CO2 for EOR

Injection of CO2 in oil fields has for many years been used as a method to enhance oil recovery, primarily in the United States, where the CO2 source has mostly come from reservoirs with almost pure CO2. The CO2 injected for enhanced recovery will at the end be stored.

On the Norwegian shelf, several oil fields have been examined with regard to possible enhanced recovery through CO2 injection. Some of the fields have proved to be promising candidates. Others are not suitable for CO2 flooding due to reservoir conditions.

The best effect of CO2 is obtained when CO2 and oil are miscible in the reservoir. In addition, CO2 has many properties that enables to increase production. It swells the oil, reduces oil viscosity and increases oil density. It is soluble in water, can evaporate and extract oil, and it reduces surface tension between oil and water providing a more efficient displacement. The sweep efficiency of CO2 flooding can be improved by applying WAG, which is alternating injection of CO2 and water. Corrosion is a critical factor as CO2 mixes with water. This fluid will eventually reach the wells and process plant.

Field Example

Gullfaks. Several studies of CO2 injection in the Brent reservoir were conducted in 2003 -2004. These studies showed a potential for increased recovery of approximately 14 million Sm3. This is equivalent to about 3 % of the remaining resources with an injection of 5 million tons CO2/year over a 10-year period. Continued injection of reproduced CO2 for another 10 years might increase the reserves by 22 million Sm3, including a profitable tail production, i.e. a total increase of approximately 8%. Net injection of CO2 in the field was estimated at about 50 million tons over a 20-year period. The field owners concluded that the project was not profitable due to the estimated oil price path at the time.