Carbon Storage

Once CO₂ is captured from a power plant, it can be transported via pipeline or truck to locations where appropriate geologic conditions will allow for safe storage. 

Depleted Oil and Gas Reservoirs

Oil and gas reservoirs are formations that held crude oil and natural gas.  Generally, they consist of a layer of porous rock with a dome-shaped layer of non-porous rock above.  The dome shape, which historically trapped oil or gas, has the potential to act as a carbon trap once oil and gas drilling is completed. According to the Department of Energy's (DOE) National Energy Technology Laboratory (NETL), “more than 88 billion metric tons of geologic storage potential exists in 9,667 oil and gas reservoirs distributed over 27 states and 3 [Canadian] provinces.”

In addition, CO₂ injected into an oil reservoir may dissolve into oil trapped in the porous rocks of the formation, thus reducing the oil’s viscosity.  That, in turn, allows an additional 10 to 15 percent of the oil to be recovered from the well. This process of enhanced oil recovery has been in use in the U.S. since the 1970s.

Unmineable Coal Seams

Some coal seams are either too deep or too thin to be mined economically.  However, all coal seams contain methane, and wells may be drilled to collect the methane for use in energy applications.  Once the initial stores of methane are recovered, CO₂ may be pumped into the wells, where it is preferentially stored in the coal, releasing additional methane.  According to NETL, between three and 13 molecules of CO₂ are absorbed for each molecule of methane, making coal seams an excellent storage location for CO₂.  “More than 180 billion metric tons of CO₂ sequestration potential exists in unmineable coal seams…distributed over 24 states and 3 provinces,” according to NETL.

Saline formations

Less understood but very promising is the storage potential of deep saline aquifers, or brine-saturated rock formations that occur deep underground or under the ocean.  An analysis by the Massachusetts Institute of Technology (MIT) in 2006 showed that wells deep underground consisting of porous rock, such as limestone or sandstone, saturated with saltwater would form an effective trap for injected CO₂.  Geologically, over time, some CO₂ would react with rock minerals to form solid carbonates, further immobilizing it.  Deep saline aquifers could potentially store between 3,300 to more than 12,200 billion metric tons of CO₂, according to NETL.  

The Sleipner project off the coast of Norway has been using deep saline storage since 1996 as part of their natural gas drilling efforts.  CO₂ from the project is injected into the Utsira formation, a sandy reservoir 800 meters beneath the North Sea.  Twenty thousand tons of CO₂ are added to storage each week.  After more than 10 years the project continues to be successful. 

Additional pilot programs for deep saline aquifer storage are currently under development all over the world.