Geothermal Potential Within Devonian Carbonates in the Clarke Lake Gas Field, Northeastern British Columbia, Canada

Abstract

Although most commonly associated with young volcanic terranes and active hot springs, sedimentary basins hold tremendous geothermal potential. Several factors make many sedimentary basins ideal locations to explore for geothermal energy: low thermal conductivity of sedimentary rocks results in higher than average geothermal gradients; porous and permeable regional aquifers are conducive to the production of geothermal fluids; and existing oil and gas exploration results are available to characterize and evaluate potential fields. The Clarke Lake gas field south of the city of Fort Nelson in northeastern British Columbia, Canada, is hosted by Middle Devonian carbonate rocks that have long been known to exhibit remarkable permeability and temperatures in excess of 110°C. This permeable dolomite aquifer is controlled by the diagenetic alteration of the original depositional trend of reef facies in the Keg River through Slave Point formations, and is over 200m at its thickest. Estimates of the recoverable thermal energy within the aquifer at Clarke Lake using a Volume Method Monte-Carlo model indicate the resource is significant in size (mean 10.1 X 1014 kJ; standard deviation 3.2 X 1014 kJ). Using binary geothermal technology, this thermal energy can be used to generate electricity. It is estimated that purpose-built wells would be able to access enough thermal energy to generate more than 1MW of electricity each. Geothermal plants could be supplied by multiple directional wells to provide greater capacity than is capable from a single well. The resource assessment indicates that the Clarke Lake field could be used to generate between 12 to 74 MW (mean 34MW; standard deviation 10.8MW) of electricity.