CO_2 STORAGE IN OIL AND GAS RESERVOIRS IN WESTERN CANADA: EFFECT OF AQUIFERS, POTENTIAL FOR CO_2-FLOOD ENHANCED OIL RECOVERY AND PRACTICAL CAPACITY

摘要

The Prairie region in western Canada produces approximately one third of Canada's CO_2 emissions. Two thirds of these emissions occur at large, stationary sources that are suited for CO_2 capture and storage in geological media. There are approximately 10,300 oil pools and 31,100 gas pools in the underlying Alberta and Williston sedimentary basins, and they will most likely be primary targets for early implementation of CO_2 storage. A comprehensive approach and associated methodology have been developed and applied for the evaluation of the theoretical, effective and practical capacities for CO_2 storage in these oil and gas reservoirs that take into account the presence and effect of underlying aquifers, reservoir heterogeneity, CO_2 properties, and, in the case of oil pools, suitability for CCVflood enhanced oil recovery (EOR). The flow strength and impact of the underlying aquifers can be established on the basis of the water-oil or water-gas ratio (WOR and WGR), respectively, together with the gas-oil ratio (GOR) in the case of oil reservoirs with a gas cap. The theoretical storage capacity in gas pools in western Canada is estimated to be greater than 10 Gt CO_2, while the storage capacity in oil pools is in the order of 2.4 Gt CO_2. The presence of underlying aquifers overall reduces the theoretical storage capacity by 8% for gas pools and 35% for oil pools. The effective storage capacity is in the order of 8.5 Gt CO_2 in gas reservoirs and 450 Mt CO_2 in oil reservoirs that are not commingled and that are currently in primary production. An additional 640 Mt CO_2 could be potentially stored in 4,748 oil reservoirs that have been identified as being suitable for CO_2-flood EOR, if 50% reservoir pore volume is flooded with CO_2. Considering reservoir size (greater than 1 Mt CO_2), location and depth, the practical CO_2 storage capacity in western Canada is 3.2 Gt in 771 gas reservoirs and 560 Mt in 98 oil reservoirs, of which 81 are suitable for CO_2 EOR.