Turning Carbon into Stone

克里斯-现在我们听说老煤矿被使用d as a place to dump our old CO₂but how about old volcanoes? Our next guest on is Peter McGrail and he's from the Pacific Northwest National Laboratory in Washington State and he's been looking at the carbon catching properties of flood basalt. That's a type of rock that's left over from when lava flowed out of volcanoes. Hello Peter...

Peter - Good evening.

Chris - Thank you for joining us so what's the basis to this technique? How does it work?

Peter - Basically we would be looking at capturing CO₂from a stationary source like a coal-fired power plant and then injecting that CO₂deep underground (2000ft-3miles). That CO₂would then enter into a special structure in the continental flood basalt. You have to think of these things the way they were produced. There were these massive cracks that were in the Earth's structure and these massive lava flows extruded out of those massive cracks and extended out over many hundreds of miles. These individual folds would have been separated by hundreds of thousands or millions of years. What happens is that contacts between these individual flows there were cracks, crevices and bubbles that are present. This is where the porosity and permeability exists in these continental flood basalts for injections and movement of fluids including CO₂.

Chris - So what would you do? Would you put the CO₂down as a gas or would you dissolve it into the water first and then pump the water through those holes in the lava?

Peter - It would go down the injection wells as a liquid. That liquid CO₂would then enter into the formation displacing the water that was present in the pore space and fracture spaces in those interflow zones. Eventually the water would then absorb the CO₂. The thing that we found is quite intriguing about these flood basalts is that once the CO₂dissolves in the water we have a very rapid reaction that occurs between the CO₂saturated water and the basalt. CO₂gets converted back into a solid rock: calcium carbonate is the end product.

Chris - Quite literally it's turning the CO₂into stone.

Peter - Absolutely. With no additional energy input required of then getting the CO₂into the basalt formation.

Chris - Here's the killer question: does it work?

Peter - That's a question that we're attempting to answer through some pilot studies that we're just about ready to start. We plan to drill our first pilot well here in Eastern Washington State in March or early April this year. Then about the summer of 2008 we would be injecting 3000 tonnes of CO₂into this Columbia River basalt route, here in Washington State.

Chris - That sounds like a lot, 3000 tonnes but putting that in perspective that must be the output from a big, coal fired station over the course of a couple of hours?

Peter - Depending on size, yes that would be a few hours to maybe one shift in terms of CO₂production.

Chris - How are you going to trace where the CO₂goes once it's in the ground?

Peter - A variety of ways: monitoring techniques that we use. There are techniques that we extract fluid samples from depth and so looking at the change in water chemistry around the injection well. We also use what we call geophysical techniques so these are seismic techniques that allow us to look at an image of the CO₂in the subsurface.

Chris - Are there any possible negative effects to doing this?

Peter - One of the things that has to happen in any geological sequestration project is the containment of CO₂and so in these deep flood basalts one of the research areas that we want to investigate is whether the CO₂is staying in the place that we think it will. That is we don't want to have cracks, crevices and fractures that would allow that CO₂to migrate a significant distance vertically. Computer simulations don't suggest that's possible but of course they're just computer simulations. The fieldwork is critical to proving what we're seeing in our computer models.

Chris - Finally, how much CO₂do you think the world realistically could lock away in this way, assuming you're successful?

Peter - Well, one of the things we've done is taken advantage of geological data. The department of energy in Washington State has spent almost a 1/2 billion dollars characterising the Columbia River basalts here. That information database has been extremely valuable to allow us to continue to compute these numbers. What we see is that conservative estimates would be about 20 gigatons to 50 gigatons of CO₂capacity in just the Columbia basalt rift which, in perspective what that means is about 10-20 years of all the CO₂emissions from all the coal fired power plants in the United States. The capacity is actually quite significant.

Chris - Well, we wish you luck and I guess we'll be talking to you in a year or so to see if it worked.

Peter - I'll be happy to join you again!