This paper is the result of oil and gas exploration engineering.

Objective The present−day in−situ stress orientations within deep shale reservoirs of the Wufeng–Longmaxi Formation in the southern Sichuan Basin are intricate and have not been comprehensively evaluated. Moreover, the mechanisms through which local structures influence these stress orientations remain poorly understood.

Methods The Yongchuan shale gas field was selected as the study area to systematically investigate the characteristics and controlling factors of in−situ stress orientations. This evaluation employed a multi−faceted approach that included paleomagnetic analysis, seismic wave velocity anisotropy measurements, specialized well logging techniques, microseismic monitoring, and numerical simulations.

Results The accuracy of interpreting dipole shear wave logs significantly increased when the bidirectional stress difference coefficient exceeds 0.2 and the shear wave anisotropy index is above 18%. In the strata with steep dips (>60°), it is essential to consider the influence of bidirectional stress differentials and high−angle fracture development on the interpretation of in−situ stress orientations. The in−situ stress orientations in the northern and southern synclinal regions of Yongchuan area predominantly follow east−west trend. However, these orientations exhibit significant deviations in anticlinal and fault−influenced zones, with maximum angular discrepancies of approximately 70°±5°. Based on the observed reverse trends in stress orientations above and below a specific stratigraphic level, we hypothesize that the neutral surface is located within the 1–2 layers of the Longmaxi Formation in the Yongchuan area. Furthermore, the fold−induced stress, ranging from 10 MPa to 30 MPa, significantly impacts the principal stress field and cannot be overlooked. As the distance from the fault decreases, Poisson’s ratio (ν) increases, leading to a deflection in the in−situ stress orientations and exhibiting greater sensitivity to changes in ν.

Conclusions The orientation of maximum principal stress promotes the preservation of shale gas in syncline areas, while high−angle natural fractures in anticline areas are more likely to develop into effective fractures. We recommend deploying horizontal wells with an SN−NEE orientation in syncline areas, and a NE orientation with a layered well layout in anticline and fault zones.