Thermal State Assessment of the St. Lawrence Lowlands with a 3D Geological Model

Karine Bedard1, Jasmin Raymond2, Maher Nasr1 and Michel Malo1, (1)Institut national de la recherche scientifique (INRS), Eau Terre Environnement, Québec, QC, Canada, (2)Institut national de la recherche scientifique (INRS), Centre Eau Terre Environnement, Quebec City, QC, Canada

Contact First Author: Karine Bedard; karine.bedard@ete.inrs.ca

Previously Published Material: The portion of the reasearch concerning BHT corrections has been partially presented to the Geothernal Ressources Concil 2014 annual conference as a poster (september 2014, Portland, Oregon).

Abstract ID#: 33296

 

English Abstract:
The Cambrian-Ordovician St. Lawrence Lowlands sedimentary basin covers approximately 20 000 km2 in southern Quebec, Canada. Deep saline aquifers contain warm water that could potentially be used for geothermal energy. The thickness of the sedimentary cover reaches more than 3000 meters in the south-eastern part of the basin, offering significant thermal insulation. Basal sandstones of the Potsdam Group are prospective targets for natural reservoirs and the crystalline basement of the Grenville province may be a suitable host for enhanced geothermal systems.

The thermal state of the sedimentary basin has been assessed with a 3D geological model to evaluate the potential for geothermal power generation and direct use. The data used to create the 3D model included the geological map of the area, the interpreted basement structural map as well as oil and gas exploration well data. The bottom hole temperature (BHT) data available for 93 of those wells were corrected to estimate equilibrium temperatures that were integrated to the model. Thermal conductivity analyses of 56 outcrop rock samples were performed with a needle probe to determine properties of the modelled geological units. The temperature and conductivity results were then used to calculate the surface heat flow and estimate temperature at depth, assuming a purely conductive heat transfer.

In the 3D model, results indicate heat flow in the range of 36x10-3 to 107x10-3 W/m2 with an average of 67x10-3 W/m2. Local areas of higher heat flow (68x10-3 to 85x10-3 W/m2) situated in the eastern part of the basin, close to Logan’s Line, have sedimentary cover thickness of 3000 to 5500 meters. The equivalent thermal conductivity of the insulating caprocks in this area ranges from 2.4 to 2.7 W/mK. At a depth of 4 km, temperature above 120°C could be expected for the most promising areas. Power production potential appears to be mostly associated to the deep basement whereas temperature of the basal sandstones indicates potential for direct use.

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