Deep geothermal resource potential in Connecticut; progress report

The Connecticut and Massachusetts Geological Surveys are collaborating on a National Geothermal Data Project funded by the US Department of Energy through the Association of American State Geologists.Geothermal resources in Connecticut (CT) to date have been exploited using near surface ground source heat pump technology. This is the first investigation of CT deep geothermal resources. Many CT granitoids contain heat producing elements. The goal is to identify geologic units capable of producing enough heat, at reasonable drilling depths, to operate a viable geothermal power plant. Target rock units must contain enough uranium, thorium and potassium (U/Th/K) in combination with heat generated through the natural geothermal gradient of the Earth to generate electricity and co-produced direct heating. Heat at depth can be concentrated by an overlying insulating layer of sedimentary rocks and glacial sediments. 27 CT bedrock units were selected for sampling using existing mapping. 120 samples were analyzed using X-Ray Fluorescence Spectrometry. Heat production values (HPVs) at or greater than 4 mu W/m (super 3) were considered to be of interest. Values ranging from 4 to 18 mu W/m (super 3) were calculated for 7 of the 27 rock units. Elevated concentrations of thorium, ranging from 10.5 ppm to 245 ppm, were the primary contributors to increased HPVs. Initial results indicate that the warmest rocks are Permian and Precambrian, which is consistent with earlier results from granitoid bodies underlying the Atlantic Coastal Plain of Virginia (Speer et al., 1979). Additional bedrock samples will be analyzed to further characterize geochemical variations and potential HPVs of target rock units. Direct thermal conductivity measurements are being made of select bedrock samples in addition to sedimentary rocks of the Hartford Basin. Theoretical thermal profiles derived from rock geochemistry will provide an estimate of heat generated at depth for geologic units of interest and assist in determining the potential for an insulating layer overlying heat producing granitoids. Direct thermal conductivity measurements of unconsolidated materials throughout CT are also being made to support the ground-source heat pump industry. All data and mapping will be accessible via the National Geothermal Data System (NGDS).