Abstract: Gas adsorption capacity of shale is a key parameter of gas potential evaluation and resource potential prediction. The marine shale of Silurian Longmaxi Formation in the Baojing area is high in thermal evolution degree, and its gas adsorption capacity is unclear and will be a focus to be figured out. In this paper, 12 core samples of Longmaxi Formation shale in Well BY-1 in the study area were collected and tested in terms of total organic carbon (TOC), thermal maturity (R_o), X-ray diffraction, field emission scanning electron microscopy (FESEM), low-pressure liquid nitrogen adsorption and high-pressure isothermal methane adsorption. The results show that the marine shale in the study area is high in organic abundance and thermal maturity with TOC and Ro in the range of 0.57%-2.16% and 2.86%-3.76%, respectively. The mineral composition includes quartz (33.7%-73.9%), plagioclase (0.7%-16.9%), and clay mineral (15.8%-54.4%). Nano-scale pores are developed in shale dominantly in the forms of intergranular pore and organic pore. According to the low-pressure liquid nitrogen adsorption test, the pore diameter of shale is in a large range and mesopores (2-50 nm) are dominant. The high-pressure isothermal methane adsorption test revels that the gas adsorption capacity of Longmaxi Formation shale in the Baojing area is high-0.82-3.56 m³/t, averaging 1.93 m³/t. The gas adsorption capacity is mainly controlled by the organic abundance and the specific areas of mesopores and micropores. The organic matter in the Longmaxi Formation shale is of high maturity. With the thermal evolution of organic matter, abundant micropores and mesopores are generated and their specific area is large, providing large space for shale gas adsorption, resulting in high gas adsorption capacity of shale.

Key words: Baojing area, marine shale, high maturity, gas adsorption capacity, influential factor