EXPERIMENTAL COMPARATIVE STUDY ON PORE STRUCTURES OF CONTINENTAL AND MARINE SHALES

China has abundant shale oil and gas resources, which are mainly distributed in marine and continental shale reservoirs. The comparative study of the pore structures of typical continental and marine shale reservoirs can provide scientific guidance for the prediction of shale reservoir sweet spots. In this paper, taking the Lower Cambrian Niutitang Formation shale in southern China and the Upper Triassic Yanchang Formation shale in the Ordos Basin as examples, the microscopic pore structure characteristics of marine and continental shale reservoirs have been systematically compared, using a large number of thin sections, field emission scanning electron microscopy, CO2 adsorption, N-2 adsorption, high pressure mercury intrusion and methane adsorption experiments. The results of the study show that the nanopores in the Niutitang Formation shale are mainly developed in the organic matter-clay complex, and the microcracks are relatively developed; while the Yanchang Formation shale mainly develops mineral intercrystalline pores. The experimental results of the full aperture show that the marine Niutitang shale mainly develops mesopores and micropores, while the Chang 7 shale of the continental Yanchang Formation mainly develops mesopores and macropores. The organic matter in shale has an important influence on the amount of methane adsorption. According to the adsorption characteristics of methane, and the calculation results of adsorption heat and adsorption entropy, the methane adsorption performance of marine shale is stronger than that of continental shale. In addition, as the degree of thermal evolution increases, the amount of methane adsorption in both continental and marine shale increases. The fractal dimension of marine shale is larger than that of continental shale, indicating that its pore structure is more complex, that is, the smaller the size of nanopores, the more complex the pore structure of the rock, and the lower its permeability. The fractal dimension of marine and continental shale has a good positive correlation with rock permeability. Therefore, the fractal dimension can be used to quantitatively characterize the pore structure of continental and marine shales.