Compensating Mechanical Seal For Use With A Downhole Electrical Submersible Pump

Abstract

An electrical submersible pumping system having a pump, a motor, a shaft connecting the pump and motor, and a mechanical seal assembly on the shaft. The mechanical seal assembly includes a sleeve circumscribing the shaft that is axially movable with respect to the shaft. The shaft is retained within a guide mount, an inner circumference of the guide mount extends radially outward to define a shoulder. An annular seat is disposed on the shoulder. One end of a resilient retention assembly couples on the outer surface of the sleeve with its other end compressively urged against the seat. A resilient member is compressively mounted on one end to the sleeve and on another end to the shaft at a location past the end of the sleeve distal from the seat.

1 . An electrical submersible pumping assembly, comprising:
 a housing member having a passage;   a shaft extending through the passage;   an annular member that fits over and rotates with the shaft and that is slidable along the shaft;   a seat ring statically mounted to the housing member in the passage and encircling the shaft;   a bellows having a first end fixed and sealed to the exterior of the sleeve and a runner on a second end that is urged by the bellows into sliding engagement with the seat ring; and   an annular resilient assembly having a first end circumscribing and fixed to the shaft and a second end that urges the second end of the bellows toward the seat ring.   
     
     
         2 . The electrical submersible pumping assembly of  claim 1 , further comprising an elastomeric seal between the annular member and the shaft and wherein the annular member comprises an elongate sleeve that extends past the first and second ends of the bellows. 
     
     
         3 . The electrical submersible pumping assembly of  claim 1 , further comprising registrable axial grooves respectively in the shaft and in the annular member and a key selectively disposable in both the grooves so that the annular member rotates with shaft rotation. 
     
     
         4 . The electrical submersible pumping assembly of  claim 1 , wherein the annular resilient assembly comprises a coil spring and the second end of the annular resilient assembly engages the first end of the bellows. 
     
     
         5 . The electrical submersible pumping assembly of  claim 1 , wherein thermal growth of the shaft causes the shaft to move along an axis of the shaft relative to the annular member, which remains substantially stationary relative to the seat ring. 
     
     
         6 . The electrical submersible pumping assembly of  claim 1 , wherein the first end of the resilient assembly comprises a collar retained by a snap ring set in the shaft. 
     
     
         7 . An electrical submersible pump assembly disposable within a wellbore comprising:
 a motor;   a pump coupled to the motor;   a shaft coupled to the pump and the motor and extending through a passage formed in a guide mount;   a seat ring encircling the shaft and statically mounted in the guide mount; and   a mechanical seal assembly comprising:
 a runner coaxial to and having a side compressed against a side of the seat ring opposite the guide mount, 
 a sleeve circumscribing the shaft and axially moveable thereon, 
 an elastomeric seal member between the sleeve and shaft, 
 a bellows circumscribing and coupled to the sleeve and having an end in compressive engagement with a side of the runner opposite the seat ring, and 
 a resilient member compressively mounted on one end to a location on the sleeve and coupled on another end to a location on the shaft past the end of the sleeve distal from the seat, so that when the shaft axially expands compressive engagement of the annular seat is maintained. 
   
     
     
         8 . The electrical submersible pump assembly of  claim 7 , wherein the bellows comprises a retaining ring that is secured to the sleeve at a point between ends of the sleeve. 
     
     
         9 . The electrical submersible pump assembly of  claim 7 , wherein the sleeve is circumscribed by the seat ring. 
     
     
         10 . The electrical submersible pump assembly of  claim 7 , wherein the end of the resilient member coupled to the shaft is set on a radial flange circumscribing the shaft and abutable with a lower surface of the sleeve, wherein the radius of the shaft increases at a location along the axis of the shaft to define a shoulder, so that when the shaft elongates, the shaft elongates through the sleeve to move the radial flange out of contact with the lower surface of the sleeve and abuts the shoulder against the upper surface of the sleeve. 
     
     
         11 . The electrical submersible pump assembly of  claim 7 , further comprising a slot on the sleeve inner circumference, a cavity formed in the shaft, and a key that is biased radially outward from the shaft and disposable in the cavity and the slot to rotationally couple the shaft and the sleeve. 
     
     
         12 . The electrical submersible pump assembly of  claim 7 , further comprising an o-ring seal between an outer circumference of the seat and an inner circumference of the guide mount. 
     
     
         13 . The electrical submersible pump assembly of  claim 7 , further comprising a groove provided along a radius of the inner surface of the sleeve and an elastomeric member disposed in the groove. 
     
     
         14 . The electrical submersible pump assembly of  claim 7 , further comprising production tubing having an end coupled to an end of the pump and an opposing end configured for attachment to a wellhead assembly. 
     
     
         15 . The electrical submersible pump assembly of  claim 7 , further comprising an elastomeric seal between the resilient retention member and the sleeve. 
     
     
         16 . A method of operating a centrifugal pump assembly having a housing member with a passage, a shaft driven by a motor and extending through the passage, a seat ring statically mounted in the housing member and surrounding the shaft, a bellows that rotates with the shaft and has a runner that engages the seat ring, the improvement comprising:
 mounting an annular member around the shaft for rotation with the shaft, but such that the shaft is movable along an axis of the shaft relative to the annular member;   connecting the bellows to the annular member on an end opposite the runner;   providing a force that biases the annular member toward the seat ring;   rotating the shaft, which in turn rotates the annular member and the bellows; and   allowing the shaft to grow thermally, which moves portions of the shaft axially relative to the annular member and the bellows.   
     
     
         17 . The method of  claim 16 , wherein the end of the bellows opposite the seat ring remains at a constant distance from the seat ring as the portion of the shaft grows. 
     
     
         18 . The method of  claim 16 , wherein the biasing force onto the annular member and seat ring is maintained as the shaft thermally elongates.