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CO2 Storage Potential in Devonian Deep Saline Aquifers and Hydrocarbon Reservoirs in North-Central Alberta, Canada


Increasing oil production from the bitumen deposits in Alberta requires lowering the CO2 footprint of the oil sands plants. These deposits are located at the shallow edge of the Alberta basin where no CO2 storage potential exists. The Devonian formations located to the west of these deposits contain multiple saline aquifers and hydrocarbon reservoirs that can be used for CO2 storage. This study presents an assessment of the potential for CO2 storage in the Devonian saline aquifers and oil and gas fields of north-central Alberta. The Devonian succession consists of two sandstone and ten carbonate units capped by shales and evaporites. The carbonates consist of platform deposits and overlying reefs. All strata dip towards the southwest, and successively subcrop at the sub-Cretaceous unconformity. Pressure versus depth analysis indicates that the Devonian aquifers are isolated from the overlying Cretaceous bitumen-bearing sediments, except along their subcrops. Localized hydraulic communication between some Devonian aquifers occurs through a few pinnacle reefs and along the Peace River Arch in the northwest. Salinity ranges from >20 g/L in subcrop areas to >300 mg/L in the deep southwest. All aquifers are normally pressured. Porosity was evaluated based on core analyses and geophysical logs. Average well-scale values range from 4% to 15% in carbonates and from 9% to 14% in sandstones. Permeability was evaluated based on core analyses and drillstem tests and, at the well scale, ranges between >1 mD and >5000 mD. The highest permeability is observed in the shallower aquifers of Woodbend and Winterburn groups, while the lowest permeability is observed in the deeper aquifers of the Beaverhill Lake Group. Initial assessments indicate the highest potential CO2 storage capacity in the aquifers of Woodbend, Winterburn and Wabamun groups. Nine oil reservoirs have been identified with individual CO2 storage capacity of >5 Mt, and cumulative storage capacity of 83.5 Mt CO2. Of those, seven are unsaturated oil reservoirs, and two are saturated oil reservoirs with a gas cap. All oil reservoirs are located in the western part of the study area, away from the oil sands operations. The storage capacity in ten large gas reservoirs is estimated to be 360 Mt. This analysis shows that the area west of the Athabasca oil sands deposits in Alberta has significant potential for storing CO2 emissions from oil sands operations, thus reducing their carbon footprint.