreased number of grooves between the impeller 158 and the diffuser 160A (e.g., 2, 3, 5, 6, 7, 8, 9, 10, or more grooves). In some embodiments, the impeller 158 may be formed so that the upwardly extending edge 192 of the balance ring 190 (and/or downwardly extending edge 194 of the diffuser 160A) is longer than in the illustrated embodiment in order to accommodate an increased number of labyrinth seal grooves. In addition, the labyrinth seal 200 may include any desirable shape of grooves formed into the impeller 158, the diffuser 160A, 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 seal 200 is provided, the labyrinth seal 200 may include corresponding threaded grooves formed in both the impeller 158 and the diffuser 160A.
The disclosed labyrinth seal 200 reduces the possibility of the impeller 158 coming into direct contact with the diffuser 160A as a result of an upthrust condition. This may increase the stability of operation and the efficiency of the pump stage 156 since no impacts occur between the impeller 158 and the diffuser 160A. In addition, the labyrinth seal 200 may extend the overall lifespan of the pump 120, since the washer 196 does not have to endure the wear it would if the labyrinth seal 200 was not present. Further, the labyrinth seal 200 may be formed into an already existing portion of the impeller 158 and/or the diffuser 160A, making it relatively easy to manufacture.
It may be desirable to maintain the impeller 158 in a slight downthrust condition relative to both the diffuser 160A above the impeller as well as the diffuser 160B below the impeller. Even though the pump 120 generally includes the seal section 130 (shown in
In
The labyrinth seal 200B at the bottom may be formed between similar components of the impeller 158 and/or the diffuser 160B as the above labyrinth seal 200A. For example, the labyrinth seal 200B may be formed into a downwardly extending outer edge 210 of the impeller 158, adjacent a corresponding upwardly extending inner edge 212 of the diffuser 160B. In other embodiments, however, the labyrinth seal 200B may be formed into an inner edge of the impeller 158 adjacent a corresponding outer edge of the diffuser 160B.
The labyrinth seal 200B may separate a fluid passage of the pump 120 from a cavity 214 formed between the impeller 158 and the diffuser 160B. Thus, the labyrinth seal 200B provides a tortuous path between the fluid passage and the cavity 214. As the net forces on the impeller 158 reach a downthrust condition, pushing the impeller 158 toward the diffuser 160B (as shown by arrow 216), the labyrinth seal 200B seals the cavity 214 off from the fluid passage. Thus, pressurized fluid that previously entered the cavity 214 cannot flow out of the cavity through the labyrinth seal 200B. The fluid trapped in the cavity 214 presses upward against the impeller 158, balancing the forces on the impeller 158 so that the impeller 158 does not come into direct contact with the diffuser 160B. In this manner, the labyrinth seal 200B seals the impeller passage from the cavity 214 to maintain the impeller 158 in a stable, floating condition relative to the diffuser 160B.
When two labyrinth seals 200A and 200B are utilized, as in
A more detailed view of an embodiment of the pump 120 with two labyrinth seals 200A and 200B on a single impeller 158 is shown in
It should be noted that different arrangements or combinations of the disclosed labyrinth seals 200 may be implemented in different embodiments of the presently disclosed pump 120. For example, in some pumps 120, the labyrinth seal 200B may formed between the impeller 158 and the diffuser 160B below the impeller 158, without the above labyrinth seal. In other embodiments, the labyrinth seal 200A may be present between the impeller 158 and the diffuser 160A above the impeller 158, without the below labyrinth seal. In still further embodiments, both labyrinth seals 200A and 200B may be present, as illustrated in
As illustrated in
Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the following claims.
Filing Document | Filing Date | Country | Kind |
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PCT/US2014/047975 | 7/24/2014 | WO | 00 |