System Optimization of Submersible Electric Progressing Cavity Pump: Design and Field Application of PCP Specially Used for Submersible Motor

In the low production and low permeability well, electric submersible progressive cavity pump (ESPCP) has its own advantages of no rod-tubing wearing, high efficiency, less maintenance work over the beam pump unit. There has been using more than 200 wells in CNPC. However, from the statistic of field application failures, about half of the failures are stator rubber swelling of the PCP. By analyzing the failure, we designed a new PCP specially used for bottom drive system in this paper. The design speed of top drive PCP is 100 RPM, because high speed may cause serious rod tubing wearing. Without the constraint of rod, the design speed of bottom-drive PCP has no constraint either. To coordinate with the submersible permanent magnetic motor characteristics, we chose 300 RPM as the design speed. To decrease the running torque, we set up the finite element model of PCP and optimized the dimensions and references of stator and rotor. The optimized PCP is manufactured and evaluated in the test well. The results in the test well showed the optimized bottom-drive PCP has three advantages. First, the running torque decreased 45% by reducing the interference, and there was no torque surge when the system started up. Without the starting torque surge, the system can use the motor with less installed power. It would save the one-off investment of ESPCP. Second, the less torque leads to less current. It means that the PCP designed for bottom-drive has better energy saving performance compared to the top-drive PCP. It can save 9% electric consumption. Third, it prolongs the running time of ESPCP field applications. We have used ESPCP with optimized PCP in two wells of field application. The running time of the systems are both more than 700 days compared to average running time of 460 days previously and they are still running. The PCP designed for submersible motor solves the problem of PCP failures and prolong the running time with better energy saving performance. This paper will present the details of this design and experiments.