Heat and 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会迅速和广泛地迁移，这是由于离散的裂缝和裂缝相互连接所提供的路径。相反，热传输发生在一个慢得多的速度，但也由裂缝路径提供地下水速度足够高（即注入或提取条件下）。运输过程包括个别裂缝内的路径的曲折度，基质孔隙度的可变性，裂缝互连的可变性，通过优先路径的横向迁移，水力梯度的时间效应，以及裂缝交叉点处发生的分散效应。在拟议的研究中，我们将集中在两个规模的运输断裂岩石，一个在本地规模（即附近的注入或回抽井），另一个在很大的运输距离（>150米）在裂缝网络。局部尺度研究的目的是检查离散裂缝中的热传输的关键过程，以评估“短路”的可能性，即裂缝中的流体与周围岩石之间的热交换的显著低效率，以及热分散，热交换过程中的另一种潜在低效率。当地规模的研究将通过在多个裂缝特征遍布的结晶岩中的一个特征良好的地点的钻孔之间进行的示踪剂实验进行。该研究的这一部分将由两名硕士生和一名博士生进行。大规模的研究将涉及运输数据集的汇编和使用离散裂缝网络模型的模拟（由于大规模计算的限制，可能的话），目的是解决裂缝路径的减少和障碍的影响将如何影响这些规模的运输预测。还将使用替代拉格朗日（与流体一起移动的参考系）方法和平均技术来寻求更有效（即更易处理）的方法来模拟这种规模的运输，这些方法捕获了大块中裂缝和岩石之间的溶质交换过程。一项博士研究将进行大规模研究。硕士和博士生将在他们的研究支持由本科暑期学生在每年。所有学生将接受水文地质学领域和实验室技术的培训，以及协助分析现场和实验室数据的分析和数值建模。这项研究的结果将提供一个评估的基本过程中的污染物和热迁移的裂缝，并将有实际应用的水文地质学家和工程师在风险管理和废物设施的补救，碳捕获在深地下的管理，地热能和地下储热的设计和应用。

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. Conversely, heat transport occurs at a much slower rate but is also governed by fracture pathways provided groundwater velocity is high enough (i.e. under injection or withdrawal conditions). 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 focus on two scales of transport in fractured rock, one at the local-scale (i.e. adjacent to an injection or withdrawal well) and the other at much large transport distances (>150 m) in fracture networks. The intent with the local scale studies is to examine the key processes of heat transport in discrete fractures to evaluate the potential for "short-circuiting", a significant inefficiency in heat exchange between the fluid in the fractured and the surrounding rock, and thermal dispersion, another potential inefficiency in the heat exchange process. The local scale studies will be conducted via tracer experiments conducted between boreholes in a well-characterized site in crystalline rock pervaded by multiple fracture features. This component of the study will be conducted by two Masters students and one PhD student. The large-scale study will involve the compilation of transport data sets and the simulation of these using a discrete fracture network model (where possible due to computational limits at large scale), with the intent to resolve how the diminishment of fracture pathways and the impact of barriers will influence prediction of transport at these scales. More efficient (i.e. tractable) means by which to simulate transport at this scale will also be sought using alternative Lagrangian (frame of reference which moves with the fluid) approaches, and averaging techniques which capture the process of solute exchange between the fractures and the rock in large blocks. One PhD study will conduct the large-scale study. The Masters and PhD students will be supported in their research by an undergraduate summer student in each year. All students will be trained in the field and laboratory techniques used in hydrogeology, and in the analytical and numerical modeling that assist in the analysis of the field and lab data. The outcome of this research will provide an assessment of the fundamental processes governing contaminant and heat migration in fractures, and will have practical application by hydrogeologists and engineers in the risk management and remediation of waste facilities, the management of carbon capture in the deep subsurface, and the design and application of geothermal energy and subsurface heat storage.