Demonstration of CO2 Containment and Non-Endangerment at the Southeast Regional Carbon Sequestration (SECARB) Anthropogenic Test Site near Citronelle, Alabama

The Southeast Regional Carbon Sequestration Partnership (SECARB) Anthropogenic Test is a collaborative demonstration of CO₂ capture, transport, geologic storage, and monitoring technologies. This demonstration, which is primarily funded by the United States Department of Energy, Southern Company, Mitsubishi Heavy Industries and the Electric Power Research Institute, has injected 114,104 metric tons (tonnes) of CO₂ during injection operations. Class V Experimental Injection Well underground injection control (UIC) permits were issued in November 2011 and the project’s injection wells were installed shortly thereafter. Injection operations began on August 20, 2012 and terminated on September 1, 2014. The project is now in the Post Injection Site Care (PISC) period. This presentation will provide a summary of the storage demonstration results with a focus on the demonstration of CO₂ containment and non-endangerment of underground sources of drinking water (USDWs) which are requirements for UIC permit closure.

The source of the CO₂ is Alabama Power’s Plant Barry, a 2,657 MW coal and natural gas-fired power plant located in Mobile County, Alabama.^[1]The injection and storage site is located approximately 12 miles from Plant Barry in the Citronelle Field, an historic oil field situated on the crest of the Citronelle Dome geologic structure. The storage zone is the Paluxy Formation which occurs at a depth of about 9,400 ft and is stratigraphically shallower than the Field’s oil reservoir.

The Class V permits require extensive monitoring of injected CO₂ at the surface and at deep and shallow depths. The safety, integrity and information objectives of the CO₂ monitoring plan are in place to: (1) create and sustain wellbore integrity; (2) assure safe CO₂ injection operations; 3) verify the location and migration of the injected CO₂ plume; and (4) monitor for any CO₂ leakage. The monitoring plan developed for the deep monitoring includes pressure monitoring of multiple zones, seismic methods, cased hole saturation logging, reservoir fluid sampling and injection surveys.

In addition to these goals, monitoring data are used to generate input to and for refinement of geological models and simulations. Monitoring the location of the CO₂ plume provides valuable detail about the reservoir permeability, particularly flow unit heterogeneity and mapping of low and high permeability flow paths. In this way, detection and monitoring of the CO₂ plume will help to refine the reservoir model that provides the basis for periodic revisions of the project’s Area of Review (AoR) determination and the PISC monitoring plan. The sandstones of the upper Paluxy are the target reservoirs for CO₂ injection. Target sands in the Paluxy range in thickness from 20 to 60 ft. Confining horizons for CO₂ injected into the Paluxy formation include multiple area-scale mudrocks present within the Paluxy and in the overlying Washita-Fredericksburg Group.

Shallow monitoring tools deployed at the Anthropogenic Test site include groundwater sampling and analysis, CO₂ tracer monitoring and soil CO₂ fluxes. These methods have not detected the presence of CO₂ or brine leakage, providing evidence of non-endangerment of USDWs.

The in situ monitoring methods that have shown promise for CO₂ containment demonstration at the Anthropogenic test are pressure and seismic. Pressure data from multiple wells have been used to calibrate the reservoir simulation, monitor for out of zone leakage, evaluate changes in CO₂ saturation, and to assure that maximum allowable injection pressures are not exceeded. Vertical seismic profiles (VSP) and crosswell seismic methods have been deployed. Crosswell seismic techniques appear to be well suited to address the challenges of monitoring CO₂ at this test due to the limited volume of CO₂ injection and the geology of the Paluxy formation. Baseline and injection-phase surveys were run between the project’s primary injection well, which contained the acoustic source, and the project’s near-offset monitoring well, which contained the receivers. These wells are located 840 feet apart at reservoir depth. The results of the time-lapse imaging indicates a decrease in seismic velocity in the upper injection zone, suggesting an increase in CO₂ saturation. More importantly, no negative velocity anomalies are observed in or above the confining unit implying no detectable leakage out of the injection zone.

Reservoir monitoring will continue throughout the PISC period until permit closure.