Mechanical safety analysis of the gas lift completion string used for a high-pressure sandwich layer

This study examines the mechanical safety of a gas lift completion string in a certain oilfield, Algeria 438B block, having complex geological characteristics (a high salt and high-pressure sandwich). When an annulus is not supported within fluid column after unloading using conventional single-tube gas lift completion with positive lift oil production, inner pressure is so low that the pressure differential between the annulus and external casing is very large, which may damage the casing. Hence, a dual tube completion annulus filled with fluid that can resist pressure was used to overcome this problem, in the adjacent blocks using a gas lift production string with positive and reverse lift oil. However, this technology is complex and characterized by poor system reliability, large construction costs and maintenance difficulty. Considering the three aspects of a casing string, the squeeze strength, tensile strength and internal pressure strength, a gas lift completion string with dual concentric tubes and positive lift was preferably selected under conditions that have been verified as safe for production and a shut-in state. It was shown that this gas lift completion string design is feasible.