Patent Grant
11131179
Embodiments of the invention described herein pertain to the field of electric submersible pumps. More particularly, but not by way of limitation, one or more embodiments of the invention enable an electric submersible pump gas separator.
Fluid, such as gas, oil or water, is often located in underground formations. When pressure within the well is not enough to force fluid out of the well, the fluid must be pumped to the surface so that it can be collected, separated, refined, distributed and/or sold. Centrifugal pumps are typically used in electric submersible pump (ESP) applications for lifting well fluid to the surface. Centrifugal pumps impart energy to a fluid by accelerating the fluid through a rotating impeller paired with a stationary diffuser, together referred to as a “stage.” In multistage centrifugal pumps, multiple stages of impeller and diffuser pairs may be used to further increase the pressure lift.
Currently available submersible pump systems are not appropriate for pumping fluids with a high gas to liquid ratio, also termed a high gas volume fraction (GVF). One problem that arises is that gas bubbles become entrained in the well fluid before entering the pump stages. If there is a sufficiently high GVF, typically around 10% to 15%, the pump may experience a decrease in efficiency and decrease in capacity or head (slipping). Additionally, gas may accumulate on the suction side of the impeller due to a pressure differential, resulting in gas bubbles blocking off the passage of fluid through the impeller. When this occurs, the pump is said to be “gas locked,” which may cause delays to operation and damage to the pump components.
In gassy wells, ESPs sometimes include a gas separator interposed in the string upstream of the centrifugal pump. The gas separator attempts to remove gas from multi-phase fluid before the fluid enters the pump. Conventional vortex gas separators separate lighter components, like gas, from heavier liquids using a vortex generator that rotates with the shaft in a separation chamber. The vortex rotates the fluid, and the resulting rotational momentum encourages separation of higher density fluid and lower density fluid. Higher density fluid then continues to the pump whereas it is intended that lower density fluid vent to the casing annulus surrounding the ESP assembly.
A problem with conventional gas separators is that the conventional designs fail to remove a sufficient amount of trapped gas from the multi-phase fluid, which results in losses to efficiency and an increased likelihood of gas locking. In conventional gas separators, an auger is typically used to impart axial momentum to multi-phase fluid entering the gas separator. Augers are used because they are not as susceptible to gas locking. Unfortunately, the augers do not impart enough axial momentum to the gas particles to launch a sufficient percentage of the gas into the casing annulus. As a result, the gas does not vent, and instead becomes undesirably trapped in the fluid traveling into the pump. This causes gas locking, slipping and a decrease in pump capacity.
As is apparent from the above, currently available gas separators employed in ESPs do not remove enough gas from multi-phase fluid in high GVF applications. Therefore, there is a need for an improved electric submersible pump gas separator.
One or more embodiments of the invention enable an electric submersible pump gas separator.
An electric submersible pump gas separator is described. An illustrative embodiment of an electric submersible pump (ESP) gas separator includes a propeller upstream of a fluid entrance to a crossover, the propeller including a plurality of blades, each blade of the plurality of blades including washout twist, the crossover including a production pathway and a vent pathway, and wherein gas rich fluid of multi-phase fluid travelling through the gas separator flows through the propeller and into the vent pathway, and gas poor fluid of the multi-phase fluid flows around the propeller and through the production pathway. In some embodiments, the propeller imparts axial momentum to the gas rich fluid exiting one of a vortex generator or rotary. In certain embodiments, the ESP gas separator is secured between a centrifugal pump and an induction motor, the production pathway extends to the centrifugal pump, and the vent pathway is configured to extend to a casing annulus. In some embodiments, the propeller further including a hub and a shroud, wherein the hub is keyed to a shaft of the ESP gas separator, and wherein each blade of the plurality of blades spans between the hub and the shroud. In certain embodiments, the shroud is axially aligned with a skirt of the crossover, and the gas rich fluid flows between the hub and the shroud. In some embodiments, the washout twist includes pitch that increases in coarseness from the hub to the shroud of the propeller. In certain embodiments, each blade includes an inner edge that curves concavely along an outer diameter of the hub and an outer edge that curves convexly along an inner diameter of the shroud.
An illustrative embodiment of an electrical submersible pump (ESP) gas separator includes an intake section serving as an intake for fluid from a casing annulus into an ESP assembly, a separation chamber enclosed by a supportive housing and fluidly coupled to the intake section, the separation chamber including a rotatable shaft extending centrally and longitudinally through the separation chamber, a vortex generator rotatably coupled to the rotatable shaft, a propeller within the separation chamber that receives fluid from the vortex generator, the propeller rotatably coupled to the rotatable shaft downstream of the vortex generator, the propeller including at least one blade extending between a hub and a shroud of the propeller, wherein a pitch of each of the at least one blade increases in coarseness from the hub towards the shroud, and a fluid channel extending outward of the shroud inside the housing, and a crossover downstream of the propeller, the crossover including a vent passage fluidly coupled to an inside of the shroud and the casing annulus, and a production passage fluidly coupled to the fluid channel and a production pump of the ESP assembly. In some embodiments, each of the at least one blades includes an inner edge that curves concavely along an outer diameter of the hub, and an outer edge that curves convexly along an inner diameter of the shroud. In certain embodiments, each of the at least one blade twists such that at a leading edge of the at least one blade, the inner edge is in front of the outer edge, and at a trailing edge of the at least one blade the outer edge is in front of the inner edge. In some embodiments, each of the at least one blade includes washout twist. In certain embodiments, an angle of incidence of each of the at least one blade, measured from a longitudinal axis, about doubles from the hub to the shroud. In some embodiments, a leading edge of each of the at least one blade is below a trailing edge of the at least one blade. In certain embodiments, an upper face of each of the at least one blade includes a convex portion and a concave portion. In some embodiments, the propeller includes four blades circumferentially spaced around the hub and the four blades curve helically around the hub. In certain embodiments, the propeller imparts axial momentum to fluid flowing through an inside of the propeller between the shroud and the hub.
An illustrative embodiment of an electric submersible pump (ESP) assembly includes a gas separator between a centrifugal pump and an induction motor, the gas separator serving as an intake for fluid into the centrifugal pump and including a propeller in a separation chamber, the propeller including a plurality of blades, each blade having a pitch that increases in coarseness from a hub towards a shroud of the propeller. In some embodiments, the ESP assembly further includes a channel surrounding the shroud, the channel fluidly coupled to a centrifugal pump. In certain embodiments, a portion of the fluid that flows between the hub and the shroud of the propeller is coupled to a vent port of a crossover and the channel surrounding the shroud is fluidly coupled to the centrifugal pump. In some embodiments, the fluid includes gas and liquid, and wherein the portion of the fluid that flows between the hub and the shroud includes gas rich fluid and the channel includes gas poor fluid. In certain embodiments, the gas separator includes a vortex generator upstream of the propeller. In some embodiments, the gas separator includes a rotor upstream of the propeller. In certain embodiments, the ESP assembly is configured for placement in a downhole well and the fluid includes oil and gas. In some embodiments, each blade of the plurality of blades includes washout twist. In certain embodiments, each blade of the plurality of blades is concave at the hub and convex at the shroud.
In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.
Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. The drawings may not be to scale. It should be understood, however, that the embodiments described herein and shown in the drawings are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.
An electric submersible pump (ESP) gas separator is described. In the following exemplary description, numerous specific details are set forth in order to provide a more thorough understanding of embodiments of the invention. It will be apparent, however, to an artisan of ordinary skill that the present invention may be practiced without incorporating all aspects of the specific details described herein. In other instances, specific features, quantities, or measurements well known to those of ordinary skill in the art have not been described in detail so as not to obscure the invention. Readers should note that although examples of the invention are set forth herein, the claims, and the full scope of any equivalents, are what define the metes and bounds of the invention.
As used in this specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a “blade” includes one or more blades.
“Coupled” refers to either a direct connection or an indirect connection (e.g., at least one intervening connection) between one or more objects or components. The phrase “directly attached” means a direct connection between objects or components.
As used herein the terms “axial”, “axially”, “longitudinal” and “longitudinally” refer interchangeably to the direction extending along the length of the shaft of an ESP assembly component such as an ESP intake, multi-stage centrifugal pump, seal section, gas separator or charge pump.
“Downstream” refers to the longitudinal direction substantially with the principal flow of lifted fluid when the pump assembly is in operation. By way of example but not limitation, in a vertical downhole ESP assembly, the downstream direction may be through the well in a direction towards the wellhead. The “top” of an element refers to the downstream-most side of the element, without regard to whether the ESP assembly is horizontal, vertical, angled or extends through a bend.
“Upstream” refers to the longitudinal direction substantially opposite the principal flow of lifted fluid when the pump assembly is in operation. By way of example but not limitation, in a vertical downhole ESP assembly, the upstream direction may be through the well in a direction opposite the wellhead. The “bottom” of an element refers to the upstream-most side of the element, without regard to whether the ESP assembly is horizontal, vertical, angled or extends through a bend.
As used herein, with respect to a blade angle, “course” means angled towards horizontal, where horizontal is 90° from longitudinal. “Fine” means angled towards a longitudinal direction.
As used herein, “washout” refers to the twist of a propeller blade such that thrust remains constant across the span of the blade.
With respect to multi-phase fluid flowing through a gas separator, the gas separator of illustrative embodiments may divide the multi-phase fluid into two portions, a first portion having higher density, gas poor fluid and a second portion having lower density, gas rich fluid. As used in this specification and the appended claims, “gas poor fluid” means fluid that has a lower gas volume fraction (GVF) than the “gas rich fluid,” where both the gas poor fluid and the gas rich fluid are produced from the multi-phase fluid entering the gas separator of illustrative embodiments.
For ease of description, illustrative embodiments described herein are primarily in terms of a downhole ESP assembly employing a vortex type gas separator. However, illustrative embodiments may equally be applied to rotary type gas separators and/or any pump lifting multi-phase fluid using rotational momentum where it is desirable to separate gas from liquid.
Illustrative embodiments may reduce GVF in a multi-phase fluid before the fluid enters an ESP centrifugal pump. Illustrative embodiments may increase axial momentum of gas rich fluid in a separation chamber, provide improved ventilation of gas rich fluid into the casing annulus and may reduce the volume of gas entering the production pump. Illustrative embodiments may increase axial momentum of lighter density, gas rich fluid using a propeller that imparts constant thrust across the span of the propeller blades. They propeller of illustrative embodiments may minimize radial momentum of gas rich fluid after the gas rich fluid has been separated from gas poor fluid, thereby decreasing the likelihood of re-entrapment of gas. During operation, the propeller of illustrative embodiments may be aligned to increase axial momentum of the gas rich fluid while having little or no effect on the momentum of the gas poor fluid. The propeller of illustrative embodiments may improve fluid dynamics within the separation chamber by placing the propeller inside the separation chamber rather than inside the crossover.
An illustrative embodiment of a gas separator includes a propeller inside a separation chamber of a gas separator, downstream of a vortex generator or a rotor. The propeller may be smaller diametrically than the inner diameter of the separation chamber housing, and arranged centrally around the shaft of the separation chamber. The propeller of illustrative embodiments may be axially aligned with slower, gas rich fluid, which tends to concentrate inward near the shaft, and may impart axial momentum to such gas rich fluid traveling through the separation chamber towards the crossover vents. On the other hand, higher density, gas poor fluid, which tends to concentrate outward near the housing of the separation chamber, may flow through a production channel passing around the outer diameter of the propeller before continuing towards a centrifugal pump. Separation of gas and liquid in multi-phase production fluids may thus be improved.
Illustrative embodiments may include an artificial lift assembly, such as an ESP assembly, which may be located downhole below the surface of the ground.
Multi-phase well fluid may enter intake ports 120 and travel downstream through separation chamber 210. Auger 235 may be keyed to gas separator shaft 260 to rotate with shaft 260, and may impart axial momentum to multi-phase well fluid travelling through separation chamber 210. Auger 235 may be a conveyer auger (screw auger) that includes a rotating helical flighting. In some embodiments, auger 235 may be replaced with an impeller as a fluid moving element in separation chamber 210. In separation chamber 210, gas and liquid of the multi-phase fluid may be separated or at least partially separated. In vortex type gas separators 150 as shown in
From separation chamber 210, the multi-phase fluid may proceed to passages of crossover 220 where lower-density, gas rich fluid may be vented into casing annulus 205 through vent passage 250 and vent ports 215, whereas higher-density, gas poor fluid may continue through production passage 245 and production passage openings 255 to pump 130. Fluid continuing through production passage openings 255 to pump 130 may have a lower GVF than fluid entering intake ports 120.
The inventors have observed that when multiphase fluid exits a rotary or vortex generator 240, faster moving fluid is propelled outwards towards housing 225, whereas slower moving fluid remains closer to shaft 260. The inventors have also observed that the slower moving fluid, concentrated around shaft 260, contains a higher percentage of gas than liquid. Gas, such as natural gas, may have a lower density than liquid, such as oil, in a multi-phase fluid. Vortex generator 240 therefore may impart less momentum to the lower-density gas than to the heavier liquid. Additionally, axial momentum imparted on the well fluid by auger 235 may be more readily lost by the gas than the liquid, which may further decrease the likelihood of efficient gas ventilation.
A gas separator of illustrative embodiments may include an enclosed aircraft-style propeller within separation chamber 210, which propeller may receive lighter, gas rich fluid 405 from vortex generator 240 and/or a rotor and beneficially propel the gas rich fluid towards crossover 220.
Turning to
Propeller 300 may be aligned with crossover skirt 355 and/or may be commensurate or about commensurate in diameter with crossover skirt 355. As shown in
Referring to
Turning to
Returning to
Axial momentum of gas rich fluid 405 may increase due to the thrust imparted by propeller 300, which propeller 300 may increase the efficiency of gas removal of gas separator 150. On the other hand, gas poor fluid 400 may experience little or no change in momentum as a result of propeller 300. In some embodiments, propeller 300 may be located directly upstream of skirt 355 of crossover 220. In certain embodiments, propeller 300 may be located proximate vortex generator 240 or a rotor. In some embodiments, the diameter of propeller 300 may be similar to the diameter of skirt 355. The diameter of propeller 300 may be smaller than the inner diameter of housing 225 and/or liner 230 to provide space for channel 320.
The size and/or location of propeller 300 may be determined by fluid dynamics and/or shape of crossover 220, separation chamber 210, and/or other components of gas separator 150. In some embodiments two or more propellers 300 may be included in succession in separation chamber 210. In one example, elongating separation chamber 210 may increase the overall efficiency of gas separator 150 and/or may provide more time for gas poor fluid 400 and gas rich fluid 405 to separate prior to reaching crossover 220. Additional propellers 300 may be included in such elongated separation chamber 210 to provide gas rich fluid 405 sufficient axial momentum to proceed longitudinally through separation chamber 210 and pass through crossover 220 for ventilation into casing annulus 205.
In ESP assemblies where multiple gas separators 150 are used in tandem, propeller 300 may be used in one, some or all gas separators 150. In some embodiments, propeller 300 may have an open propeller design omitting shroud 305 but maintaining blades 310 of outwardly decreasing pitch and/or having washout twist.
Crossover 220 may be located downstream from separation chamber 210 and/or propeller 300.
Illustrative embodiments may allow more efficient removal of unwanted gas from production fluid which may reduce the likelihood of gas locking and/or gas-induced damaged to an ESP assembly. Illustrative embodiments may provide gas rich fluid 405 with improved axial momentum while preventing and/or reducing centrifugal forces that might otherwise increase the likelihood of re-entrapment of the gas. A method of illustrative embodiments may include employing propeller 300 inside gas separator 150 of ESP assembly 100. Propeller 300 may be placed inside separation chamber 210 and may be keyed or otherwise rotatably coupled to shaft 260. Propeller 300 may impart axial momentum of constant thrust across the span of blade 310 to gas rich fluid 405 exiting vortex generator 240 or rotor. Rather than passing through propeller 300, gas poor fluid 400 may pass around the outer diameter of propeller 300 through channel 320 and then into production passage 245 fluidly coupled to centrifugal pump 130. The additional momentum provided by propeller 300 may allow gas rich fluid 405 to be propelled through crossover 220 and exit vent ports 215, rather than being entrained in the production fluid, thereby reducing the GVF of fluid entering centrifugal pump 130.
An electric submersible pump gas separator has been described. Further modifications and alternative embodiments of various aspects of the invention may be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the scope and range of equivalents as described in the following claims. In addition, it is to be understood that features described herein independently may, in certain embodiments, be combined.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/022242 | 3/13/2018 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2018/170002 | 9/20/2018 | WO | A |
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| 4411598 | Okada | Oct 1983 | A |
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| Entry |
|---|
| Patent Cooperation Treaty, International Search Report and Written Opinion, PCT Appln. No. PCT/US2018/022242, dated Jun. 27, 2018. |
| Number | Date | Country | |
|---|---|---|---|
| 20190162063 A1 | May 2019 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62472683 | Mar 2017 | US |
