FLUID-FLOW THROUGH ROCK JOINTS - THE EFFECT OF SURFACE-ROUGHNESS
FLUID-FLOW THROUGH ROCK JOINTS - THE EFFECT OF SURFACE-ROUGHNESS
复制标题
DOI：
10.1029/jb092ib02p01337
复制
发表时间：
1987-02-10
期刊：
影响因子：
--
通讯作者：
BROWN, SR
中科院分区：
文献类型：
--
作者：
BROWN, SR
通过岩石节理的流体流动通常用平行板模型来描述，其中体积流量随着节理孔径的立方而变化。然而，与该模型的偏差是预料之中的，因为真实的接合表面是粗糙的并且在离散点处相互接触。为了进一步研究这个问题，对粗糙表面之间的流动进行了计算机模拟。使用表面形貌的分形模型以数字方式生成真实的粗糙表面。这些表面成对放置在一起，形成具有随机孔径分布的“接头”。雷诺方程描述了轻微非平面和非平行表面之间的层流，通过有限差分法在二维孔径网格上求解。解决方案是通过接头的局部体积流量。该解决方案直接用于三次定律中以获得所谓的“水力孔径”。对于各种表面粗糙度（分形维数），将水力孔径与表面的平均间距进行比较。在大间距下，表面形貌几乎没有影响。在小间距处，流动是曲折的，倾向于通过大孔径区域。对粗糙接缝中的流体流动影响最大的参数是表面之间的平均间距与均方根表面高度的比率。该参数描述了表面粗糙体突出到流体中的距离，并解释了与平行板模型的大部分不一致。分形维数的变化仅对流体流动产生二阶效应。对于弹性变形过程中预期的接缝闭合范围，这些结果表明，粗糙表面之间的实际流速约为平行板模型预测的 70-90%。
Fluid flow through rock joints is commonly described by the parallel plate model where the volume flow rate varies as the cube of the joint aperture. However, deviations from this model are expected because real joint surfaces are rough and contact each other at discrete points. To examine this problem further, a computer simulation of flow between rough surfaces was done. Realistic rough surfaces were generated numerically using a fractal model of surface topography. Pairs of these surfaces were placed together to form a “joint” with a random aperture distribution. Reynolds equation, which describes laminar flow between slightly nonplanar and nonparallel surfaces, was solved on the two‐dimensional aperture mesh by the finite‐difference method. The solution is the local volume flow rate through the joint. This solution was used directly in the cubic law to get the so‐called “hydraulic aperture.” For various surface roughnesses (fractal dimensions) the hydraulic aperture was compared to the mean separation of the surfaces. At large separations the surface topography has little effect. At small separations the flow is tortuous, tending to be channeled through high‐aperture regions. The parameter most affecting fluid flow through rough joints is the ratio of the mean separation between the surfaces to the root‐mean‐square surface height. This parameter describes the distance the surface asperities protrude into the fluid and accounts for most of the disagreement with the parallel plate model. Variations in the fractal dimension produce only a second‐order effect on the fluid flow. For the range of joint closures expected during elastic deformation these results show that the actual flow rate between rough surfaces is about 70–90% of that predicted by the parallel plate model.