Algorithm for Fault Diagnosis in the Electric Submersible PCP System, A Case Study

Shale oil had been mostly explored deep underground, ESPCP (electric submersible PCP) was more adaptive to low output, high viscosity and deep well. So far hundreds of shale wells were equipped with ESPCP. However, motors and PCP were subject to harsh downhole environment, faults like tubing choked by wax and rubber over swelling were common, how to diagnosis these two faults correctly meant a lot to the measures ensued, since tubing choked by wax called for downhole heating while rubber problem required its replacement. In this paper, an algorithm was developed to identify these two faults, relevant software was completed to make the judgement automatically, finally field applications were trialed. The algorithm was based on the change of D-value of electrical current between the real and the theoretical, as well as the liquid output, usually the D-value of output dropped if tubing was waxed seriously, while the value remained even or raised if the rubber swelled abnormally. The calculation process involved additional parameters of downhole pressure, rotating speed and water percentage, meanwhile data like well structure, oil viscosity, and pump specifications were also taken into account. The software could make the judgement with the input of at least 25 days information. According to the field trial, faults could be identified whether it was tubing or PCP that went wrong provided the operation parameters were smooth, the future electric current could be predicted and the tendency was correct in short term. Model training had been completed and its application were expanding. The software prescribed in the paper helped improve the integrity of ESPCP system by predicting its future operation status, it also served as an important reference to the next move when it came to downhole accidents.