Water Adsorption and Its Pore Structure Dependence in Shale Gas Reservoirs.

Investigating the occurrence characteristics of water molecules in shale is of great resource, economic, and environmental significance. In this work, the adsorption behavior of water vapor on Longmaxi shale samples is tested, and several isothermal adsorption models are employed to fit the experimental data and primary and secondary adsorption processes. Furthermore, the influence of organic matter content, mineralogical composition, and pore structure on the adsorption process is discussed, and their special combination relationship is revealed correspondingly. The results indicate that the Dent model is suitable for the experimental data with excellent goodness of fit, and the Langmuir and Freundlich models are suitable for the primary and secondary adsorption processes, respectively. The adsorption of water vapor is controlled by the pore volume and specific surface area (SSA) of shale. Mesopore structure parameters mostly determine the water adsorption amount. Massive micropores developed in organic matter with a huge SSA contribute strongly to the primary adsorption process. In general, the combination of organic matter and clay minerals controls the pore structure of shale, which further controls the primary and secondary adsorption processes of water vapor. These findings contribute to a better understanding of water adsorption in different adsorption carriers and in microscopic pores of different sizes occurring in shale gas reservoirs.