Online

Caulk, Robert

Civil and Environmental Engineering

2015

MS

Geothermal energy has become a focal point of the renewable energy revolution. Both shallow and deep types of geothermal energy have the potential to offset carbon emissions, reduce energy costs, and stimulate the economy. Before widespread geothermal exploration and exploitation can occur, both shallow and deep technologies require improvement by theoretical and experimental investigations. This thesis investigated one aspect of both shallow and deep geothermal energy technologies. First, a group of shallow geothermal energy piles was modeled numerically. The model was constructed, calibrated, and validated using available data collected from full-scale in-situ experimental energy piles. Following calibration, the model was parameterized to demonstrate the impact of construction specifications on energy pile performance and cross-sectional thermal stress distribution. The model confirmed the role of evenly spaced heat exchangers in optimal pile performance. Second, experimental methods were used to demonstrate the evolution of a fractured granite permeability as a function of mineral dissolution. Steady-state flow-through experiments were performed on artificially fractured granite cores constrained by 5 MPa pore pressure, 30 MPa confining pressure, and a 120 degrees Celsius temperature. Upstream pore pressures, effluent mineral concentrations, and X-Ray tomography confirmed the hypothesis that fracture asperities dissolve during the flow through experiment, resulting in fracture closure.