Research on Simulation of Abnormal Annulus Pressure Process

Annulus pressure buildup simulation constitutes the foundation for conducting integrity testing, diagnostics, and overall integrity evaluation of gas wells. However, there is a lack of a comprehensive theoretical simulation methodology for annulus pressure buildup processes in gas wells. This study establishes mathematical models for abnormal annulus pressure caused by gas migration through cement sheaths and that induced by natural gas infiltration into the annulus between tubing and casing. By simulating the abnormal pressure buildup processes in the annulus, with a typical well M009-X5 as a case study, on-site tests were conducted to analyze annulus pressures, then the A/B annulus pressure buildup processes was simulated. These efforts aimed at determining leak locations within the well string and facilitating fitting calculations for parameters such as the air column height in the tubing-casing annulus, leakage point pressure and equivalent diameter along the tubing string, as well as the air and liquid column heights, and cement sheath permeability in the technical annulus. The computational outcomes revealed that the leakage point in the tubing string of M009-X5 is situated at 4678 m, with an air column height of 3.5 m in A annulus, a leakage point pressure of 60.7 MPa, and an equivalent leakage diameter of 0.25 mm. For B annulus, the air column height was 0.9 m, the liquid column height reached 5.5 m, and the cement sheath permeability was measured at 230 md. The calculation model demonstrated a high predictive accuracy, with the theoretically simulated curves for pressure relief and recovery closely mirroring the actual measurements, achieving an average prediction precision exceeding 80%. This level of accuracy satisfies engineering requirements and effectively simulates the pressure relief and recovery processes in the annulus. The methodology developed in this research enables studies predicting the extent of gas leakage in wells, the rate of annulus pressure recovery, thereby providing robust theoretical support for gas well integrity testing, diagnostics, and overall well integrity assessment.