Stabilization of Gas-Distribution Instability in Single-Point Dual Gas Lift Wells

Abstract

Summary While casing-heading instability in single gas lift wells has attracted a lot of attention, gas-distribution instability in dual gas lift wells has not. In this paper, we present a simple, nonlinear dynamic model that is shown to capture the essential dynamics of the gas-distribution instability despite the complex nature of two-phase flow. Using the model, stability maps are generated showing regions of stable and unstable settings for the production valves governing the produced flows from the two tubings. Optimal steady-state production is shown to lie well within the unstable region, corresponding to a gas distribution between the production tubings that cannot be sustained without automatic control. A simple control structure is suggested that successfully stabilizes the gas-distribution instability in simulations and, more importantly, in laboratory experiments.