Qualitative-quantitative multi scale characteristics of shale pore structure from Upper Paleozoic coal-measures in Linxing area

In order to reveal the micro-pore structure characteristics of marine-continental transitional shale and its main controlling factors in the eastern margin of Ordos Basin, and to enrich the understanding of pore development characteristics and pore structure of marine-continental transitional coal-bearing shale in the block, scanning electron microscope, high-pressure mercury injection and liquid nitrogen adsorption analysis were used to characterize the micro-pore structure characteristics of shale in Linxing area. Furthermore, porosity, total content of organic carbon, mineral content, clay relative content and organic matter maturity were tested to study the main controlling factors of development of shale pore structure. The results show that there are intra-granular pores, intergranular pores, dissolution pores and micro-cracks developed in the shale. There are occasional pores and micro-cracks in the organic matter, when it is associated with minerals, micro-cracks develop around the shale. The total pore volume of shale is between 0.001 46 mL/g and 0.010 81 mL/g, the mesoporous proportion is 81.9%, and the specific surface area is between 0.35-3.65 m²/g in the study area. The pore size distribution is dominated by single peak type, the distribution range is mainly within 200 nm, and the main peak pore size is about 45 nm. The pore connectivity of shale in Benxi Formation and Taiyuan Formation is better than that Shanxi Formation, the macro-pore ratio of shale in Taiyuan Formation is better than that in Benxi Formation and Shanxi Formation. The total organic carbon content has a complex effect on the development of shale pore, but it has a positive effect on macro-pore development. The brittle mineral content of shale have positive effect on total pore and mesoporous development, while the clay mineral content has negative effects on mesoporous development. Brittle mineral and clay mineral control the development degree of pores in shale mainly by affecting the development of mesoporous pores. The study of qualitative-quantitative multi-scale characterization of shale pore structure and its controlling factors has important guiding significance for the evaluation, sweet spot optimization and development of marine-continental transitional shale gas resources in Linxing area, and enrich the geological understanding of marine-continental transitional shale reservoir.