Gas migration behavior in saturated bentonite under flexible conditions with consideration of temperature effects.

Investigation of thermal effects on gas migration behavior in saturated bentonite materials is of great significance for the assessment of long-term safety and performance efficiency of a deep geological repository. In this study, a self-designed experimental apparatus was employed and the systemic water infiltration and subsequent gas injection experiments were performed on compacted GaoMiaoZi (GMZ) bentonite under temperature-controlled flexible conditions. Results show that both the capillary displacement and gas-induced pathway dilation played important roles for advective movement of gas through compacted bentonite, due to the reduction of water content and increases in specimen volume observed during gas injection tests. Experimental results also reveal that gas transport through saturated bentonite was extremely slow with an effective (apparent) gas permeability ranged from 1.12 × 10−23 to 1.25 × 10−22 m2. The confining pressure effects on the effective gas permeability depend on temperature. As the confining pressure increased from 3 to 7 MPa, the effective gas permeability decreased almost one order of magnitude for bentonite tested at 20 °C, while no obvious influence could be observed for higher temperatures. Meanwhile, at a same confining pressure, the impact of the gas injection pressure on the effective gas permeability could be neglected under lower temperature conditions, while the gas permeability showed a constant decreasing trend with increasing gas injection pressure at temperatures of 40 and 60 °C. This observation could be attributed to the relative importance of diffusional and advective gas fluxes at different temperatures. Moreover, as temperature continuously increased, the dominant mechanism for gas advection would convert from the dilatancy-controlled flow to visco-capillary flow under temperature-controlled flexible conditions. [ABSTRACT FROM AUTHOR]