Permeability and Elastic Properties of Fractured Rock: Systematic Experimental Investigation and Model Development

裂隙岩含水层是一种重要的水资源。大多数岩石中复杂的裂隙分布使地下水在其中的流动变得难以描述和理解。需要成本效益高的方法来确保在地下水管理方面作出合理的决策。使用井水位和跨孔测试来确定地下水流动路径的方法是有用的，但仅根据这些数据绘制的地图的分辨率取决于井的数量，由于资金和时间的限制，这通常是不够的。在这种情况下，有必要依靠额外的数据，特别是地震速度，来改进地下流动路径的测绘。这项研究将是首次对具有良好特征的三维裂缝网络中的流动特性进行系统的实验研究，将地震速度的变化与渗透率的变化联系起来。这一建议建立在十多年来使用冰作为岩石模型的工作基础上，这表明控制岩石和冰的脆性破坏的基本过程是相似的。然而，冰在实验上比岩石有明显的优势。拟议的实验和模型开发提供了深入了解各种破碎的、结晶的天然(即岩石)和合成材料的弹性特性和渗透性的机会。因此，这项研究适用于材料科学、工程和地球科学中的许多学科。在裂隙岩石中识别狭窄的、连续的高电导率带是水文地质学中的一个紧迫挑战。水压层析成像(多次井间试井的反模拟)在这项任务中显示出越来越大的前景，但水压层析成像的分辨率对井眼和井间测试的数量很敏感，而井眼和井间测试的数量通常太少。在这种情况下，有必要依赖额外的数据类型，特别是地球物理调查，以提高水文地质特征的分辨率。当地球物理参数和水文地质参数，特别是地震速度和渗透率之间的关系已知时，将水力和地球物理数据结合在一起是最有效的。渗透率和地震速度都取决于裂缝密度。这项研究考察了将地震速度与渗透率联系起来的这些关系。具体地说，以冰为模型材料，这将是首次对具有良好特征的三维裂隙网络的流动特性进行系统的实验研究，旨在阐明地震速度变化和裂隙地质介质中渗透率变化之间的关系。尽管裂缝引起的弹性性质和渗透率的变化很重要，但在脆性变形过程中，很少有系统地观察到这些性质的共同演变。这些数据对于完善连接水文地质和地球物理参数的本构模型至关重要。拟议的研究结合了实验室测量和机械模型开发，作为实地应用的必要先导，旨在获得关于渗透率的空间密集信息，从而改善地下水流动和运输的量化特征。

Fractured-rock aquifers are an important water resource. Complex fracture distributions in most rocks make it difficult to characterize and understand groundwater flow in them. Cost-effective methods are needed to ensure sound decisions in groundwater management. Methods using well water levels and cross-hole tests to identify groundwater flow pathways are useful, but the resolution of maps based on these data alone depends on the number of wells, which is commonly inadequate due to financial and time constraints. In these cases, it is necessary to rely on additional data, particularly seismic velocities, to improve the mapping of subsurface flow pathways. This research will be the first systematic experimental study of the flow properties in well-characterized 3D fracture networks that will relate changes in seismic velocity to changes in permeability. This proposal builds on more than a decade of work using ice as a model for rock, which has shown that the basic processes controlling brittle failure of rocks and ice are similar. However, ice has distinct experimental advantages over rock. The proposed experiments and model development offer the opportunity to gain insights into the elastic properties and permeabilities of a broad range of fractured, crystalline natural (i.e., rocks) and synthetic materials. Thus, this research has applicability to many disciplines in materials science, engineering, and the geosciences. Identifying narrow, continuous high conductivity zones in fractured rock is a pressing challenge in hydrogeology. Hydraulic tomography (the inverse modelling of multiple cross-hole well tests) has shown increasing promise for this task, but the resolution of hydraulic tomography is sensitive to the number of boreholes and cross-hole tests, which are commonly too few. In these cases it is necessary to rely on additional data types, particularly geophysical surveys, to improve the resolution of the hydrogeological characterization. Combining hydraulic and geophysical data is most effective when the form of the relationship that links geophysical and hydrogeological parameters, particularly the relationship between seismic velocities and permeability, is known. Both permeability and seismic velocity depend on fracture density. This research examines these relationships to link seismic velocity to permeability. Specifically, using ice as a model material, this will be the first systematic experimental study of the flow properties of well-characterized 3D fracture networks designed to elucidate the relationship between changes in seismic velocity and changes in permeability in fractured geologic media. Despite the importance of fracture-induced changes in elastic properties and permeability, there are few systematic observations of the co-evolution of these properties during brittle deformation. Such data are critical for refining constitutive models linking hydrogeologic and geophysical parameters. The proposed research is a combination of laboratory measurements and mechanistic model development that serves as a necessary precursor to field applications designed to obtain spatially dense information about permeability that will improve the quantitative characterization of groundwater flow and transport.