November 18, 2008

Greenhouse Gases Going Underground

Greenhouse gases injected underground? It's new way to significantly cut the amount of carbon dioxide that reaches the atmosphere and spurs global warming, according to MIT engineers.

Although promising, the technique has never been tested in a full-scale industrial operation.

However, MIT engineers have developed a software tool to determine how much CO2 can be sequestered safely in geological formations.

The work will be presented Wednesday, Nov. 18 at the 9th International Conference on Greenhouse Gas Control Technologies (GHGT-9), in Washington D.C.

According to the 2007 MIT study, "The Future of Coal," capturing CO2 at coal-burning power plants and storing it in deep geological basins will alleviate its potentially negative effects on the atmosphere.

Ruben Juanes, assistant professor of civil and environmental engineering (CEE) and one of the authors of the work warned injecting too much CO2 could create or enlarge underground faults that may become conduits for CO2 to travel back up to the atmosphere.

"Our model is a simple, effective way to calculate how much CO2 a basin can store safely. It is the first to look at large scales and take into account the effects of flow dynamics on the stored CO2," he said.

Juanes and graduate student Michael L. Szulczewski have applied their model to the Fox Hills Sandstone in the Powder River basin straddling Montana and Wyoming.

The two discovered that the formation would hold around 5 gigatons of CO2 -- more than half of all the CO2 emitted by the United States each year.

"A lot of people have done studies at small scales," Szulczewski said. "If we're going to offset emissions, however, we're going to inject a lot of CO2 into the subsurface. This requires thinking at the basin scale."

CO2 has been stored in small pilot projects in Norway, Algeria and elsewhere.

In fact, during 2004, 1,600 tons of CO2 were injected 1,500 meters into high-permeability brine-bearing sandstone of the Frio formation beneath the Gulf coast of Texas.

Current proposals call for injecting billions of tons within the United States.

The McClelland Fund, administered by the MIT Energy Initiative, and by the Reed Research Fund, paid for the research.


Image 1: Grayish white sandstone at the top of the Fox Hills sandstone in the south bank of the Cannonball River, 3.5 miles west of Solen, Sioux County, North Dakota. (USGS)

Image 2: Schematic that illustrates the application of MIT's new mathematical model to the sequestration of carbon dioxide in the Powder River basin, between the statesof Wyoming and Montana. Shown are a plan view (left) and avertically magnified cross section of the basin (right). Carbon dioxide is injected from a line-drive array of wells (black line) fora period of decades. The extent of the CO2 plume at the end of theinjection period is shown in dark blue. After injection, the plumecontinues to migrate in the direction of the regional groundwater flow(indicated by black arrows). During this process, part of the CO2 is trapped by capillary forces and left behind in the form of immobile blobs. The amount of CO2 injected in the basin is designed such that the footprint of the plume when all the CO2 is trapped (light blue) remains within the boundaries of the basin. Image / Michael L. Szulczewski/Ruben Juanes; MIT


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