Gas migration characteristics in saturated bentonite under flexible boundary conditions considering temperature effects

To investigate the characteristics and mechanisms of gas migration and to predict the effective gas permeability in saturated bentonite within deep geological repositories, water saturation, gas injection, and mercury intrusion porosimetry (MIP) tests were conducted on GMZ bentonite specimens under a confining pressure of 8 MPa, taking temperature effects into account. The results indicate that the intrinsic permeability measured with water increases as temperature rises. During the gas injection test, the gas pressure recorded downstream exhibits a three-stage evolution process. Gas displaces pore water and induces pore shrinkage in the specimen, with the shrinkage ratio varying with temperature. As the gas injection pressure increases, mechanical gas breakthrough may ultimately be triggered by pore expansion. At the same injection pressure, effective gas permeability increases with rising temperature. A prediction model for effective gas permeability was developed based on the water-measured intrinsic permeability and the Hagen-Poiseuille model, validated by considering the influences of temperature, the Klinkenberg effect, and gas injection pressure.

为探究深地质处置库内饱和膨润土的气体运移特征与机制，并预测其有效气体渗透率，研究团队在8MPa围压条件下，将温度效应纳入考量，对GMZ膨润土试样开展了饱水试验、注气试验及压汞法（Mercury Intrusion Porosimetry, MIP）孔隙测试。试验结果表明，水测法得到的固有渗透率随温度升高而增大。在注气试验过程中，下游记录的气压力呈现三阶段演化过程。气体驱替孔隙水并引发试样孔隙收缩，且收缩率随温度发生变化。随着注气压力升高，孔隙膨胀最终可能触发机械性气体突破。在相同注气压力下，有效气体渗透率随温度上升而升高。研究基于水测固有渗透率与哈根-泊肃叶（Hagen-Poiseuille）模型构建了有效气体渗透率预测模型，并通过考量温度、克林肯伯格效应（Klinkenberg effect）及注气压力的影响对模型进行了验证。