Evaluation of CO2 storage capacity in Devonian hydrocarbon reservoirs for emissions from oil sands operations in the Athabasca area, Canada

Geological Storage of CO 2 has been identified by the provincial Alberta government as the major component of its strategy for reducing greenhouse gas emissions in the province. The issue of reducing atmospheric CO 2 emissions is particularly important for oil sands plants, whose emissions in 2013 were in the order of 55 Mt CO 2 eq. Unfortunately, the oil sands operations are located near the shallow edge of the Alberta basin, which is not suitable for CO 2 storage. However, CO 2 storage in deep Devonian oil and gas reservoirs located westward of the oil sands operations may constitute a solution for storing CO 2 from these operations. The volumetric CO 2 storage capacity in 1225 oil and gas reservoirs in 13 different Devonian formations in an area covering approximately 126,000 km2 was estimated using information from reserves and production databases. The CO 2 storage capacity has been calculated by reservoir type and by production stage. The aggregate CO 2 storage capacity in oil and gas reservoirs in the Devonian sedimentary succession in the study area is in the order of ∼700 Mt. However, most of the reservoirs have small storage capacity, and only 9 oil reservoirs and 10 gas reservoirs have CO 2 storage capacity greater than 5 Mt each, for a cumulative total of ∼447 Mt CO 2 . The strength of underlying aquifers was evaluated by performing material balance calculations for these 19 oil and gas reservoirs and it was found that they do not have a significant effect in reducing the CO 2 storage capacity of these reservoirs. The CO 2 storage capacity in the study area is bound to be greater if one considers the fact that, once the infrastructure, including pipelines, is built to bring CO 2 to any of these very large reservoirs, then smaller reservoirs in the same oil or gas field can be accessed with relatively minimal extra costs. The aggregate CO 2 storage capacity in the fields where the 19 very large oil and gas reservoirs are found has been considered as well, raising the CO 2 storage capacity in these fields to ∼491 Mt CO 2 . The storage capacity in oil reservoirs in the study area can be further increased by using CO 2 in enhanced oil recovery. Although 705 oil pools have been identified as being technically suitable for CO 2 -EOR, only 12 oil reservoirs have remaining oil in place greater than 60 million barrels that would economically justify implementation of CO 2 -EOR. Assuming various incremental recovery factors and net CO 2 utilization factors, the additional amount of CO 2 that may be stored in these 12 oil reservoirs varies between 31 and 412 Mt CO 2 , thus increasing the CO 2 storage capacity in these oil reservoirs. This evaluation shows that the potential CO 2 storage capacity in oil and gas reservoirs in Devonian strata west of the Athabasca oil sands area in Alberta is significant and has the potential to reduce the carbon footprint of the oil sands operations for several decades until other technological advances for reducing CO 2 emissions will come into being.

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