Failure Analyses of Gas Lift Valves that Caused Improper Tubing-Annular Communication in Subsea Wells

Abstract

This work presents the results of several failure analyses of gas lift valves retrieved from Petrobras subsea wells. These valves were unable to prevent the backflow from tubing to annulus, so compromising the well integrity. The purpose of these analyses was to unveil the root causes of the failure, which is essential information to prevent its recurrence. When a tubing-annulus communication is detected and a damaged gas lift valve is identified as the cause of the problem, the valve is retrieved and transported to the workshop preserving as much as possible the conditions found when it came out of the well, allowing the inspection of solid deposits, elastomers and debris. At the workshop, the valve is opened and thoroughly examined, debris and solids are collected and, if relevant, chemically analyzed to lay down the root causes of the failure. The results point to different causes for the failures: inorganic incrustations deposited in various parts of the equipment; abrasion caused by erosion and even pieces of foreign bodies, such as fabrics and wood, stuck in the valve. By associating the well operational history with the failure conditions, the causes and the chronology of events can be determined. These investigations allow a more precise diagnosis of the gas lift valve failures, that tend to reduce the risk of recurrence of the problems and guide the correction of fragilities in current designs. They also can contribute to better planning and definitions on future well completions, resulting in increased reliability for this method of artificial lift.