Objective  Research on in situ stress serves as a bridge between geological and engineering analyses. Accurate insights into in situ stress regimes are crucial for ensuring engineering efficiency and development benefits. However, microstructures are well developed in deep coal seams, for which no effective model is currently available for calculating in situ stress.

Methods and Results By classifying structures into macrostructures and microstructures, this study established a novel model for calculating in situ stress in deep coal seams while considering microstructural characteristics. In the novel model, the horizontal in situ stress was decomposed into three components: the horizontal components induced by vertical stress and macroscopic and microscopic tectonic stresses. The novel model allows for the simultaneous calculation of the magnitude and orientations of in situ stress through stress tensor decomposition. This model was applied to calculate in situ stress in two vertical wells. The calculated magnitudes and orientations of in situ stress were compared with acoustic emission experimental data and log interpretation data, respectively, yielding maximum relative errors of 8.20% and 4.58%. Based on the novel model and the data from adjacent wells, the magnitudes and orientations of in situ stress in three unlogged horizontal wells were calculated in a staged manner. The predicted in situ stress orientations were validated using microseismic monitoring results, yielding relative errors ranging from 0.29% to 13.89%. Based on the calculated in situ stress, the propagation morphologies of simulated fractures in a horizontal well were predicted. The prediction results aligned well with microseismic monitoring results. The novel model provides a new approach for calculating in situ stress, enabling fine-scale determination of in situ stress within individual wells.

Conclusions The fine-scale calculation results of in situ stress hold great values in applications in two aspects in the field of petroleum engineering: (1) in drilling engineering, accurate in situ stress parameters help significantly enhance the reliability of wellbore stability analysis, optimize drilling fluid density design, and mitigate the risks of wellbore collapse and lost circulation; (2) In reservoir fracturing, single-well in situ stress profiles can provide guidance the design of fracturing stages and clusters to effectively mitigate stress shadowing effects and enhance the complexity and conductivity of fracture networks, thereby achieving efficient reservoir stimulation and production growth.