From oil field to geothermal reservoir: assessment for geothermal utilization of two regionally extensive Devonian carbonate aquifers in Alberta, Canada
<p>The Canadian province of Alberta has one of the highest per capita CO<sub>2</sub>-equivalent emissions in Canada, predominantly due to the industrial burning of coal for the generation of electricity and mining operations in the oil sands deposits. Alberta's geothermal...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-07-01
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| Series: | Solid Earth |
| Online Access: | https://www.solid-earth.net/9/953/2018/se-9-953-2018.pdf |
| Summary: | <p>The Canadian province of
Alberta has one of the highest per capita CO<sub>2</sub>-equivalent emissions
in Canada, predominantly due to the industrial burning of coal for the
generation of electricity and mining operations in the oil sands deposits.
Alberta's geothermal potential could reduce CO<sub>2</sub> emissions by
substituting at least some fossil fuels with geothermal energy.</p><p>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 thermophysical 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 geothermal utilization. Samples
taken from outcrops were used as analogues to equivalent formations in the
reservoir and correlated with core samples of the reservoir. Analogue
studies enable the determination and correlation of facies-related rock
properties to identify sedimentary, diagenetic, and structural variations,
allowing for more reliable reservoir property prediction.</p><p>Rock samples were taken from several outcrops of Upper Devonian carbonates
in the Rocky Mountain Front Ranges and from four drill cores from the
stratigraphically equivalent Leduc Formation and three drill cores of the slightly
younger Nisku Formation in the subsurface of the Alberta Basin. The samples
were analyzed for several thermophysical 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.</p><p>The results from both carbonate complexes indicate good reservoir conditions
regarding geothermal utilization with an average reservoir porosity of about
8 %, average reservoir permeability between 10<sup>−12</sup> and
10<sup>−15</sup> m<sup>2</sup>, and relatively high thermal conductivities
ranging from 3 to 5 W m<sup>−1</sup> K<sup>−1</sup>. The most promising target
reservoirs for hydrothermal utilisation are the completely dolomitized reef
sections. The measured rock properties of the Leduc Formation in the
subsurface show no significant differences between the Rimbey-Meadowbrook
Reef Trend and the Southesk-Cairn Carbonate Complex. Differences between the
dolomitized reef sections of the examined Leduc and Nisku Formation are also
minor to insignificant, whereas the deeper basinal facies of the Nisku
Formation differs significantly.</p><p>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 not valid proxies for the buried reservoirs in the Alberta
Basin.</p><p>Taken together, all available data suggest that dolomitization enhanced the
geothermal properties, but depositional patterns and other diagenetic
events, e.g., fracturing, also played an important role.</p> |
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| ISSN: | 1869-9510 1869-9529 |