Development of Composite Progressing Cavity Pumps

Abstract

Abstract The newest technological advancement in the Progressing Cavity Pump (PCP) industry has been the development of composite stators and rotors. Included in this design concept is a reversing of the conventional elastomer and hard surface interface. The stator, in this design concept, is made of a hard composite material and is placed in a steel tube jacket. The rotor can be made of steel or composite material and coated with an even thickness of a soft and durable polyurethane. The urethane offers increased wear resistance and mechanical properties over conventional elastomers and the even thickness offers additional performance enhancements. Also, the elastomeric placed on the rotor offers the well-servicing advantages of the wear element being located on the end of the sucker rod string rather than on the end of the tubing string. The composite PCP becomes a low cost, highly durable PCP that incorporates the emerging even thickness elastomer technology. Introduction Until recently, the Progressing Cavity Pump (PCP) most widely used in down-hole conditions consisted of a stator made of a nitrile based elastomer that is injected and permanently bonded inside a steel tube, and a rotor, machined from steel and coated with a relatively thick layer of chrome plate. Both the stator and rotor are helical where the stator always has one more helix than the rotor. In this configuration the stator is the wear section and the rotor is the longer wearing element. In the most widely used design the elastomer in the stator has consistent thick and thin sections corresponding to the major and minor diameters of the stator bore. This variance in elastomer thickness leads to difficulties optimizing performance due to swell resulting from incompatibility with well fluids and thermal expansion resulting from elevated well bore temperatures plus heat generated by internal friction in the pump. For some time now the industry has been seeking a cost effective approach to this inherent design problem and have made some advancements in "even wall" or "even thickness" elastomer stators. The even thickness elastomer optimizes performance with respect to swell and thermal expansion plus offers additional performance enhancements with respect to operating efficiencies. Another inherent design problem is that the stator is located on the bottom end of the production tubing string and the rotor is located on the bottom end of the sucker rod string. As the stator wears or fails and pump performance deteriorates to a point the pump requires service, the rod string and rotor are pulled from the well, then the production tubing string and stator are also pulled from the well. The need to pull tubing each time the pump requires service is a major drawback in using PCP's in most applications. The newest technological advancement that addresses the problems normally associated with PCP's; elastomer incompatibility and/or wear, changing stator geometry under operating conditions, and lengthy/costly well service is currently in the early stages of development. In this new configuration, the stator is made of a hard composite material bonded to the inside of a steel tube. The composite material offers wear characteristics similar to or better than metal and makes the stator the longer lasting element. The rotor is made of steel or composite and coated with an even thickness of soft and durable polyurethane (PU). The polyurethane offers increased wear resistance and mechanical properties over conventional nitrile elastomers in the same applications. The requirement of pulling tubing each time the pump requires service is eliminated with the placement of the elastomer on the rotor.