From oil field to geothermal reservoir: First assessment for geothermal utilization of two regionally extensive Devonian carbonate aquifers in Alberta, Canada

Abstract

The Canadian Province of Alberta has the highest per capita CO 2 -equivalent emission of any jurisdiction in the world, predominantly due to industrial burning of coal for the generation of electricity and the mining operations in the oil sands deposits. Alberta's geothermal potential could reduce CO 2 -emission by substituting at least some fossil fuels with 15 geothermal energy.The Upper Devonian carbonate aquifer systems within the Alberta Basin are promising target formations for geothermal energy. To assess their geothermal reservoir potential, detailed knowledge of the thermo-and petrophysical rock properties is needed. An analogue study was conducted on two regionally extensive Devonian carbonate aquifers, the Southesk-Cairn Carbonate Complex and the Rimbey-Meadowbrook Reef Trend, to furnish a preliminary assessment of the potential for 20 geothermal utilization. Samples taken from outcrops were used as analogue to equivalent formations in the reservoir and correlated with core samples of the reservoir. Analogue studies enable determination and correlation of facies related rock properties to identify sedimentary, diagenetic, and structural variations, allowing more reliable reservoir property prediction.Rock samples were taken from several outcrops of Upper Devonian carbonates in the Rocky Mountain Front Ranges as well as from four drill cores from the stratigraphically equivalent Leduc and three drill cores of the slightly younger Nisku 25Formation in the subsurface of the Alberta Basin. The samples were analyzed for several thermo-and petrophysical properties, i.e., thermal conductivity, thermal diffusivity and heat capacity, as well as density, porosity and permeability.Furthermore, open-file petrophysical core data retrieved from the AccuMap database were used for correlation. In contrast, the outcrop analogue samples have lower porosity and permeability, likely caused by low-grade metamorphism and deformation during the Laramide Orogeny that formed the Rocky Mountains. As such, the outcrop analogues are no valid proxies for the buried reservoirs in the Alberta Basin. 10Taken together, all available data suggests that dolomitization enhanced the geothermal properties, but depositional patterns and other diagenetic events, e.g. fracturing, also played an important role. As for the development of the Devonian aquifers in the Alberta basin as geothermal reservoirs, repurposing abandoned oil and gas wells has the potential to produce geothermal energy cost efficiently, providing new business strategies.

Geothermal play typing in Germany, case study Molasse Basin: a modern concept to categorise geothermal resources related to crustal permeability

“…In regions like Europe or North America, where sedimentary systems in the subsurface come together with a high heat demand at the surface, the crustal permeability structure at 2-5 km depth will obviously be of increasing interest for geothermal applications (e.g. Tester et al, 2006;Weydt et al, 2018). In Germany, the geothermal development is most pronounced in the Molasse Basin, the German part of the North Alpine foreland basin (Bachmann et al, 1987;Bachmann & Müller, 1992).…”