CHARACTERISTICS OF NANOPORES AND THEIR CONTROLLING FACTORS IN NIUTITANG FORMATION SHALE: A CASE STUDY OF THE UPPER YANGTZE PLATFORM CHINA

Shale gas exploration is continually developing in China. Diagenesis of shale influences the quality and productivity of its gas reservoirs. This study explored the characteristics and controlling factors of nanopores in organic-rich shale in the Niutitang Formation. Six samples were collected from the Upper Yangtze platform in Northern Guizhou Province, China, and experiments were conducted to investigate the pore structure of these high-maturity shale samples. Total organic carbon content varied between 4.81-17.51 % (average: 10.18 %). X-ray diffraction analysis showed that samples were dominated by quartz (44-71 %) with significant clay mineral content (8-27.5 % illite). Based on low-pressure liquid N-2 sorption measurements, the pore structures were divided into groups. The first group was characterised by slit-like pores, mesopores, and macropores, while the second group contained narrow slit-like pores, providing extensive adsorption space for shale gas. The mesopores, macropores, porosity, and specific surface area of the second group were more developed than the first. Sample pore combinations shared similar features. By comparing shale pore structure with organic matter and mineral content, it was apparent that the dissolution of quartz and feldspar was an important factor controlling pore development. The results indicate that diagenesis processes have complex effects on the pores, including compaction, dissolution, and cementation.