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

点击翻译按钮获取中文摘要

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.