Assessing integrity of the gas-lift valves by analyzing annular-pressure-transient response

• Model proposed for test analysis involving integrity of gas-lift valves.
• Model validated with three sets of field data.
• A robust, nonintrusive test procedure proposed for saving time and expense

Gas-lift valves (GLV) by definition are designed to allow influx of the annular gas into the tubing and prevent any backflow even when a pressure differential exists 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 with a wireline from the side-pocket mandrel for inspection. 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 developed, we propose a robust, nonintrusive test procedure saving time and expense. The proposed method is validated with field data from three offshore wells. We also present a forward model that helps design test methodology.