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25 comments on Can we get by with fossil fuels ?

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Ender on February 28, 2006 - 12:25am Permalink | Subthread | Comments top
Just one question about using CO2 for EOR.

Is the CO2 sequestered in the oil bearing structure or does it just bubble up with the oil when it is extracted?  If it is not 'safely' sequestered then using CO2 in this way does not contribute to measures to combat climate change.

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plucky underdog on February 28, 2006 - 1:11am Permalink | Subthread | Parent | Comments top
The CO2 eventually finds its way from the injection wells to the production wells and comes back to the surface. This is perfectly natural and not a problem; it's allowed for in the design of any EOR scheme. The CO2 is just another part of the well effluent stream, so it's fully contained. You strip it out in the separators, recompress it and reinject it to dissolve out the next lot of oil... and so on. This is called "gas cycling".

Eventually you would have a reservoir full of CO2 (or, more realistically, CO2-rich solvent plus injected water) and some residual trapped oil (probably quite heavy as all the light ends would have vaporized), with smaller and smaller quantities of liquids coming out. When oil production falls below some economic limit, you shut everything down and abandon the wells (you DID provide for abandonment costs in your project plan, didn't you?). The CO2 would remain trapped underground.

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Dave Cohen on February 28, 2006 - 1:27pm Permalink | Subthread | Parent | Comments top
It might be good to remind readers here that projects like Weyburn and the Otway basin (Australia) are pilot projects. Yes, CO2 injection has been in use for a long time. Sequestration really is the new part of all this.

The way people are speaking about CO2 injection, capture and storage on this (and other) threads leaves the impression that all the angles have already been worked out (the capture and storage issues). But that's why these are trials with monitoring programs to see if the techniques involve will really work.

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Heading Out on February 28, 2006 - 1:15am Permalink | Subthread | Parent | Comments top
It depends in part on how it is injected.  If it is below the critical depth where it turns to a liquid under the pressure, then it will likely be absorbed into the oil, thinning it and reducing its adhesion.  The combination will then be pumped from the ground, however it then goes to a refinery, where the different bits are separated and the carbon dioxide can be recovered and sent back for reinjection.

If it is injected as a gas (and there is a current example here) then it stays in the formation displacing, in this case the natural gas, but in other cases the oil, toward the producing well, as the gas flows out from the injection wells.

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plucky underdog on February 28, 2006 - 1:56am Permalink | Subthread | Parent | Comments top
Heading Out wrote:

> If it is below the critical depth where
> it turns to a liquid under the pressure,
> then it will likely be absorbed into the oil,
> thinning it and reducing its adhesion

First contact miscibility certainly exists, but it's very rare to base an EOR scheme around this mechanism. FCM is very uneconomical of injected gas - you can get excellent results with much more dilute solvents.

> If it is injected as a gas...then it
> stays in the formation displacing...

Gas is pretty mobile stuff - it's perfectly capable of finding its way into a producer by itself if you're careless or unlucky, or if you wait long enough. Why do you think BP needs 7 bcf/d of gas compression at Prudhoe Bay? They sure don't have that much miscible solvent available! Sure, you'll drill & perf the wells to avoid the gas, but it will get through eventually.

And please don't let's give our readership the impression that gas injection - CO2 or otherwise - is anything new. It's being going on for many decades in a large percentage of the world's oilfields, large and small. The new thing is the carbon sequestration angle - and if you're getting your CO2 from flue gas, even $60 oil isn't always going to make it economical.

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Ender on February 28, 2006 - 2:37am Permalink | Subthread | Parent | Comments top
The only reason I mentioned it is because of its connection with Clean Coal.  The impression that I get from Clean Coal advocates is that CO2 for EOR is a way of sequestering the CO2 from coal plants thereby reducing emissions.

From the responses

  1. you cannot guarantee that the CO2 is sequestered safely.

  2. As the CO2 is recycled there is not enough CO2 needed for offsetting the huge amounts of CO2 produced from power plants.

Sorry a bit off topic however it does go to the sustainable use of fossil fuels and clearly CO2 for EOR is not going to help.
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TJ on February 28, 2006 - 10:03am Permalink | Subthread | Parent | Comments top
That's not what they said.  They actually said that the gas will migrate and exit through a producer (well).  As HO said after the producer wells are shut down if there is a caprock on the field you've got centuries at least.  The fact that the gas can migrate thru the whole field is a good thing, it means most of the void space of the field is available for CO2 storage.
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Ender on February 28, 2006 - 9:42pm Permalink | Subthread | Parent | Comments top
TJ - however is this guaranteed sequestration?  It is not really no good if the CO2 just starts bubbling up after a few centuries.
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