Thermo-Mechanical Coupled Analysis of Wellbore Integrity in Perforated Underground Gas Storage Wells During Injection

Abstract

Aiming at the severe alternating loads and failure risks faced by the perforated wellbore section under the cyclic high-rate injection and production conditions of underground gas storage (UGS), this paper conducts a thermo-mechanical coupled analysis of wellbore integrity during the gas injection process. A 3D fully thermo-mechanical coupled finite element model of the perforated casing-cement sheath-formation system was established, accurately reconstructing the 3D geometric morphology of spiral perforations. Based on the verification of the model's computational accuracy, the sensitivity laws of injection temperature and pressure on the stress and deformation characteristics of the casing and cement sheath were systematically investigated. The results indicate that the injection temperature is the most critical parameter controlling the casing strength. The "cold shock" effect below 80°C causes the local equivalent stress of the P110 casing to exceed its yield limit (reaching 820.5 MPa), simultaneously increasing the risk of cracking and failure in the cement sheath. Furthermore, the elevation of injection pressure intensifies the radial expansion of the casing, pushing it toward the yield limit. Although the local tensile stress of the cement sheath decreases due to the confining pressure effect, its equivalent strain surges dramatically (up to 1.009×10-1), substantially elevating the risk of interfacial micro-annulus formation. This study reveals the damage mechanisms of the perforated wellbore section under multi-field coupling. It is recommended that on-site gas injection operations should co-optimize temperature and pressure parameters to avoid the superposition of extreme low-temperature and high-pressure conditions, providing quantitative theoretical support for the long-term safe operation of UGS and the optimization of gas injection schemes.