Patent Application
20200300265
The present disclosure generally relates to pumps and in particular, to a pump diffuser configured to optimally transfer fluid from one impeller to another impeller during the operation of a downhole centrifugal pump system.
Submersible pumps are generally used to provide “artificial lift” or artificial means that increase upward fluid flow from downhole sources such as production wells. In most instances, submersible pumps include a motor portion that drives a shaft coupled to impellers which are in turn rotationally coupled to diffusers. The impellers and diffusers are alternatingly situated around the shaft in a manner that causes fluid to flow from one impeller into a diffuser, and from the diffuser into another impeller as the shaft rotates. This process of fluid transfer from impeller to diffuser, and from diffuser to an adjacently upper impeller, repeats itself until the fluid travels from the downhole source to an upper destination.
Impellers are designed to accelerate fluid flow upwardly. Diffusers are built to direct fluid flow to an adjacently upper impeller. Specifically, diffusers are designed to have vanes that direct the fluid flow and build fluid pressure when transferring fluid to the adjacently upper impeller. The vanes of a diffuser include a lower pressure surface that receives fluid from an adjacently lower impeller and a higher pressure surface that directs the fluid to the adjacently upper impeller. The low pressure surface usually poses the problem of creating swirling in the fluid being pumped, which in turn reduces the ability of the adjacently upper impeller to optimally receive and accelerate the fluid upwardly.
Additionally, fluid pressure often builds up at the boundary of space, sometimes called a “dead zone,” between the diffuser and the adjacently upper impeller. This fluid pressure, which can be considered as potential energy, is generally desirable in centrifugal pumps since an increase in this pressure generally improves the overall efficiency of downhole centrifugal pump systems. However, existing structural limitations of diffuser vane edges at the dead zone restrict the amount of this fluid pressure buildup within the dead zone.
It would be desirable to address these issues.
According to one aspect of the subject matter described in this disclosure, a stationary diffuser that is operable to interact with an adjacently lower impeller rotationally coupled to the stationary diffuser and operable to reduce fluid flow velocity from the adjacently lower impeller and build fluid pressure in a dead zone between the stationary diffuser and an adjacently upper impeller rotationally coupled to the stationary diffuser is presented. As used herein, the dead zone defines an open rotational area between the stationary diffuser and the adjacently upper impeller. In one implementation, the stationary diffuser comprises a first side for receiving fluid from the adjacently lower impeller and a second side for transferring the fluid upwardly to the adjacently upper impeller rotationally coupled to the diffuser at the second side. The stationary diffuser further includes a central axis cavity extending through the stationary diffuser from the first side to the second side, the central axis cavity having an inner circumferential wall configured to allow a rotational shaft to pass through the stationary diffuser. The rotational shaft is operable to impart rotation to the first and second impellers; the central axis cavity further comprises an outer circumferential surface. The stationary diffuser also includes an axis rim at the second side of the stationary diffuser at the top of the inner circumferential wall. The axis rim in one embodiment circumscribes the central axis cavity at the second side. Moreover, the stationary diffuser includes a skirt circumscribing the central axis cavity and defining a fluid passageway which directs the fluid from the first side to the second side between the outer circumferential surface of the central axis cavity and the skirt. The skirt further has a skirt rim around the axis rim such that the skirt rim is raised above the axis rim and is circumferentially displaced around the axis rim. The stationary diffuser also includes a plurality of vanes which directs fluid flow from the first side to the second side of the stationary diffuser. Each vane of the plurality of vanes of the stationary diffuser comprises a first edge at the first side and a second edge at the second side. The first edge at the first side and the second edge at the second side are connected via a curved fluid passageway. Each curved fluid passageway defines portions of the fluid passageway which directs the fluid from the first side to the second side and reduces a velocity of the fluid. The curved fluid passageway is bounded by the outer circumferential surface of the central axis cavity and the skirt. The second edge also includes a bulge between a proximal edge on the outer circumferential surface and a distal edge on the skirt. The bulge extends upwardly toward the adjacently upper impeller and thereby reducing the dead zone relative to if the second edge extended linearly from the proximal edge on the outer circumferential surface to the distal edge on the skirt.
These and other implementations may each optionally include one or more of the following features. In one implementation, an unprotuberated dead zone is defined as a dead zone that would exist if the second edge extended linearly from the proximal edge on the outer circumferential surface to the distal edge on the skirt. With this definition, the bulge extending upwardly toward the second impeller is of a height sufficient to effectively reduce the dead zone relative to the unprotuberated dead zone by at least 1%. In other embodiments, the bulge extending upwardly toward the second impeller is of a height sufficient to effectively reduce the dead zone relative to the unprotuberated dead zone by at least 5%. In some embodiments, the bulge extending upwardly toward the second impeller is of a height sufficient to effectively reduce the dead zone relative to the unprotuberated dead zone by at least 10%.
The stationary diffuser further converts kinetic energy imparted upon the fluid by the first impeller into potential energy useable by the second impeller to facilitate optimal upward flow of the fluid in the downhole centrifugal pump. Additionally, the inner circumferential wall associated with the central axis cavity is further configured to rotationally couple the first impeller to the stationary diffuser at the first side. Further, the bulge occupying a portion of the dead zone creates a fluid pressure buildup in the dead zone to facilitate optimal transfer of fluid from the diffuser to the second impeller. Moreover, the bulge occupying a portion of the dead zone is adaptable to facilitate a variable fluid pressure buildup within the dead zone based on one or more of: a distance between a proximal point of the proximal edge on the outer circumferential surface, and a distal point of the distal edge on the skirt, a height of the bulge, an angle associated with the bulge, and a planar length associated with the bulge. In some implementations, the height of the bulge is a function of the distance between the proximal point and the distal point, the height of the bulge being substantially perpendicular to the distance between the proximal point and the distal point. Additionally, the height of the bulge is a percentage of the distance between the proximal point and the distal point, the percentage comprising one of 10%, 20%, 30%, and 40%. It is further noted that the height of the bulge depends on a targeted fluid pressure in the dead zone that improves an efficiency of the downhole centrifugal pump. In some instances, the height of the bulge depends on a parameter of reduction that factors at least a targeted fluid pressure desired in the dead zone into computing the height of the bulge. Additionally, the angle associated with the bulge is greater than zero degrees. Further, the bulge edges/bulge surfaces may be filleted or chamfered to further reduce eddy currents in the dead zone, which further facilitates laminar flow of fluid from the diffuser to the second impeller.
The disclosed embodiments provide a diffuser configuration that improves the overall efficiency of downhole centrifugal pumps during diffuser-impeller fluid transfers. Specifically, the present disclosure describes a diffuser configuration that reduces fluid velocity and builds head pressure as fluid travels from a stationary diffuser to an adjacently upper impeller. Moreover, the diffuser described herein facilitates laminar fluid flow from the diffuser to an adjacently upper impeller to allow the adjacently upper impeller to more efficiently receive and upwardly accelerate the fluid. Additionally, the present disclosure describes a diffuser configuration specially purposed to reduce space associated with the dead zone and increase fluid pressure (also referred to as head pressure elsewhere herein) at the dead zone between the diffuser and an adjacently upper impeller. This fluid pressure can be leveraged by the adjacently upper impeller in further accelerating the fluid upwards, thereby improving the overall efficiency of the downhole centrifugal pump.
The disclosure is illustrated by way of example, and not by way of limitation in the figures of the accompanying drawings in which like reference numerals are used to refer to similar elements. It is emphasized that various features may not be drawn to scale and the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.
At a high level, downhole centrifugal pump systems generally include at least a downhole structure housing a pump coupled to a motor. In some implementations, the downhole structure may include a plurality of pumps coupled to a plurality of motors. Depending on the use scenario, the downhole structure can be submerged in one or more fluid sources (e.g., oil or gas reservoir, aquifer, etc.) as needed. The plurality of pumps in the downhole structure can upwardly pump the fluid from the fluid source to receiving containers (e.g., tanks, vessels, etc.) at a higher elevation relative to the fluid source.
Turning to the downhole centrifugal pump system 100 of
The pump 110 may include a series of impellers and diffusers that are alternatingly coupled to each other. For example, and as shown in
Turning back to
The protector device 130 may be configured to ensure electrical and mechanical integrity of the motor 140. In some implementations, the protector device 130 may act as an oil reservoir that facilitates the expansion capacity of the motor 140. The protector device 130 may include a secure seal that keeps the motor 140 running smoothly. Additionally, the protector device 130 may further include one or more chambers adapted to prevent wellbore fluid contamination of the motor 140 by creating a low-pressure boundary between the well fluid and the clean oil used to lubricate the motor 140. Moreover, the protector device 130 may facilitate: torque transfer from the motor shaft to the gas handling device 120 and/or pump intake shaft; reinforcement of the pump shaft; and adaptation of the downhole centrifugal pump system 100 to specific implementation considerations.
The motor 140 may be configured to drive a shaft coupled to the pump 110 of the downhole centrifugal pump system 100. In some embodiments, the motor 140 may be an electric submersible motor configured for variable-speed operations, high temperature tolerance, and deep well pumping. The motor 140 may include one or more circuitry that allows 3-phase operations, 2-pole inductions, etc. In some implementations, the motor 140 may be configured to have sizes such as 375, 420, 456, and 540 and temperature ratings of up to 450 degrees Fahrenheit. The motor 140 may be fabricated using corrosion resistant materials such as stainless steel.
The monitoring device 150 may include software and/or firmware and other hardware that enables monitoring of the downhole centrifugal pump system 100. In some embodiments, the monitoring device 150 may include one or more sensors (e.g., temperature sensors, pressure sensors, etc.) that capture a plurality of information during the operation of the downhole centrifugal pump system 100. This information may be transmitted via a wired and/or wireless channel to user interfaces that facilitate viewing of monitoring data associated with various operations of the downhole centrifugal pump system 100 and/or conditions in which the downhole centrifugal pump system 100 operates.
Additionally, the impeller 214 has a plurality of vanes 213 configured to accelerate fluid upwards as the drive shaft causes the impeller 214 to spin. The diffusers 212a and 212b also include a plurality of stationary vanes 210 that direct fluid to an adjacently upper impeller. An example stationary vane 210 of the diffuser 212b is shown in exploded view 210 and in the cross-sectional views 220 of
During the normal operation of the downhole centrifugal pump system 100, each impeller within the diffuser-impeller-diffuser configuration 200 transfers kinetic energy from the shaft driven by the motor 140 into fluid being pumped by accelerating the fluid upwards/outwards from a center of rotation. Specifically, each impeller 214 of the diffuser-impeller-diffuser configuration 200 may be configured to have an open inlet called an eye which receives incoming fluid which is subsequently accelerated by the vanes 213 of the impeller 214 upwards to a matching diffuser 212. The velocity of the impeller 214 imparts kinetic energy upon the fluid which is later converted to pressure or potential energy by the matching diffuser 212. That is to say that the matching diffuser 212 converts kinetic energy imparted upon the fluid by the impeller 214 (i.e., as the impeller 214 rotates) into potential energy or head pressure that is useable by another impeller rotationally coupled to the diffuser 214 at the dead zone (also called dead zone space elsewhere herein) in order to facilitate optimal upward flow of the fluid in the downhole centrifugal pump system 100. It is noted that each impeller within the diffuser-impeller-diffuser configuration 200 may be fabricated using bronze, stainless steel, cast iron, polycarbonate, and/or other materials.
Each diffuser 212 in the diffuser-impeller-diffuser configuration 200 may be configured to have stationary vanes 210 that surround a matching impeller (i.e., an adjacently lower impeller 214). More specifically, the stationary vanes 210 of the diffuser 212 may receive fluid from an adjacently lower impeller 214 at a low pressure side of the diffuser 212 and transfer the received fluid to a high pressure side of the diffuser 212 via the stationary vanes 214. For example, the diffuser 212a may have an adjacently lower impeller 214 (see either
During the transmission of fluid from the adjacently lower impeller 214 to the matching diffuser 212, the fluid passes through a curved fluid passageway 222 (see
In some implementations, the diffuser-impeller-diffuser configuration 200 may be a multi-stage configuration where the fluid pressure is progressively increased as fluid travels from one stage to another. The pressure buildup at any stage, or a combination of stages associated with the diffuser-impeller-diffuser configuration 200, is desirable as this pressure can be leveraged in improving the overall efficiency of the downhole centrifugal pump system 100.
For example,
Also shown in
Moreover, the diffuser 212 includes a plurality of stationary vanes 210 that direct a high velocity fluid from the matching impeller 214 at the lower pressure side 410a to another impeller 214 at the higher pressure side 410b. For example, the plurality of stationary vanes 210 of diffuser 212 include stationary vanes 210a, 210b, 210c, 210d, and so forth, that direct the high velocity fluid from a matching impeller 214 at the lower pressure side 410a to another impeller 214 at the higher pressure side 410b. The plurality of stationary vanes 210 of the diffuser 212 are stationary relative to the impellers 214 of the downhole centrifugal pump system 100.
Turning to
The second edge 450b includes a bulge which protrudes into the dead zone space 242a. More specifically, the bulge extends/protrudes upwardly toward the adjacently upper impeller 214 thereby reducing the dead zone relative to if the second edge 450b extended linearly from the outer circumferential surface to the skirt. The extent to which the bulge of the second edge 450b protrudes into the dead zone space 242a is a design parameter that can be adapted to meet the needs of varying pumping scenarios. For instance, the bulge of the second edge 450b of each vane may protrude into the dead zone to create an accumulation of protrusions occupying a percentage of the dead zone space as determined by a virtual rotation of the fluid in the dead zone as described herein. In some embodiments, the effective percentage of the dead zone space 242a occupied by the accumulated protrusions/bulges could be at least one of 10%, 20%, 30%, or 40% of the dead zone space 242a depending on the application, and in accordance with design needs and the principles described in the present application. For example, in a configuration associated with performance graph 300 of
In other embodiments, the reduction of the dead zone is further clarified based on an unprotuberated dead zone. An unprotuberated dead zone is defined as a dead zone that would exist if the second edge extended linearly from the outer circumferential surface to the skirt as discussed elsewhere herein. However, because the second edge 450b has a bulge that extends upwardly toward the adjacently upper impeller 214, the height of the bulge associated with the second edge 450b is sufficient to effectively reduce the dead zone relative to the unprotuberated dead zone by a designated amount. Example unprotuberated dead zone is prior art dead zone space 242a while the reduced dead zone space 242b may be associated with the diffuser 212 of
Structurally, the bulge of the second edge 450b may be connected to the outer circumferential surface 480 and the skirt 472. As seen in
The protuberated structure/bulge of the second edge 450b is highly desirable over existing diffuser configurations lacking this feature. As shown via the experimental results in the plots of
Additionally, within the preferred operating range 360 of the performance graph 300, the efficiency plot 340 which is the efficiency plot corresponding to a downhole centrifugal pump system having the protuberated edge (or bulge) shown in
h=α×d, such that h≤d, and a is a parameter of reduction.
In some implementations, α may be a percentage having a value of at least one of 10%, 20%, 30% and 40%, in accordance with design needs and the design principles described in the present specification. In other embodiments, a may be a percentage less than or equal to 99% by which the distance d can be reduced to obtain h. In some instances, α may be a parameter that factors at least the targeted fluid pressure desired in the dead zone space into the computation of the height h. It is noted that the height h is selected based on design considerations that improve the overall efficiency of the downhole centrifugal pump system 100. For example, a test may be conducted such that given the distance d, various values of α may be selected and a head pressure is observed and recorded for each corresponding h computed for each α for a given operating range 360 of the downhole centrifugal pump system 100. The targeted head pressure that comparatively improves the efficiency of the downhole centrifugal pump system 100 may be selected from the observed and recorded head pressures associated with each α. Other factors other than those stated herein may also be considered when computing the height h. Additionally, the height h shown in the illustrated embodiment of
Further, the bulge 510 of the protuberated second edge 450b may be structured to facilitate a more laminar flow of fluid and also build head pressure in the dead zone. In one embodiment, the bulge 510 may be chamfered or filleted to ease the bulge surface 520 in a manner that optimally allows fluid to flow into the dead zone space 242b and to the adjacently upper impeller 214. In some instances, the bulge surface 520 may be based on the angle 2θ as shown. For example, if the planar length l is substantially parallel to the distance d between the proximal point 513 and the distal point 512, and moving in the clockwise direction, θ may be an angle between the height h and the planar length l. Thus, the illustrated example indicates that θ may be given by θ<90°.
If θ is 0° (i.e., 0 degrees), then the planar edge 530 of the bulge surface 520 would be a pointed surface since the bulge surface 520 would sharply decline towards the planar points 521 and 522. However, if θ is greater than 0° but less than or equal to 90° (i.e., 90 degrees), then the planar edge 530 eases gently towards the planar points 521 and 522 to form a filleted surface or a chamfered surface. That is to say that the bulge surface 520 may be filleted or chamfered based on the angle θ. Other techniques other than those described herein may also be employed in designing the bulge 510 to accomplish desired operational requirements of the downhole centrifugal pump system 100. It is noted, that the planar length l associated with the bulge and the angle θ may be selected in combination with h to enhance the efficiency of the downhole centrifugal pump system 100. For example, although the bulge surface 520 is shown as being filleted or chamfered along the length of the vane, it may be desired that the bulge surface 520 also be chamfered or filleted across its width (i.e., into and out of the plane of the illustration of the bulge surface 520). Thus, the foregoing indicates that in addition to transferring fluid in a laminar fashion to an adjacently upper impeller 214, the bulge 510 of the diffuser 212 may also be adaptable to facilitate a variable fluid pressure buildup within the dead zone based on one or more of the angle θ, the planar length l, and in some cases, the height h discussed above.
Reference in the specification to “one implementation” or “an implementation” means that a particular feature, structure, or characteristic described in connection with the implementation is included in at least one implementation of the disclosure. The appearances of the phrase “in one implementation,” “in some implementations,” “in one embodiment,” or “in some embodiments” in various places in the specification are not necessarily all referring to the same implementation.
Finally, the foregoing description of the implementations of the present disclosure has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the present disclosure be limited not by this detailed description, but rather by the claims of this application. As will be understood by those familiar with the art, the present disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Likewise, the particular naming and division. Accordingly, the disclosure of the present disclosure is intended to be illustrative, but not limiting, of the scope of the present disclosure, which is set forth in the following claims.
