Text

theses

There is a growing need to understand the hydraulic properties of fractured rock for the development and extraction of natural resources and also to engineer remediation strategies at contaminated sites. The characterization of fractured rock is inherently complex due to the multifaceted interrelationships between stress, temperature, roughness and fracture geometry that affect hydraulic conductivity and flow paths that have hydraulic properties varying over orders of magnitude. Often, sparse data points are interpolated from borehole locations to infer the spatial distribution of flow and transport within fractures. However, these fracture distributions are often poorly resolved due to the heterogeneity of these networks between the borehole locations. Electrical resistivity tomography (ERT) is a viable technology to characterize fractured rock as the electrical pathways mimic hydraulic pathways in fractured rock, assuming surface conduction is small. Previous work using ERT in fractured rock gave limited hydrogeological information due to finite element modeling techniques which were not physically appropriate for fractured rock and lack of instrumentation to permit imaging of isolated fracture zones. Synthetic and field datasets were used to incorporate field information to yield an improved hydrogeological interpretation. Specifically, model constraints were incorporated in the inversion modeling and borehole deviations defining these boundaries were explicitly defined in the discretization. Where this information was incorporated, ERT time-lapse changes in conductivity were more focused surrounding fracture locations and borehole effects were minimized. A rigorous examination of localized effects of de-regularization was undertaken and it was found that uncertainty in these boundaries can lead to spurious inversion artifacts. Electrode arrays within seven boreholes were designed, which included isolation bladders and a water sample/injection line. This design facilitated multiple tracer tests in a fractured mudstone to be conducted. The spatial scale of this experiment was such that the primary hydrogeological heterogeneity controlling flow and transport was captured, providing unique information relative to that acquired from borehole logging methods alone. The modeling techniques and instrumentation advancements detailed in this dissertation demonstrates the potential of ERT at fractured rock sites to work towards creating comprehensive flow and transport models.

ETD_6206

Ph.D.

Includes bibliographical references

Includes vita

by Judith L. Robinson

doi:10.7282/T3DF6T3V

ETD doctoral

The author owns the copyright to this work.