三轴压力下水与砂岩反应的实验研究

Experimental Study of Water-sandstone Reaction under Triaxial Stress

通过饱水砂岩的三轴压缩实验，研究了含水层砂岩的破裂过程及其伴随的水化学变化，并探讨了砂岩在蠕变和剪切破裂过程中地震水化异常现象的形成机理。用离子色谱仪（IC）和等离子原子发射光谱仪（ICP—OES）测定了不同压力条件下实验溶液的F^-、Cl^-、NO3、SO2^-4、Ca^2＋、Mg^2＋、Na^2＋浓度。饱水砂岩在差应力作用下，随着蠕变时间延长和剪切作用的强化实验，溶液中主要离子的浓度均有不同程度的增大，仅Mg^2＋浓度是降低的。F^-和Cl^-浓度变化最明显，在2～12小时的蠕变时间内分别增大约10倍和4倍，而随剪切作用的强化分别增大约5倍和3倍。这种变化主要与矿物的溶解和流体包裹体的混入有关。实验结果表明，F^-、Cl^-和Ca^2＋可作为砂岩含水层地震水化前兆监测的灵敏组分。

Hydrochemical variations associated with the creeping and shearing deformation of saturated sandstone under triaxial compression were experimentally investigated, and genetic mechanism of hydrochemical anomalies related to earthquake was discussed. Con- centrations of F^- , Cl^- , NO3 , SO^2- 4 , Ca^2＋ , Mg^2＋ and Na^＋ in the produced solutions under different stresses were measured by IC and ICP-OES. With the time of creeping increasing and the differential stresses on the saturated sandstone, the concentrations of different ions in the produced solution increased to different extents, only the concentration of Mg^2＋ decreased. Concentrations of F and Cl^ , which varied most obviously, increased by 10 and 4 times with creeping from 2 to 12 hours,and 5 and 3 times with the shearing stress increases respectively. These phenomena are mainly caused by the dissolution of minerals and mixture of fluid inclusions. The experiment results indicate that F , Cl^- and o Ca^2＋ can be considered as sensitive components for monitoring earthquake in sandstone aquifers.