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Study: Saline Aquifers Can Provide Safe Storage for CO2

8 February 2007

Co2diagramenlarged
Most of the injected CO2 would be immobilized (light blue), trapped as small bubbles (white) in the pore space of the rock (gray). Only a small portion of the CO2 (dark blue) will continue to flow up towards the impermeable layer of caprock (yellow). Click to enlarge. Source: Ruben Juanes

A new analysis by a team led by MIT has concluded that carbon dioxide injected into deep saline aquifers can be trapped as tiny bubbles and safely stored in the briny porous rock for centuries. The carbon dioxide eventually will dissolve in the brine and a fraction will adhere to the rock in the form of minerals such as iron and magnesium carbonates.

In a paper published in a recent issue of Water Resources Research, the team, which also includes researchers from Stanford University, Imperial College London, and Chevron Energy Technology Company, asserts that injected carbon dioxide will thus likely not flow back up to the surface and into the atmosphere, as some researchers fear.

We have shown that this is a much safer way of disposing of CO2 than previously believed, because a large portion—maybe all—of the CO2 will be trapped in small blobs in the briny aquifer. Based on experiments and on the physics of flow and transport, we know that the flow of the CO2 is subject to a safety mechanism that will prevent it from rising up to the top just beneath the geologic cap.

—Ruben Juanes, MIT

Researchers have considered the possibility of sequestering CO2 beneath the Earth’s surface in at least three types of geologic formations: depleted oil and gas fields, unminable coal seams and deep saline aquifers.

The study shows that compressed carbon dioxide could be injected through a well deep underground into a natural sublayer consisting of porous rock, such as sandstone or limestone, saturated with saltwater.

The injected gas will form a plume and begin to rise through the permeable rock. Once the injection stops, the plume will continue to rise, but saltwater will close around the back of the gas plume. The saltwater and CO2 will juggle for position while flowing through the tiny pores in the rock.

Because the rock’s surface attracts water, the water will cling to the inner surface of the pores. These wet layers will swell, causing the pores to narrow and constrict the flow of carbon dioxide until the once-continuous plume of gas breaks into small bubbles or blobs, which will remain trapped in the pore space.

As it rises, the CO2 plume leaves a trail of immobile, disconnected blobs, which will remain trapped in the pore space of the rock, until they slowly dissolve and, on an even larger timescale, react with rock minerals. It is a good example of how a process that occurs at the microscopic scale affects the overall pattern of the flow at the geologic scale.

—Ruben Juanes

The paper also describes how the mechanism of capillary trapping can be exploited (e.g., by controlling the injection rate or alternating water and CO2 injection) to improve the overall effectiveness of the injection project.

The work was funded by industrial affiliates of the Petroleum Research Institute at Stanford.

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February 8, 2007 in Carbon Capture and Storage (CCS) | Permalink | Comments (15) | TrackBack (0)

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Comments

Now we just have to actually do it.

This is bad news. The plants need that C02 to live.

There are a lot of saline aquifers on every continent. Sequestration of flue gases from coal- and gas-fired power stations is not a sustainable substitute for energy conservation, but it will buy some time and reduce the need for new nuclear power stations.

I still prefer algae-based flue gas recycling to sequestration because it has the added benefit of displacing the oil that would otherwise come out of the ground anyway. However, this could be used in places where there isn't enough land for the bioreactors.

Or we could build more nuclear power stations, and reduce the need for coal-fired plants. And what coal plants remain, we could sequester the carbon dioxide.

This approach needs a capping layer, a porous sublayer and water with I guess the right degree of salinity. I'd bet the lab test was able to highly diffuse the CO2 within the medium. Since big CO2 emitters like coalfired generators tend to be near coal basins the required geology may be absent or some distance away.

It all points to one thing...produce less CO2 in the first place.

Excellent research! It is still far from an industrialized process but it moves sequestration closer.

For those who have a preference for other uses for CO2: There is no shortage, have at it!

In the mean time, we do not have the luxury of seeing if this can be commercialized. We need to move promptly to replace the existing coal fleet with nuclear. This would mean, for the US, approximately 250 1GW plants. If this technology pans out in 8-10 years, perhaps we could slow the growth of nuclear.

Bill:

Currently developing big reactors are more than 1.5 GWe. One power plant usually has couple of reactors, and old nuclear plants could add or retrofit couple of reactors easily. It will substantially reduce NIMBY opposition.

This is great research, but who's going to pay for this to happen? As of right now, how could you make money doing this to make it worth doing?

The only way this could make enough money to sustain itself is if there were super strict regulations on CO2 emissions and corporations had to pay for disposal of the CO2.

There is currently 35% too much CO2 in the atmosphere. Eliminating this from the air will have no effect on plant life.

Tom:

There is no such thing as “optimum CO2 level”. CO2 is food for plants, vastly improving their growth rate and water utilization efficiency. Carbon fertilization is responsible for double % digits higher biomass growth world wide, including agricultural crops. It is routinely used in green houses. Check, for example, CO2science.com, go to subject indecs and "agriculture".

Same effect occurs in aquacultures, for example with darling of GCC web site – algae biodiesel.

""There is currently 35% too much CO2 in the atmosphere. Eliminating this from the air will have no effect on plant life""
Who says this is the iptimal amount of plant life? Add another billion souls needing to be fed and how much "over" do your calculations suggest. Ho, Ho.

Andrey,

When I wrote 250 1GW plants, my intent was 250 reactors not 250 sites.

Certainly you are correct that the new fleet of reactors on the horizon is larger than 1GW but it does make for a nice round number. I will settle for 250 1.6GW reactors :) We will need the extra power for the electric cars by the time we get them built.

Bill

Is there an article which describes how they intend to separate the CO2 from the atmosphere? How much energy is involved in the injection process? How much energy these processes would require? How they intend to generate that energy?

Lacking the above information, I can easily imagine a scenario in which the CO2 generated by the CO2 sequestration process exceeds the amount being sequestered...

The leader, "Can Provide Safe Storage for CO2" absent real engineering standards verification makes the assertion "safe" look a lot more like political/sharemarket rhetoric than scientific hubris.

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