Characterization and controlling factors of pores in the Lower Cambrian Niutitang shale of the Micangshan Tectonic Zone, SW China

Lower Cambrian marine shale has become a new target of shale gas resource evaluations in the complex geological region of southern China, where the Niutitang Formation is among the most important shale gas reservoirs. Recently, the micropore structural characterization and main controlling factors of the ancient shale have become popular research topics. The micropore structures of certain shale samples from the Niutitang Formation in the Micangshan tectonic zone were investigated at the microscale and nanoscale using low-temperature nitrogen gas adsorption (GA) and a combination of broad ion beam (BIB) milling and field-emission scanning electron microscopy (FE-SEM). Then, we analyzed how the mineral composition and thermal evolution affect the pore development in the Niutitang shale through the results of X-ray diffraction (XRD) and vitrinite equivalent reflectance (VRoequiv) calculated by bitumen reflectance (R-b). The BSE images by the BIB/FE-SEM system show that multiple pore types are present in the ancient Niutitang shale and form a complex pore network under the influences of mineral contents and thermal maturation.