Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), P.O. Box 3640, 76021 Karlsruhe, Germany; Friedrich-Schiller-University Jena (FSU), Institute of Geosciences, Applied Geology, Burgweg 11, 07749 Jena, Germany.
Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), P.O. Box 3640, 76021 Karlsruhe, Germany.
J Contam Hydrol. 2019 Feb;221:82-97. doi: 10.1016/j.jconhyd.2018.11.008. Epub 2018 Nov 22.
The impact of fracture geometry and aperture distribution on fluid movement and on non-reactive solute transport was investigated experimentally and numerically in single fractures. For this purpose a hydrothermally altered and an unaltered granite drill core with axial fractures were investigated. Using three injection and three extraction locations at top and bottom of the fractured cores, different dipole flow fields were examined. The conservative tracer (Amino-G) breakthrough curves were measured using fluorescence spectroscopy. Based on 3-D digital data obtained by micro-computed tomography 2.5-D numerical models were generated for both fractures by mapping the measured aperture distributions to the 2-D fracture geometries (x-y plane). Fluid flow and tracer transport were simulated using COMSOL Multiphysics. By means of numerical simulations and tomographic imaging experimentally observed breakthrough curves can be understood and qualitatively reproduced. The experiments and simulations suggest that fluid flow in the altered fracture is governed by the 2-D fracture geometry in the x-y plane, while fluid flow in the unaltered fracture seems to be controlled by the aperture distribution. Moreover, we demonstrate that in our case simplified parallel-plate models fail to describe the experimental findings and that pronounced tailings can be attributed to complex internal heterogeneities. The results presented, implicate the necessity to incorporate complex domain geometries governing fluid flow and mass transport into transport modeling.
本文通过实验和数值模拟研究了单一裂隙中裂隙几何形状和开度分布对流体运动和非反应性溶质运移的影响。为此，研究了热液蚀变和未蚀变的花岗岩岩芯中的轴向裂隙。通过在裂隙岩芯的顶部和底部设置三个注入点和三个提取点，考察了不同的偶极流场。使用荧光光谱法测量了保守示踪剂（Amino-G）的突破曲线。基于微计算机断层扫描获得的 3D 数字数据，通过将测量的开度分布映射到 2D 裂隙几何形状（x-y 平面），为两个裂隙生成了 2.5D 数值模型。使用 COMSOL Multiphysics 模拟了流体流动和示踪剂运移。通过数值模拟和层析成像，可以理解并定性重现实验观测到的突破曲线。实验和模拟表明，蚀变裂隙中的流体流动受 x-y 平面上的 2D 裂隙几何形状控制，而未蚀变裂隙中的流体流动似乎受开度分布控制。此外，我们证明在我们的情况下，简化的平行板模型无法描述实验结果，明显的拖尾现象可归因于复杂的内部非均质性。本研究结果表明，在运移模拟中需要将控制流体流动和质量传输的复杂域几何形状纳入其中。
