Carbon Sequestration

The term “Carbon Sequestration” refers to processes, either natural or artificial, in which carbon dioxide is removed from the atmosphere, captured, secured, and stored in solid or liquid form. Carbon dioxide is a heat-trapping greenhouse gas that comes from both natural and human activities. Natural sources of carbon dioxide include animal exhalation, decomposing vegetation, outgassing from the ocean, and volcanoes. Human-generated carbon dioxide comes primarily from energy production, including burning coal, oil, or natural gas, and cement production. The build-up of carbon dioxide and other greenhouse gases in the atmosphere can trap heat and contribute to climate change. The capture and long-term storage of carbon dioxide in solid and dissolved forms is now recognized as a key part of a comprehensive climate change mitigation strategy to limit the amount of human-made carbon dioxide contributed to Earth’s atmosphere.

The three types of carbon sequestration

• Natural or biological carbon sequestration occurs where carbon dioxide is captured, secured, and stored in land-based vegetation, soils, and oceans. On land, carbon dioxide from the atmosphere is collected by trees and plants through photosynthesis and stored as carbon in soils and biomass (tree trunks, branches, foliage, and roots). Large volumes of carbon dioxide are also absorbed, released, and stored by the oceans. Increasing the amount of carbon dioxide stored in the ocean may be accomplished by increasing the productivity of ocean biological systems by iron fertilization or by pumping carbon dioxide into the deep sea.
  
• Technological carbon sequestration uses innovative mechanical processes to capture, secure, and store carbon dioxide either at the point of emission (point source capture), or directly from the atmosphere (direct air capture (DAC)). The captured carbon dioxide can then be injected into the ground to be mineralized or may be reused for secondary industrial purposes such as food and beverage, greenhouse horticulture, and materials manufacture (fuels and plastics).
  
• Geologic carbon sequestration is the process in which carbon dioxide is captured and then stored in underground geologic rock formations. Carbon dioxide may be stored in a variety of places, including oil and gas reservoirs, saline aquifers, unmineable coal seams, high-organic-content shale formations, and basalt. Typically, carbon dioxide is captured from an industrial source, such as a power plant or natural gas processing facility, converted into a liquid, and injected deep (thousands of feet) into porous rocks for long-term storage. Once underground, the carbon can be safely and permanently stored.
  

Carbon dioxide emissions in Oregon

According to the Oregon Department of Environmental Quality, Oregon’s emissions of carbon dioxide are approximately 60 to 70 million tons annually. In 2021, Oregon released 61.4 million tons of carbon dioxide. Oregon emissions have been relatively consistent in the period of measurement between 1990 and 2021. The top sources of carbon dioxide are transportation (cars, boats, planes, trains), heating for homes and workplaces, industrial applications, and agriculture.

Graph showing Oregon's greenhouse gas inventory by type: transportation, heating for homes and workplaces, industrial applications, and agriculture between 1990 and 2021. Total emissions during this time period were relatively constant averaging around 65 million metric tons per year. Credit:Oregon DEQ, Action on Climate Change.

Point Sources

Map of carbon dioxide point sources in Oregon as of 2021. The graphic includes nearby sources in Washington and Idaho. Larger yellow circles indicate bigger sources of carbon dioxide. Credit: Data from the Environmental Protection Agency Data Sets. Click the image to expand the map.

Geologic carbon sequestration possibilities in the Pacific Northwest

Credit: U.S. Geological Survey Geologic Carbon Dioxide Storage Resources Assessment Team (2013)

Mafic rocks, particularly extensive stacked basaltic lava flows, are significant potential reservoirs for carbon dioxide storage and mineralization (Blondes and others, 2019). Thick and deep lava flow sequences of the 17 to 6 million-year-old Columbia River Basalt Group (CRBG), a continental flood-basalt province, serve as potential reservoirs for carbon dioxide storage and mineralization in the Columbia Basin of eastern Oregon and Washington (Blondes and others, 2019; Franczyk and others, 2020). 

Target reservoirs in the CRBG lie within the Grande Ronde Basalt in the Columbia Basin. These rocks have been the focus of many studies on carbon dioxide storage and mineralization. The Grande Ronde Basalt is composed of ~100 individual, laterally extensive, basalt and basaltic andesite lava flows, encompassing an area of nearly ~65,599 square miles, a thickness up to 14,760 feet, and a volume of approximately 36,083 cubic miles (Reidel and Tolan, 2013). Grande Ronde lava flows consist of highly fractured, weathered, brecciated, and/or vesicular flow tops and bases with dense, crystalline colonnade and/or entablature interiors. Lava flow tops and bottoms have an estimated porosity of 14 to 39%, while most flow interiors are estimated to have a porosity around 1 to 2% (Sublette, 1986; Whiteman and others, 1994; Reidel and others, 2002; Cao and others, 2023). Estimates of carbon dioxide storage potential in the CRBG range from 10 metric gigatons (Gt) to 100 Gt (McGrail and others, 2006; Gislason and others, 2010).

Geologic carbon sequestration is not the only type of storage project proposed in the CRBG. The CRBG has also been investigated for natural gas storage, as a possible nuclear waste storage site in the vicinity of Hanford, WA, for reservoir thermal energy storage (RTES) in the Portland Basin, and for low temperature geothermal resources across the Columbia Basin that include potential for energy production. Several cities in Oregon, including Beaverton, Cornelius, Salem, and Pendleton each have existing aquifer storage and recovery (ASR) projects that utilize the basalt interflow zones for seasonal storage of potable water. 

Credit: Blondes and others (2019)

Extent of CRBG in Oregon, Washington, and Idaho and a schematic section of typical CRBG lava flows. Targets for carbon dioxide storage would be the porous tops of lava flows.

References