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Going underground for a greenhouse gas solution
Jun 9 - McClatchy-Tribune Regional News - Tom Fowler Houston Chronicle While world leaders made pledges to cut greenhouse gases at this week's G8 Summit in Germany, Sue Hovorka was in the backwoods of East Texas working to help them keep those promises. Their goal: to find even the slightest hint that the carbon dioxide they injected 4,000 feet underground two years ago had made it to the surface at the heavily wooded site near the Trinity River. Known as the Frio Brine Project, the site is on the leading edge of Department of Energy-funded studies looking into carbon sequestration, the process of injecting CO2 -- a byproduct of burning fossil fuels -- deep into the ground. Carbon capture and storage could be part of the solution to global warming, which many climatologists attribute at least partly to a greenhouse effect that occurs when carbon dioxide and other gases trap heat in the atmosphere. The hope is that CO2 can be stripped from the emissions of power plants and other users of fossil fuels, shipped by pipeline and injected deep underground into old oil and natural gas fields or brine formations. The idea may seem simple, particularly because companies have been injecting CO2 into the ground to force oil and natural gas out of hard-to-reach formations for decades. But no one has tried to keep so much CO2 in storage, particularly the millions of tons that would need to be injected to keep up with annual CO2 emissions. The U.S. generates about 6 billion tons of CO2 per year from all sources, according to the Department of Energy. Not easy, and not cheap Experts say it also isn't going to be easy or cheap. The notion of putting power plant byproducts deep underground may sound a bit like the controversial Yucca Mountain, Nev., storage site for spent nuclear fuel. But Hovorka said the two aren't anything alike. CO2 isn't considered a toxic or hazardous substance like uranium, she said. And once CO2 is injected into a formation, like the brine reservoir near Dayton, it is hard to get it back out. About 20 percent of it dissolves in the brine, creating a weak acid much like what puts the fizz in a carbonated soda. The rest is trapped in the sand and rock of the formation through a process called phase trapping, Hovorka said. It's a process similar to a sponge soaking up a fluid, except that it's much harder to wring the gas back out. "It's like getting grease on your tie," Hovorka said. "You can't just rinse it out with water. You have to use another chemical to separate it." During Thursday's tests researchers found traces of CO2 in the soil around the wellheads, but after hours of testing they determined it came from a tiny leak in the wellhead. Avoiding aquifers A more likely hazard from CO2 injection would be if the salty water it displaces in the brine were pushed into a fresh water aquifer that was being used for drinking water, Hovorka said. That can be avoided by using brine formations that aren't near drinking water sources. Finding such formations shouldn't be hard. Between brine formations like the one Hovorka is working with and oil and gas reservoirs, there may be capacity for as much as 500 billion tons of CO2 storage in the U.S., according to studies done by the University of Texas' Bureau of Economic Geology. South Texas alone has capacity to store an estimated 171 billion metric tons of CO2. Hovorka and Meckal hope to take their work to the next level this fall. That's when they will begin working with Denbury Resources to inject 1 million tons of CO2, or roughly the annual output of a coal-fired power plant, into an underground formation in Mississippi. The technology for carbon capture and storage already exists, and in some instances has been used for decades, said Mark Morey, a director at Cambridge Energy Research Associates. But it can add a lot of cost to a project. The greatest cost in the process is carbon capture, or removing the CO2 from the fuel of a power plant before it is burned or from the exhaust afterwards. Morey says a typical coal plant can cost between $50 and $60 per megawatt hour to build and operate, but adding the capacity to capture the CO2 can add an additional $25 to $30 per megawatt hour, he says. The cost of transporting and storing the CO2 underground would be $10 to $15 per megawatt hour, Morey said, but that's assuming the pipeline and storage infrastructure were already in place. For companies to invest in such systems there would have to be an economic incentive, such as a tax on carbon emissions greater than the cost of capture and storage. Even if the penalties for emitting CO2 were high enough to convince companies to capture it, a number of serious legal liabilities also would keep companies from rushing into the storage business, said Tim Bradley, head of Kinder Morgan's CO2 business. tom.fowler@chron.com |