Failure Mode and Sensitivity Analysis of Gas Lift Valves

Gas-lifted oil wells are susceptible to failure through malfunction of gas lift valves. This is a growing concern as offshore wells are drilled thousands of meters below the ocean floor in extreme temperature and pressure conditions and repair and monitoring become more difficult. Gas lift valves and oil well systems have been modeled but system failure modes are not well understood. In this paper a quasi-steady-state fluid-mechanical model is constructed to study failure modes and sensitivities of a gas-lifted well system including the reservoir, two-phase flow within the tubing, and gas lift valve geometry. A set of three differential algebraic equations of the system is solved to determine the system state. Gas lift valve, two-phase flow, and reservoir models are validated with well and experimental data. Sensitivity analysis is performed on the model and sensitive parameters are identified. Failure modes of the system and parameter values that lead to failure modes are identified using Monte Carlo simulation. In particular, we find that the failure mode of backflow through the gas lift valve with a leaky check valve is sensitive to small variations in several design parameters.