Date of Award:

5-2014

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

James P. Evans

Committee

James P. Evans

Committee

John W. Shervais

Committee

Douglas R. Schmitt

Committee

Anthony R. Lowry

Committee

Thomas E. Lachmar

Abstract

Geothermal energy is being explored as a supplement to traditional fossil fuel resources to meet growing energy demand and reduce carbon emissions. Geothermal energy plants harvest heat stored in the Earth’s subsurface by bringing high temperature fluids to the surface and generating steam to produce electricity. Development of geothermal resources is often inhibited by large upfront risk and expense. Successful mitigation of those costs and risks begins with efficient characterization of the resource before development. A typically successful geothermal reservoir consists of a fractured reservoir that conducts hydrothermal fluids and a cap rock seal to limit convective heat loss through fluid leakage. The controls on the system include the density and orientation of fractures, mechanical rock properties, and the local stress field acting on those rocks.

The research presented in this dissertation utilizes diverse data sets to characterize core, wireline borehole logs, and laboratory data to describe the distribution of fractures, rock properties, and the orientation and magnitude of stresses acting on the borehole. The research demonstrates there is a potential resource in the region and describes the controls on the vertical extent of the hydrothermal fluids. The distribution of fractures is controlled by the distribution of elastic rock properties and rock strength. A cap rock seal is present that limits hydrothermal fluid loss from a fractured artesian reservoir at 1,745 m (5,726 ft). In addition to characterization of the resource, this research demonstrates that an equivalent characterization can be used in future exploration wells without the expense and risk of collecting core. It also demonstrates that multiple methods of analysis can be utilized simultaneously when some data are not available. Data collection from deep wellbores involves risk and data loss or tool failure is a possibility. In these cases, our methods show that successful characterization is still possible, saving time and money, and minimizing the financial risk of exploration

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