Influence of differential structural deformation on pore structure and fractal characteristics of shale reservoirs: a case study of the Longmaxi Formation in the Yongchuan area, South Sichuan Basin

Abstract

In complex structural settings, clarifying the influence of differential structural deformation on reservoir pore systems is crucial for shale gas exploration. This study investigates the shale reservoirs of the first member of the Longmaxi Formation in the Yongchuan area of the Sichuan Basin, with emphasis on the effects of differential structural deformation on pore characteristics and their fractal properties. Mineral composition, pore types, pore structures, and gas content were analyzed using X-ray diffraction (XRD), petrographic thin-section observation, scanning electron microscopy (SEM), and low-temperature nitrogen adsorption experiments. The shale is predominantly siliceous, rich in quartz and clay minerals, and highly brittle, favoring fracture development. Variations in structural deformation across different structural units lead to distinct pore types, pore structures, and fractal characteristics. Weakly deformed areas (synclines) are dominated by organic pores and relatively simple pore networks, whereas strongly deformed areas (anticlines and fault blocks) exhibit inorganic pores, microfractures, and composite pores with complex networks and higher fractal dimensions.These findings indicate that structural deformation not only alters pore geometry but also significantly affects the fractal scaling of the pore system, thereby controlling shale gas enrichment. The study provides a theoretical framework for the efficient exploration and development of shale gas in complex structural settings.