Strength analysis of perforated casing in ultra-deep horizontal shale wells during sublevel acidizing and hydraulic fracturing process

Abstract

In the process of sublevel acidizing and fracturing, the non-uniform load on production casing is complex, and casing failure occurs frequently, which seriously affects the next step of production, stimulation, and underground safety of the oil and gas well. Aiming at the deformation and failure problem of perforated casing in ultra-deep horizontal wells, residual strength analysis and safety evaluation of directional perforated casing under sublevel acidizing and fracturing conditions were carried out. Due to the large scale difference between the underground formation and casing and the complex geometry of the model, an indirect coupled two-step method was proposed to determine the external load of casing first and then calculate its mechanical strength. By using this method, the stress level and distribution of perforated casing in in-situ stress field of X well are determined, and the safety factor of casing is analyzed. On this basis, considering the redistribution of in-situ stress field in the sublevel acidizing and hydraulic fracturing process, the stress situations on perforated casing under different in-situ stress differences are studied, and the measures to prevent casing failure are given. The proposed calculation method can provide references for casing selection and perforation process design of ultra-deep horizontal wells.