Water Adsorption and Its Pore Structure Dependence in Shale Gas Reservoirs

Investigatingthe occurrence characteristics of water moleculesin shale is of great resource, economic, and environmental significance.In this work, the adsorption behavior of water vapor on Longmaxi shalesamples is tested, and several isothermal adsorption models are employedto fit the experimental data and primary and secondary adsorptionprocesses. Furthermore, the influence of organic matter content, mineralogicalcomposition, 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 experimentaldata with excellent goodness of fit, and the Langmuir and Freundlichmodels are suitable for the primary and secondary adsorption processes,respectively. The adsorption of water vapor is controlled by the porevolume and specific surface area (SSA) of shale. Mesopore structureparameters mostly determine the water adsorption amount. Massive microporesdeveloped in organic matter with a huge SSA contribute strongly tothe primary adsorption process. In general, the combination of organicmatter and clay minerals controls the pore structure of shale, whichfurther controls the primary and secondary adsorption processes ofwater vapor. These findings contribute to a better understanding ofwater adsorption in different adsorption carriers and in microscopicpores of different sizes occurring in shale gas reservoirs.