Onshore and Offshore Geologic Carbon Storage Areas in the Northeastern Region

In 2013, the USGS identified and assessed several onshore areas in the northeastern region where CO₂ could be stored in underground geologic reservoirs, and Gupta (2019) identified and assessed offshore areas adjacent to the northeastern region that could be suitable for geologic CO₂ storage (fig. 1). The USGS has the expertise to assess subsurface geologic resources in the northeastern region, including areas with the potential for subsurface CO₂ and energy storage.

Carbon Dioxide Mineralization Opportunities in the Northeastern Region

Carbon dioxide mineralization is a chemical process by which CO₂ becomes part of a solid mineral, such as a carbonate. This chemical reaction happens naturally when certain rocks are exposed to CO₂, and this process can also be sped up artificially. An advantage of CO₂ mineralization is that CO₂ can be effectively trapped in the newly formed mineral. Rocks that have the potential for CO₂ mineralization are mostly igneous (primarily mafic and ultramafic) or metamorphic (for example, rocks that contain asbestos) rather than sedimentary rocks. There are two primary types of geologic CO₂ mineralization: injection of CO₂ or a mixture of CO₂ and water into rock formations deep underground, and exposing broken pieces of rock at Earth’s surface, such as leftover rocks from mining (mine tailings), to CO₂ (Blondes and others, 2019). Areas within and adjacent to the northeastern region where CO₂ mineralization might be feasible are shown in figure 2; however, more research is needed to quantify the total CO₂ storage potential at each of these sites. Nationally, CO₂ mineralization storage resources are poorly defined. Globally, CO₂ mineralization may have the potential of sequestering up to 60,000,000 billion metric tons of CO₂ (Kelemen and others, 2019).

Adding Carbon Dioxide-Reactive Minerals to Coastal Beaches and Wetlands

On geologic timescales, weathering of some kinds of igneous rocks is an important control on atmospheric CO₂ concentrations because this geochemical process removes CO₂ from the atmosphere. One approach that may help with CO₂ capture and storage is the addition of amendments such as olivine (a mineral found in mafic and ultramafic igneous rocks) to coastal beaches and wetland areas. When olivine weathers, the process not only removes CO₂ from the atmosphere, it also increases ocean alkalinity by sequestering CO₂ in seawater in the form of a bicarbonate ion. Seawater bicarbonate ions make up about 85 to 90 percent of seawater alkalinity and have a residence time of about 100,000 years in seawater (Emerson and Hedges, 2008), making this olivine weathering process an effective way to sequester CO₂. Ocean CO₂ removal technologies based on this weathering process could mitigate both ocean acidification and climate change (Montserrat and others, 2017; National Academies of Sciences, Engineering, and Medicine, 2022).

The northeastern region has over 2,000 kilometers of coastline with associated coastal wetlands that might be potential candidates for the application of mafic and ultramafic mineral amendments (fig. 1). Additional research is needed to evaluate and model the effects of application of mineral amendments to salt marshes, beaches, coastal wetlands, and similar environments, including effects on biota, soils, and coastal ocean chemistry. Models of the CO₂ storage potential resulting from large-scale applications of mineral amendments to coastal environments need to be developed. Ultrabasic sand amendments could be spread in thin layers or combined with dredge spoils that are added to coastal wetlands as a way to use natural materials to increase elevation resilience relative to sea-level rise. This is particularly important in the approximately 25 percent of U.S. wetlands that are in degraded condition and have subsided soils (Kroeger and others, 2017). More research is needed to identify suitable application sites and potential effects on the environment.

Methane Emission Mitigation

Many opportunities exist in the northeastern region to reduce GHG emissions of methane (CH₄) that is released from abandoned and unplugged orphaned oil and gas wells and active and abandoned coal mines.

Abandoned and Unplugged Orphaned Oil and Gas Wells

Fugitive or leaking GHG emissions, particularly CH₄ from unproductive abandoned oil and gas wells, are significant sources of GHG that can be remediated through proper well decommissioning or plugging. Unplugged orphaned wells are nonproducing wells that no longer have an operator to properly plug them. Some abandoned wells may be plugged; however, because of the methods and materials used or age of the plugging material, these wells can also be a source of emissions. The EPA estimated that all abandoned oil and gas wells in the United States, including orphaned or idle wells, emitted 276,000 metric tons of CH₄ in 2020. The 2021 Bipartisan Infrastructure Law, formally called the Infrastructure Investment and Jobs Act (Public Law 117-58, 135 stat. 429), provides funding to plug these wells and reduce their GHG emissions.

During the early history of oil and gas exploration in the United States, locations of many oil and gas wells often were not well-documented, and some of these wells were subsequently abandoned or orphaned. Without location data for abandoned or orphaned oil and gas wells, emissions cannot be checked, and these wells cannot be prioritized for proper decommissioning. Records of abandoned and orphaned oil and gas well locations from oil- and gas-producing States may or may not be complete, but a preliminary national dataset of locations of unplugged orphaned oil and gas wells was recently published by the USGS (Grove and Merrill, 2022; Merrill and others, 2023) (fig. 3). This dataset can be used for planning which orphaned wells to prioritize for decommissioning. The USGS is also assisting other Bureaus in the Department of the Interior with measurements of CH₄ emissions from unplugged orphaned oil and gas wells before and after plugging and site remediation. Improved measurements of CH₄ emissions will help to better characterize the GHG emission reductions resulting from plugging orphaned wells.

Active and Abandoned Coal Mines

All coal mines release CH₄ during mining, and the amount released depends on the geologic setting of the mine and operational and design factors. Gassy active underground coal mines emit more than 100,000 cubic feet of CH₄ per day. The EPA reported that CH₄ emissions from coal mining and abandoned coal mines accounted for about 7 percent of total U.S. CH₄ emissions in 2021. Removal of CH₄ from coal beds and capture of CH₄ released during mining are effective methods to reduce emissions from active mines. With global trends in energy transitions from fossil fuels to renewable energy sources and the declining need for coal to produce steam, many coal mines are closing, with more likely to close. Thousands of closed coal mines are potentially leaking CH₄ from surface deformations, boreholes, or mine-shaft seals (fig. 4). These mines that are leaking CH₄ can be identified, and the best available research and assessment methodologies can be used to quantify and mitigate CH₄ emissions with a particular focus on high-emission sources.

Unlike other greenhouse gases, CH₄ can easily be converted to usable energy. Methane emissions from active and abandoned coal mines can be captured and utilized to alleviate both the global warming effects of CH₄ and to create another energy sector in nearby communities where coal mining jobs may have been lost. Methane from active and abandoned coal mines can be viewed as a beneficial resource from what would otherwise be waste. Capture and utilization of CH₄ that is complemented by research as well as inventory and forecast studies to minimize the GHG effect of these emissions can support of the U.S. Methane Emissions Reduction Action Plan (White House, 2021), and to take full advantage of their resource potential. The USGS is developing measurement strategies to better monitor and assess CH₄ emissions at active and abandoned coal mines.