Objective In view of the complicated and unclear reasons for the annular pressure of X gas well on a certain platform in the South China Sea, a diagnosis of annular pressure and performance evaluation of plugging system was carried out.

Method The depressurization-pressure recovery curve and gas components analysis were used to diagnosis the annular pressure and identify the leakage point location, and the multi-factor coupled with annular pressure diagnosis model was used to quantitatively characterize the parameters of leakage point. Based on the results of the annular pressure diagnosis, the chemical plugging system suitable for gas wells was optimized through the evaluation experiments of viscosity, curing time, compressive strength, cementation strength and plugging performance.

Result The A annulus of X gas well was thermodynamic trapped annulus pressure, and the B annulus was sustained annular pressure. The average permeability of the B annulus cement ring was about 33×10⁻³ μm², and there existed a significant channel. If other well barriers have a leakage aperture greater than 10 mm, the well integrity risk level is medium risk. In order to solve the problem of channeling in a cement ring, a WS-1 resin plugging system with good injection performance, high compressive strength and bonding strength was selected, and the plugging pressure difference was greater than 15 MPa/m, which had good plugging ability.

Conclusion The research findings can provide a scientific basis for addressing annular pressure issues in offshore gas wells, while also offering valuable references for gas production regulation and wellbore integrity management.