Prediction and Analysis of Sustained Casing Pressure Caused by Cement Sheath Leakage in Gas Storage Well

During the operation of underground natural gas storage, drastic wellbore temperature and pressure fluctuations impose complex and variable loads on cement sheaths. This impairs cement sheath sealing integrity, triggers fluid leakage along interfacial gaps and continuous annular pressure rise, severely threatening the operational safety of gas storage injection–production wells. Based on the analysis of potential gas leakage paths in injection–production wells of underground gas storage, a calculation model for annulus pressure buildup induced by cement sheath leakage of gas storage wells is established with consideration of influencing factors, including formation pressure, annulus temperature, and cement property parameters. Model verification indicates that the maximum relative error of the test well is 9.20%, the average relative error is 2.64%, the mean absolute error (MAE) is 0.08 MPa, and the average root-mean-square error (RMSE) is 0.09 MPa. Calculations for field case wells are performed to quantitatively predict the variation in annulus pressure, followed by sensitivity analysis on the annulus pressure buildup of the studied wells. Formation pressure and cement permeability act as core controlling factors, positively correlating with annular pressure. In contrast, temperature exerts a relatively minor influence on annulus pressure. Optimized cementing design and reduced cement permeability can effectively mitigate leakage-induced annular pressure. The proposed model and findings offer reliable theoretical support for annular pressure management and safe long-term operation of gas storage wells.