Progressing Cavity Pump (PCP) is a well-known artificial lift mode which is widely used for dewatering of coal bed methane (CBM) wells because it has good sand & gas handling capacity and better performance in deviated well in comparison to other rod pumps. However, compatibility of elastomer in downhole condition is always a challenging task for PCP operation. In this study, failure analysis of PCP well # A from ONGC field has been done in detail and suggest suitable remedial measures for multiple challenges.
In well # A, high torque was observed during dewatering and after that sucker rod unscrewed. During work over it was observed that rotor got stuck up in the stator due to damage of elastomer. Based on reservoir study, it was found that unexpected gas breakthrough occurred from upper coal seam. Pump was placed above the upper coal seam therefore gas directly entered at the pump intake and elastomer got damaged. Another issue was high rod-tubing contact load due to highly deviated profile of the well. One guide per rod configuration was adopted for this well which is not enough to protect rod and tubing where maximum contact load simulated in standard software. The depth of failure of sucker rod is exactly matching with the depth of the maximum rod-tubing contact load.
Based on two main challenges- high rod-tubing contact load & gas interference, different approaches have given in this study for safe pump operation keeping in view the field constraints.
For high rod-tubing contact load, conclusions are drawn in this study with respect to important parameters causing significant effect. Suitable type and accurate configuration of rod guides are also suggested in this study.
For gas interference problem, natural gas anchoring, tail pipe and use of different types of gas anchors have been compared and discussed to mitigate challenges in view of solid fines. Suitable elastomer type is also suggested depending on the well parameters.
In case of multiple and complex problems observed in the well, this study gives novel idea to increase mean time between failure (MTBF) of PCP for dewatering of CBM wells in a relatively simple and effective manner.