Geothermal Assessment of Two Regionally Extensive Upper Devonian Carbonate Aquifers in Alberta, Canada

Abstract

The Canadian province of Alberta has the highest per capita CO2-equivalent emissions in Canada, predominantly due to the industrial burning of coal for the generation of electricity and mining operations in the oil sand deposits. The use of Alberta’s geothermal potential could reduce CO2 emissions significantly by substituting at least some fossil fuels. Relatively little is known about the potential for geothermal energy utilization in Alberta despite of a number of geothermal studies conducted over several decades. To assess the geothermal reservoir potential, detailed knowledge of the thermo- and petrophysical rock properties is needed. We conducted an analogue study that compared a number of rock properties from the Devonian Southesk-Cairn Carbonate Complex and of the Rimbey-Meadowbrook Reef Trend with selected outcrop samples from stratigraphically correlative outcrops in the Rocky Mountains. Samples from the Leduc and Nisku formations were analyzed for thermal conductivity, thermal diffusivity and heat capacity, as well as density, porosity and permeability. Our data suggest that the extensively dolomitized and highly fractured reef zones with permeabilities of up to 10−12 m2 and thermal conductivities of higher than 4 W m−1 K −1 are promising reservoirs for geothermal utilization. Our dataset is complemented by open-file core and reservoir data retrieved from the AccuMap data base for mapping of reservoir temperature, TDS, sour gases (H2S, CO2, N2) and petrophysical core data (density, porosity and permeability). A preliminary 3D geological model of the Nisku and Leduc aquifers in the western part of the Rimbey-Meadowbrook reef trend was created with GOCAD/SKUA to determine the potential for geothermal utilization on a local scale (e g. on the scale of a few townships). Preliminary findings confirm those from previous studies that the Upper Devonian carbonate aquifers are worth investigating as geothermal reservoirs.