Evaluation of Storage in Fractured-Rock Aquifer Systems

许多重要的地方和区域含水层发生在断裂和断裂的结晶岩系统中。有效孔隙度和相关储层存在于原生、次生裂缝网络以及基质块体中。许多水力测试旨在量化压裂系统的流量和渗透率，但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，因此无法准确量化储层和孔隙度的分布。在松散的抽水盆地中，一种非常有效地提供应力-应变关系来量化骨架特定存储特性的设备是井管柱伸量计。我们建议在一个具有良好特征的裂缝和断裂的结晶岩含水层系统中安装一个管道延伸计，该系统已知包含一个来自逆冲断层的主要裂缝带和一个包含在低渗透基质中的次级裂缝网络。延伸计的设计将允许精确测量岩石（和裂缝）压缩率为10-1l m2/N的应变。可以监测和有效消除来自潮汐、气压和降雨载荷以及温度影响的残余应变。设计的循环水力试验将产生迟滞应力-应变曲线，从而量化初级和次级裂缝的压缩储存特性。利用热脉冲流量计和类型曲线分析进行流量随时间的分析建模，可以估计裂缝透过率和总裂缝储存量。耦合的延伸计和分析建模分析可以量化孔隙度和块体水力导电性以及准确的存储估计。ABAQUS的有限元建模允许在双重渗透率/孔隙度系统中使用瞬态参数，从而进一步了解应力条件下的水力特性和响应。这项研究的广泛影响是重大的，因为即使使用详细和昂贵的含水层测试技术，裂缝岩石的储存和孔隙度量化通常也是难以捉摸的。将延伸仪数据与分析和数值模拟相结合，可以提供裂缝所有重要水力特性的详细估计。本研究中所使用和开发的技术可以很容易地应用于所有的压裂环境。这将是美国东部第一个也是唯一一个运行的管道延伸仪（全国唯一一个在破碎的结晶岩石中运行的管道延伸仪），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其将产生的应变测量。从拉伸仪获得的数据将被纳入弗吉尼亚理工大学的两门水文地质学课程中，作为与应变、储存和断裂力学有关的课程的一部分。它也将提供给学生实地考察的岩石断裂研究网站，我们正在继续发展在蓝岭省。

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.