两种有效应力下花岗岩和充填体渗透率变化规律研究

干热岩是地热资源的主要载体。干热岩体花岗岩受地质构造运动影响产生裂隙,熔融岩浆侵入到花岗岩裂隙中,形成含有充填体的花岗岩体。故采用压力脉冲法,以花岗岩母岩和充填体为研究对象,研究改变围压或孔隙压力两种路径下有效应力对花岗岩母岩和充填体渗透率的影响规律。研究表明:在孔隙压力一定情况下,随着围压增大,花岗岩母岩和充填体的渗透率都有一个快速大幅下降阶段和缓慢小幅降低的阶段;通过孔隙压力不变时卸载围压的路径减小有效应力,可以有效恢复花岗岩的渗透率。但通过围压不变时提高孔隙压力的路径减少有效应力达到恢复渗透率的目的时,存在一个“失效围压阈值”,当围压低于该阈值时,提高孔隙压力可以使渗透率得到有效恢复,高于该阈值,提高孔隙压力对渗透率不会有太大的提高;采用孔隙压力一定时降低围压和围压一定时(低于“失效围压阈值”)增大孔隙压力两种路径测试同一试样渗透率时,若两种路径下有效应力相同,则试样渗透率相差不大;通过波速对比和偏光镜图像对比分析了试样在试验前后的孔隙裂隙的压密和塑性变形,从宏观和微观角度证明了“失效围压阈值”存在的合理性。

Study on Permeability of Granite and Backfill in Two Effective Stress Paths

Dry hot rock is the main carrier of geothermal resources. The granite of dry hot rock mass is affected by the geological tectonic movement to produce cracks, and the molten magma intrudes into the cracks of granite, forming a granite body with a filling body. The pressure pulse method was used to study the granite parent rock and the backfill body, and the influence of the effective stress on the permeability of the granite parent rock and the backfill body under two paths of confining pressure or pore pressure was studied. The research shows that under certain conditions of pore pressure, as the confining pressure increases, the permeability of the granite parent rock and the backfill both have a rapid and sharp decline stage and a slow and small decline stage. By reducing the effective stress through the path of unloading confining pressure when the pore pressure is constant, the permeability of granite can be effectively restored. However, there is a “failure confining pressure threshold” when the effective stress is reduced through the path of increasing the pore pressure when the confining pressure is constant. When the confining pressure is lower than this threshold, increasing the pore pressure can effectively restore the permeability Above this threshold, increasing the pore pressure will not increase the permeability too much. When the two paths of reducing the confining pressure when the pore pressure is constant and increasing the pore pressure when the confining pressure is constant are used to test the permeability of the same sample, the effective stress in the two paths is the same, so the permeability of the sample is not much different. Through the comparison of wave velocity and polarizing mirror image, the changes of pore fracture compaction and plastic deformation before and after the test are analyzed, and the rationality of “failure confining pressure threshold” is proved from macro and micro perspectives.