The concept of permanently storing carbon dioxide (CO2) underground is often referred to as sequestration, i.e., to isolate or keep apart. Rocks with the potential to store fluids, such as oil and natural gas, are called reservoirs. Since rock formations can be considered geologic reservoirs for CO2, scientists refer to this concept as geologic sequestration. It is part of a broader approach to reducing global CO2 emissions. It first involves capturing CO2 from the emissions of power plants and other industrial facilities. The CO2 is then injected through a deep well into a carefully chosen geologic formation. There, the CO2 is permanently stored in rock formations thousands of feet below drinking water supplies. These rock formations are similar to those that have stored natural gas and oil for millions of years. Suitable candidate formations for geologic sequestration include saline or brine (saltwater) reservoirs, depleted oil and gas fields, or coal beds that are too thin or deep to be cost effectively mined. The MRCSP tests involve injection into deep saline reservoirs. These reservoirs are located at least 3,000 feet below the surface and way below drinking water supplies, which are typically less than 200 feet deep in this region.
A schematic of the components of a typical geologic sequestration system that captures CO2 from an electricity generating plant is shown below.
Phase I - Characterization
Initial mapping indicates that well-defined, deep saline formations within the MRCSP region could potentially sequester several hundred billion metric tons of CO2. The estimated CO2 storage resource is very large compared to the present-day emissions, enough to accommodate CO2 emissions from large stationary sources for hundreds of years. Saline formations in the MRCSP region are widespread, close to many large CO2 sources, and are thought to have large pore volumes available for injection use. However, CO2 sequestration capacity is not evenly distributed across the region. The Phase I Final Report can be accessed by clicking this link.
The map of the general regional geology below shows the major uplifts and basins in the MRCSP region, as well as the location of the MRCSP field tests within these basins. MRCSP has developed an interactive mapping tool which can be accessed here that allows the user to select areas within the region and explore CO2 sources and sinks. The rock layers within these large regional structures can be further divided into formations, based on observable rock characteristics. A formation has a distinctive composition and texture that is extensive enough to be mapped, allowing geologists to trace geologic strata across wide distances. The thickness of formations may range from less than a meter to several thousand meters. Deep saline rock formations like the Mt. Simon Sandstone and the St Peter Sandstone are among the largest CO2 storage resources in the region.
Phase II - Validation
Based on the mapping activity conducted in Phase I of the DOE’s Regional Carbon Sequestration Program, the MRCSP recommended several locations for small-scale field tests during the second phase, or Validation Phase, of the Regional Partnership program. As shown in the map above, the MRCSP conducted three Phase II field tests to help assess the effectiveness of storing CO2 deep underground. During the period from October 2005 through October 2009, the MRCSP conducted the demonstrations in areas that represent a broad spectrum of the geology underlying the region.
These geologic test sites were selected for a variety of reasons including: vicinity to significant CO2 sources, geologic setting, availability of a host site with a MRCSP partner, and overall benefits for advancing CO2 sequestration in the Midwest. The three field tests were not commercial-sized projects, but rather small-scale tests that involved injecting only a small amount of CO2. Despite their small size, however, these Phase II projects were an important step in proving the feasibility of geologic sequestration in the MRCSP region.
This technology could be economically important to the Midwest where large amounts of CO2 from coal-fired plants, gas processing operations and cement and steel industries are emitted. Click here to view the final reports on the results of these individual tests in addition to the comprehensive Phase II report.
Phase III - Development
Each of the seven Regional Partnerships is conducting at least one large-scale field test during Phase III. The locations for these tests are being selected to ensure that each takes place in a regionally significant geologic formation. The Phase III projects are designed to demonstrate that CO2 storage sites have the potential to store regional CO2 emissions safely, permanently, and economically for hundreds of years.
During the third, or Development Phase, MRCSP will conduct a larger-scale geologic field test in Otsego County, Michigan. This project will leverage existing EOR operations to inject carbon dioxide into a small number of oil fields located within the Niagaran pinnacle reef trend.
Both small-and large-scale projects involve a series of steps designed to ensure that they are implemented safely and comply with all regulations. They include:
Based on the findings of the preliminary assessment and planning, a site-specific characterization effort is initiated. The purpose is to confirm the geologic features of the site and determine the suitability of the site for injecting CO2. Typically, this includes a seismic survey of the area and drilling a test well, which takes approximately six months.
- Initial planning and preliminary assessment
- Site characterization including seismic survey and implementation of a test well
- Conversion of the site to injection operations including additional wells if needed
- CO2 injection
- Monitoring prior to, during and after injection
- Closing or capping the well after the research is completed
A seismic survey is conducted in and around the proposed well location. The seismic survey involves sending low level vibrations into the ground. Engineers and scientists then develop below-surface images by placing sensitive microphones on the ground in an area around the locations selected for the tests so that they can listen to the echoes from the vibrations. The echoes are transmitted by cable to a truck where they are recorded. The results of the survey are used to determine the rock properties, including continuity of the geologic rock layers and presence or absence of faulting in the area.
Based on the survey results, the next step is to drill and test a deep well. Appropriate drilling permits are obtained from the regulators at the state or federal level. The project team works with a contractor who sets up a drilling rig at the demonstration site and constructs the well. The project team may take core samples and conduct reservoir tests in the wells as needed. These tests can be used to provide more information about the nature and strength of the underground rock and indicate the maximum pressure that the rock formation can withstand if injection occurs. The Science Program "Habitable Planet" filmed the drilling at the MRCSP's R.E. Burger test well. Click here and scroll down to "10. Energy Challenges" to see the video. [Note: the video can be viewed at no charge on this external site but users must register].
If these site characterization studies confirm that the location is a good candidate for injection, the study team completes the application for an experimental injection permit, develops a plan for monitoring the operation and designs the injection system. A variety of controls are written into the drilling and injection permits, which are mandated to ensure the safety and protection of underground drinking water supplies.
As part of the demonstration, extensive monitoring is conducted both during and after the injection phase. Once the CO2 injection is finished, the monitoring continues until the demonstration is complete. At the end of the project, the MRCSP team reviews and evaluates the results of the demonstration and the well is plugged or capped.
In addition to the site-specific project fact sheets, some general information fact sheets provide more detail about the activities involved in conducting geologic field tests. They include a fact sheet on Frequently Asked Questions and fact sheets entitled: How Does Geologic Storage Work? and What is a Seismic Survey?
To Learn More
The following links will take you to each of the individual test sites where you can learn about specific plans and activities.
East Bend -- Cincinnati Arch
R.E. Burger -- Appalachian Basin