Dynamic Simulation of Gas-Lock Instability in an Electrical Submersible Pump Induced by Annulus Valve Closure

This study presents a rigorous investigation into the adverse effects of impaired annulus gas venting on the performance of an Electrical Submersible Pump (ESP). The innovation of this work lies in the dynamic simulation of complex gas-lock system behavior and the detailed quantification of its impact on production rates. A dynamic multiphase flow model was developed and validated against field data from an incident involving the inadvertent closure of the annulus valve. The valve closure triggered a severe gas-lock condition, evidenced by a surge in the pump intake gas flow rate from 0.2 to 0.4 MMscf/d. This led to a significant reduction in liquid flow rate up to 300 STB/d, accompanied by severe oscillations, and an overall production decline of up to 23%. Consequently, amperage fluctuated between 40-58A, Pump Intake Pressure (PIP) oscillated with an amplitude of 30 psi, and the fluid temperature deviated from its stable state of 88°C, indicating impaired motor cooling. The findings demonstrate that a gas lock can lead to operational instability, underscoring the critical importance of proper annulus venting in ESP design and the necessity of stringent operational procedures to prevent its occurrence, thereby mitigating the risk of premature equipment failure and significant production loss.