Rock n' Roll: Is Pumping CO2 into Peridotite a Good Idea?

mt simon In Illinois, researchers are performing a large-scale test to sequester carbon dioxide (CO2) underground.   It's not the first such test of a process known as geological sequestration. It aims to take CO2, for example from coal-fired power plants, and pump it under pressure into hollows in underground rock formations.  There it should permeate rock and remains for thousands of years, if the geology is favorable.

The Illinois project will rely on the Mt. Simon sandstone layer, a huge platform of permeable sandstone running under Illinois, Indiana and Kentucky and topped by three reportedly impermeable layers of rock that will hopefully keep the million tons of CO2 from ‘leaking out'.

At a cost of $84 million, it is hoped the geologists aren't overlooking anything. Sequestering CO2 underground sounds like the ideal solution, and at 6,022 million tons per year produced in the U.S. in 2007 alone, such sequestration would literally put CO2 out of sight and out of mind.

Odds are however, it's a bridge to nowhere. First, we don't have the technology to effectively extract CO2 from gas flows from a power plant, and second, the amount of energy needed to pump it underground might use up a good percentage of the energy the power plant produces. This is a negative energy equation.

Last, even if we can successfully put CO2 underground - and keep it there without leaking - we are merely creating a problem future generations will have to deal with. As scientists from the Massachusetts Institute of Technology (MIT) point out, current geological sequestration projects do not have the monitoring capacity to insure that the process can be done safely, with large quantities of gas for a very long period of time. 

There are so many things that could go wrong. The gas could leak, or earthquakes could release it. Sequestering could even cause changes in soil chemistry, or earthquakes. Or the pressure could alter the underground water table, destroying the source for municipal water supplies. 

There is, potentially, another way. In Iceland and in Oman, researchers are exploring the possibility of turning the CO2 into a mineral form. Called mineral carbonation, this historic but poorly understood technique might enable safe and reliable underground sequestration.

In most sequestration projects, CO2 is compressed and injected into a geologic formation, often one filled with water. In time, the gas forms calcium carbonate. However, in order for this to happen the CO2 must first dissolve into the water.  Scientists don't know how long that takes, but the interval appears to be enough to allow a portion of the CO2 to escape first.

In Reykjavik, Iceland, an international team of scientists aiming to bypass the perhaps agonizingly slow natural process are putting the CO2 into water and injecting the water instead.

The fluid is being injected into a layer of basalt about 1,300 feet down, and scientists hope the initial injection will be able to tell them how long it takes for the mixture to react with the basalt and begin forming calcium carbonate. In the laboratory, such carbonization began within a month and was extensive in six months.

Six months may not be fast enough to support vast amounts of sequestration, so scientists in Oman are attempting to accelerate mineralization for the potential future sequestration of about 4 billion tons of CO2 in a peridotite layer under Oman that occupies 16,000 cubic miles.

The group is currently negotiating with an oil company in Oman. If the acceleration process is successful, sequestration could begin in any of the extensive peridotite or basaltic layers underlying every continent except Antarctica. In fact, according to the United Nations' Intergovernmental Panel on Climate Change, or IPCC, there is enough storage space in geologic formations on earth to sequester at least two trillions tons of CO2.

Even successful mineralization faces drawbacks, however. The process itself may plug underground reservoirs, requiring new wells and pipelines. The energy equation remains the same as with gaseous CO2, the cost - at about $110 per ton - significant enough to be daunting. Mineralization also uses vast quantities of water, or about 27 tons per ton of CO2, and water is becoming an increasingly limited resource.

Either process seems fraught with difficulties. It's like trying to diet for a summer on the beach beginning in April. Better, perhaps, to moderate food intake all winter. In the case of coal and fossil fuel use, it is probably better to stop now than try to undo the damage in the immediate future.

Related Reading:
Geoengineering, Sequestering Crops, another Bad Idea
Geoengineering Gaia: A Shot in the Dark, or A Shot in the Foot?

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  • Posted on March 17, 2009. Listed in:

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