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"The technical challenge right now is efficient C02 capture. We've largely shown that long-term C02 sequestration should work. However, we still don't have a to

by rsync 7y ago

"The technical challenge right now is efficient C02 capture. We've largely shown that long-term C02 sequestration should work. However, we still don't have a ton of ways to capture carbon at scale that don't involve significant energy expenditures. The whole system needs to be carbon negative to work ..." Thank you for this interesting contribution ... I agree that the full-lifecycle accounting of CO2 and the requirement that the entire cycle come out carbon negative is the really challenging part. I would go a step further: I am skeptical of carbon sequestration in gaseous form. Call me timid, but I wouldn't want to make high stakes bets on gas staying in the places where we put it. Instead, I would like to see a reaction that converts the CO2 to a solid form (chalk ?) that is stable in physical form. I believe that weird seed-the-oceans-with-iron-dust proposal accomplishes, roughly, the same thing - carbon sequestered in a solid, stable form.

jofer 7y ago
You don't actually sequester C02 in gaseous form when you do geologic carbon sequestration. First off, even the simplest methods wind up with it dissolved in water. You basically can't just inject gaseous C02 into the ground and have it remain a gas. The rocks you're injecting it into are filled with water and it's highly soluble in water. Under certain conditions, you can inject liquid C02 and actually displace the water already there. However, that's mostly not what's being proposed. Geologic carbon sequestration can take a handful of different approaches. The two you'll hear talked about the most are: 1) Inject it into a reservoir where you expect it to react with something and eventually form carbonate minerals (in-situ mineral sequestration, or mineral trapping). 2) Inject it into a very deep reservoir where it will dissolve into the brine already there and/or is unable to find a way back out again due to the geometry of the reservoir. (Solubility trapping and/or residual trapping) The first method is preferable, but actually hard to guarantee in practice. The second may sound more risky, but we're actually pretty good at identifying regions that can store a buoyant phase over geologic time -- it's exactly what we do in hydrocarbon exploration. Both are being actively explored along with several others. There's a lot of geologic research being done on carbon sequestration right now (and has been for quite awhile, actually, though the government funded it well before industry started to). The risk of the "seed the oceans" approaches (or the olivine beach proposals as well) are the environmental side effects. Altering ocean chemistry _will_ have significant effects. Similarly, putting olivine on beaches will result in a lot of heavy metal contamination (you can't get pure olivine -- you're going to have a lot of chromite and fun other odds and ends in ultramafic rocks). I'd argue we're better off impacting the deep underground where more or less nothing lives than we are altering the oceans.
- AstralStorm 7y ago
  In general, agreed, though our deep underground storage is limited. We could create more such sites at great expense after we run out of natural sites and abandoned mines. Have to be also very careful to not break underground water reservoirs.

by rsync 7y ago

jofer 7y ago

You don't actually sequester C02 in gaseous form when you do geologic carbon sequestration. First off, even the simplest methods wind up with it dissolved in water. You basically can't just inject gaseous C02 into the ground and have it remain a gas. The rocks you're injecting it into are filled with water and it's highly soluble in water. Under certain conditions, you can inject liquid C02 and actually displace the water already there. However, that's mostly not what's being proposed. Geologic carbon sequestration can take a handful of different approaches. The two you'll hear talked about the most are: 1) Inject it into a reservoir where you expect it to react with something and eventually form carbonate minerals (in-situ mineral sequestration, or mineral trapping). 2) Inject it into a very deep reservoir where it will dissolve into the brine already there and/or is unable to find a way back out again due to the geometry of the reservoir. (Solubility trapping and/or residual trapping) The first method is preferable, but actually hard to guarantee in practice. The second may sound more risky, but we're actually pretty good at identifying regions that can store a buoyant phase over geologic time -- it's exactly what we do in hydrocarbon exploration. Both are being actively explored along with several others. There's a lot of geologic research being done on carbon sequestration right now (and has been for quite awhile, actually, though the government funded it well before industry started to). The risk of the "seed the oceans" approaches (or the olivine beach proposals as well) are the environmental side effects. Altering ocean chemistry _will_ have significant effects. Similarly, putting olivine on beaches will result in a lot of heavy metal contamination (you can't get pure olivine -- you're going to have a lot of chromite and fun other odds and ends in ultramafic rocks). I'd argue we're better off impacting the deep underground where more or less nothing lives than we are altering the oceans.

AstralStorm 7y ago
In general, agreed, though our deep underground storage is limited. We could create more such sites at great expense after we run out of natural sites and abandoned mines. Have to be also very careful to not break underground water reservoirs.