Dynamic Water Vapor Sorption on Marcellus Shales: Equilibrium, Thermodynamic and Kinetic Analyses

Water sorption and transport behaviors are of great importance affecting hydrocarbon extraction and wellbore stability due to water-involved drilling and fracking methods. Dynamic water vapor sorption experiments on two Marcellus shales at 20 °C, 30 °C, 40 °C were performed. Based on BET multilayer theory, specific surface area estimated by water vapor sorption is apparently larger than that by low pressure nitrogen adsorption, possibly due to the complex surface chemistry and water vapor sorption heterogeneity in shale. The heat of adsorption decreases with the water content and approaches progressively to the latent heat of the condensed water, indicating an initially strong intermolecular bonding and the subsequent form of capillary condensation. Kinetic analyses of water adsorption data show that diffusion coefficient of water vapor varies under different water vapor pressures and the maximum of diffusion coefficient occurs near monolayer coverage for the case of 20 °C and 30 °C. It was found that the temperature negatively influences water adsorption capacity and positively influences water vapor diffusivity. These findings contribute to a better understanding of water distribution characteristic in shale reservoirs during soaking period and thus providing clues to gas storage and transport behavior under fully or partial water saturations.