Research on Coal Seam Deformation Risk Based on In Situ Stress Evaluation and Numerical Simulation

Coal seam casing deformation is a key engineering challenge restricting the efficient development of coalbed methane. Frequent casing deformation in complex tectonic stress zones seriously affects wellbore integrity and fracturing performance. This study takes the in situ stress characteristics of coal seams and the mechanism of casing deformation as the research objects, comprehensively employing theoretical analysis and numerical simulation methods to systematically carry out in situ stress evaluation, numerical simulation of casing deformation, and sensitivity analysis of formation dip angle. First, based on five indicators, including stress difference, stress ratio, maximum shear stress, lateral pressure coefficient, and failure proximity, a comprehensive risk index evaluation model was constructed, and the analytic hierarchy process was used to determine the weights of each indicator. Second, numerical simulations of casing deformation under different stress differences and rock Young’s modulus conditions were carried out, and the influence of formation dip angle variation on casing deformation was analyzed. The results show that in the in situ stress reversal zones, multiple indicators overlap, indicating an extremely high risk of casing deformation, with stress difference and stress ratio being the main controlling factors. For the formation block in this study, when the stress difference exceeds 15 MPa, the radial displacement of the casing increases significantly. In addition, when the formation dip angle exceeds 50°, casing deformation increases sharply, and the coupling effect of compression and shear significantly increases the risk of casing deformation. The above results have important guiding significance for casing deformation assessment in the target block.