Differential pore development characteristics in various shale lithofacies of Longmaxi Formation in Jiaoshiba area, Sichuan Basin

It is of great significance for shale gas exploration and development to understand different pore characteristics in various shale lithofacies. In this paper, the reservoir characteristics of different shale lithofacies of Longmaxi Formation in the Jiaoshiba area were studied by using X-ray diffraction, thin section analysis, cathodoluminescence, FE-SEM, high pressure mercury intrusion-gas adsorption joint test, and nuclear magnetic resonance porosity. Four preliminary conclusions were obtained:(1) Three main types of shale lithofacies were identified in the Longmaxi Formation in the Jiaoshiba area, including siliceous shale, mixed shale and argillaceous shale. (2) Organic porosity developed well in the siliceous shale, but did not develop in the mixed shale and argillaceous shale, in which inorganic pores were more developed. (3) The reservoir heterogeneity characteristics of various shale lithofacies were remarkable. The siliceous shale was the most outstanding in TOC content, porosity, pore volume, specific surface area and gas content, while the mixed shale the second, and the argillaceous shale the least. (4) When the siliceous shale was deposited, bioproductivity was high, which was conducive to the enrichment of organic matter and the development of organic porosity. The mixed shale and argillaceous shale controlled by deep-water currents and terrigenous clastic material supply showed low TOC contents and poor organic pore development.