Shale shear fracture mirrors are key indicators of localized shear deformation, yet their high reflectivity origin remains unclear. This study employs electron microscopy and Raman spectroscopy to analyze fracture mirrors from the Lower Cambrian Qiongzhusi shale. Results reveal the shiny surface is not merely a product of mechanical polishing but is primarily attributed to the formation of highly ordered nanocoatings on fracture surface. The coatings comprise aligned clay minerals and, crucially, organic materials that have undergone shear-induced partial graphitization. Transmission electron microscopy reveals a about 0.46 nm lattice fringe spacing, and Raman spectroscopy confirms a moderate structural order and an elevated thermal maturity of organic matter. This transformation yields a dense material dominated by ultra-micropores, which minimizes light scattering of fracture surface. The formation of fracture mirrors results from shear displacement and frictional heating, which lead to mechanical comminution and microstructural reorganization. This finding establishes the shear fracture mirrors as the key indicators for revealing beddingparallel slip history in shale-involved detachment and, more practically, for assessing fluid migration pathways, seal integrity, and natural fracture networks in shale gas systems.

Atomic force microscopy coupled with infrared spectroscopy (AFM-IR) is one of the most effective and widely employed mixed techniques capable of providing direct access to infrared spectroscopic imaging and chemical analysis at the nanoscale spatial resolution. In this communication, AFM-IR was applied to the evaluate the in-situ nanoscale mineralogy and to characterize the organic structure of shale. Significant chemical and microstructural heterogeneity could be observed on the mirror-like surface of naturally deformed shale. It was also apparent that slickensides formed on the mirror-like surface potentially influence the spatial distribution of organic matter. This technique provides an effective combination for direct and in-situ studies of the morphology and physicochemical properties of geological rocks at the nanoscale, opening a new avenue for investigations to help reveal some complex geological phenomena, such as organic carbon graphitization and mineral transformation during fault deformation. Furthermore, this technique makes it possible to determine the chemical composition, molecular structure and functional group information of shale organic matter, which is crucial information for investigating the hydrocarbon generation potential, maturity evaluation, and oil and gas migration mechanisms in shale.

This paper investigates the mechanical properties and damage laws of marine shale from the Silurian Longmaxi Formation by conducting uniaxial compression experiments with varying lamination angles with respect to the loading direction. Data are analyzed via computed tomography scanning and fractal theory to reveal a series of mechanical properties, considering stress-strain curve, compressive strength, Young’s modulus, and Poisson’s ratio. The results indicate three damage modes in shale samples: shear, tension-shear, and tension. The shales are anisotropic as the mechanical properties vary with the lamination orientation and the loading direction. The compressive strength decreases non-linearly with increasing lamination angle, whereas the Young’s modulus and Poisson’s ratio correlate almost linearly with the lamination angle. To overcome the defect of visual images when quantitatively evaluating cracks and rock damage to investigate the mechanical properties of shale, we propose block fractal dimension and crack fractal dimensions calculated using post-experimental photographs and computed tomography images. Fractal dimensions are useful tools for identifying variations in uniaxial compressive strength and correlate positively with the sample damage, particularly their damage class. This study highlights the value of applying fractal theory for the quantitative characterization of shale mechanical properties, and reveals that the lamination orientation to the loading direction is a parameter that significantly controls the mechanical properties of shale.

Shale gas exploration and development have taken significant strides in the relatively straightforward intra-basin stability zone and intra-basin weak deformation zone of marine shale in the Sichuan Basin, South China. In addition, the extra-basin strong tectonic modification zones have been actively explored. However, the results have been limited, which reveals the complexity of shale gas formation and preservation conditions in the context of multi-scale geological processes. These tectonic geological conditions have a significant impact on the shale gas content, while it has been difficult to figure out how tectonic deformation modifies reservoir structure and what specific mechanism causes shale gas content anomalies. Based on subjecting geologic samples to combined high-temperature and high-pressure experiments, this study summarizes the tectonic constraint mechanism of shale petrophysical structure evolution and its impact on shale gas storage, reveals the intrinsic connection and mechanism of shale pore-fracture and organic matter, inorganic mineral particle structure evolution and tectonic stress, and identifies the remodeling mechanism of the shale reservoir physical property change. The findings contribute to the theory of shale deformation and gas accumulation, as well as offer a scientific foundation for the exploration of marine shale gas in the complex tectonic zones outside the Sichuan Basin.