Experimental measurements of permeability evolution during triaxial compression of initially intact crystalline rocks and implications for fluid flow in fault zones
Experimental measurements of permeability evolution during triaxial compression of initially intact crystalline rocks and implications for fluid flow in fault zones
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DOI：
10.1029/2008jb005588
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发表时间：
2008-11-26
影响因子：
3.9
通讯作者：
Faulkner, D. R.
中科院分区：
文献类型：
--
作者：
Mitchell, T. M.;Faulkner, D. R.
对地壳岩石在变形过程中渗透性发展的详细实验研究对于帮助理解断层力学和限制预测地壳内大量流体流动的大尺度模型至关重要。渗透性在断层的损伤区中特别增强，其中微裂缝损伤在小于宏观破坏所需的应力下累积。在破坏前区域进行的实验可以提供直接适用于这些区域的微破裂损伤周围的故障的数据。强度，渗透率，和孔隙流体体积的演变最初完整的结晶岩（Cerro Cristales花岗闪长岩和西风花岗岩）下增加的差异负载导致宏观故障已被确定在水孔隙压力为50 MPa，有效压力从10到50 MPa。渗透率被认为是增加高达，并超过，2个数量级之前，宏观故障，最大的增加，在最低的有效压力。破坏后的渗透率被证明是超过3个数量级高于初始完整的渗透率和方法的下限预测在原地散装地壳渗透率。增加振幅的循环载荷测试显示出渗透率-应力滞后，随着差应力的减小，保持高渗透率，并且在破坏应力的90%至99%之间观察到最大渗透率增加。故障前渗透率是近7至9个数量级低于一些高压扩散模型的预测，这表明，如果这些模型是正确的，微裂缝基质流不能占主导地位，和大量的流体流动必须占主导地位的大型结构，如macrofracture。我们提出了一个模型，根据我们的数据，在低渗透性结晶岩中的高应力断层尖端过程区的渗透率增加了2个数量级以上。应力减少有关的断层尖端关闭损伤区裂纹向前迁移，而一些渗透性保持由于永久性微裂缝损伤的滞后。
Detailed experimental studies of the development of permeability of crustal rock during deformation are essential in helping to understand fault mechanics and constrain larger-scale models that predict bulk fluid flow within the crust. Permeability is particularly enhanced in the damage zone of faults, where microfracture damage accumulates under stress less than that required for macroscopic failure. Experiments performed in the prefailure region can provide data directly applicable to these zones of microfracture damage surrounding faults. The strength, permeability, and pore fluid volume evolution of initially intact crystalline rocks (Cerro Cristales granodiorite and Westerly granite) under increasing differential load leading to macroscopic failure has been determined at water pore pressures of 50 MPa and varying effective pressures from 10 to 50 MPa. Permeability is seen to increase by up to, and over, 2 orders of magnitude prior to macroscopic failure, with the greatest increase seen at lowest effective pressures. Postfailure permeability is shown to be over 3 orders of magnitude higher than initial intact permeabilities and approaches the lower limit of predicted in situ bulk crustal permeabilities. Increasing amplitude cyclic loading tests show permeability-stress hysteresis, with high permeabilities maintained as differential stress is reduced and the greatest permeability increases are seen between 90 and 99% of the failure stress. Prefailure permeabilities are nearly 7 to 9 orders of magnitude lower than that predicted by some high-pressure diffusive models suggesting that if these models are correct, microfracture matrix flow cannot dominate, and that bulk fluid flow must be dominated by larger-scale structures such as macrofractures. We present a model, based on our data, in which the permeability of a highly stressed fault tip process zone in low-permeability crystalline rocks increases by more than 2 orders of magnitude. Stress reduction related to the onward migration of the fault tip close damage zone cracks, while some permeability is maintained due to hysteresis from permanent microfracture damage.