Pore characteristics and influencing factors of the Lower Cambrian marine shale in the Lower Yangtze area

The marine shale samples of the Lower Cambrian Mufushan Formation collected from the Well GD1 in the Lower Yangtze area are systematically studied in this paper for pore structure characteristics and their influencing factors. Various testing methods, such as field emission scanning electron microscope, X-ray diffraction analysis, gas adsorption, high-pressure mercury injection and organic geochemical analysis are adopted for this research. It is revealed that the Mufushan shale is mainly composed of quartz, calcite and clay minerals in mineralogy. The total organic carbon content is quite high, and the organic matter is dominated by the type I of kerogen overmatured. The pores are dominated by matrix pores including intergranular and intragranular pores, organic matter pores and microfractures. Organic matter pores are well developed, and the proportion of intergranular pores is the highest. Organic matter abundance has certain influence on the pore size and specific surface area of organic matter pores. Compaction is the main factor for pore evolution in the overmatured stage, while rigid minerals, as supporting components, play a positive role in the preservation of organic matter pores. The fractal dimension has a good correlation with the total organic carbon content and specific surface area but weak correlation with pore volume, suggesting that the roughness of the pore wall and the complexity of the pore structure are affected by organic matter abundance.