DE-FC26-06NT43029

Goal
The goal of this project is to conduct CO₂ injection tests at the Citronelle oilfield in Mobile County, AL. The project will introduce CO₂-enhanced oil recovery (EOR) for tertiary recovery from Alabama’s uniquely structured sandstone reservoirs, providing oilfield operators and CO₂ producers with improved estimates of oil yields from EOR and the capacity of the depleted reservoirs to sequester CO₂. The research work will improve the reliability of computer simulations of oil yield from CO₂-EOR, calculations of sequestration capacity, and the rate at which CO₂ can be introduced into underground formations. The simulations of Citronelle field will be integrated with computer visualizations of the migration of oil, water, and CO₂ and the results will be made accessible to reservoir engineers, geologists, utility planners, and researchers studying carbon sequestration.

Performers
University of Alabama at Birmingham, Birmingham, AL
Alabama Agricultural and Mechanical University, Normal, AL
Denbury Resources Inc., Plano, TX
Geological Survey of Alabama, Tuscaloosa, AL
Southern Company, Birmingham, AL
University of Alabama, Tuscaloosa, AL
University of North Carolina at Charlotte, Charlotte, NC

Background
CO₂-Enhanced Oil Recovery is a well-established method for increasing oil recovery from the Permian Basin oilfields of Texas and New Mexico and from the Williston Basin in North Dakota and Montana. Denbury Resources has also been successful in applying the technique in Mississippi oilfields. Typically, ten percent of the original oil which is present in a reservoir at the start of production can be recovered using CO₂-EOR. A recent study by Advanced Resources International of Arlington, VA, estimated that 64 million additional barrels of oil could be recovered from the Citronelle field using this technology. When oil production is complete, the reservoir and adjacent formations can provide sites for storage of CO₂ produced from the combustion of fossil fuels in power plants and other industrial processes that generate large quantities of CO₂. Southern Company is evaluating the capacity of such reservoirs as possible sites for permanent sequestration of CO₂ that has been separated from coal and natural gas combustion products produced by its power plants.

The Citronelle field is an ideal site for CO₂-EOR and sequestration from both reservoir engineering and geological perspectives. The field is mature and waterflooded, with existing infrastructure, including deep wells, and consists of fluvial-deltaic sandstone reservoirs in a simple structural dome. Because of the presence of the regionally extensive Ferry Lake Anhydrite seal, four-way structural closure, and lack of faulting, it is naturally stable with respect to CO₂ storage. However, the geology of the heterogeneous siliciclastic rocks in this field is very different from fields where CO₂-EOR has been applied commercially, such as in the carbonate strata of the Permian and Williston basins. The proposed demonstration will introduce CO₂-EOR for tertiary recovery from Alabama’s uniquely structured energy resources and thus realize benefits to the nation from additional petroleum production.

Impact
A successful demonstration of the technology in this project could lead to new commercial CO₂-EOR and sequestration efforts across the nation, including reservoir types where CO₂-EOR has thus far not been applied, offering a potential two-for-one solution to the United States' energy security and environmental concerns.

Accomplishments
Shear-wave velocities were measured using the Refraction Microtremor technique to depths of 12,500 feet. Wireless geophones were placed along two straight paths spanning 30,100 and 25,600 feet to the south and southwest, respectively, of the injection well. Shear-wave velocities recorded before and during CO₂ injection suggested a 10% increase in stress associated with CO₂ injection in the geologic layers above the injection zone. An interesting systematic increase in the dependence of shear-wave velocity on depth below ~4500 feet has been observed during injection of the CO₂ and water.

A parametric study of WAG recovery, using the MASTER 3.0 reservoir simulator, showed that a properly designed WAG recovers as much oil as continuous CO₂ injection. Using the simulation results, three-dimensional animations were programmed showing the evolution of fluid saturations in Donovan Sands 14-1 and 16-2 during two CO₂ injections of 7500 tons each, followed by water. The animations nicely capture the mobilization of oil by CO₂, development of the oil bank, the role of water in mobilizing the bank, and the residual oil left unrecovered.

Carbon dioxide injection began for Field Test No. 1 (the first of two CO₂-EOR pilot tests in the heterogeneous sandstone reservoirs of the Citronelle field) at the end of November 2009. After resolution of some initial difficulties in pumping, injection of CO₂ continued without significant interruption at an average rate of 31 tons/day from January 27 to September 25, 2010, in good agreement with the average of 35 tons/day anticipated by reservoir simulations. Injection of the 7500 tons of CO₂ allocated for the first test is complete. Incremental oil recovery is predicted to be 11,500 stock tank barrels, an increase of 60 percent over the yield expected from conventional secondary oil recovery by water flood.

The principal focus (January 1, 2007 to August 31, 2008) was on selection and preparation of the test site and thorough studies of its geology, environmental conditions (air, soil, and vegetation), seismic imaging, and produced fluids to establish the background conditions prior to CO₂ injection. The petrology, sedimentology, and stratigraphy of the Rodessa Formation in the vicinity of the test site were determined and documented at an unprecedented level of detail. Realistic and informative reservoir simulations and visualizations were performed. The environmental and ecological background conditions surrounding the site are well documented. Seismic signals have been recorded under both baseline water flood conditions and during CO₂ injection. The minimum miscibility pressure and absence of precipitation from oil in the presence of CO₂ were established and an economic analysis identified the optimum CO₂ slug size for water-alternating-gas oil recovery under specified CO₂ cost and oil price constraints. All indications are that the pilot test will provide an unequivocal demonstration of CO₂-enhanced oil recovery and essential data and simulations on which to base a commercial CO₂ flood in the Citronelle Field. The CO₂ storage capacity of depleted oil reservoirs and saline formations in Citronelle Dome was estimated by static calculations to be between 0.5 and 2 billion short tons of CO₂, sufficient to sequester the CO₂ from a nearby 1500 MW(electric) coal-fired power plant for 35 years.

Current Status (October 2011)
Researchers will begin the associated testing of models, flow visualization, analysis of produced fluids, geophysical testing, ambient air monitoring, and measure of soil gas fluxes and vegetative growth at the test site.

Upcoming work will focus on understanding the petrology and stratigraphy information to support field data interpretation, reservoir simulation analyses to determine optimum water injection periods, visualization of simulation results, interpretation of seismic surveys, results of environmental monitoring, and determination of oil-CO₂-N₂ mixture properties.

A second injection of 7500 tons of CO₂ is planned. The second injection is predicted to increase incremental oil recovery to 37,700 STB by the end of the project. This injection should provide additional data for testing and validating the fine grid-large scale reservoir simulations and flow visualizations used to determine optimum injector placement. A production strategy for a commercial CO₂ flood at the Citronelle Field will also be determined.. Estimates of the EOR potential at Citronelle range from 40 to 64 million bbl. Assuming 10% (38 million bbl) of the original oil in place (OOIP) is economically recoverable using CO₂-EOR and the production rate increased to 1.25 million bbl/year (twice present production), field life would be extended by 30 years. The capacity of the formation for CO₂ storage when oil recovery is complete will also be assessed.

Project Start: January, 1 2007
Project End: August 31, 2012

Anticipated DOE Contribution: $4,692,957
Performer Contribution: $4,053,321 (46 percent of total)

Contact Information
NETL – Chandra Nautiyal (chandra.nautiyal@netl.doe.gov or 281-494-2488)
University of Alabama at Birmingham – Peter Walsh (pwalsh@uab.edu or 205-934-1826)
If you are unable to reach the above personnel, please contact the content manager.

Publications
J.C. Pashin and R.A. Esposito, "Citronelle Dome: A Giant Opportunity for Multi-Zone Carbon Storage and Enhanced Oil Recovery in the Mississippi Interior Salt Basin of Alabama," Annual Convention and Exhibition of the American Association of Petroleum Geologists, Long Beach, CA, April 1-4, 2007.

R.A. Esposito, J.C. Pashin, and P.M. Walsh, "Citronelle Dome: A Giant Opportunity for Multi-Zone Carbon Storage and Enhanced Oil Recovery in the Mississippi Interior Salt Basin of Alabama," 2007 Annual Convention of the Gulf Coast Association of Geological Societies and the Gulf Coast Section of the Society for Sedimentary Geology, Corpus Christi, TX, October 21-23, 2007.

R. A. Esposito, J. C. Pashin, and P. M. Walsh, "Citronelle Dome: A Giant Opportunity for Multi-Zone Carbon Storage and Enhanced Oil Recovery in the Mississippi Interior Salt Basin of Alabama," accepted for publication in Environmental Geosciences, June 2008.