Strength analysis of perforated casing under non-uniform in-situ stress in ultra-deep wells

Perforate casing to damage often to occur in the process of oil test and production of ultra-deep oil and gas wells under the combined action of non-uniform in-situ stress and internal pressure. The traditional finite element method requires a lot of time and energy to consider the model size, calculation scale, calculation accuracy and other issues when calculating the strength of perforated casing. In this paper, a method of calculating casing strength based on step-by-step finite element method is proposed. Firstly , the contact pressure in casing outer wall of non-uniform in-situ stress is calculated according to the two-dimensional model, and then it is loaded into the three-dimensional perforation casing finite element model by programming to simplify the evaluation of casing bearing capacity. The research shows that perforation changes the distribution of casing stress. After perforation, the maximum stress of casing occur to the perforation hole, and the local stress at the perforation hole increases. The maximum equivalent stress of perforating casing occurs to the direction of minimum horizontal stress. With the increase in perforation holes, casing is more prone to damage. This study provides a calculation method and theoretical basis for the design and application of ultra-deep well casing.