Abstract:

Since shale gas mainly occurs in shale pores, research on the pore structure characteristics is key to understand shale gas accumulation mechanism. Based on the experiments of CO2 adsorption, N2 adsorption, CH4 isothermal adsorption and high pressure mercury injection, the wholeaperture pore structure of the Longmaxi Formation shale is characterized in the Southeastern Sichuan Basin and the controlling effects of pore structure on the gas content are explained. Micropores (<2.0 nm), mesopores (2.050.0 nm) and macropores (>50.0 nm) are developed in shale samples, and the distribution characters change obviously in each sample. In the aspect of pore volume, the mesopores have the biggest contribution to the whole pore volume, taking about 40.8%. It is followed by micropores, taking about 34.7%. The macropores have the minimum proportion in the whole pore volume, only taking 24.5%. In the aspect of surface area, the micropores have an absolute advantage in the whole surface area, accounting for about 76.87%. The second is mesopores, taking about 23.05%. The macropores only provide surface area of 0.07%. The main pore volume is provided by mesopores and micropores, which controls the content of free gas. The surface area of micropores has a good positive correlation with the largest CH4 adsorption contents, and makes up the main surface area in shale samples, which controls the content of adsorbed gas. The macropores are not dominant in pore volume and surface area, and its influence on the content of adsorbed gas and free gas is relatively weak. But the macropores can be the main channels for shale gas seepage. Therefore, understanding the distribution characteristics of micropores, mesopores and macropores, especially the contribution of micropores on the enrichment of adsorbed gas and free gas, has an important guiding significance to the shale gas exploration and development.

Key words: Southeastern Sichuan Basin, Longmaxi Formation, shale gas, pore structure, wholeaperture, gas content