Thermo–Fluid–Solid Coupled Prediction of Trapped Annular Pressure in Multi-Annulus Wells

Annular trapped pressure is an important factor affecting wellbore integrity during the production of high-temperature and high-pressure oil and gas wells. In wells with multilayer casing structures, one or more enclosed annuli may form because of cement top, packer setting, wellbore structural constraints and wellhead sealing. When the temperature and pressure fields in the wellbore change during production, the annular fluid undergoes thermal expansion, compressive deformation and possible phase-state changes, causing trapped pressure to evolve continuously with time. Conventional annular pressure prediction methods are usually based on a single annulus, quasi-static assumptions or simplified fluid properties, and therefore cannot fully describe deformation transfer among annuli, thermal expansion of tubular strings and nonlinear gas–liquid compression. To address this problem, this study analyses the formation mechanism of annular trapped pressure from the perspective of thermal–fluid–solid coupling and develops a dynamic pressure evolution model that accounts for transient temperature variation, annular fluid thermal expansion and compression, elastic deformation of tubular strings and multi-annulus coupling. The analysis indicates that annular trapped pressure is essentially a pressure response produced by fluid thermal expansion under structural confinement. A multi-annulus system is not a set of independent annuli, but a pressure–deformation–volume feedback system coupled through shared casing walls. The proposed solution framework and pressure evolution analysis provide a theoretical basis for annular pressure prediction, casing safety assessment and wellbore-integrity management in high-temperature and high-pressure gas wells.