Large-Scale Solute Transport in Fracture Networks

基岩含水层中的工业和废物场所产生的污染物通常由于离散裂缝和裂缝互连提供的通道而迅速而广泛地迁移。运移过程包括单个裂缝内通道的弯曲度、基质孔隙度的可变性、裂缝互连的可变性、通过优先通道的横向运移、水力梯度的时间效应、以及裂缝交叉处发生的弥散效应。在拟议的研究中，我们将从现有的特征良好的地点收集几组数据集，并进行有限数量的大规模示踪实验，以提供通过数值分析调查主要运输机制的基础。最初的研究将集中在离散裂缝中发生的过程，以及通过裂缝孔径变化发展的路径的复杂性，以及由于基质扩散的影响预计将占主导地位。在全裂缝网络研究中，数值分析将再次用于评估主要的输运机制。在这种情况下，主要机制预计是裂缝互连的复杂性，以及裂缝相交造成的色散效应。在离散断裂研究和全网络分析之间，需要两名硕士生。网络实验的分析在计算上提出了一个非常重大的挑战，研究的一个重要组成部分将在比较欧拉（空间固定的参考系）和拉格朗日（随流体移动的参考系）方法上进行，这将需要一个博士生的全职努力。对比将在局部尺度（150米）上进行。为了支持数值研究，将在结晶岩现场环境中进行离散裂缝和裂缝相交的局部尺度研究。申请人在花岗岩片麻岩中开发了一个独特的、最先进的油田场地，在大约20 × 30米的面积上钻了8个井眼。初步的水力测试结果表明，几口井由一条或多条裂缝连接，其中一些有相交。将在这些井之间进行溶质和溶质热示踪实验，以具体探索裂缝孔径非均质性和裂缝相交所起的色散效应。研究的这一部分将涉及两名博士生和一名硕士生。这项研究的结果将提供控制裂缝中污染物迁移的基本过程的评估，并将被水文地质学家和工程师实际应用于预测废物设施的风险，以及这些环境中污染场地的管理。

Contaminants emanating from industrial and waste sites in bedrock aquifers typically migrate rapidly and widely due to the pathways provided by discrete fractures and fracture interconnections. Transport processes include the tortuosity of pathways within individual fractures, the variability of matrix porosity, the variability of fracture interconnections,*lateral migration through preferential pathways, temporal effects in the hydraulic gradients,*and the dispersive effects that occur at fracture intersections.*In the proposed study we will assemble several data sets from existing well characterized*sites and the limited number of tracer experiments conducted*at large scale to provide a basis to investigate through numerical analysis the dominant transport mechanisms. Initial studies will*focus on the processes which occur in discrete fractures, and the complexity of pathways developed through the variability in fracture aperture, and the effects due to matrix diffusion are expected to dominate. In the full fracture network study, numerical analysis will again be used to evaluate the principal transport mechanisms. In this case, the dominant mechanism is expected to be the complexity of the fracture interconnections, and the dispersive effects due to the fracture intersections. Between the discrete*fracture study and the full-network analysis, two Masters students will be required. The analysis of the network experiment poses a very significant*challenge computationally and a significant component of the research will be conducted in comparing Eulerian (spatially fixed frame of reference) and Lagrangian (frame of reference which moves with the fluid) approaches for this setting that will require the fulltime*effort of one PhD*student. The comparison will be conducted at both local scale (150 m).*In order to support the numerical studies, local-scale*investigations of discrete fractures and fracture intersections will be conducted in a*crystalline rock field setting. The Applicant has developed a unique state-of-the art field site with eight boreholes drilled in an area of*approximately 20 by 30 m, in a granite gneiss. Preliminary hydraulic testing results have shown several wells which are connected by one*or more fractures, some with intersections. Tracer experiments using both solute and solute and heat will be conducted between these wells to specifically explore the dispersive effects played by fracture aperture heterogeneity and fracture intersections. This component of the study will involve two PhD students and one Masters student.*The outcome of this research will provide an assessment of the*fundamental processes governing contaminant migration in fractures, and will have practical application by hydrogeologists and engineers in the prediction of risk from waste facilities, and the management of contaminated sites in these settings.