But in spite of these efforts, “we are not on track to reduce global climate emissions,” Thomas Halsey of ExxonMobil Upstream Research said during a public lecture Wednesday. Renewable energy, improved transportation and energy efficiency have the potential to greatly reduce global emissions, but not to the degree that is necessary. If this is true, how do we fill the gap? One major factor will be carbon capture and storage - preventing carbon emissions from entering the atmosphere and causing warming.
“A lot of the carbon dioxide in the atmosphere comes from relatively concentrated sources,” e.g. power plants rather than car tailpipes, Halsey said.
A few technologies exist for capturing carbon at power plants, with varying costs and efficiency. Post-combustion CO2 filtration is commercially available already. Pre-combustion carbon capture separates CO2 and injects only hydrogen as fuel for the turbine. Demonstration plants exist, but are plagued by problems due to the complexity of the technology. Oxy-Fuel combusts pure oxygen, but requires very high temperatures and thus large amounts of energy (somewhat negating the positive benefits).
The one thing all three technologies seem to have in common is their high cost. In countries that have a carbon tax, like Norway, carbon capture is more feasible. But in the United States, adoption of the technology is slow-going.
And carbon capture is just one part of the equation. Once extracted, where could the CO2 be put to prevent it from entering the atmosphere? Enhanced Oilfield Recovery (EOR) is one possibility for use; when CO2 is injected into oil or gas reservoirs, it increases rates of recovery. EOR has been practiced for many years and is already in use at more than 100 oil fields, although many more could potentially benefit.
Carbon sequestration, the traditional option, involves injecting captured CO2 into the earth, into either unmine-able coal beds, deep saline aquifers or depleted oil/gas reserves. Geological barriers prevent the gas from returning to the surface.
|Oil/Gas Reservoirs||Increased recovery||Scale and capacity|
Other people have drilled wells; might not know where they all are
|Saline Aquifers||Large scale, distribution and capacity||Lack of research|
|Unmine-able Coal Beds||Increase coal bed methane production||Injectivity problems (coal swells with CO2 injection and blocks pathways);|
Pilot programs didn't work
Pros and cons must be carefully considered because “we don’t want to put the CO2 down and have it come back up,” Halsey said.
The Sleipner oil field in the North Sea, in use since 1998, has successfully injected 10 million tons of CO2 into an underground reservoir. Constant monitoring has shown some upward CO2 migration, but there is no evidence for leakage through the overlying shale barrier. The potential for earthquake activity is troublesome, but it is “a standard oil industry technical problem,” according to Halsey.
The monitoring required for such projects bring up an interesting issue-- who will be responsible for long-term storage stewardship? Companies would not be willing to invest if saddled with liability for hundreds of years. At some point, liability would need to be transferred to the public sector. Many issues exist, but if they are overcome, CCS could be a crucial tool for reducing catastrophic climate change.