应力-温度对低渗透介质渗透率影响研究

Study of permeability evolutions in low permeability media under different stresses and temperatures

在石油/天然气地下储存、核废料地下处置等工程中,低渗透介质的渗透率测试及其随着应力、温度的变化是工程稳定性和环境评价的基础。通过研制的低渗透介质温度-渗流-应力耦合三轴仪(T-M-PTS),对不同静水压力、不同温度条件下锦屏大理岩的渗透率进行了渗透特性测试,并通过微裂隙模型从理论方面对致密岩石渗透率演化进行了研究。研究结果表明:(1)致密岩石中气体渗透的Klinkenberg效应显著,不能忽略;(2)基于统计理论和逾渗理论的圆盘裂隙模型可以较好地模拟致密岩石扩容和压密过程中渗透率演化特征;(3)静水压力增大,渗透率降低,其降低趋势是开始压缩阶段降低速率较快,随后降低速率越来越小;(4)温度升高,岩石弹性模量降低,岩石被压缩得更加致密,渗透率降低较为明显,从15℃升高至40℃即会降低一个量级,低至3.9×10-21m2。

Determination of permeabilities of low permeability rock （〈10 18 m^2） under different stress conditons and temperatures is the basis of stability evaluation in geological disposal of radioactive waste, underground gas and oil storage tanks and construction of deep cavern groups. Based on the developed low permeability test equipment（T-M-PTS）, gas transport properties of typical Jinping marbles are studied under different hydrostatic pressures and temperatures. Based on microcrack linkage model, evolution of permeability is also studied theoretically. Some results are achieved： （1） Klinkenberg effect is remarkable when gas transport through dense rocks, and should be considered; （2）based on statistic theory and percolation theory, a 3-D penny-shaped microcrack moded has been developed to predict and investigate the evolution of permeability due to microcrack closure in compressive regime; （3） permeability decreases as hydrostatic stress increases because of the decrease of porosity under compression, and permeability decreases faster at the first stage of compression; and （4） permeability decreases from 21.9×10-21 m^2 to 3.9× 10 ^-21 m^2 as temperature increases from 15℃ to 40℃ because of the decrease of elasticity, which lead to decrease of porosity under the same hydrostatic stress.