Patent Application
20170241424
This disclosure relates in general to electrical submersible well pumps and in particular to a centrifugal pump having impeller and diffuser stages, each of the impellers having apertures formed in and spaced around the circumference of a bottom shroud of the impeller.
Electrical submersible well pumps (“ESP”) are commonly used to produce well fluid from hydrocarbon producing wells. A conventional ESP has a pump operatively coupled to an electrical motor for driving the pump. A pressure equalizer or seal section is normally located between the motor and the pump. One common type of pump is a centrifugal pump.
A centrifugal well pump has a large number of stages, each stage having a rotating impeller and a non rotating diffuser. The impeller has a tubular hub through which the pump shaft extends. Impeller vanes extend outward from a central intake area. Top and bottom shrouds are mounted to upper and lower edges of the vanes to define impeller passages. The impeller has a downward extending cylindrical skirt that engages in a sliding fit with a skirt guide on an upper side of the diffuser immediately below. As the shaft rotates the impellers, the well fluid discharged upward creates a down thrust on each impeller, the down thrust being absorbed by a thrust washer between the bottom shroud and the diffuser immediately below.
Some wells produce considerable quantities of abrasive particles such as sand. The abrasive particles cause wear on various surfaces of the impellers and diffusers. One place of wear occurs on the skirt, creating an annular clearance between the skirt seal area and the mating surface on the next lower diffuser. The increasing annular clearance increases leakage and reduces the differential pressure across the skirt seal area. With a lower pressure differential, the pressure acting upward on the bottom shroud reduces, increasing the down thrust of the impeller. The increased down thrust can lead to production loss.
A submersible well pump assembly includes a pump and a motor operatively coupled to the pump for driving the pump. The pump has a large number of stages, each stage having a rotatable impeller and a nonrotating diffuser. Each impeller has a plurality of vanes extending from a central inlet area of the impeller to a periphery of the impeller. A top shroud overlies and joins to upper edges of the vanes. A bottom shroud abuts and joins lower edges of the vanes. A plurality of apertures are formed in the bottom shroud outside of the central inlet area.
A down thrust washer is between a lower side of the bottom shroud and the diffuser directly below. The apertures are located outward from the down thrust washer. The apertures may be radially farther from the axis than the top shroud circumference.
Each of the apertures has a circumferential width. A circumference distance between each of the apertures is greater than the circumferential width.
The apertures may comprise notches formed in a circumference of the bottom shroud, the notches being circumferentially spaced apart from each other. Notches define a serrated edge at the circumference of the bottom shroud. Spaces in the circumference between each of the notches have circumferential lengths at least equal to a circumferential dimension of each of the notches.
In the embodiment shown, each of the notches has a curved outward facing base. Each of the notches may have a circumferential dimension greater than a radial depth.
The diffuser has an annular diffuser inlet and a plurality of diffuser passages extending inward and upward from the diffuser inlet. The diffuser inlet has an annular outer wall portion located radially outward from the circumference of the bottom shroud. A radial clearance between the circumference of the bottom shroud and the outer wall portion oscillates between a smaller dimension and a larger dimension as the notches rotate past the outer wall portion.
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.
Referring to
Referring to
Each diffuser 27 has a plurality of diffuser passages 31 that extend upward and outward from a diffuser passage inlet 31a. The terms “upper”, “upward”, “lower”, “downward” and the like are used only for convenience as pump 15 may operate horizontally as well as vertically. An annular, diffuser central inlet 33 joins all of the diffuser passage inlets 31a. In this example, diffuser central inlet 33 has a cylindrical outer wall portion 33a that joins the lower end of a curved outer wall portion 33b of larger inner diameter. The junction of cylindrical outer wall portion 33a with curved outer wall portion 33b creates a corner. Each diffuser 27 has a counterbore or cylindrical balance ring guide 37 on its lower side. Each diffuser 27 has a counterbore or cylindrical skirt guide 39 on its upper side.
Each stage of pump 15 has an impeller 41 that is secured to shaft 23, typically by a key and a slot, for rotation therewith. Each impeller 41 has a plurality of passages 43 that extend outward as well as curve away from the direction of rotation. If a mixed flow type, as shown, each impeller passage 43 also extends in an upward and outward direction. Impeller 41 has vanes 45 that define sides of each impeller passage 43. A top or downstream shroud 47 overlies and joins upper edges of all of the vanes 45. A bottom or upstream shroud 49 joins lower edges of all of the vanes 45. Top and bottom shrouds 47, 49 define upper and lower sides of each impeller passage 43.
Bottom shroud 49 has a skirt 51 with a cylindrical outer diameter that slides in rotational and sealing engagement with the skirt guide 39 of the next lower diffuser 27. Impeller 41 has an annular central impeller inlet 53 that joins all of impeller passages 43. A down thrust washer 55 locates between bottom shroud 49 and the next lower diffuser 27 for transferring down thrust from each impeller 41 to the next lower diffuser 27.
The top shroud 47 of each impeller 41 has a balance ring 57 on an upper side. Balance ring 57 has an outer diameter that slides in rotational and sealing engagement with the diffuser balance ring guide 37 of the next upper diffuser 27. Each impeller 41 has a hub 59 with a cylindrical bore that slides over shaft 23 and rotates with shaft 23. Hub 59 has an outer diameter that slides in rotational engagement with a diffuser bore 61 in the next upper diffuser 27. Spacer tubes 62 may mount between hubs 59 to transfer down thrust. Top shroud 47 may have balance holes 63, each extending down from the upper side of top shroud 47 to one of the impeller passages 43. Some of the well fluid discharge from impeller passages 43 leaks through the clearance between balance ring 57 and balance ring guide 37 to the upper side of top shroud 47. Balance holes 63 recirculate some of this well fluid through balance holes 63 back into impeller passages 43, reducing down thrust imposed on down thrust washer 55.
In a well laden with a high content of sand particles, wear can occur at the interface between impeller skirt 51 and skirt guide 39. The wear increases the clearance between impeller skirt 51 and skirt guide 39, causing leakage through the clearance to increase. The differential pressure at the seal between impeller skirt 51 and skirt guide 39 will drop, and the down thrust on down thrust washer 55 will increase. The result is a loss in production of the pump.
In this disclosure, apertures are formed at the outer periphery of bottom shroud 49. The apertures may be grooves, scallops, recess or notches 65 formed in the circumferential outer edge 67 of bottom shroud 49. Alternately, the apertures could be circular holes (not shown) formed outward from impeller inlet 53 and near but radially inward from outer edge 67. As shown in
Referring again to
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 only a few embodiments of the invention have been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. 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.
This application claims priority to provisional application Ser. No. 62/298,654, filed Feb. 23, 2016.
| Number | Date | Country | |
|---|---|---|---|
| 62298654 | Feb 2016 | US |
