Abstract: Shales of the Silurian Longmaxi Formation in the Yibin Region, Sichuan, were investigated and their geological parameters, including total organic carbon (TOC) contents and clay mineral contents, were measured. Scanning electron microscopy, high pressure mercury injection, low temperature nitrogen adsorption-desorption, and carbon dioxide gas adsorption methods were employed to qualitatively and quantitatively analyze pore structure characteristics. The mass method was utilized to conduct isothermal adsorption and desorption experiments on shale samples at different temperatures and adsorption and desorption processes were explained using the adsorption potential theory. The results demonstrate that these shale samples have relatively high TOC contents, and pore structures are dominated by micropores, followed by mesopores and macropores. Connected micropores and mesopores increase surface areas of shales, and provide more adsorption spaces, thus facilitating adsorption of shale gas. The isothermal adsorption curves of the shale samples reveal that as the pressure increases, the adsorption volume increases rapidly at first and then levels off gradually. The desorption curves resemble the adsorption ones, but show some delays. The TOC contents indicate relatively good positive correlations with the adsorption performances of shales. The zero-potential point of the absorption potential curve is generally consistent with the turning point of the adsorption curve. The occurrence of shale gas during adsorption and desorption can be explained by variations in adsorption potentials.

Key words: shale gas, micropore characteristic, isothermal adsorption, isothermal desorption, adsorption potential