The initial targets for the geologic storage of carbon dioxide (CO2) at the site were the Oriskany and Clinton Sandstones at depths between 5,500 and 8,000 feet in the Appalachian Basin. This region is geologically complex and little is known about these formations, especially in the western portion of the basin. Since the nearest well penetrations are more than 20 miles away from the Burger injection well, any and all data collected from the region is useful in determining the suitability of potential field test locations for CO2 storage in the future.
Results of the formation evaluation indicated that the porosity, void space, and permeability of the target formations were lower than expected. The pressure in the formations also rose unexpectedly with very low injection rates. This does not mean that the entire western flank of the Appalachian Basin will show these same rock properties; instead, it confirms the complex nature of the formations within the basin. The work demonstrates the importance of extensive drilling, formation evaluation, and testing to characterize and identify appropriate formations for CO2 storage within the Appalachian Basin prior to injection.
Other lessons learned include the following:
- Site Selection—Although the Burger site was determined not to be in the optimal location for CO2 storage from a geologic perspective, it was an excellent place to drill and test because of the extensive cooperation provided by FirstEnergy and the potential to co-locate the storage site with the plant. Data derived from rock property models and characterization information suggested that the site would have good geologic storage potential; however, the pressures necessary to inject CO2 into the target formations proved to be much higher than anticipated. Additional testing methods must be developed to provide more information about the character of geologic formations chosen for injection testing. Power plants in the Appalachian region may eventually need to transport CO2 relatively short distances to areas that have adequate storage formation characteristics.
- Design of Robust Formation Imaging, Evaluation, and Testing Program—Because of the geologic complexity of this region, a robust wire line logging, imaging, and testing program should be designed and implemented at every potential geologic storage site considered within the region. Stakeholder understanding of the type of data collected from the various logging and testing tools and its interpretation will benefit future siting decisions. This evaluation plan will decrease overall costs at future field test sites. If economically feasible, drilling a pilot hole prior to drilling the injection hole would be ideal to develop a robust logging, coring, and testing program.
- Formation Stimulation—As part of the project design process, project developers should request the ability to hydro-fracture the formation to create fractures that extend from a borehole into the targeted formation. This could provide a better injection rate into rocks that have moderate porosity and low effective permeability.
- Well Completion—Project developers should also consider plans to complete the well at the target formation. Given the low permeability and porosity that exist at some areas in the Appalachian Basin, care should be taken so that well drilling and construction operations do not reduce or eliminate the effective permeability that is naturally present.
- Communications—Continuous communications with all stakeholders, including those who are non-technical, is vital throughout the field testing process, especially at key decision points, including collection of data to allow informed decision-making.
Ultimately, the goal of geologic sequestration field testing is to successfully demonstrate the viability of safely storing injected CO2 in geologic formations. To achieve this goal, DOE will continue to collect pertinent geologic information as part of its characterization phase within the Appalachian and other basins. Drilling deep wells into proposed injection zones, performing formation evaluations to understand their rock properties, and testing injection capability within the zones are all necessary to develop a clear understanding of the overall potential of geologic formations to store CO2.
As DOE and its partners continue to gain understanding and experience related to geologic carbon storage by extensive characterization and injection of CO2 at various sites across the United States and Canada, various best practices will be developed for undertaking sequestration projects. These best practices will provide guidance on site selection through monitoring of stored CO2 after injection and well closure.
The Midwest Regional Carbon Sequestration Partnership is managed by the Battelle Memorial Institute, headquartered in Columbus, Ohio. The characterization and test were sponsored by the DOE Office of Fossil Energy’s National Energy Technology Laboratory, with support from FirstEnergy, Praxair, and the Ohio Geological Survey.