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The effect of structural deformation on shale pore structure is a key scientific problem in the development of shale gas resources in structurally complex areas. In this study, we investigated the evolution rules and mechanisms of pore structures in organic-rich shale subjected to structural deformation of varying mechanisms and intensities, by conducting whole-aperture pore structure characterization on experimentally deformed shale rather than naturally deformed shale. Results showed that brittle deformed samples developed more mesopores, macropores, and fracture pores. The inter-granular pores between mineral fragments and the inter-layer pores and micro-fractures were the primary sources of the increased pore structures. The ductile deformation of shale promoted large-aperture transitional pores, mesopores, and small-aperture macropores but was adverse to small-aperture transitional pores, large-aperture macropores, and fracture pores. The primary contributors to the enhanced pore structures were inter-granular pores and inter-layer micro-fractures formed during crumpled deformation and inter-layer sliding of clay minerals, and inter-granular pores caused by the grinding, rounding, and rotation of mineral fragments under the flow deformation of the shale matrix. The irreversible compression of organic matter pores, mineral-related pores, and pre-existing large-aperture pores and fractures was the main reason for the reduction in small-aperture transitional pores, large-aperture macropores, and fracture pores. [Display omitted] • Pore structure evolution of experimentally deformed shale rather than naturally deformed shale was studied. • Whole-aperture pore structures of deformed shale (chunks) were characterized qualitatively and quantitatively. • Response patterns of shale pore structures to structural deformation and deformation conditions were clarified. • Mechanisms governing the pore structure evolution during brittle and ductile deformation were revealed. [ABSTRACT FROM AUTHOR]

We aimed to reveal the structural styles and evolution sequences of the superimposed folding zone in the southern Sichuan Basin, South China, and to predict the distribution rules of tectonic fractures in the Longmaxi shale. The field survey and geological section analysis showed that the structural pattern is characterized by the superposition of near-N–S-trending folds and near-E–W-trending compressive structures. The two structural systems experienced multistage development, and the finalization of the E–W structures was later than the N–S ones. By combining these findings with the back-stripping method and fluid inclusion analysis, the burial, thermal, and structural evolution histories were reconstructed. The results indicate that the E–W-trending compressive structures were finalized at the end of the Late Cretaceous whereas the N–S-trending folds were formed by the Oligocene Epoch. A comparative analysis was conducted to reveal the relationship between tectonic fractures and fold structures. The analysis revealed that the Longmaxi shale in the core zones of the N–S-trending anticlines and the cores and near-core zones of the E–W folds is more likely to show a well-developed natural fracture system, which was verified by fracture observations on shale cores and outcrops. These places have potential for the exploration and development of shale gas resources. • Multi methods were adopted to reveal structural evolution of southern Sichuan Basin. • N-S and E-W structures finalized at end of Late Cretaceous and Oligocene, respectively. • Planar distribution of tectonic fractures is controlled by major fold structures. • E-W anticlines and core zones of N-S folds show well-developed tectonic fractures. [ABSTRACT FROM AUTHOR]