Carbon Storage – Enhanced Oil Recovery

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Carbon Storage – Geologic Sequestration

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Carbon Storage and Sequestration

In geologic carbon sequestration, industrial CO2 is compressed into a semi-liquid state, and then injected deep underground into porous rock where it becomes trapped along with existing fluids. 


The sequestration process 

Porous rock structures, such as depleted oil fields or brine formations that have held fluid for millions of years, are excellent candidate sites for carbon sequestration. A layer of nonporous stone, called caprock, helps ensure the CO2 is contained.  


Over time, injected CO2 becomes trapped inside the rock - most immediately through the capillary pressure in the pores, then by dissolving into a liquid, and in the case of brine, by eventually hardening into solid calcium carbonate. 


Oil and gas companies have been injecting CO2 underground to stimulate additional oil production since the mid-1970s. Over 60 million tons of CO2 is injected for enhanced oil recovery (EOR) every year. About 30% of CO2 injected for EOR remains trapped in the formation. The remaining CO2 is recycled for additional injection, which results in more permanent storage.  


Deep brine or saline formations have great capacity for sequestration. These areas are composed of porous rock that contains brackish water with naturally high salt and contaminant levels. Sites for geologic carbon sequestration can be located on land, off shore or under the ocean.  


Other formations, such as coal beds that cannot be mined and basalt structures, may also be able to sequester CO2. However, the geochemical and geophysical trapping mechanisms are different and less well understood, particularly for basalt formations. 


Capacity for sequestration 

The Intergovernmental Panel on Climate Change (IPCC) has estimated there is sufficient global capacity to sequester 10,000 billion tons of CO2. The U.S. Department of Energy estimates for CO2 sequestration capacity are shown below.


Formation Type Billion metric tons of CO2 Sequestration
Saline Formations 919 to 3378
Oil and Gas Formations 8.24
Unminable Coal Beds 156.1 to 183.5

In comparison, the US power sector currently emits 2.4 billion metric tons annually. 


Safety and Security 

The IPCC has estimated that an adequately developed and managed sequestration site will retain 99% of sequestered CO2 for 1,000 years. The 1% failure rate is attributed to potential well failure. 


As noted above, the EOR industry has safely injected millions of tons of CO2 into porous rock formations for several decades. Other industries have similar long-term experiences with underground storage. For instance, natural gas has been safely and routinely in deep geologic formations for 80 years, in some cases under major urban areas. The United States disposes of more fluids by deep well injection every year than the quantity of CO2 emitted by the nation’s power plants.  


Adequate oversight is necessary for environmental protection.  


While there is substantial industrial experience on which to build a carbon sequestration industry, rapid scale up will require strong regulatory oversight as well as research and development support to lower costs and better manage risks.