THERMAL PROPERTIES OF NEW HAMPSHIRE ROCKS FOR GEOTHERMAL EXPLORATION

Geothermal exploration in the northeastern United States has recently gained steam with the advent of Enhanced Geothermal System (EGS) technology. Assessing the feasibility of EGS relies on a comprehensive understanding of the heat distribution within the upper crust and the parameters that control it. Chief among these parameters are thermal conductivity, radiogenic heat production and heat capacity. Knowledge of these thermal properties enables the evaluation of heat flow and temperature in the assessment of potential geothermal reservoirs.

New Hampshire has been suggested as one of these potential EGS reservoirs due to its high heat flow relative to the rest of the northeastern United States (Birch et al., 1968; Jaupart et al., 1982; Blackwell and Richards, 2004). However, lack of data on the thermal properties of rocks in the state has hindered accurate investigation into the state’s geothermal potential. To reach a comprehensive assessment of the thermal variation in New Hampshire’s rocks, Benson (2009) and Benson and Van Baalen (2009) synthesized limited available data on heat flow, thermal conductivity, heat capacity and radiogenic heat production with new values calculated from modal analyses of rocks across the state. These calculated data match the limited previous data very well and fill much-needed gaps where no (or some) thermal data was available.

These data are used in basic thermal modeling and are presented with the results of the models. The models confirm that the area around the Conway and Sebago granites in central New Hampshire display the thermal conditions most favorable for geothermal energy production. These data, especially the new values for thermal conductivity, will be useful for future investigations into the Granite State’s geothermal resources and can potentially serve as a model for evaluating other prospective EGS localities.