Green Energy

Carbon Capture and Storage 101: Common Terms

Carbon Capture and Storage 101: Common Terms

While decarbonization is top of mind for many oil and gas companies, carbon reduction initiatives are also becoming standard business practice across industries. For those outside the energy sector, developing a strategy to reduce their company’s carbon footprint across supply chain and operations may be the first time they’ve been introduced to these concepts. Whether you are new or are looking for a refresher, this collection of brief definitions clearly defines what each term means and provides context for how they fit into the broader carbon emissions and decarbonization discussion. 

CCS/CCUS: Carbon capture and storage (CCS) refers to capturing carbon dioxide emissions that are created from burning fossil fuels or from heavy industrial processes like steel production. Carbon emissions can be captured using one of three methods: pre-combustion carbon capture, post-combustion carbon capture, and oxy-combustion carbon capture. Once the carbon dioxide is captured, it is transported via ship or pipeline to its designated storage location, where it is then injected underground to be stored within the pore space of geologic formations. Similar to CCS, carbon capture, utilization, and storage (CCUS) refers to this same capture and storage process with the addition of possibly reusing the captured carbon to create biofuels or plastics—thereby replacing more carbon-intensive source materials.

CO2 Emissions: Carbon dioxide (CO2) is produced from a variety of sources, such as the raising of livestock, but the primary source of carbon dioxide is from burning fossil fuels. Fossil fuels are burned to produce electricity, power factories, and enable vehicles to run. When fossil fuels are burned, the combustion reaction results in the release of CO2. Carbon dioxide emissions are a key cause of climate change; as they are produced and released into the atmosphere, they essentially insulate our planet by trapping heat and leading temperatures to rise over time.  

45Q Tax Credit: The 45Q tax credit is a credit for carbon oxide sequestration—or capture and storage. The amount of credit is computed per metric ton of qualified carbon oxide captured and sequestered. 

Enhanced Oil Recovery (EOR): Enhanced oil recovery (EOR) occurs after primary and secondary techniques for extracting oil from a well have already transpired. In primary and secondary recovery, pressure differences between the surface and the well allow hydrocarbons to flow to surface. In EOR, oil and gas operators change the chemical composition of the oil in the well so it is easier to extract. However, it is not always economical to use EOR methods; should oil prices be too low, the time and expense of using EOR to extract oil may lead profit margins to shrink too low to justify using this method. 

Pore Space: Pore space is the portion of a formation that is porous enough for water and air to flow through it. Within the context of CCS, pore space is the porous area that is used to store carbon dioxide after injection. 

Paris Climate Accord: Also known as the Paris Agreement, the Paris Climate Accord is an international treaty signed by 192 countries in 2015 to limit the effects of climate change. The agreement broadly covers strategies for climate change mitigation, but the aspect you’re most likely to hear discussed is the “2-degree Celsius pathway.” This refers to the long-term temperature goal of keeping the global increase in temperature to well below 2°C (3.6°F) above pre-industrial levels. Achieving this goal would dramatically reduce the effects of climate change, and carbon capture is an important part of many countries’ strategies for emission reduction.

Carbon Emissions: In this instance, “carbon” is used interchangeably with “carbon dioxide.” Carbon emissions and carbon dioxide emissions are the byproduct of burning fossil fuels for transportation, industrial processes, and electricity. 

Flue Gas: Flue gas is the gas that is produced from factories and combustion plants, and it contains particulate matter (dust), sulfur oxides, nitrogen oxides, carbon dioxide, and carbon monoxide. Because flue gas is one of the major sources of carbon dioxide, it is frequently targeted for carbon capture efforts. 

Direct Air Capture (DAC): DAC refers to extracting CO2 from the atmosphere, rather than from flue gas or other products emitted by industrial processes. An energy-intensive process, there are two approaches currently used: solid and liquid DAC. 

Caprock: A caprock (or cap rock) is an impermeable layer of rock that lies on top of a more porous rock type; because it is less permeable, the caprock prevents fluids found in more porous layers of rock from migrating upward toward the surface. An oversimplification, it can be thought of as a pie crust preventing liquid from the pie filling from bubbling up.

Class VI Permit: In the US, the Environmental Protection Agency monitors and regulates injection wells, which are wells that are used to store or dispose of fluids underground. Municipal waste or brine produced during oil and gas extraction are examples of fluids that are stored in injection wells. Depending on the type of fluid stored or disposed of in an injection well, the EPA issues a different type of permit. A Class VI injection permit is a relatively new type of permit created for injection wells that store carbon dioxide in deep rock formations for long periods of time.

CO2 Plume: A CO2 plume refers to the extent to which carbon dioxide migrates through a rock formation after it is injected for storage.

Supercritical Fluid: A supercritical fluid occurs when a substance is subjected to a temperature and pressure that exceeds its critical point; that critical point varies by substance. At this point, the substance does not have distinct liquid and gas phases, and it instead takes on characteristics of both stages of matter. Carbon dioxide becomes a supercritical fluid at temperatures higher than 88°F and pressures higher than 1,057 psi. At this point, CO2 becomes denser but maintains gas-like viscosity. Carbon dioxide is intentionally stored in a supercritical state because it is denser and thus takes up less space for storage. 

Subsurface Storage Complex: A subsurface storage complex is the geologic formation that has been selected for carbon storage. When the captured carbon arrives at the storage site, it is then injected underground into the subsurface storage complex, where it is stored within the pore space.  

This is part 1 of our series defining common carbon capture and storage terms. Refer back to this page for these definitions or for links to future installments of our glossary. If you are looking for additional insights into CCS or assistance with CCS-related endeavors, contact us today.



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