The fracture network generated by hydraulic fracturing in unconventional shale reservoirs contains numerous microfractures that are connected to macroscopic fractures. These microfractures serve as crucial pathways for shale gas to flow out from micro- and nano-scale pores, playing a critical role in enhancing shale gas recovery. Currently, more attention is being given by academia and industry to the evolution of macroscopic fracture networks, while the understanding of the microfracture mechanisms and evolution is relatively limited. A significant number of microfractures are generated during the hydraulic fracturing process of shale. These microfractures subsequently propagate, merge, and interconnect to form macroscopic fractures. Therefore, studying the fracture process of rock masses from a microscale perspective holds important theoretical significance and engineering value. Based on the authors’ research experience and literature review, this paper provides a brief overview of current progress in shale microfracture research from five aspects: in situ observation experiments of microfractures in shale, formation and evolution processes of discontinuous microfractures, the impact of inhomogeneity on microfracture propagation, measurement methods for microscale mechanical parameters and deformation quantities in shale, and numerical simulation of shale microfractures. This paper also summarizes the main challenges and future research prospects in shale microfracture studies, including: (1) quantitative characterization of in situ observation experimental data on shale microfractures; (2) formation and evolution laws of macroscopic, mesoscopic, and microscopic multi-scale discontinuous fractures; (3) more in-depth and microscale characterization of shale heterogeneity and its deformation and fracture mechanisms; (4) acquisition of shale micro-mechanical parameters; (5) refinement and accuracy improvement of the numerical simulation of microfractures in shale. Addressing these research questions will not only contribute to the further development of microfracture theory in rocks but also provide insights for hydraulic fracturing in shale gas extraction.

To understand the macroscopic fracture behavior of shale under different confining pressures, it is necessary to study the process of microcrack propagation from a microscopic perspective. In this study, a cohesive zone model for heterogeneous shale based on mineral distribution was constructed. Numerical simulation experiments were conducted under different confining pressures to investigate the effects of confining pressure on the extension of microcracks under tensile and shear loading from three perspectives: microcrack morphology, acoustic emission characteristics, and mechanical responses of different minerals. This study reveals the influence of different confining pressures on the extension of microcracks under tensile and shear loading conditions in shale and their microscopic mechanisms, which holds theoretical and practical significance for the exploitation of deeply buried shale gas.

Rock fracture develops through crack opening, frictional sliding, pore collapse and grain rearrangement, whose interactions govern the transition from local damage to macroscopic failure. Resolving these interactions requires measurements with different physical sensitivities, spatial supports and temporal resolutions. We critically synthesize time-resolved optical imaging, acoustic emission, X-ray tomography and electron microscopy, focusing on surface strain localization, internal crack connectivity and microstructural control of crack paths. We develop an evidence framework that links acquired signals to reconstructed quantities and mechanical interpretations through explicit spatial and temporal compatibility criteria. Within-experiment comparisons show why these distinctions matter. In one published sandstone experiment, the local fracture-energy estimate is 32% lower than the bulk estimate evaluated at the same tomographic observation times. Reanalysis of public three-dimensional strain fields quantifies how detection thresholds change the spatial overlap of incremental shear and dilation. These examples show that mechanical assumptions and reconstruction choices influence interpretation and that shared inputs limit the independence of apparently corroborating observations. The framework distinguishes correspondence among measurements from independent evidence for a fracture mechanism, and it defines priorities for spatial registration, uncertainty propagation and specimen-level replication in experiments on rock fracture.