Carbon dioxide injection—an important part of carbon capture and storage (CCS) technology—is underway as part of a pilot study of CO2 enhanced oil recovery (EOR) in the Citronelle Field of Mobile County, Alabama. 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.
In the United States, 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 still remain trapped in the ground. Funded through the Department of Energy’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 United States.
The Citronelle Field appears to be an ideal site for concurrent CO2 storage and EOR. The field is composed of sandstone reservoirs in a simple structural dome, and has existing infrastructure that includes deep wells. When the 5-month injection is completed, incremental oil recovery is anticipated to be 60% greater than that of conventional secondary oil recovery by water flood. A recent study by Advanced Resources International of Arlington, Va., estimates that approximately 64 million additional barrels of oil could be recovered from the Citronelle Field by using this tertiary recovery method.
The geologic structure and lack of faulting also make the field naturally stable for CO2 storage. 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 2 billion tons of CO2. Southern Company of Birmingham, Ala., 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 study of background conditions. The SENSOR reservoir simulator—a generalized 3D numerical model used to optimize 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.
Project performers include the University of Alabama at Birmingham (Birmingham, Ala); Alabama Agricultural and Mechanical University (Normal, Ala.); Denbury Resources Inc. (Plano, Texas); the Geological Survey of Alabama (Tuscaloosa, Ala.); Southern Company, (Birmingham, Ala.); the University of Alabama (Tuscaloosa, Ala.); and the University of North Carolina at Charlotte (Charlotte, N.C.).