DIFFUSIVITY OF IONS IN PORE WATER AS A QUANTITATIVE BASIS FOR ROCK DEFORMATION RATE ESTIMATES
DIFFUSIVITY OF IONS IN PORE WATER AS A QUANTITATIVE BASIS FOR ROCK DEFORMATION RATE ESTIMATES
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DOI：
10.1016/0040-1951(94)00234-z
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发表时间：
1995-05
期刊：
影响因子：
2.9
通讯作者：
S. Nakashima
中科院分区：
文献类型：
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作者：
S. Nakashima
提出了对岩石孔隙水中离子扩散的系统处理，以便提供适合定量解决水-岩石相互作用问题（包括流体对岩石变形的影响）的数据。水饱和的高孔隙度沉积物中离子的扩散率主要由总孔隙度和颗粒尺寸控制。水饱和的中孔隙度岩石（øtot=0.005至0.5）中离子的扩散率主要受传输孔隙度øtra（> 5 nm）控制，但受到通过互连微孔的快通道和包括纳米孔（小于25 nm）的慢通道之间的曲折度差异的影响。有效扩散率 Devs。获得的 øtotrelations 对于预测岩石中的扩散系数及其在水-岩石相互作用过程中的时间依赖性可能有用。根据上述和文献数据，评估了“孔隙水扩散”系数（Dpw）和“晶界扩散”系数（Dgb）在25℃时的取值范围。将这些数据与最近较高温度的数据进行比较表明，Dpwan 和 Dgb(15 kJ mol−1) 的活化能估计较低。由此获得代表性的 Dgb 值趋势，在 150–350°C 下，产量“湿”晶界扩散系数 Dgb 约为 10−14m2s−1。基于 Shimizu 方法，使用上述 Dgb 值，给出了流体辅助岩石变形（例如压力溶解）中应变率的计算示例。在 350°C 下，典型晶粒尺寸（d = 0.1 mm）、差异应力（σ = 100 MPa）和典型晶界宽度约为 1–10 nm 时的应变率估计在 10−11 至 10−9s−1 左右非常快，通过“润湿”晶界扩散。对于“非润湿”变形，估计应变速率非常慢，约为 10−17s−1。晶界的润湿特性和含水流体膜的性质对于增强岩石变形具有重要作用，特别是对于低孔隙率岩石。
A systematic treatment of diffusion of ions in rock pore water is presented in order to provide data suitable for quantitatively addressing water-rock interaction problems including the influence of fluids on rock deformation. Diffusivity of ions in water-saturated, high-porosity sediments is primarily controlled by total porosity øtotand grain size. Diffusivity of ions in water-saturated, medium-porosity rocks (øtot= 0.005 to 0.5) is mainly controlled by the transport porosity øtra(> 5 nm), but is influenced by the tortuosity difference between fast pathways through interconnected micropores and slow pathways including nanopores (less than 25 nm). The effective diffusivity Devs. øtotrelations obtained are potentially useful for the prediction of diffusion coefficients in rocks and also their time-dependence during water-rock interactions. Based on the above and literature data, the value ranges at 25°C of “pore-water diffusion” coefficients (Dpw) and of “grain-boundary diffusion” coefficients (Dgb) are evaluated. Comparison of these with recent higher temperature data suggests low activation energies estimated for both Dpwand Dgb(15 kJ mol−1). Representative Dgbvalue trends thus obtained yield “wet” grain-boundary diffusion coefficients Dgbof the order of 10−14m2s−1at 150–350°C. An example calculation of strain rates in fluid-assisted rock deformation such as pressure solution is given based on the method of Shimizu using the above Dgbvalues. The strain rates at 350°C with typical grain size (d = 0.1 mm), differential stress (σ = 100 MPa) and typical grain-boundary width of about 1–10 nm are estimated to be very fast around 10−11to 10−9s−1via diffusion through “wetted” grain boundaries. Very slow strain rates of about 10−17s−1are estimated for “non-wetted” deformation. Wetting characteristics of grain boundaries and the nature of aqueous fluid films have a significant role in the enhancement of rock deformation, especially for low-porosity rocks.