Date of Award:

5-2013

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

James P. Evans

Committee

James P. Evans

Committee

Alvar Braathen

Committee

Susanne U. Janecke

Abstract

Anthropogenic carbon dioxide (CO2) primarily resulting from the combustion of fossil fuels can be captured and stored by injection into underground porous sandstone reservoirs. This process has been proposed as a method for reducing greenhouse gas emissions that contribute to global warming. Two of the major risks associated with this technology include: 1) upwards migration and leakage of injected fluids along natural fault and fracture networks, and 2) possible induced seismicity (earthquakes) resulting from increasing the pressure in reservoirs and along existing faults.

We use geologic field mapping, petrographic analysis, characterization of the fault zone, analysis of altered and mineralized rocks in and around the fault zone, and computer-based modeling to better understand of the Iron Wash fault zone. We use studies of exposed natural analogs of subsurface geology to evaluate the impacts of faulting and fracturing on reservoir and top-seals. We examine the Iron Wash fault, a 25-km long normal fault which cuts Jurassic sedimentary rocks and has throws that range from 20-120 m, to examine how a fault may affect seal integrity. We incorporate field data and observations with subsurface data derived from oil and gas exploration boreholes to produce three types of models for the Iron Wash fault: 1) geometric model of the fault in the subsurface, 2) predictive models of fault zone behavior and fault seal analysis, and 3) predictive models of the response of the fault zone to an imposed stress field and increasing reservoir pressures.

We conclude that the Iron Wash fault zone has low sealing capacity and would likely fail to behave as a lateral barrier to fluid flow. Analysis of fluid alteration and mineralization around the fault zone indicates that the fault zone was conduit for paleofluids. Modeling results indicate that increases in reservoir pressure against the Iron Wash fault in the current stress field could potentially result in the failure of the fault resulting in earthquakes or increased hydraulic conductivity of fractures. It is impossible to predict the magnitude of potentially induced earthquakes or how much fluid may leak along faults that have failed, but this study provides insight into the potential risks associated with injection of large volumes of fluid into the subsurface

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