Deep shale reservoirs in the southern Sichuan Basin have undergone strong tectonic reworking, producing pore structure heterogeneity that affects reservoir quality and hydrocarbon preservation. In this study, shales with different deformation intensities are analyzed using field emission scanning electron microscopy (FE-SEM), low-pressure nitrogen gas adsorption (LP-N₂GA) and fractal analysis to investigate tectonic control on pore–fracture evolution and fractal characteristics. Weakly deformed shales are dominated by intraparticle pores and regular organic matter (OM) pores, whereas strongly deformed shales develop abundant interparticle pores and microfractures along brittle mineral boundaries with irregular, preferentially oriented OM pores. The large-pore fractal dimension (D₂) consistently exceeds the small-pore fractal dimension (D₁) in both wells, indicating greater adsorption-related structural complexity of larger pores. Strongly deformed shales exhibit a higher mean box-counting fractal dimension (D_b), indicating greater geometric complexity of OM pores. Supervised machine-learning image analysis reveals pore-size differentiation associated with deformation intensity. Intense tectonic compression may cause some 80–350 nm pores to contract, whereas localized pressure release and shear-induced dilation may promote pore expansion and fracture propagation, producing pronounced multiscale heterogeneity. Overall, stable overpressure preserves the primary pore system in weakly deformed zones, whereas compressive deformation and localized pressure release drive the coupled evolution of pore structure and fractal characteristics, with potential implications for shale gas storage and preservation.

Faults are critical to the preservation or destruction of shale gas concentration. The Lower Silurian Longmaxi Formation in the southern Sichuan Basin hosts relatively developed faults, which pose a huge challenge to the exploration and exploitation of shale gas. An urgent need to quickly determine the widths of fault damage zones (FDZs) arises in locating horizontal shale gas wells. In this study, FDZs were estimated using the fault likelihood. The results are as follows: (1) It is rational to constrain the FDZ width using a fault likelihood greater than 0.2. The six major NEE-trending faults in the Fuji syncline of the Luzhou block have complex structures and varying FDZ widths from about 240–1220 m. (2) The degree of influence of FDZs is negatively correlated with their distance from the faults. In other words, a greater distance from a fault is associated with a weaker influence and a smaller fault likelihood. (3) Based on the ratio of the fault throw to the FDZ width, we propose that the width of seismic-scale fault damages can be directly constrained using a ratio value of 3.5. This method is fast and accurate and can provide support for the evaluation of the shale gas preservation conditions and well placement in the Longmaxi Formation of the southern Sichuan Basin.