Optimal model of isothermal adsorption for shale gas under high temperature and high pressure

In order to study the adsorption characteristics of shale gas at high temperature and high pressure in Niutitang formation of Guizhou, the adsorption isotherms of CH₄ and CO₂ in shale at 50 ℃, 60 ℃ and 80 ℃ were measured by high-pressure gas isothermal adsorption apparatus，were fitted by the adsorption model which accords with the adsorption law，and the fitting effect was evaluated by average relative error.The results show that the adsorption temperature of CH₄ and CO₂ is increasing in stage, and it has the characteristics of type Ⅰ adsorption curve; by analyzing the physical meaning of the model fitting parameters, the adsorption characteristics, saturation adsorption capacity V_L and microporous adsorption.The amount of V₀is negatively correlated with the temperature and positively correlated with the content of TOC, and the adsorption b value decreases with the increase of temperature, and the adsorption law reflected by the other fitting parameters is different; the fitting of each model is evaluated the effect of the three-parameter model is better than that of the two-parameter model, the best for the CH₄ fitting is the L-F model; the best effect of the CO₂ fitting is the E-L model.In the high pressure stage, the linear regression equation of CH₄ and CO₂ is good, and the adsorption capacity of CH₄ and CO₂ on the shale surface is negatively correlated with the pressure.At the same time, the important influence of research results on shale gas exploitation and reserve assessment is discussed, which provides the theoretical basis for shale gas development.