Adaptive control of geothermal systems requires high fidelity knowledge of the mechanical behavior of reservoir rock and the response of materials to thermal and mechanical stresses. The presence of large fractures and smaller microcracks in otherwise low porosity igneous rocks make the mechanical behavior highly stress- and temperature-dependent. We present the results of a suite of laboratory measurements of the static elastic properties of a fractured granitoid rock from the Patua geothermal field. Measurements were made from 10-70 MPa confining pressure and from room temperature to 150C. We find that both increases in confining pressure and increases in temperature up to 150C increase elastic moduli and stress-dependent behavior is observed within the entire range of experimental conditions. We interpret this behavior to be the result of the interaction between large and small fractures within the rock. These results are discussed within the context of reservoir geomechanics and the response of geothermal systems to thermal, hydraulic and mechanical perturbation.

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