Field-Constrained Dual-Correction Model for Predicting Casing Stress During Multi-Stage Hydraulic Fracturing in Deep Coalbed Methane Horizontal Wells

Deep coalbed methane reservoirs exhibit strong heterogeneity and complex stress environments, making accurate prediction of casing loads during multi-stage hydraulic fracturing challenging. This study developed a coupled prediction framework integrating three-dimensional geomechanical modeling, modified induced stress calculation, and numerical simulation. The geomechanical model was constructed using logging, drilling, rock mechanics, and in situ stress data and validated against fracture monitoring results. The simulated fracture half-length and stimulated area differed from the monitored values by less than 10% and 8%, respectively, with a spatial matching degree exceeding 92%. A modified analytical model was then established by introducing correction coefficients for fracture net pressure and stress propagation. Among the results obtained using five parameter inversion methods, the sparrow search algorithm achieved the highest fitting accuracy, with an (R2) of 0.9371 and an RMSE of 0.3761, yielding (A = 0.7330) and (B = 0.9238). These coefficients indicate an approximately 26.7% reduction in effective net pressure and enhanced attenuation of induced stress in heterogeneous, cleat-developed coal seams. Furthermore, a multi-parameter casing stress model was developed by coupling treatment scale, injection rate, fracture spacing, and stage number. Sensitivity analysis showed that the number of fracturing stages and injection rate were the dominant factors, followed by fracture spacing and treatment scale. The proposed framework quantitatively characterizes casing stress evolution and facilitates casing load assessment under different multi-stage fracturing conditions.