Assessing integrity of gas-lift valves by analyzing annular pressure-transient response
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By definition, gas-lift valves (GLVs) are designed to allow influx of the annular gas into the tubing and prevent any backflow, even when there is a pressure differential toward the annulus. However, elements such as erosion, corrosion, scale, fatigue, vibration, and temperature and pressure effects may cause the GLV to leak, thereby posing a serious safety issue. Because of the well integrity concern, suspected GLVs are often retrieved for inspection with a wireline from the side-pocket mandrel. Proactive testing is a way to minimize such costly intervention. This paper details a methodology for determining a GLV's integrity that avoids retrieving the valve and relies on examining the annular transient-pressure response. Based on the models that have been developed, we propose a robust, nonintrusive test procedure that can save both time and expense. This proposed method has been partially validated with field data from three offshore wells.
