Patent Application
20110171047
1. Field of the Invention
The present invention relates to an apparatus and method for connecting a pump shaft to an adjacent shaft. More specifically, the invention relates to connecting the pump shaft of an electrical submersible pump to a motor shaft or seal section shaft such that upthrust forces from the pump are transferred to a thrust bearing in the seal section.
2. Description of the Related Art
Electrical submersible pumps (“ESP”) are used for pumping fluids from a wellbore. A typical ESP configuration includes an electric motor, a seal section, and a pump assembly. The pump assembly typically has a plurality of impellers connected to a shaft. A shaft from the motor rotates a shaft in the seal section, which in turn rotates the pump shaft and thus the pump impellers.
Two axial forces typically act on a pump impeller during operation—downthrust force and upthrust force. Downthrust force is defined as a force on the impellers acting against the direction of flow, thus urging impellers downward, toward the seal section (the upstream direction). Downthrust forces occur, for example, when head pressure exerts force on the impellers, thus urging the impellers in a direction opposite the direction of flow.
Upthrust force is defined as force acting on the impellers in the same direction as the direction of flow, thus urging impellers away from the seal section and toward the discharge tubing (the downstream direction). Upthrust forces occur, for example, when the discharge fluid from an impeller exerts axial force against the subsequent impeller.
Under normal operating conditions, downthrust force exceeds upthrust force, thus urging impellers in an upstream direction relative to flow (“downthrust condition”). In some circumstances, upthrust force may exceed downthrust force. This “upthrust condition” may occur during startup, before the pump develops head pressure, or during a maximum flow condition when there is little or no head pressure. Pump assemblies may not have adequate thrust bearings to support the pump shaft during upthrust conditions.
The seal section frequently has an upthrust bearing, which is a downward facing thrust bearing adapted to engage an upward facing thrust runner to support the seal section shaft in the upward axial direction. Many couplings between seal section shafts and pump assembly shafts, however, do not transfer upward axial force from the pump assembly to the seal section shaft. Indeed, the couplings must allow for axial insertion of at least one of the shafts when connecting the pump assembly or intake section to the seal section. It is desirable to have a device that allows for easy axial insertion of a shaft into a coupling that can be locked to prevent axial movement.
A coupling is used to join a pump shaft to a seal section shaft for an electrical submersible pump (“ESP”). The seal section has a thrust bearing and a thrust runner connected to the seal section shaft, for transferring upthrust force from the seal section shaft to the thrust bearing. The coupling is used to transfer upthrust axial force from the pump shaft to the seal section shaft, and thus to the thrust bearing.
In one embodiment, the coupling is assembled by sliding the sleeve over the end of the coupling, then sliding a spring onto the coupling, and then installing a spring retainer to hold the spring in place. The coupling is then bolted to the seal section shaft. The pump intake and the pump assembly are connected to form a single unit. The pump intake and the seal section are brought together. As the intake and seal section are moved toward each other, the pump shaft moves axially into the coupling. Support plates, which protrude from the interior of the coupling into a recess in the pump shaft, are not yet installed, so the pump shaft is able to slide into the coupling. Bolts are used to join the housings of the seal section and the intake.
An operator can then reach through an access port, either by hand or with a tool, to retract the sleeve and thus expose a plurality of slots used for retaining plates. With the slots exposed, the operator can insert the retaining plates through the slots. The plates engage the edges of the slots and also engage a groove on the pump shaft. The operator then releases the sleeve to allow the spring to urge the sleeve toward a lip on the end of the coupling. The lip halts axial movement of the sleeve. With the sleeve now covering the slots, the plates are bounded in all directions—by the slots on four sides, by the groove, and by the sleeve. The plates thus lock the coupling to the pump shaft and prevent axial movement of the coupling relative to the pump shaft. The pump shaft has splines that engage splines on the interior of the coupling, and thus rotational movement is transferred from the coupling to the shaft. Similarly, a fastener prevents axial movement of the coupling relative to the seal section shaft, and splines on the coupling transfer rotation from splines on the seal section shaft to the coupling. The seal section shaft and the pump shaft thus move as a single unit in both the axial and rotational directions. Any upthrust axial forces acting on the pump shaft are transferred, to the plates, the coupling, the fastener, the seal section shaft, the thrust runner, the thrust bearing, and finally to the seal section housing.
To decouple the seal section shaft from the pump shaft, the operator retracts the sleeve and withdraws the plates. The seal section housing can then be removed from intake, and the pump shaft will slide out of the coupling in the axial direction.
So that the manner in which the above-recited features, aspects and advantages of the invention, as well as others that will become apparent, are attained and can be understood in detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the drawings that foau a part of this specification. It is to be noted, however, that the appended drawings illustrate only preferred embodiments of the invention and are, therefore, not to be considered limiting of the invention's scope, for the invention may admit to other equally effective embodiments.
Referring to
For the sake of clarity in describing an embodiment of an ESP with a removable locking coupling, some references refer to “upper” and “lower,” as though ESP 100 is in a substantially vertical position. These positional references are for description only, and should not be construed to limit the invention to an application wherein electrical submersible pump 100 is in a vertical orientation. Indeed, ESP 100 may be in a horizontal orientation or any other orientation. Furthermore, the positional references are not intended to limit the claimed invention to the arrangement of the exemplary embodiment.
Seal section 106 has a housing 118, a seal section shaft 120, and device for equalizing pressure (not shown) of the lubricant in motor 108 with the hydrostatic fluid in well 102. Motor 108 has a shaft (not shown) that connects to seal section shaft 120. Seal section shaft 120 is a rotatable shaft that passes through seal section 106 to pump shaft 122. Pump assembly 104 includes impellers (not shown) that are rotated by pump shaft 122, which is a rotatable shaft, and diffusers (not shown) that are stationarily located within pump housing 118.
Referring to
One or more coupling access ports 116 are located on the circumference of housing 124. Coupling access ports 116 are apertures for accessing members located within pump intake 112. Indeed, access ports 116 may be large enough for a person's hand or a tool such as pliers (not shown) or a spanner wrench (not shown) to reach through housing 124 for manipulating members located within housing 124. During normal operation of ESP 100, wellbore fluids may pass through coupling access ports 116 into the bore of pump intake 112. Because wellbore fluids normally pass into pump intake 112, there may be no need to cover coupling access ports 116, although a cover (not shown) may be used. In some embodiments, apertures 114 and coupling access ports 116 are one in the same, wherein wellbore fluids are drawn through coupling access port 116 and additional apertures 114 are not required.
Still referring to
Thrust runner 132, which can be conventional, may be located on the outer diameter of seal section shaft 120. Thrust runner 132 may be an annular ring or plate affixed to seal section shaft 120 by a variety of common techniques. Thrust bearing 134 may be fixedly connected to seal section housing 118 above thrust runner 132. Thrust bearing 134 is conventional and may be used to provide axial support to seal section shaft 120, via thrust runner 132, while, seal section shaft 120 is rotating relative to seal section housing 118. Thus, thrust bearing 134 prevents upward axial movement of seal section shaft 120.
Pump shaft 122 is connected to impellers (not shown) inside pump assembly 104. Splines 142 are located on the seal section end of pump shaft 122, thus establishing a splined end, and splines 142 are used to transfer torque to pump shaft 122. Groove 144 is a recess. In one embodiment, groove 144 may be an annular recess located on the outer diameter of pump shaft 122. In a preferred embodiment, the sidewalls of groove 144 are generally perpendicular to the axis of pump shaft 122 and the bottom of groove 144 is generally parallel to the axis pump shaft 122. Alternatively, groove 144 may be a plurality of individual notches, recesses, or bores (not shown) space apart around the outer diameter of pump shaft 122.
Coupling 150 is a cylinder for transferring torque from seal section shaft 120 to pump shaft 122. The inner diameter of coupling 150 includes two sections, lower bore 152 and upper bore 154, each separated by shoulder 156. The inner diameter of lower bore 152 is generally the same as the outer diameter of seal section shaft 120. Lower splines 158 are internal splines located on the inner diameter of lower bore 152 and are adapted to engage splines 128 of seal section shaft 120. Similarly, the inner diameter of upper bore 154 is generally the same as the outer diameter of pump shaft 122. Upper splines 160 are internal splines located on the inner diameter of upper bore 154, and are adapted to engage splines 142 of pump shaft 122.
Shoulder 156 protrudes inwardly from the bore of coupling 150. In a preferred embodiment, shoulder 156 is a rib having at least one flat surface facing downward, toward lower bore 152. Fastener 162, which may be a threaded fastener, such as a bolt, can pass through the cylindrical opening formed by shoulder 156. Other fastener configurations can be used to detachably or permanently connect coupling 150 to one of seal section shaft 120 or pump shaft 122. For example, horizontal threaded fasteners (not shown) may pass through the sidewall of coupling 150 into the sidewall of seal section shaft 120, wherein the fasteners are perpendicular to the axis of shaft 120. In alternative embodiments, coupling 150 may be welded (not shown) to shaft 120, or may be machined as an integral member (not shown) of shaft 120.
Slots 164 are a plurality of apertures through the sidewall of coupling 150. In a preferred embodiment, slots 164 are a pair generally rectangular openings passing from the exterior of coupling 150 to the upper bore 154 region of the interior of coupling 150. Regardless of the number of slots 164, slots 164 may be equilaterally spaced apart from one another. Keys 166 are rigid elements that are sized to pass through slots 164 to engage groove 144 of pump shaft 122 and thus function as an axial locking member. Keys 166 may be, for example, steel plates having a rectangular profile. The length of keys 166 may be roughly equal to the sum of the thickness of the sidewall of coupling 150 at slot 164 plus the depth of groove 144. Thus, keys 166 fit flush in slot 164 when inserted through slot 164 to engage groove 144. Keys 166 and slots 164 may have alternative shapes. For example, keys 166 may have a round profile (not shown), and slots 164 may have a similar round profile. Keys 166 are spaced apart from each other around the circumference of coupling 150.
Other embodiments may have an axial locking member that includes, for example, pins, dowels, or plates, any of which may be pass through slots 164 to engage a feature on pump shaft 122. For example, in one alternative embodiment, pump shaft 122 may have a horizontal bore (not shown) that is perpendicular to the axis of pump shaft 122. A pin (not shown) may pass through round slots (not shown) in the sidewall of coupling 150 to engage coupling 150 and pump shaft 122.
Retainer sleeve 172 is a cylinder adapted to slidingly engage the outer diameter of coupling 150. Sleeve 172 has an upper or retaining position that encloses the outer ends of keys 166 to retain them in engagement with groove 144. Sleeve 172 has a lower or released position that is spaced below slots 164 to insert or withdraw keys 166. The axial length of sleeve 172 is preferably less than the axial length of coupling 150. Lip 174 protrudes from the outer diameter of one end of coupling 150 to stop sleeve 172 from moving axially past the end of coupling 172.
Spring 176 is concentrically located on the outer diameter of coupling 150. Spring 176 urges sleeve 172 to the retaining position in engagement with lip 174. Spring retainer 178 supports one end of spring 176 and thus prevents spring 176 from extending past the end of coupling 150. Spring retainer 178 may include snap-ring 180 located in a groove on the outer diameter of coupling 150. Spring retainer 178 may also include support surface 182 for engaging spring 176 and transferring force from spring 176 to snap-ring 180. Support surface 182 may be, for example, an annular ring such as a washer. In alternative embodiments, spring retainer 178 may use different types of members for supporting spring 176 such as, for example, pins (not shown), threads (not shown), or a flange (not shown). In one embodiment (not shown), spring retainer 178 is located at the sleeve end of coupling 150 to prevent sleeve 172 from moving past the end of coupling 150, and lip 174 is located on spring end of coupling 150 to retain spring 176.
In operation of one embodiment, coupling 150 is assembled by sliding sleeve 172 over the end of coupling 150, then sliding spring 176 onto coupling 150, and then installing spring retainer 178. Coupling 150 is then bolted to seal section shaft 120 with fastener 162. Intake 112 and pump assembly 104 are then connected to each other. As intake 112 and seal section 106 are moved toward each other, pump shaft 122 moves axially into coupling 150. Keys 166 are not yet installed, so pump shaft 122 is able to slide into coupling 150. Bolts are used to join the housings of seal section 106 and intake 112.
An operator can then reach through access port 116, either by hand or with a tool, to retract sleeve 172 to the released position and thus expose slots 164. With slots 164 exposed, the operator can insert keys 166 through slots 164. The keys engage the edges of slots 164 and also engage groove 144. The operator then releases sleeve 172, thus allowing spring 176 to urge sleeve 172 toward lip 174. Lip 174 halts axial movement of sleeve 172. With sleeve 172 now covering slots 164, keys 166 are bounded in all directions—by slots 164 on four sides, by groove 144, and by sleeve 172. Keys 166 thus lock coupling 150 to pump shaft 122 and prevents axial movement of coupling 150 relative to pump shaft 122. Pump shaft splines 142 engage coupling splines 160, and thus rotational movement is transferred from coupling 150 to shaft 122. Similarly, fastener 162 prevents axial movement of coupling 150 relative to seal section shaft 120, and splines 158 transfer rotation from seal section shaft 120 to coupling 150. Seal section shaft 120 and pump shaft 122, thus, move as a single unit in both the axial and rotational directions. Upthrust axial forces acting on pump shaft 122 are transferred to keys 166, coupling 150, fastener 162, seal section shaft 120, thrust runner 132, thrust bearing 134, and finally to seal section housing 118. As wellbore fluid is drawn in through coupling access port 116, the wellbore fluid may flow past and contact sleeve 172. The retaining position of sleeve 172 may be in the downstream direction, and thus the force exerted on sleeve 172 by the fluid can urge sleeve 172 toward the retaining position.
To decouple the seal section shaft 120 from the pump shaft 122, the operator retracts sleeve 172 and withdraws keys 166. Seal section housing 118 can then be removed from intake 112, and pump shaft 122 will slide out of coupling 150 in the axial direction.
Referring to
Shoulder 210 protrudes from the bore, and may be used to engage seal section shaft 202. The downward facing surface of shoulder 210 is supported by seal section shaft 202. Bolt 212 passes through shoulder 210 to engage a threaded receptacle 206 on seal section shaft 202.
Slots 214 are apertures passing through the sidewall of threaded coupling 200. Slots 214 may be rectangular, square, round, or any other shape. Threads 216 are located on the outer circumference of threaded coupling 200. Threads 216 may be located in the vicinity of slots 214, or may be above or below slots 214. Collar stop 218 is a shoulder that may protrude beyond an outer diameter of threaded coupling 200.
In this embodiment, threaded collar 222 may be a retainer sleeve. Threaded collar 222 is an annular ring having threads 224 located on its inner diameter. Threads 224 threadingly engage threads 216 of collar shaft. When collar 222 is threadingly engaged with coupling 200, collar 222 can cover all or a portion of slots 214 on coupling 200. In some embodiments, collar 222 can be tightened on coupling 200 until an end of collar 222 engages collar stop 218, thus preventing further rotation of collar 222.
As shown in
One or more set-screw bores 228 may pass through the sidewall of collar 222, perpendicularly to the axis of collar 222. Each set-screw bore 228 may be used to engage set screw 230, set screw 230 being a threaded bolt or screw. In some embodiments, set screw 230 is an “allen-head” screw. In some embodiments, set screw 230 does not have a shoulder at its head and thus may be sunk flush with the outer diameter of collar 222. After collar 222 is threadingly engaged to coupling 200, set screws 230 may threadingly engage threaded bore 228 and an end of set screw 230 may engage an outer diameter surface of coupling 200, thereby preventing collar 222 from rotating relative to collar 200.
Pump shaft 204 may have groove 234 on its outer diameter. Groove 234 may be a single groove around the circumference of pump shaft 204, or may be a plurality of slots or notches spaced apart around the circumference of pump shaft 204. Keys 236 may pass through slots 214 of coupling 200, and engage groove 234 of pump shaft 204.
In operation, coupling 200 is bolted to seal section shaft 202 using bolt 212 to engage shoulder 210 and threaded receptacle 206. Thus, splines 205 of coupling 200 engage splines 206 of seal section shaft. Preferably, collar 222 is placed on coupling 200 before coupling 200 is connected to pump shaft 204. As seal section housing (not shown) is connected to intake housing 240, coupling 200 engages pump shaft 204 (and thus splines 207 of coupling 200 engage splines 208 of pump shaft 204).
Collar 222 is then rotated, if necessary, to expose slots 214. Keys 236 are inserted into slots 214 until keys 236 engage groove 234 on pump shaft 204. Collar 222 is then tightened on threads 216. In embodiments having collar stop 218, collar 222 may be tightened against collar stop 218. A tool (not shown) may be used to engage sockets 226 to tighten collar 222 to a predetermined torque. Collar 222 now covers slots 214 and thus prevents keys 236 from disengaging groove 234 or slots 214. Set screws 230 may be tightened into bores 228 to prevent collar 222 from rotating relative to coupling 200. In one embodiment, oval shaped access ports 242 are openings in the sidewall of intake 240. Access ports 242 allow sufficient clearance to access coupling 200 for inserting keys 236 and to rotate collar 222 with a tool (not shown).
While the invention has been shown or described in only some 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 without departing from the scope of the invention.
