Evaluation of Storage in Fractured-Rock Aquifer Systems

许多重要的地方和区域含水层都存在于裂隙和断层结晶岩系统中。有效孔隙度和相关储集量存在于原生和次生裂缝网络以及基质块中。已经设计了许多水力测试来量化裂缝系统的流动性和渗透性，但是由于在应力条件下测量裂缝或基质块的压缩是困难且昂贵的，因此存储和孔隙度的准确量化和分布一直是难以捉摸的。一种非常有效地提供应力-应变关系以量化疏松泵送盆地中的骨骼特定存储特性的装置是钻孔管伸长计。我们建议安装一个管道引伸计在一个良好的特点是断裂和断层结晶岩含水层系统，已知包含一个主要的断裂带逆冲断层和一个二级断裂网络内包含一个低渗透性矩阵。引伸计的设计将允许对岩石（和裂缝）压缩率为10- 1 l m2/N的情况进行精确的应变测量。来自固体潮、气压和降雨负荷以及温度效应的残余应变可以被监测并有效地消除。设计的周期性水力试验将产生滞后应力-应变曲线，从而量化主裂缝和次裂缝的压缩储存性能。使用热脉冲流量计和类型曲线分析的流量随时间变化的分析模型可以提供裂缝transmittance和总裂缝存储的估计。耦合引伸计和分析建模分析可以允许量化孔隙度和块体导水率沿着准确的存储估计。ABAQUS有限元建模允许使用瞬态参数在一个双渗透率/孔隙度系统，这将提供进一步了解的水力特性和应力条件下的响应，这一拟议的研究的更广泛的影响是显着的，因为存储和孔隙度定量在断裂岩石往往是难以捉摸的，即使是详细和昂贵的含水层测试技术。结合使用引伸计数据，再加上分析和数值模拟，将提供详细的估计所有重要的水力特性的裂缝。本研究中使用和开发的技术可以很容易地应用于所有的嵌岩环境。这将是美国东部第一个也是唯一一个在运行的管道引伸计（国内唯一一个在断裂结晶岩中运行的管道引伸计），并将为其他大学和美国地质调查局的研究人员和学生提供重要的数据和机会，否则他们将无法使用该设备或它将产生的应变测量。从引伸计获得的数据将被纳入两个水文地质课程在弗吉尼亚理工大学的一部分，有关应变，存储和断裂力学讲座。它也将提供给学生实地考察断裂岩石研究网站，我们正在继续在蓝岭省发展。

Many important local and regional aquifers occur in fractured and faulted crystalline-rock systems. Effective porosity and related storage occur in primary and secondary fracture networks as well as the matrix block. Many hydraulic tests have been designed to quantify flow and permeability of the fractured system, but accurate quantification and distribution of storage and porosity have been elusive because measuring the compression of the fractures or matrix block under stressed conditions is difficult and costly. One device that has been highly effective for providing stress-strain relations for quantifying skeletal specific storage properties in unconsolidated pumped basins is the borehole pipe extensometer. We propose to install a pipe extensometer in a well characterized fractured and faulted crystalline-rock aquifer system that is known to contain a major fracture zone from thrust faulting and a secondary fracture network contained within a low permeability matrix. The extensometer design will allow for accurate strain measurements for a rock (and fracture) compressibility of 10-1l m2/N. Residual strains from earth tides, barometric and rainfall loading and temperature effects can be monitored and effectively eliminated. Designed cyclical hydraulic tests will yield hysteretic stress-strain curves leading to quantification of primary and secondary fracture compressive storage properties. Analytical modeling of flow verses time using the heatpulse flow meter and type-curve analysis can provide estimates of fracture transmissivity and total fracture storage. The coupled extensometer and analytical modeling analysis can allow for quantification of porosity and block hydraulic conductivity along with accurate storage estimates. Finite-element modeling with ABAQUS allows for the use of transient parameters in a dual permeability/porosity system that will provide further understanding of the hydraulic characteristics and response under stressed conditions.The broader impacts of this proposed research are significant because storage and porosity quantification in fractured rocks is often elusive, even with detailed and costly aquifer testing techniques. The combined use of extensometer data coupled with analytical and numerical modeling will provide detailed estimates of all important hydraulic properties of fractures. The techniques used and developed in this research can be readily applied to all fractured-rock settings. This would represent the first and only operating pipe extensometer in the eastern United States (the only one in the country in fractured crystalline rocks) and would provide important data and opportunities for researchers and students from other universities and the US Geological Survey who would not otherwise have access to this device or the strain measurements it will yield. The data obtained from the extensometer will be incorporated into two hydrogeology courses at Virginia Tech as part of lectures pertaining to strain, storage, and fracture mechanics. It will also be available for student field trips to the Fractured Rock Research site that we are continuing to develop in the Blue Ridge province.