Characterization of methane adsorption on the shales in Niutitang formation at Dazhuba-Huijunba Oblique

The Dazhuba-Huijun Oblique syncline is located at the center of the Micangshan-Hannan paleo-uplift with structural coupling between the Sichuan Basin and the Qinling Orogenic Belt. In order to study the adsorption charac- teristic of the Niutitang Formation shale in this region,the isothermal adsorption experiments at different temperatures were combined with TOC,Ro% ,XRD,and pore structure analysis. The absorption thermodynamic parameters of the samples were calculated according to the three-parameter excess sorption function combined with the principle of ther- modynamic adsorption,and the main factors affecting the adsorption of shale were analyzed. The equal adsorption heat of the samples is between 5. 3 and 22. 2 kJ / mol, and the standard adsorption entropy are - 48. 8 to -98. 8 J /(mol·K). It is influenced by the degree of thermal evolution in the study area,and the thermodynamic parameters show a certain adsorption characteristic of type II and Type III kerogen. The pore BET specific surface area has two peaks in the range of pore diameter less than 2 nm,providing the main sites for methane adsorption. When the adsorption pressure is lower than 2. 8 MPa,the adsorption of organic matter dominated the methane adsorption of shale. While the adsorption pressure is higher than 2. 8 MPa,the clay mineral and organic matter determine the methane adsorption of shale.