Ultimate load analysis of casings in slip-working sections of underground gas storage wells

During high-intensity injection and production in underground gas storage (UGS), the biting behavior of packer slip teeth on the casing's inner wall can cause damage, leading to anchoring failure and compromising string safety. To ensure stable casing performance in the slip zone of deep UGS wells, a mathematical model for casing stress distribution is developed based on elastic-plastic mechanics. The ultimate tensile load of the casing is calculated using both the Tresca yield criterion and the von Mises strength criterion. The slip biting depth is analyzed using slip-line theory, and the residual casing strength after slip embedding is evaluated according to the API minimum wall thickness method. Additionally, the effects of pressure fluctuations, slip profile angle, and inclination angle on the casing's ultimate bearing capacity are examined. The results indicate that the Tresca criterion predicts a 15.7% lower ultimate load than the von Mises criterion, providing a safer UGS casing strength assessment. Increasing bite depth reduces residual collapse strength. The first five slip teeth bear most stress, and optimal load-bearing capacity occurs at a slip profile angle of 85° and inclination of 30°. These findings support the strength design of slips and casings, enhancing well safety and efficiency.