Carbon dioxide (CO2) injection — an important part of carbon capture and storage (CCS) technology — is underway in the Citronelle Field of Mobile County, Alabama, as part of a pilot study of CO2 enhanced oil recovery (EOR).
A project team led by the University of Alabama at Birmingham is conducting the injection. Study results of the 7,500-ton CO2 injection will provide estimates of oil yields from EOR and CO2 storage capacity in depleted oil reservoirs.
According to the US Department of Energy (DoE), CO2 injection has already helped recover nearly 1.5 billion barrels of oil from mature oil fields, yet the technology has not been deployed widely.
It is estimated that nearly 400 billion barrels of oil remain trapped in the ground. Funded through the DoE’s Office of Fossil Energy, the primary goal of the Citronelle Project is to demonstrate that remaining oil can be economically produced using CO2-EOR technology in untested areas of the US. This is expected to reduce dependency on oil imports, provide domestic jobs, and prevent the release of CO2 into the atmosphere.
The Citronelle Field is composed of sandstone reservoirs in a simple structural dome and has existing infrastructure that includes deep wells.
When the five-month injection is completed, incremental oil recovery is anticipated to be 60 per cent greater than that of conventional secondary oil recovery by water flood.
A recent study by Advanced Resources International of Arlington, Virginia, estimates that approximately 64 million additional barrels of oil could be recovered from the Citronelle Field by using this tertiary recovery method.
Once the oil has been recovered, the remaining storage capacity of the depleted oil reservoirs and saline formations in the Citronelle Dome is estimated to be between 0.5 and two billion tons of CO2.
Southern Company of Birmingham, Alabama, is evaluating the potential of the reservoirs as permanent storage sites for CO2 produced from fossil-fuel combustion in power plants. A successful demonstration at the Citronelle Field could offer new opportunities to introduce the latest CO2-EOR and carbon-storage technologies to the commercial market.
The Citronelle project is currently in its second phase, which includes injection, associated validation of models and determination of oil-CO2 mixture properties.
Containment of CO2 at the test site will also be monitored in the ambient air, soil and vegetation.
During phase I, the project focused on selection of the test site, analysis of the site geology and a study of background conditions. The SENSOR reservoir simulator — a generalised 3D numerical model used to optimise oil and gas recovery processes — was used to determine the amount of CO2 required for a successful demonstration and the effect of CO2 on oil production within the project time frame.