Characterization of multi-scale pore structure and analysis of adsorption capacity influencing factors in Zhaotong shallow shale gas reservoir

In order to explore the reservoir characteristics of shallow shale gas reservoir in Zhaotong and its differences with other shale gas blocks in Sichuan Basin, the pore structure of Zhaotong shale gas reservoir was comprehensively studied by various means, including X -ray diffraction, gas adsorption (CO2, N-2), NMR, and field emission-scanning electron microscopy. In addition, the adsorption capacity of samples in this area was measured by volume method and the main controlling factors were analyzed. The results show that the shale reservoir in the Zhaotong demonstration area is dominated by clay and quartz minerals, with an average content of 23.1% and 34.3%, respectively. Pore-size distribution is concentrated in the range of 0.5-1000 nm, with micropore and mesopore as the main body. Scanning electron microscopy shows that the reservoir space types are mainly organic pores, intergranular pores, intragranular pores, and microfractures. Among them, organic pores are the most developed and most of them appear in large area network structures with good connectivity. The results of the methane isothermal adsorption test show that the adsorption capacity of shale in the Zhaotong area is positively correlated with TOC content, specific surface area, and micropore volume ( D <= 10nm), but poorly correlated with total pore volume. Due to the influence of mineral types and genesis, the adsorption capacity of shale in this area is negatively correlated with clay content and poorly correlated with quartz content. Through data comparison and analysis, the adsorption capacity of shale in the Zhaotong area is higher than that in the Fuling and Changning-Weiyuan areas. Additionally, due to the influence of mineral genesis, the changing trend of shale adsorption capacity with quartz content is also different in different regions.