Water Vapor Adsorption Behavior in Shale Under Different Temperatures and Pore Structures

Abstract

In this paper, fractal dimension analysis was used to describe pore structure. We proposed a shale water vapor multi-layer adsorption model that considers the control of pore structures. In this respect, the change curve of the water vapor adsorption capacity was found to be consistent with a type II curve. In addition, water vapor adsorption in shale occurs at primary and secondary adsorption sites. When the relative pressure was low, water vapor adsorption in shale occurs at primary adsorption sites. Thus, primary adsorption capacity is greater than secondary adsorption capacity, and changes in the primary adsorption capacity conformed to the characteristics of a type I curve. However, with increasing relative pressure, secondary adsorption sites began to be occupied. The adsorption capacity curves of the two types of adsorption sites intersected. In addition, temperature changes altered the pore structures, and the pore structure had a controlling effect on the adsorption capacity of shale. Temperature was also found to be one of the important factors affecting shale adsorption. Then, we introduced a shale water vapor multi-layer adsorption model that considers both pore structure and temperature. With increasing relative pressure, the water vapor adsorption capacity of shale still maintained the characteristics of a type II curve. However, temperature had an inhibitory effect on the adsorption characteristics in shale. Based on analysis of the changes in shale adsorption at different temperatures, the sorption-induced deformation mechanism caused by water vapor adsorption in shale was further analyzed.