Unload Procedure with Control of Liquid Flow Rate Through Gas Lift Valve

Abstract

Abstract Gas lift unloading is a transient process to lift well bore fluids and remove the liquid from the annulus (between tubing and casing). The field procedure developed in this work consists of finding the maximum allowable gas lift injection pressure during unloads. Its objective is to avoid erosion of gas lift valve by liquid flow rate and increase its service life. It was observed that the maximum injection pressure was not constant during the unload process. Two pressure gauges are required, one at the tubing and one at the casing (or gas lift flow line) since the pressures must be monitored during the unloading process. The liquid flow rate during its displacement is controlled by the gas lift injection choke. The procedure was designed for offshore gas lift wells due to its high intervention costs to replace damaged valves by erosion. Damages in gas lift valves might decrease the maximum flow rate and cause production instabilities. This procedure can be equally applied to all gas lift wells that have at least two pressure gauges, one in the tubing and the other in the casing. The practice can only be applied in wells which have one single gas lift injection point. Given that it is not possible to measure the liquid flow rate through gas lift valves in field applications, the procedure was validated against transient simulations. It was possible to observe a very good match with simulation results. The Injectivity Index (II) could be used to calculate liquid flow rate through the gas lift valve. Unfortunately, the Injectivity Index is usually unavailable. Besides that, the production flow rate measurement is likewise sometimes unavailable during unloading. The procedure was developed to deal with these limitations. Other possible benefit is the optimization of unloading time by injecting the maximum liquid flow rate allowable.