An Optimization Design Method for Offshore Perforated Gas Lift Parameters Based on Transient Multiphase Flow Simulation

Process parameters for perforated gas lift in offshore water-breakthrough gas wells are often selected empirically and still lack systematic optimization. This study therefore develops a parameter design and optimization approach grounded in transient multiphase flow simulation. Based on a transient flow model that couples the reservoir, wellbore, tubing–-casing annulus, and perforated gas-injection nodes, the gas-lift intervention timing was investigated. With the maximization of daily formation gas production as the optimization objective, the simulation results under different operating conditions were comprehensively evaluated. Based on the variations in daily formation gas production, wellbore liquid holdup, and flow patterns, the gas injection parameters (i.e., gas injection rate and injection depth) were optimized. Meanwhile, the tool dimensions (i.e., gas-lift valve orifice diameter and the internal through-bore diameter of the packer assembly) were also optimized. The results demonstrate that an optimal reservoir pressure range exists for perforated gas lift in water-breakthrough gas wells, providing an important basis for timing gas-lift intervention. With increasing gas-injection rate, daily formation gas production follows a pattern of initial increase, subsequent stabilization, and final decline, indicating an optimal gas-injection rate. When the injection point lies more than a certain depth below the liquid-loading location, further increasing the injection depth gives limited improvement in daily formation gas production but raises operational difficulty. Gas-injection rate and injection depth affect wellbore liquid holdup and flow patterns differently: the gas-injection rate has an optimum that balances liquid carrying and friction loss, while injection depth mainly influences liquid holdup below the injection point. Thus, the gas-injection rate should be optimized and the injection depth reasonably selected. A larger gas-lift valve orifice effectively reduces wellhead injection pressure, whereas the internal through-bore diameter of the packer assembly has little impact on gas-lift performance. A larger internal through-bore is preferable when machining conditions permit. The parameter design and optimization method for offshore perforated gas lift established in this paper has been successfully applied to an offshore gas well that was shut in due to liquid loading. This demonstrates the field feasibility of the method and provides guidance for the process design of perforated gas lift in offshore water-producing gas wells.