Development mechanism of organic-inorganic composite pores in the shale of the Niutitang Formation at the Huijunba syncline

The Niutitang Formation at the Huijunba syncline south of Hanzhong, China, has large shale gas resource potential. The development characteristics of shale nanoscale pores are key factors affecting the storage capacity of shale gas. To study the development mechanism, the shale pores in the area were systematically observed using scanning electron microscopy combined with argon ion polishing and low-pressure gas adsorption. The determination of structural parameters (e.g., the pore specific surface area, pore volume, and pore size distribution) of the mineral components provided an in-depth analysis of the development characteristics and mechanisms of organic-inorganic composite pores. Morphological analysis revealed that the development of organic-inorganic composite pores is dominated by the sedimentary action of organic matter and mineral components due to differences in physical properties, the fracture of brittle minerals, the plastic deformation of organic matter, structural effects, and other factors. Syndeposition forms a symbiotic relationship between organic matter and mineral components in the shale that leads to specific surface area and pore volume parameters that are smaller than the individual components. Because the mineral and organic particles in shale have diameters primarily larger than 2 nm, the abovementioned factor primarily affects mesopores and macropores and has a relatively limited impact on micropores.