Project ECO2S, located in Kemper County, Mississippi, near Mississippi Power Company's Plant Ratcliffe NGCC facility, is positioned as a potential regional CO2 storage hub with the capability to store CO2 from multiple large sources. The overarching goals of the project are to demonstrate the safe and secure subsurface storage of commercial volumes of CO2 at Kemper and to evaluate the commercial viability of post-combustion coal- and gas-fired capture, transportation, and storage in the southeastern U.S.

The project has identified a large portfolio of potential sinks and seals in east-central Mississippi, with the main storage targets located in the Paluxy-Tuscaloosa section. The primary reservoir rock is fluvial sandstone, complemented by mudrock and chalk seals. The sandstone is subarkose with significant dissolution porosity, averaging 28.5% porosity and 3.6 Darcies of permeability. The site boasts major stacked storage potential, with over 1,300 net feet of sandstone. Preliminary P50 storage resource estimates suggest approximately 22 million tonnes per square mile, amounting to 1.2 gigatonnes within the storage complex.

During the project, two Class VI Underground Injection Control (UIC) permit applications were prepared, with each well having the capacity to store 1.45 million metric tons of CO2 per year. The Area of Review (AoR) model will be finalized following the full integration of geologic data from the 2021 wells.

Throughout Phase II and III, a total of six characterization wells were drilled, and three storage reservoirs (Massive Sand/Dantzler, Washita-Fredericksburg, and Paluxy) were identified and characterized. A 92-mile 2D seismic survey was completed on July 25, 2021, and a United States Drinking Water (USDW) characterization well was finished the following day. The Class VI UIC permit applications are currently in preparation.

Preliminary modeling of pipelines and CO2 capture assessments are underway at Plant Miller (coal) and Plant Ratcliffe (natural gas). For Plant Daniel, a third source, a separately funded Front-End Engineering Design (FEED) study is in progress (FE0031847).

Lessons learned from the project include the scope change from a modest 3D seismic survey to a larger area 2D survey, which was extensively discussed due to the size of the storage complex. If the Environmental Protection Agency (EPA) requires a 3D survey of the injection sites before operation, this will be included in a potential Phase IV scope. Conducting meaningful well tests to determine fracture pressures proved challenging in the subsurface at ECO2S. An openhole Modular Formation Dynamics Tester (MDT) fracture test on the confining interval failed due to borehole rugosity and exceptional permeability, and reservoir step rate tests could not achieve sufficient rates through tubing. As a result, laboratory and petrophysical approaches are being used to model the geomechanical response.