Permeability evolution of methane and water vapor when simultaneously transporting in shale

•A method determining methane and water vapor permeability in shale is proposed.•The evolution of methane and water vapor permeability is analyzed and compared.•The relationship between permeability and water saturation of shale is presented. Methane and water vapor transport in shale (mud rocks) is important in many resource and environmental issues, e.g., effectively exploiting shale gas and clearly understanding water and methane global cycles. To investigate methane and water vapor permeability in shale, a new permeability determination method was proposed using a linearization approach based on previous studies. The experimental samples are crushed Carboniferous shale from the eastern Qaidam Basin in China. Simultaneous methane and water vapor transport experiments in shale were performed. Water vapor was derived through deionized water evaporation under different methane pressures. The relative humidity dynamically changed during the experiment. The methane and water vapor transport processes were observed and recorded, and the methane and water vapor permeability in the shale matrix was calculated. Both the methane and water vapor permeabilities temporally varied, and a critical abrupt point occurred in the decreasing process over time. After the abrupt point, the permeability rapidly decreased, which was mainly due to capillary condensation plugging at high relative humidities. Pore throat closure could dramatically affect permeability. The relationship between permeability and water saturation (Sw) conformed to an exponential equation. Methane permeability was sensitive to water saturation variation at very low or high levels (Sw 50 %, respectively) and relatively insensitive at a moderate water content. Water vapor permeability variation with water saturation was similar to that in methane but basically remained stable at a moderate water saturation (10 %