Transient hydraulic tomography in a fractured dolostone: Laboratory rock block experiments

Abstract

The accurate characterization of fractured geologic medium, imaging of fracture patterns and their connectivity have been a challenge for decades. Recently, hydraulic tomography has been proposed as a new method for imaging the hydraulic conductivity (K) and specific storage (Ss) distributions of fractured geologic media. While encouraging results have been obtained in the field, the method has not been rigorously assessed in a controlled laboratory setting. In this study, we assess the performance of transient hydraulic tomography (THT) in a fractured dolomitic rock block. The block is characterized through flow‐through tests and multiple pumping tests. The pumping test data were then analyzed with the THT code of Zhu and Yeh (2005) to image the fracture patterns and their connectivity through the delineation of K and Ss distributions (or tomograms). Results show that the THT analysis of pumping tests yields high‐K and low‐Ss zones that capture the fracture pattern and their connectivity quite well and those patterns become more vivid as additional pumping test data are added to the inverse model. The performance of the estimated K and Ss tomograms are then assessed by: (1) comparing the tomograms obtained from synthetic to real data; (2) comparing the tomograms from two different pumping configurations; (3) comparing the estimated geometric mean of the hydraulic conductivity (KG) from the K tomogram to the effective hydraulic conductivity (Keff) estimated from the flow‐through tests; and (4) predicting five independent pumping tests not used in the construction of the K and Ss tomograms. The performance assessment of the K and Ss tomograms reveals that THT is able to image high‐K and low‐Ss zones that correspond to fracture locations in the fractured rock block and that the tomograms can be used to predict drawdowns from pumping tests not used in the construction of the tomograms with reasonable fidelity.