Accurate shale characterization is hampered by the lack of high-resolution analytical techniques to probe the in situ petrophysical and mechanical properties at the lamina scale. Here we report for the first time a comprehensive lamina-scale experimental characterization and numerical simulation, including AMICS, digital rock, fracture propagation simulation, pore network modeling, FIB-SEM, and N₂ and CO₂ adsorption experiments to investigate the effects of lamina type and thickness on the petrophysical properties and brittleness of shales. We characterized a variety of shales with laminae dominated by felsic minerals, carbonate minerals, clay minerals, and mixed minerals from the Second Member of the Kongdian Formation in the Cangdong Sag, Bohai Bay Basin. Among these laminae investigated, the felsic mineral lamina exhibits the largest porosity, average macropore radius, pore throat radius, and coordination number, and the best pore connectivity and permeability. The carbonate mineral lamina comprises the largest proportion of micropores and the smallest proportion of macropores. The mixed mineral lamina consists mainly of mesopores and micropores. Shales in the study area mainly comprise felsic-mineral-clay-mineral, carbonate-mineral-clay-mineral, and mixed-mineral-clay-mineral coupled laminasets. The felsic-mineral-clay-mineral laminaset appears to have the best permeability and brittleness. The simulated fractures in the felsic-mineral-clay-mineral laminaset show the farthest propagation and the largest aperture. An increase in the thickness of individual felsic mineral lamina would improve the shale brittleness, increase fracture propagation, and enhance fracture connectivity. Fractures tend to be initiated at the interface between the clay mineral lamina and brittle mineral lamina, especially at the boundaries between the ductile and brittle minerals. Therefore, shales with high proportions of felsic mineral lamina would thus improve the porosity, permeability, and frackability of shales. This study proposes a novel technique for characterizing the in situ petrophysical properties and brittleness of shales at the lamina scale.

Source rock strata are filled and aggregated with large-scale continuous hydrocarbon resources, including significant volumes of in-place retained, short-distance migrated and potentially generated hydrocarbons. Source rock strata simultaneously possess the properties of reservoirs and hydrocarbon source rocks, known as source-reservoir coexisting systems. Reservoir properties refer to the physical properties concerning the storage and transmission of oil and gas, while hydrocarbon source rock properties refer to the physicochemical properties related to governing the generation, retention and expulsion of oil and gas in the source rock strata. These properties fundamentally determine the technical path for the successful exploitation of petroleum and natural gas in the source rock strata. With regard to reservoir properties, in-depth research and development of the advanced energy-storing fracturing technology can aid the construction of complex fracture networks to overcome the limitations in the connectivity properties of source rock strata. Focusing on the hydrocarbon source rock properties, an underground in-situ conversion technology should be created and developed to alleviate the shortcomings of organic matter quantity and maturity properties of the source rock strata. Furthermore, selecting the appropriate exploitation path based on the property characteristics can promote the achievement of commercial and sustainable development of oil and gas in the source rock strata.