Using horizontal and vertical deformation signals to characterize water availability in fractured and faulted crystalline-rock aquifer systems

世界上很大一部分可饮用地下水存在于断裂的基岩中，这些含水层很难确定有多少水可用，以及有多容易获得。为了从断裂和断裂的结晶岩环境中获得可持续的大量饮用地下水，需要采用新颖的非侵入性方法来表征这些复杂的含水层。成功的表征取决于对控制流量、补给和存储容量的参数的准确估计。大多数裂缝表征依赖于井中水位或压力变化的测量，这已被证明不足以准确估计含水层的性质。该项目将测量地表和井内垂直和水平岩石变形信号，这些信号是由泵送引起的应力引起的。该项目将展示这些数据的使用，用于描述当地和区域裂缝含水层的特征，并用于量化参数，以支持评估这些系统中的水补给和流量。本研究结果将提高对裂隙岩石含水层可安全抽取水量的估计。此次调查主要集中在法国Ploemeur和美国Virginia，这将建立雷恩大学和弗吉尼亚理工大学之间的合作，为研究生提供出国学习的机会，拓宽他们的研究视野和国际视野。该研究将调用不同时空尺度的地表水平和垂直变形信号，反向校准三维耦合孔隙力学和流动模型，以准确估计裂缝和宿主岩石的性质（透过率和储存）以及流动几何形状（裂缝或断层的方向和根部深度）。本文将研究Ploemeur附近结晶岩中的局部和次区域流动系统。那里存在两种不同的水平变形信号：一种是与平缓倾斜的水平接触带有关的季节性变形信号，另一种是与为期2天的含水层试验有关的沿亚垂直裂缝带走向方向的收敛变形信号。Ploemeur站点将用于展示如何使用随季节水位变化的垂直变形信号来准确量化地下水补给。该研究将开发一种新的分析含水层测试工具，根据在弗吉尼亚州断裂岩石现场收集的数据估计应力相关参数。这项研究的结果改进了使用强制梯度封隔器的传统压裂测试，由于测量的水位和裂缝应变依赖于应力，传统封隔器测试被证明不起作用。

A large portion of the world's potable groundwater occurs in fractured bedrock, and these aquifers are difficult to characterize for how much water is available and how easily accessible it is. The ability to secure sustainable and significant quantities of potable groundwater from fractured and faulted crystalline-rock environments requires novel non-invasive ways to characterize these complex aquifers. Successful characterization depends upon accurate estimates of the parameters that govern flow, recharge, and storage capacity. Most fracture characterization relies on measurements of water levels or pressure changes in wells which have been shown to be inadequate for accurately estimating aquifer properties. This project will measure vertical and horizontal rock deformation signals at the land surface and within the borehole that result from pumping-induced stresses. This project will demonstrate the use of these data for characterizing local and regional fractured aquifers and for quantifying parameters that support assessment water recharge and flow in these systems. The results of this research will improve the estimation of the quantity of water that can be safely extracted from fractured rock aquifers. The investigation is focused on sites in Ploemeur, France, and in Virginia, USA, that will establish a collaboration between the University of Rennes and Virginia Tech that affords graduate students the opportunity to study abroad and broaden their research perspectives and international exposure.The research will invoke surface horizontal and vertical deformation signals at different temporal and spatial scales to inversely calibrate a 3D coupled poromechanical and flow model to accurately estimate fracture and host rock properties (transmissivity and storage) and flow geometries (fracture or fault orientation and root depth). A local and a sub-regional flow system in the crystalline rocks near Ploemeur will be studied. Two distinct horizontal deformation signals exist there: a seasonal signal showing deformation associated with a gently dipping horizontal contact zone and a converging deformation signal oriented along strike of a sub-vertical fracture zone associated with a 2-day aquifer test. The Ploemeur site will be used to show how vertical deformation signals with seasonal water-level changes can be used to accurately quantify groundwater recharge. The research will develop a new analytical aquifer testing tool to estimate stress-dependent parameters based on data collected at the fractured rock site in Virginia. The results of this research improve upon traditional fracture tests using forced-gradient packer tests that have been shown not to work because the measured water-level and fracture strain are stress dependent.