Characterization of Methane Adsorption Behavior on Wet Shale under Different Temperature Conditions

Shale gas is usually found present in a mixture of gas and water under subsurface reservoir conditions. It is well-known that water inhibits its adsorption of methane and that higher or lower temperatures have a negative effect on the methane adsorption capacity of shale. To evaluate these effects quantitatively, we constructed a shale adsorption model to consider the joint effects of water and temperature combining the two to analyze the influence mechanism of temperature and water content on methane adsorption behavior in shale. Considerable experimental data were used to validate the proposed model, and the rationality of the model was illustrated through the similarity between the experimental data and the model. In this study, adsorption capacity of all of the shale samples decreased with increasing water content. Under low-pressure conditions, the amount of shale adsorption increased with increasing equilibrium pressure. Under high-pressure conditions, the density of the free phase of the gas gradually increased, and the adsorption capacity measured, by the volumetric method, often ignored the volume occupied by the adsorption phase. Furthermore, shale adsorption also showed a decreasing trend during an increase in temperature. However, the influence of water and temperature on the adsorption amount had a complicated negative effect. During an increase of temperature and moisture, the adsorption amount decreased. In addition, the pore structure characteristics also had a certain influence on adsorption. Nonetheless, pore surface and pore structure characteristics had different effects on adsorption. We used fractal dimensions D-1 and D-2 to represent shale surface features and pore structures, respectively. The adsorption capacity increased with the increase of the fractal dimension D-1. The relationship between D-2 and the adsorption amount was not significant, which might be related to the influence of water content.