New techniques for removing carbon from the atmosphere

November 3, 2017 by Ker Than, Stanford University
Research scientist Tae Wook Kim, left, and professor Tony Kovscek check the status of an experiment in the CT scanner. Credit: L.A. Cicero

Of the approximately two dozen medical CT scanners scattered throughout Stanford's main campus and medical centers, two can be found nestled in basement labs of the Green Earth Sciences Buildings.

The scanner duo is being put to some decidedly off-label uses in research led by Anthony Kovscek, a professor of energy resources engineering at Stanford's School of Earth, Energy & Environmental Sciences (Stanford Earth). The machines in this case have helped scientists extract oil and gas more efficiently, and are now revealing ways of storing carbon dioxide (CO2) deep underground while the world continues to rely on fossil fuels for energy and transportation.

The motorized tables that would normally slide patients in and out of the scanners' openings instead support machines made from a daunting array of connected pressure vessels, nozzles and gauges shrouded beneath wires and tubing. The larger of the two scanners is about the length of a person and looks like something devised by a mad scientist to power a time-traveling DeLorean. "I'll still sometimes say 'Whoa' when I see it," said Muhammad Almajid, a graduate student in Kovscek's lab.

The ad hoc devices, which Almajid and his colleagues painstakingly craft and assemble by hand, are designed to force pressurized oil, water or gas through slim cylinders of seemingly solid rock, which the scanners then analyze with X-rays.

"We try to visualize things that people say you can't visualize," said Kovscek, who is the Keleen and Carlton Beal Professor of Petroleum Engineering at Stanford. "It's happened more than once, where someone will say, 'Well, you just can't do it.' And I point to our results and say, 'Well, I beg to differ.'"

The lab experiments are intended to recreate, in miniature, the movement of various substances through vast rock formations and to provide real-world validation of computer simulations of the same processes. This type of experimentation and simulation has helped the United States move toward energy security by enabling the nation to tap vast reserves of previously inaccessible oil and natural gas, such as shale oil.

But what's learned from that mass of tubes and gauges could also help mitigate the effects of burning 100 million barrels of oil per day, which is expected to continue for at least 50 years while the world transitions to renewable energy sources. Results like the ones from Kovscek's lab are now guiding new ways of sequestering the powerful greenhouse gas , which is released from burning fossil fuels, deep within rocks, for eons, while avoiding leaks and other negative consequences – a strategy many experts say is going to be necessary in order to avoid the hazards of climate change.

"Greater efficiency in and conversion of the energy system to renewables has to happen. But there is a multi-decade period where we really have to make sure that CO2 emissions are under control while hydrocarbons are still being consumed at high rates," said Hamdi Tchelepi, a professor of energy resources engineering who frequently collaborates with Kovscek. "The only way to achieve that is through a serious, large-scale deployment of carbon sequestration. It's not optional. In the eyes of the scientific community, this has to happen."

Trapping carbon underground

Some of the strategies for efficiently extracting oil and natural gas from reservoirs that came out of work like Kovscek's are also a first step toward carbon sequestration.

Especially relevant is a practice called (EOR) by gas injection, which involves pumping pressurized gases into existing oil fields to displace or reduce the viscosity of crude oil, making it easier to extract. Even the best performing fields still leave about 50 percent of oil in the ground, Kovscek said. For unconventional resources such as shale rocks, which are even more difficult to extract oil from, the recovery rate can be as low as 5 percent.

"That means if we don't do anything further on a well after the initial recovery, we're going to leave as much as 95 percent of the resource in the ground," Kovscek said. "That's a huge waste of all the energy that it took to drill the well and the water injection and hydraulic fracturing that may have been required to operate it."

CO2, it turns out, mixes very well with crude oil, making it, in petroleum engineering parlance, an excellent "EOR fluid." Thus, for decades now, and for its own purposes, the fossil fuel industry has been refining the process of injecting huge amounts of CO2 deep underground.

CT scanner in the lab of Anthony Kovscek conducts experiments meant to mimic the flow of liquids and gases deep underground. Credit: Ker Than

The challenge for people like Kovscek and his colleagues is keeping that gas imprisoned underground and out of the atmosphere for long periods of time without unanticipated consequences.

"Oil companies are mostly interested in what's called the active injection period because their goal is to get a return on investment within one or two decades," Tchelepi said. "For sequestration, you need to inject CO2 for a couple of decades and then turn the valves off. And the physics of what happens after you stop injecting is more complicated than the physics used for oil recovery. You have to truly go a step beyond, because the time scales are so long."

Understanding the dangers

A major focus of Tchelepi's research is using 4-D computer simulations to predict how sequestered CO2 will interact with faults deep within the Earth across centuries and eons. "In some cases, we've modeled 3,000 to 4,000 years into the future," Tchelepi said. "The ideal target for sequestration would be a large, reasonably homogenous rock basin that doesn't have any fractures. But nature isn't always so kind to us."

The dangers associated with CO2 interacting wrongfully with faults are myriad. One risk is that the highly pressurized gas might nudge an already stressed fault toward its breaking point, generating earthquakes. Another risk that an existing crack is widened by the CO2, creating a pathway for other, more noxious gases to seep to the surface or pollute aquifers used for drinking and agriculture. "Carbon dioxide and water is Pellegrino [sparkling water]," Tchelepi said, "but it's not pure Pellegrino, because CO2 usually contains harmful impurities that get generated when coal is burned but that aren't fully removed before injection."

Trying to minimize the risk of CO2 leakage is a focus of Lou Durlofsky's research. Durlofsky, who is a professor of energy resources engineering, is adapting techniques from oil and gas applications to simulate the impacts of placing CO2 injection wells in different locations and varying the rates at which injection occurs. With powerful computer simulations, Durlofsky's team can play virtual "what-if" games that allow it to determine well locations and injection sequences that nudge sequestered CO2 toward a desired fate.

The best-case scenario for trapped CO2 is for it to react with rock and form long-lasting minerals, but this process requires very long timescales to occur. However, there are two other favorable outcomes, which can happen much faster: dissolution, whereby the CO2 gets dissolved in salt water, and residual trapping, which is when CO2 gets broken up into very small bubbles that resist leakage.

"Because the CO2 is now in the form of discrete blobs, it can't flow as easily and is effectively trapped in place," explained Durlofsky, who is the Otto N. Miller Professor in Earth Sciences at Stanford. "By varying where and how CO2 gets injected in the formation, we can increase the likelihood that one or the other of these outcomes will occur."

'Green oil'

Despite the risks of leakage, Tchelepi said the results from Kovscek's scanner experiments and his own team's computer simulations indicate that safe, long-term carbon sequestration is within reach—and he thinks the technique should be deployed now, even though it's still in its infancy. "It's far from being perfected, but we know more than enough, in my opinion, to start using it," Tchelepi said. "Clearly, there will be issues and problems, but the only way to deal with them is to put them under the control of science and engineering, to monitor them and to spend the resources to learn from the mistakes. The risk of waiting for perfection is too big. We know enough."

One idea that Kovscek and Tchelepi's labs are exploring is combining EOR and to create what they refer to as "green oil." "If you can take all of the CO2 that is generated from burning the oil or natural gas that's extracted in the future from a reservoir, inject it back into the reservoir and store it securely, you would have net-zero carbon emissions," Kovscek said. "Sequestration is expensive. If we can recover something valuable in the process, it can be used to pay for the sequestration."

While some might see a contradiction in helping maximize the extraction of oil and , on the one hand, and working to sequester the CO2 created from the burning of those same fuels on the other, Tchelepi views the two goals as complementary.

"You have to be realistic that we will use 100 million barrels of oil a day for the next 50 years," he said. "Should we do that in a messy, uncontrolled way? Or should we do it with the best possible engineering, maximize the recovery and optimize it by coupling it with sequestration? I'm working on the second option."

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18 comments

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philstacy9
1 / 5 (7) Nov 03, 2017
Journalism and science both stopped investigating and and now launder the stories.

http://www.frontp...eenfield
PTTG
5 / 5 (7) Nov 03, 2017
The moderation on phys.org is a joke. The previous comment is naked link spam.
thomasct
1.4 / 5 (11) Nov 03, 2017
Why would we want to remove CO2 from the air? Surely the more the better for our food crops? In any case, one volcanic eruption releases more CO2 into the air as did man since the beginning of the Industrial Revolution. And.. CO2 forms only 0.03% of the atmosphere while water vapor up to 10%, and.. the suns is the primary heeater qnd cooler. Global warming?

With reference to the often used '97% of scientists concur', a major peer-reviewed paper by four senior researchers has exposed grave errors. They pointed out that the 97% number had appeared in a new and unknown journal. (Suspicious)? The researchers were led by top climatologist Dr David Legates. Their paper was published in the respected Science and Education journal and it clearly demonstrated that number was not 97.1%, as claimed, but only 0.3%!

Only 41 out of the 11,944 published climate papers examined by Dr Legates team explicitly stated that 'Man caused most of the warming since 1950'
jyro
1 / 5 (5) Nov 03, 2017
There has been 4 Billion years of climate change on Earth.
PTTG
5 / 5 (10) Nov 04, 2017
thomasct


There are a number of falsehoods in your post. All of them need addressing, but I don't have the time to do so. I recommend visiting https://skepticalscience.com/ for a thorough considerations of the errors and outright lies in your post.

So long as you define your identity by belief in or against some phenomenon, you will have a great deal of unnecessary stress. Rest assured, you can be who you are and still accept the scientific consensus.
eljo
5 / 5 (1) Nov 04, 2017
They are called trees and you can plant them everywhere.The costs are well known and they make things like wood, Fruit. Chemicals and they have a beneficial impact in most situations. I think it might be a winner. Why put CO2 into the ground quickly if you can make CO2 part of a slow process with benefits on the quality of your now greener and wetter environment.
Whydening Gyre
4.8 / 5 (5) Nov 05, 2017
They are called trees and you can plant them everywhere.The costs are well known and they make things like wood, Fruit. Chemicals and they have a beneficial impact in most situations. I think it might be a winner. Why put CO2 into the ground quickly if you can make CO2 part of a slow process with benefits on the quality of your now greener and wetter environment.

I planted so many trees on my property 20 years ago, that I now have to cut down a few just so I can have a little sunlight to grow a garden and put solar on the roof...
If it ain't one thing, it's another...
arcmetal
5 / 5 (3) Nov 05, 2017
Why would we want to remove CO2 from the air? Surely the more the better for our food crops? In any case...

Apparently, you have not heard of this before but there is a effect on the atmosphere of the planet that is caused by an increase in the amount of CO2 that is present in the air. The effect is that when light from the sun shines down past the CO2 and then hits the ground it changes frequency from it being mostly optical to a lower frequency of something nearer the infrared. Infrared light is a form of "heat". This extra "heat" does not escape back into space because it is reflected by the CO2, and it stays trapped within the thin layer of the atmosphere. This causes a general increase in the temp of the atmosphere. The term applied to this phenomena has been labeled "global warming".

Glass or plastic has the same warming effect as CO2. Homework: go sit in a car with the windows rolled up, in the middle of summer on a warm day and see if notice this effect.
KBK
5 / 5 (2) Nov 05, 2017
The easiest target, by far, is bunker fuels, to clean up ocean going vessels.

They are all in one spot, relatively speaking and are an easy and inexpensive target to clean up.

Far easier than cars. Cars are being attacked as best they can, right now, but no one is going after the bunker fuel.

Jets in the air are also in need of a clean up, as they are a very efficient pollution distribution and spreading system.

Like cleaning up ocean going vessels, jets being cleaned up also has a dramatic effect.

But the biggest elephant in the room, with the easiest clean up in overall cost, and time (soonest to being done, thus best for the environment issue)....is ocean going vessels.

Dirtiest fuel in the world by far and they burn it very very badly with the highest residual pollution by far.

Four billion barrels of it per year - and increasing.

Rated as a polluting country, bunker fuel probably comes in fifth after the US, China, India and the EU.
Dug
5 / 5 (1) Nov 05, 2017
While you can't argue with the need, this is just one more example of a research project that fails to run economic feasibility parallel to technical feasibility. The outcome as in much of past energy research is non-viable processes that no one will be able to afford to adapt. In a declining energy future that is clearly an energy limited economy - we simply can afford in economically inefficient technical blue sky research programs. Economic feasibility and viability have to show early. We many not be around to see its future potential other wise.
Whydening Gyre
5 / 5 (1) Nov 05, 2017
I would definitely like Thermodynamic's input on this one...
rrrander
1 / 5 (3) Nov 05, 2017
Another industry that produces no products, is funded by the STATE (via beaten-down tax-payers) and achieves nothing of value.
leetennant
4 / 5 (4) Nov 05, 2017
thomasct


There are a number of falsehoods in your post. All of them need addressing, but I don't have the time to do so. I recommend visiting https://skepticalscience.com/ for a thorough considerations of the errors and outright lies in your post.


I've done it repeatedly but am a little tired of doing so. No matter how many times he's debunked he keeps posting the same thing. I think he's a Trump-linked Russian spam bot because the posts are just copied and pasted on every article. He popped up post-Trump and he only posts on articles that can be linked to US politics or the fossil fuel industry in some way.
eljo
1 / 5 (2) Nov 06, 2017

I planted so many trees on my property 20 years ago, that I now have to cut down a few just so I can have a little sunlight to grow a garden and put solar on the roof...
If it ain't one thing, it's another...


Well. I would plant them in the desert. Studies show this would be beneficial for the entire Earth. Even the most exaggerated projections of C02/methane out-gassing from soils would be compensated for by the amount of treas you could plant in the deserts of the world. Over time the excess gets buried, but in the mean time we have an extra jungle rich in biodiversity and food. It would be costly, but more beneficial than building an expensive technological solution and putting it into the ground. Putting CO2 in the ground is like deliberately burying food ... or even gold.
antialias_physorg
5 / 5 (4) Nov 06, 2017
Surely the more the better for our food crops?

Agriculture doesn't work that way. Like any system agriculture works on the law of the minimum (Read: that which is available in the least amount limits plant growth). CO2 is not the limiting factor.

There has been 4 Billion years of climate change on Earth.

And over 99% of all species that have ever existed on Earth are extinct. Wanna be among them? I don't. If we don't care about having an environment in which we can live then we won't live - it's that simple.

They are called trees and you can plant them everywhere.

You need to come to grips with the magnitude of the problem. Also we are adding ever more CO2 to the atmosphere. But there is not ever more land on which you could plant trees. (And a single forest fire can destroy all your tree-CO2-sequestration efforts)
barakn
1 / 5 (1) Nov 06, 2017
thomasct


There are a number of falsehoods in your post. All of them need addressing, but I don't have the time to do so. I recommend visiting https://skepticalscience.com/ for a thorough considerations of the errors and outright lies in your post.


...I think he's a Trump-linked Russian spam bot because the posts are just copied and pasted on every article. He popped up post-Trump and he only posts on articles that can be linked to US politics or the fossil fuel industry in some way.

Ummm... no. Having read every one of thomasct's posts, I can assure you that a large number of them are devoted to cancer, how the medical industry hides cancer cures, and a variety of bogus cancer cures. I think he's a bona fide American conspiracy nut, and take his statement that he's in his 70s at face value. He's an old dog too tired to learn anything new.
leetennant
4.5 / 5 (2) Nov 06, 2017
Ummm... no. Having read every one of thomasct's posts, I can assure you that a large number of them are devoted to cancer, how the medical industry hides cancer cures, and a variety of bogus cancer cures. I think he's a bona fide American conspiracy nut, and take his statement that he's in his 70s at face value. He's an old dog too tired to learn anything new.


It's true I haven't seen his other posts. I did notice he avoids hard science articles, concentrating on those with broader implications for policy.

They are called trees and you can plant them everywhere.


This is when I realise the ignorati have no real scope of the problem we're dealing with. This is what happens when you get your science from Fox News. You'd have to plant trees across most of the Earth's surface to counteract our emissions. No room for farmland or human habitation. Also trees emit more CO2 in high CO2 conditions making them less effective.
Caliban
4 / 5 (1) Nov 06, 2017
Not to mention that the idea of underground CO2 storage is just outright stupid.

Stupid #1: Massive energy consumption to pump into underground storage. No way around that one. Guess what will be used to provide that energy.

Stupid #2: Since it is merely reverse fracking, there is absolutely no way to guarantee safety of this pressurized storage. None at all.

This research is a criminal waste of resources, a joke, an affront, and clearly an attempt by Dinosaur-head fossil fuel interests to both waste taxpayer dollars and try to promote climate change "solutions" by utilizing the same resources that create the problem in the first place via encouragement of "ease of use"-friendly policy making.

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