Insights into the pore structure characteristics of the Lower Silurian Longmaxi Formation shale in the Jiaoshiba area, Southern Sichuan Basin, China

In this paper, the pore structure characteristics of shales and its controlling factors were analyzed by means of total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FE-SEM) and low-pressure N2 adsorption (LPNA) analysis. Based on the grey relational analysis, the controlling factors of pore structure parameters were discussed. The results showed that the TOC contents range from 2.98 to 4.97%, the main minerals of shales are quartz and clay minerals with an average of 41.62 and 30.98%, respectively. The organic matter pores, the interparticle pores, the intraparticle pores, and the micro-fractures are the main pore types determined by the FE-SEM observation. The pore volume of shales is between 0.0637 and 0.1053 cm3/g, the specific surface area ranges from 16.44 to 37.61 m2/g, the average pore size is between 11.20 and 15.50 nm. The organic matter and the quartz have a positive influence on the specific surface area and total pore volume, whereas the clay minerals have a negative impact. The shales have a wide range of pore size, and the mesopores and macropores are the dominant contributor to the total pore volume while the mesoporous contribute the main specific surface area. The TOC contents and quartz contents have the most significant effect on the total pore volume and specific surface area, and the average pore size is mainly controlled by the quartz contents.