Application of adsorption potential theory to methane adsorption on organic-rich shales at above critical temperature

Abstract

The characteristic curves for methane on organic-rich shales at above critical temperature were investigated. And the adsorption equation of methane on organic-rich shales at above critical temperature was deduced. The results show that the improved Amankwah’s method is applied to obtain the suitable pseudo-saturation pressure and then the optimal characteristic curve for methane on organic-rich shales can be determined based on the adsorption potential theory. The adsorption equation is constructed by combination of the D–A equation and characteristic curve, which could reliably predict the methane adsorption capacity on organic-rich shales at different temperatures and pressures. The methane adsorption capacity first increases to maximum and then decreases with increasing the depth. When the burial depth is lower than a depth corresponding to the maximum adsorption capacity, the adsorption capacity is determined by the hydrostatic pressure gradient combined with the geothermal gradient. The higher the hydrostatic pressure gradient is, the larger the maximum adsorption capacity is. However, when the burial depth exceeds the critical depth, the methane adsorption capacity is mainly affected by the geothermal gradient. The higher the geothermal gradient is, the faster the fall rate of the adsorption capacity is.