Geologic Storage Geologic Project Descriptions Development of a Carbon Management Geographic Information System for the United States Regional Modeling of Large-Scale Hydrologic Impact of CO2 Storage Leveraging Regional Exploration to Develop Geologic Framework for CO2 Storage in Deep Formations Applications of Cutting-Edge 3-D Seismic Attribute Technology to the Assessment of Geological... Discrete Fracture Network Models for Assessment of Carbon Sequestration in Coal Fundamental Studies of Above Ground and Geologic Mineral Sequestration Reactions Geologic Sequestration of CO2 in a Depleted Oil Reservoir CO2-Water-Rock Interactions and the Integrity of Hydrodynamic Seals Storage of CO2 in the Geologic Formations in the Ohio River Valley Region The Coal-Seq II Consortium: Advancing the Science of CO2 Seq. in Deep, Unmineable Coal Seams Geological Sequestration of CO2: The GEO-SEQ Project CO2 Sequestration in Basalt Formations Strategies for Controlling Coal Permeability in CO2-Enhanced Coal Bed Methane Recovery Enhanced Coal Bed Methane Production and Sequestration of CO2 in Unmineable Coal Seams Optimal Geological Environments for Carbon Dioxide Disposal in Saline Aquifers CO2 Sequestration Potential of Texas Low-Rank Coals Terrestrial Project Descriptions Ecosystem Dynamics Project Enhancing Carbon Sequestration and Reclamation of Degraded Lands with Fossil-Fuel Combustion... Advanced Plant Growth Landfill Gas Sequestration in Kansas Application & Development of Appropriate Tools & Technologies for Cost-Effective Carbon Seq. Carbon Sequestration in Reclaimed Mine Soils of Ohio Assessing Fossil and Recent Carbon Pools in Reclaimed Mine Soils Application of Low-Cost Elevation Models to Detect Changes in the Carbon Inventory... Enhancing Carbon Sequestration and Reclamation of Degraded Lands with Fossil-Fuel... Enhancement of Terrestrial Carbon Sinks through Reclamation of Abandoned Mine Lands... Restoring Sustainable Forests on Appalachian Mined Lands for Wood Products... Carbon Sequestration on Surface Mine Lands Example World Projects Reference Shelf
	Interactive Geologic Sequestration Model To view geologic sequestration in action, click here to save the executable file to your desktop or run it from its location. Once the model is displayed, select the interactive choices in the left hand corner to display how CO2 concentrations will change over time.

Carbon sequestration encompasses the processes of capturing and storing CO₂ that would otherwise reside in the atmosphere for long periods of time. DOE is investigating a variety of carbon sequestration options. Geologic carbon sequestration involves the separation and capture of CO₂ at the point of emissions from stationary sources followed by storage in deep underground geologic formations. Terrestrial carbon sequestration involves the net removal of CO₂ from the atmosphere by plants during photosynthesis and its fixation in vegetative biomass and in soils.

Geologic Formations
The majority of geologic formations considered for CO₂ storage, deep saline or depleted oil and gas reservoirs, are layers of porous rock underground that are “capped” by a layer or multiple layers of non-porous rock above them. Sequestration practitioners drill a well down into the porous rock and inject pressurized CO₂. Under high pressure, CO₂ turns to liquid and can move through a formation as a fluid. Once injected, the liquid CO₂ tends to be buoyant and will flow upward until it encounters a barrier of non-porous rock, which can trap the CO₂ and prevent further upward migration. Coal seams are another formation considered a viable option for geologic storage, and their storage process is a slightly different. When CO₂ is injected into the formation, it is adsorbed onto the coal surfaces, and methane gas is released and produced in adjacent wells.

There are other mechanisms for CO₂ trapping as well: CO₂ molecules can dissolve in brine; react with minerals to form solid carbonates; or adsorb in the pores of the porous rock. The degree to which a specific underground formation is amenable to CO₂ storage can be difficult to discern. Research is aimed at developing the ability to characterize a formation before CO₂-injection to be able to predict its CO₂ storage resource. Another area of research is the development of CO₂ injection techniques that achieve broad dispersion of CO₂ throughout the formation, overcome low diffusion rates, and avoid fracturing the cap rock. These areas of site characterization and injection techniques are interrelated because improved formation characterization will help determine the best injection procedure.

As part of their regional characterization, the RCSP’s identified and examined the location of potential geologic storage in basins throughout each region. Initial resource estimates were calculated for the primary storage formations and these estimates will continue to be refined as the RCSP’s continue to validate storage potential in their respective region. The conservative estimates of storage potential in North America, calculated in Gigatonnes, are located in the table below.

There are three primary types of geologic formations and two possible future options in which CO₂ can be stored, and each has different opportunities and challenges:

	This map displays saline formation data which were obtained by the RCSPs and other sources and compiled by NATCARB.

Deep Saline Formations. Saline formations are layers of porous rock that are saturated with brine. They are much more extensive than coal seams or oil- and gas-bearing rock, and represent an enormous potential for CO₂ geologic storage. However, much less is known about saline formations because they lack the characterization experience that industry has acquired through resource recovery from oil and gas reservoirs and coal seams. Therefore, there is a greater amount of uncertainty regarding the suitability of saline formations for CO₂ storage.

Saline formations tend to have a lower permeability than do hydrocarbon-bearing formations, and work is directed at hydraulic fracturing and other field practices to increase injectivity. Saline formations contain minerals that could react with injected CO₂ to form solid carbonates. The carbonate reactions have the potential to be both a positive and a negative. They can increase permanence but they also may plug up the formation in the immediate vicinity of an injection well. Researchers seek injection techniques that promote advantageous mineralization reactions.

	This map displays coal basin data obtained by the RCSPs and other sources and compiled by NATCARB.

Unmineable Coal Seams.  Unmineable coal seams are too deep or too thin to be economically mined. All coals have varying amounts of methane adsorbed onto pore surfaces, and wells can be drilled into unmineable coalbeds to recover this coalbed methane (CBM). Initial CBM recovery methods, such as dewatering and depressurization, leave a considerable amount of methane in the formation. Additional recovery can be achieved by sweeping the coalbed with CO₂. Depending on the type of coal, a variable amount of methane is released, thereby providing an excellent storage site for CO₂ along with the additional benefit of enhanced coalbed methane (ECBM) recovery. Similar to maturing oil reservoirs, unmineable coalbeds are good candidates for CO₂ storage.

Coal swelling is a potential barrier to CO₂ ECBM. It has been observed that when coal adsorbs CO₂, it swells in volume. In an underground formation swelling can cause a sharp drop in permeability, which not only restricts the flow of CO₂ into the formation but also impedes the recovery of displaced CBM. Angled drilling techniques and fracturing are possible means of overcoming the negative effects of swelling.  

	This map displays the oil and gas reservoir data which were obtained by RCSPs and other sources and compiled by NATCARB.

Oil and Gas Reservoirs. Mature oil and gas reservoirs have held crude oil and natural gas for millions of years. The reservoirs consist of a layer of permeable rock with a layer of nonpermeable rock (caprock) above, such that the nonpermeable rock layer forms a trap that holds the oil and gas in place. Oil and gas reservoirs have many characteristics that make them excellent target locations for geologic storage of CO₂. The geologic conditions that trap oil and gas are also the conditions that are conducive to CO₂ sequestration.

As a value-added benefit, when CO₂ is injected into a mature oil reservoir, it can produce additional oil. This process, enhanced oil recovery (EOR), begins by injecting CO₂ into an oil reservoir. A small amount of the injected CO₂ dissolves in the oil, increasing the bulk volume and decreasing the viscosity, thereby facilitating flow to the wellbore. Carbon dioxide injection allows recovery of an additional 10–15 percent of the oil. NETL’s work in this area is focused on increasing the amount of CO₂ that remains in the ground as part of CO₂ EOR injection.

However, commercial practitioners operate their injections with the goal of minimizing the amount of CO₂ left in the ground so that the CO₂ can be used for another well. NETL’s work in this area is focused on CO₂ EOR and EGR injection practices that maximize the amount of CO₂ sequestered.

Organic Rich Shale. Shale, the most common type of sedimentary rock, is characterized by thin horizontal layers of rock with very low permeability in the vertical direction. Many shales contain 1–2 percent organic material in the form of hydrocarbons, which provide an adsorption substrate for CO₂ storage similar to CO₂ storage in coal seams. Research is focused on achieving economically viable CO₂ injection rates, given the shales’ low permeability.

Basalt Formations. Basalt formations are geologic formations of solidified lava. Basalt formations have a unique chemical makeup that could potentially convert all of the injected CO₂ to a solid mineral form, thus isolating it from the atmosphere permanently. Research is focused on enhancing and utilizing the mineralization reactions and increasing CO₂ flow within a basalt formation.

Terrestrial Ecosystems
Terrestrial sequestration is CO₂ uptake by soils and plants, both on land and in aquatic environments such as wetlands and tidal marshes. Terrestrial sequestration provides an opportunity for low-cost atmospheric CO₂ reductions and usually offers additional benefits such as habitat and/or water quality improvements. Terrestrial CO₂ sequestration efforts include tree-plantings, no-till farming, wetlands restoration, land management on grasslands and grazing lands, fire management efforts, and forest preservation. More advanced research includes the development of fast-growing trees and grasses and deciphering the genomes of carbon-storing soil microbes. NETL’s Program efforts in the area of terrestrial sequestration include a focus on increasing carbon uptake on mined lands and quantifying sequestration benefits of growing biomass for power generation. These activities complement research into afforestation and agricultural practices that are being led by the U.S. Department of Agriculture (USDA). The U.S. DOE’s Office of Science, the U.S. EPA, and the Department of the Interior are also involved in terrestrial sequestration in supporting and complementary roles.

The RCSPs are implementing 11 terrestrial sequestration field projects during the Validation Phase on abandoned mine land, wetlands, agricultural fields, prairie lands, and forests to validate the best practices for the enhancement of these sinks to store carbon emitted from distributed sources such as automobiles.  The projects are measuring the effects on carbon storage from reclaiming damaged lands and altering land-use management practices which are designed to increase the storage rate in above and below ground carbon stocks and reduce the release of stored carbon by minimizing disturbance to the soils.  Many of these projects will help to develop the MVA protocols to allow the carbon stored in these terrestrial ecosystems to be credited as greenhouse gas emissions reduction on future trading markets.