STUDY ON MOISTURE TRANSPORT CHARACTERISTICS OF SHALE BASED ON ISOTHERMAL ADSORPTION

The study on moisture transport characteristics of shales is critical, which is not only helpful to understand the physical and chemical properties in shales, but also to evaluate the adsorption, diffusion and flow ability of shale gas. In this study, the experimental device of moisture transport in shales was designed and the shale samples from Woodford in USA and Longmaxi Formation in Southern China were used. The moisture transport in shales was carried out at different temperatures and humidities, and the transport characteristics and the effects in shales were investigated. The results indicate that moisture adsorption isotherms of shales belong to type II curve, including the monolayer, multilayer adsorption and capillary condensation, and the GAB model can be used to describe the moisture adsorption process of shale rocks. With the increasing of relative pressure, the moisture adsorption of shales increases. The content of organic carbon and temperature strengthen the moisture adsorption in shales while calcite will inhibit the process. The moisture diffusion coefficient in shales initially increases, then decreases and finally increases with relative pressure, and the value ranges between 8.73\times 10^ - 9 m^2/s and 5.95\times 10^ - 8 m^2/s. The isothermal heat of moisture adsorption in Woodford shale is higher than that of Longmaxi Formation, which is related to shale maturity. These results provide some reference basis for understanding the physical and chemical properties in shales and evaluating the adsorption and flow capacity of shale gas.