The technology to store CO2 emissions from coal-fired power plants or other large industrial emitters is solid, according to a leading US expert on carbon capture and storage (CCS). The big issue that remains is, of course, cost.
Dr. Sally Benson, a groundwater hydrologist and reservoir engineer and director of the Global Climate and Energy Project at Stanford University in California, says that the science behind using depleted oil and gas reservoirs for storing CO2 emissions is well understood and advanced. First of all, oil and gas reservoirs have good seals or else the resources wouldn’t be there.
“We fundamentally understand the processes by which it’s both trapped under the seals and the processes that control the movement of CO2 in the surface. I think we’re ready to do that today,” she tells Canadian Green Tech in an interview.
“In a typical oil reservoir, you’ve got a tremendous amount of information,” Benson says. “You got all this well log, you’ve got your seismic data, you’ve got years of observing how the seal performs when you extract fluids, and when you inject water for water flooding, so you actually know a lot about those fields.”
Using saline aquifers as the host to store CO2 is still unproven and needs considerable more study, she adds. “Nobody was interested in them because there was no real resource value there, so those sites are less well characterized. And in my opinion, it’s going to take more work to build confidence that we can sequester large volumes of CO2 in saline aquifers.”
The technical feasibility of CCS came into question recently when a Saskatchewan farmer complained that CO2 was bubbling to the surface on his farm. He claimed the CO2 was coming from an enhanced oil recovery operation nearby Weyburn, located in the southern part of the province.
Benson explains that there are a number of reasons why a potential carbon storage site may leak. After the drilling boom in the 1950s many wells may have penetrated a single reservoir and after depleted those reservoirs may not have been sealed properly.
“If CO2 were to encounter one of those wells and it wasn’t sealed properly it could create a leakage pathway. So it’s the existing wells, both those that you know about and in particular those that you don’t, that are really the biggest vulnerability for depleted oil fields,” she says.
Carbon recycling is gaining some momentum with firms trying to commercialize a variety of ways to use carbon to make other useable products. Benson calls this the Holy Grail, but she cautions that to recycle CO2 into other products it takes a lot of energy.
“So if you want to recycle it, you’ve got to put all that energy back into it somehow. That’s the challenge,” she explains. “The question is where does that energy come from? If it comes from the wind or the sun or even nuclear power you could imagine that under certain circumstances, recycling would make some sense. But the fundamental problem is you’ve got find energy to put into it and all that energy costs, so there’s a cost issue.”
Benson was at the University of Toronto last week to give a presentation on whether sequestering CO2 could help combat global warming and the effects of climate change. Her presentation focused on the science underpinning carbon sequestration and why it should work if the right storage sites are chosen. She also spoke about potential problems arising from CCS, the importance of project monitoring and the need for government oversight.
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