Shaft locking couplings for submersible pump assemblies

[0001] This application is a continuation-in-part of Ser. No. 10/160,899, filed Jun. 3, 2002, now U.S. Pat. No. 6,883,604, issuing Apr. 26, 2005, which claims the provisional filing date of Jun. 5, 2001, Ser. No. 60/296,014.

[0002] The invention relates to devices and techniques for coupling shafts and other portions of submersible pump assemblies and like components.

[0003] Conventionally, electrical submersible pump (“ESP”) assemblies have been made up of a series of interconnectable modular sections including one or more pump sections with an associated fluid intake, a motor section and a seal section. Each of these sections includes an outer housing and a central drive shaft. At present, the shafts and their connections are designed so that they can primarily transmit a compression load. The shaft of each section is interconnected with the shaft of the adjacent section by straight splines for transmitting torque only. There are normally no securing members used that would resist pulling apart of the shafts. Placement of the shafts or shaft connections under tension loads will cause the connection to separate easily.

[0004] This sort of “compression only” connection between shaft members is permissible when a standard ESP configuration is used wherein the pump section(s) are located above the seal and motor sections. In pump assemblies with pumps mounted above the motor, down thrust on the shafts typically passes downward to a thrust bearing located in the seal section between the pump or pumps and the motor. The motor also normally has a thrust bearing. The thrust bearings in the seal and motor sections support the pump sections, and the shaft members in the pump sections are not placed in tension.

[0005] When a “bottom intake” ESP configuration is used, however, the pump section(s) are located below the motor and seal section in the wellbore. An expensive thrust bearing is normally mounted to the lower end of the pump section(s) to support the ESP components. Downward force on the shaft sections in the pump(s) passes to the thrust bearing at the lower end of the pump(s).

[0006] Although it might be possible to simply pin or weld the shafts of adjacent ESP sections together to transmit tension, there is an operational problem with doing so. In practice, it is difficult to assemble and disassemble the pinned shafts since they reside within the housings. If the connection is welded, it is quite difficult to disassemble the sections after removal of the pump assembly from the wellbore.

[0007] The invention provides methods and devices for interconnection of components within an electrical submersible pump assembly and the like. This interconnection is preferably between a motor assembly and a pump section. The shaft sections are interconnected to support compression loading as well as a predetermined amount of tension loading.

[0008] A coupling sleeve has a bore and is disposed between the modular component sections for receiving therein the shaft member of an adjacent component sections. The bore of the coupling sleeve and exterior portions of the shaft members have mating torque transmitting shoulders. An axial tension transmitting shoulder is carried by the shaft member of one of the modular component sections. A latch member, carried by the shaft member of an adjacent modular section, moves into engagement with the axial tension transmitting shoulder as the modular sections are moved toward each other. The engagement of the latch member with the axial tension transmitting shoulder secures the shaft members to one another for transferring axial tension from one of the shaft members to the other.

[0009] A retainer is carried by one of the shaft members and located adjacent the latch member. The retainer has a locked position that prevents the latch member from disengaging from the axial tension transmitting shoulder once engaged.

[0010] When a pump assembly is used in a bottom intake configuration, the thrust bearing in the motor assembly above the pump sections handles down thrust imposed on the shafts. Preferably, the thrust bearing is located in the seal section between the motor and the pump or pumps. The down thrust on the shafts transfers through the latch member between the seal section and the pump or pumps.

[0019] FIG. 1 illustrates a pump assembly 11 located within a well having casing 13. Pump assembly 11 is connected to a supporting string 15, which may comprise continuous coiled tubing, sections of production tubing secured together, or a cable. In this embodiment, motor 17 is located at the upper end of pump assembly 11, rather than at the more conventional lower end. Motor 17 is an AC three-phase motor that is supplied with power from the surface via a power cable that either extends through or alongside supporting string 15.

[0020] A seal section 21 connects to the lower end of motor 17. Seal section 21 is a conventional component that reduces pressure differential between the hydrostatic pressure in casing 13 and the interior pressure of lubricant contained within motor 17. The dielectric lubricant in motor 17 is in fluid communication with dielectric lubricant in seal section 21. Although normally separate components, seal section 21 and motor 17 could be permanently joined and are considered herein to be a part of a motor assembly.

[0021] At least one pump section secures to the lower end of seal section 21. In this embodiment, two pump sections 23, 25 are shown connected in tandem, but only one pump could be used. Upper pump section 23 has a discharge 24 at its upper end for discharging well fluid into the interior of casing 13. Discharge 24 could alternately be in a lower part of seal section 21. An intake manifold 27 is located at the lower end of lower pump section 25. Intake manifold 27 extends into a packer 28 that seals the lower end of lower pump section 25 to casing 13. Well fluid from perforations (not shown) in casing 13 below packer 28 flows into intake manifold 27 and is discharged out discharge 24.

[0022] Motor 17 is connected to seal section 21 by a conventional connector 29, which typically employs bolts that extend through flanges. The connector between seal section 21 and upper pump 23 and the connector between upper pump 23 and lower pump 25 are preferably constructed the same. FIGS. 2 and 3 illustrate the connector between seal section 21 and upper pump 23. Like connector 29 (FIG. 1), this connector has an upper flange 31 containing bolt holes 33 (FIG. 2) for receiving bolts. The bolts screw into a connector base 35, shown in FIG. 1 and FIG. 3.

[0023] Motor 17, seal section 21, and pumps 23 and 25 each has a segment of a drive shaft 37, shown in FIG. 2. Drive shaft 37 is rotated by motor 17 (FIG. 1) and is concentric within a cylindrical housing 39. Each segment of drive shaft 37 has axially extending splines 41 on its ends to provide radial shoulders for transmitting torque.

[0024] A stud 43 has a threaded end 45 that secures into a mating threaded receptacle in the lower end of drive shaft 37 in seal section 21. A socket 47 slides over the protruding portion of stud 43. Socket 47 is secured to stud 43 by a shear pin 49 that extends through a hole transversely formed through them. Socket 47 has a socket interior 51 that is cylindrical. An annular ramp 53 is located within socket interior 51. Ramp 53 converges inward in an upward direction to a minimum diameter at an axial tension transmitting shoulder 55. The minimum inner diameter of ramp 53 is smaller than the inner diameter of the portions of socket interior 51 located below it. The outer diameter of shoulder 55 is preferably the same as the inner diameter of the portions of socket interior 51 below ramp 53.

[0025] A rod 57 has a threaded end 59 secured to a threaded receptacle in the lower end of stud 43. Rod 57 extends downward on the longitudinal axis of shaft 37. Rod 57 has a lower polygonal end 61 in this embodiment to enable rod 57 to be engaged by a wrench to secure its threaded end 59 to stud 43. Polygonal end 61 is optional and could be replaced with other means for rotating threaded rod 57 into threaded engagement with stud 43.

[0026] A retainer 63 is carried by rod 57. In this embodiment, retainer 63 is an annular disk with a neck 65 on its lower end. Rod 57 extends through a hole in retainer 63. A coil spring 67 encircles and secures to neck 65, which has a radially extending shoulder in the embodiment of FIGS. 2-5. Coil spring 67 has a tang on its lower end that inserts into a retention hole 69 drilled transversely through polygonal end 61. Coil spring 67 is in a natural, unsearched position in FIG. 2, with retainer 63 in a first position. In this first position, retainer 63 is located approximately in alignment with axial tension transmitting shoulder 55. When retainer 63 is in the second position of FIG. 4, coil spring 67 is stretched.

[0027] Referring to FIG. 3, a coupling sleeve 71 is shown located on the upper end of the shaft portion 37 that is in upper pump section 23. Coupling sleeve 71 has internal splines that engage splines 41 on the shaft portion 37 located within upper pump section 23. The splines of coupling sleeve 71 also engage splines 41 (FIG. 2) on the lower end of shaft 37 in seal section 21. A lower retainer screw 73 extends through the side wall of coupling sleeve 71 into engagement with an upper end of shaft 37 in upper pump 23 to stop downward movement of coupling sleeve 71 on splines 41. There is a similar upper retainer screw 73 (FIG. 4) for engaging the lower end of the shaft 37 in seal section 21.

[0028] A latch member 75 has a threaded end 77 that engages a threaded receptacle formed in the upper end of shaft 37 in upper pump 23. Latch member 75 has a plurality of fingers 79 arranged in a cylindrical array. The upper ends of fingers 79 are free and resilient so that they can deflect radially inward and outward. A catch or exterior ledge 81 is located on the upper end of each finger 79.

[0029] To connect seal section 21 (FIG. 2) to upper pump 23 (FIG. 3), the operator moves seal section 21 and upper pump 23 toward each other in straight axial movement. Fingers 79 will initially be in the undeflected position shown in FIG. 3 and retainer 63 will be in its first or lower position shown in FIG. 2. Fingers 79 enter interior 51 of socket 47 as shown in FIG. 4. The inner diameter d1 (FIG. 3) defined by finger 79 while undeflected is greater than the outer diameter of retainer 63 (FIG. 4). Continued upward movement of fingers 79 causes them to engage ramp surface 53, deflecting them radially inward as shown in FIG. 4. When in the maximum radial inward position as shown in FIG. 4, the inner diameter d2 defined by fingers 79 is less than the outer diameter of retainer 63. The ends of fingers 79 thus contact retainer 63 as shown in FIG. 4. Continued upward movement pushes retainer 63 toward stud 43, causing spring 67 to elongate. Once catches 81 reach axial tension transmitting shoulder 55, the resilience in fingers 79 causes them to spring radially outward as shown in FIG. 5.

[0030] When they spring radially outward, the inner diameter defined by finger 79 again returns to the diameter d1, which is greater than the outer diameter of retainer 63. Fingers 79 thus disengage from retainer 63. Coil spring 67 pulls retainer 63 back downward to the first position in substantial alignment with catches 81 and tension transmitting shoulder 55. While in the position shown in FIG. 5, catches 81 cannot move radially inward sufficiently to release from shoulder 55 because they will first contact retainer 63, which blocks further radial inward movement.

[0031] The straight axial movement of the modular component sections toward each other thus causes latch member 75 to automatically snap into engagement with shoulder 55 as well as automatically causes retainer 63 to move to the locked position shown in FIG. 5. The operator may then secure flange 31 (FIG. 2) to base 35 (FIG. 3) with fasteners. There is no access to latch member 75 in this embodiment once it is in the locked position shown in FIG. 5. To later release latch member 75, the operator removes the fasteners that bolt flange 31 to base 35 and pulls the modular sections apart from each other. With sufficient pull, shear pin 49 will shear, which releases socket 47, from stud 43.

[0032] The connection between shafts 37 in lower pump section 25 and upper pump section 23 preferably has a latch member 75 constructed as shown in FIGS. 2-5. In the embodiment of FIG. 1, preferably the thrust bearing for pumps 23, 25 is located in seal section 21. A downward force will exist on shafts 37 within pumps 23, 25 during operation due to the weight of shafts 37 and pressure differential. FIG. 6 schematically shows a thrust bearing 83 located in seal section 21. Thrust bearing 83 has a runner 85 that is rigidly secured to the shaft 37 in seal section 21 both for rotation and axial movement. Runner 85 may be fastened to shaft 37 in a variety of manners, such as by split rings, snap rings and keys. Runner 85 rotates slidingly against a stationary base 89 that is mounted in housing 39 of seal section 21. A bushing 91 is shown located between base 89 and shaft 37. Downward force on shaft 37 in lower pump 25 transfers through latch member 75 to shaft 37 in upper pump 23, and through latch member 75 between shaft 37 in upper pump 23 to shaft 37 in seal section 21. The downward force transfers from runner 85 to base 89, which transfers the thrust to housing 39 of seal section 21.

[0033] While a similar latch member 75 could be located at the connection of shafts 37 between seal section 21 and motor 17, in this embodiment, motor 17 has its own thrust bearing (not shown) located at its upper end. Consequently, there is no need for a latch member to transmit tension between the upper end of shaft 37 in seal section 21 and the lower end of shaft 37 in motor 17.

[0034] FIGS. 7 and 8 show an alternate embodiment for connecting coil spring 67 between retainer 63′ and polygonal end 61′ of rod 57′. In this embodiment, threads are formed on neck 65′ for screwing the upper end of coil spring 67 thereto. A groove 93 is located on the lower end of rod 57′. A lower tang 95 of coil spring 67 slides into engagement with groove 93 as illustrated in FIGS. 7 and 8 to retain the lower end of coil spring 67 on rod 57′.

[0035] The invention has significant advantages. The latch member enables tension to be transmitted from the shaft to another within an electrical submersible pump assembly. The latch member is readily connected simply by pushing the modular sections into engagement with each other. The retainer prevents the latch member from becoming disengaged with the load transmitting shoulder. The latch member enables one to employ a thrust bearing above the pump or pumps when mounted below the motor assembly.

[0036] While the invention has been shown in only two of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes. For example, the latch member could be inverted with the fingers located in the upper section pointing downward for engaging the axial tension transmitting shoulder. The latch member could be utilized with pumps mounted above the motor if transmitting tension between the shafts is desired.