Thermodynamic characteristics of isothermal adsorption of methane at high temperature and pressure in shale

In order to investigate the adsorption characteristics of methane in shale under high temperature and high pressure conditions, the methane adsorption effects of shale examples, which were taken from Tianma No.1 well in Cengong area of Guizhou, were tested and analyzed using high pressure isothermal adsorption tester.Lausius-Clapeyron equation and Vant-Hoff equation were used to obtain the equal adsorption heat and limit isosteric heat of methane adsorption.The adsorption characteristics of methane on shale were analyzed based on the thermodynamics. The results show that the methane isothermal adsorption curves of shale from Tianma No.1 well in Cengong area of Guizhou are basically consistent under different temperature conditions with obvious extreme points. The thermodynamic analysis shows that the isosteric heat under low pressure increases with increasing adsorption capacity. The average isosteric heat is 43.59 kJ/mol, indicating the existence of chemical adsorption.However, in the high pressure stage, with the removal of methane molecules from the surface of shale being more difficult, the amount of adsorption heat gradually increases with the decreasing adsorption capacity.The calculated limit adsorption heat through the Vant-Hoff equation is 39.61 kJ/mol, indicating that the interaction force between the shale surface and the methane is relatively strong in Tianma No.1 well.To promote the desorption of this type of shale with strong interaction force, the combined actions such as injecting more powerful gas that acts more strongly on the surface of shale such as carbon dioxide and other gases should be considered.