UNDERGROUND CONFLICT: Fracking for natural gas may require shattering geologic formations that efforts to store CO2 permanently underground require to be impermeable.
Image: Wikimedia Commons/Richard Bartz
Natural gas production and carbon sequestration may be headed for an underground collision course.
That is the message from a new study finding that many of the same shale rock formations where companies want to extract gas also happen to sit above optimal sites envisioned for storing carbon dioxide underground that is captured from power plants and industrial facilities.
The problem with this overlap, the researchers found, is that shale-gas extraction involves fracturing rock that could be needed as an impenetrable cover to hold CO2 underground permanently and prevent it from leaking back into the atmosphere.
"Shale gas production through hydraulic fracturing can compromise future use of the shale as a caprock formation in a CO2 storage operation," said Michael Celia, a civil and environmental engineering professor at Princeton University and a co-author of the study.
"There is an obvious conflict between the two uses," the study says.
Celia's work with colleague Thomas Elliot, a postdoctoral research associate, will be published in an upcoming paper version of Environmental Science & Technology.
The two reported that 80 percent of the potential area to store CO2 underground in the United States could be restrained by shale and tight gas development. The numbers held when they examined potential CO2 storage sites close to the nation's largest greenhouse gas emitters, such as coal plants.
Natural gas is extracted from shale via hydraulic fracturing, in which rock is cracked so that injected fluids can flow through the rock more easily to extract gas. The process is designed to increase permeability of the rock over a long distance. That cracking of the shale rock is what could make it inappropriate for use as a stable, impervious rock layer blocking upper migration of injected CO2, the researchers said.
Drilling into potential storage sites
The study raises issues that would play out in the future, since carbon capture and sequestration (CCS) in deep rock formations or saline aquifers currently has never been proved at scale in the power sector. It envisions separating the greenhouse gas from power stacks and piping the CO2 to an underground storage spot to prevent release in the atmosphere.
There is a large CCS pilot project at an ethanol plant in Illinois, but otherwise the energy industry is testing the concept in nonintegrated, small pieces in the United States. Many other projects have stalled because of cost concerns. The concept is considered pivotal for coal's survival in a carbon-constrained world, since the fossil fuel releases about a third of the nation's greenhouse gas emissions.
Shale gas production also has not reached full scale.
Celia and Elliot looked at a carbon sequestration database of potential storage spots for underground CO2 created by the National Energy Technology Laboratory known as the National Carbon Sequestration Database and Geographic Information System, or NATCARB.
That analysis was then overlaid with a Department of Energy database of large shale regions such as the Marcellus formation stretching from Ohio to northern New York and the Barnett formation in Texas. The researchers considered areas already known to be rich in shale gas, in addition to regions likely to yield future production. They also considered tight gas, another uncoventional natural gas source where the fuel sits tightly in impenetrable rock.
Nationally, there is an estimated storage capacity underground for CO2 of 1,711 to 20,402 gigatons. When gas plays were added to the picture, though, the range fell to between 217 and 2,885 gigatons of space -- an 80 percent reduction. The researchers said the numbers were "an upper bound" estimate, but "appear to be compelling."
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4 Comments
Add CommentIt sounds like a loose loose situation for humans and the planet. Either stop extracting coal and burning it in the plants, or stop fracking for natural gas. It sounds like you are not going to have both and keep humans alive. Since coal is quickly running out, and we can use the remaining coal for more important things other than burning it to produce electricity; convert all coal and oil burning power plants over to natural gas, or stop fracking for natural gas. It would probably be wiser to convert coal burning plants over to natural gas since we have more natural gas than coal.
Reply | Report Abuse | Link to thisSince we really do not need coal or natural gas anymore, it would probably we wiser to stop using the two in creating electricity and start building more geothermal and safe nuclear power plants. We no longer have to use enriched uranium to power nuclear power plants and it would be cheaper to convert our nuclear power plants to using nuclear waste instead of digging for the radiation. There is about 1% pollution in geothermal and you do not have to store dangerous radiation anywhere. An even better geothermal power plant would be liquid salt. That geothermal power plant could sit above ground, with no drilling required, and you could use solar to heat the salt and liquify it to turn the water, or other liquid, or carbon to steam. Yes, you can use carbon in geothermal power plants to create electricity. That is a good way to get rid of carbon. We have plenty of salt and salt is not deadly to humans and animals like radiation, coal, and natural gas; it is the intelligent persons choice.
CO2 sequestration is a waste of money and resources to deal with an imaginary problem.
Reply | Report Abuse | Link to thisThe only way CO2 injection makes sense is for sweeping old reservoirs to maximize oil recovery.
CO2 sequestration has much bigger problems than the effects of fracturing above the zone of interest. The idea of injecting a supercritical fluid in any formation at the volumes contemplated is going to difficult. Not because of the cap rock but because to the nature of CO2 as a supercritical fluid. See the work of Michael J. Economides. There is a big difference between injecting CO2 in a depleted oil reservoir and an aquifer.
Reply | Report Abuse | Link to thisPeople continue to think that fracing destroys rock for thousands of feet it cannot without suspending the laws of physics. Frac height is limited to a few hundred feet and the frac itself is less than a 1/4 inch wide.
Let's discuss the errors reported in this article from the 'researchers' regarding fracturing:
Reply | Report Abuse | Link to this- 'Natural gas is extracted from shale via hydraulic fracturing, in which rock is cracked so that injected fluids can flow through the rock more easily to extract gas.'
- No, the injected fluids (and proppant) are used to
create and hold fractures up so that more of the
reservoir (in terms of surface area) can be connected
to the wellbore. The fluids do not 'flow' through
the rock but rather create fractures in the rock. If
they actually are imbibed (flow into) the rock it
causes formation damage and actually decreases
deliverability.
- 'That cracking of the shale rock is what could make it inappropriate for use as a stable, impervious rock layer blocking upper migration of injected CO2...'
- Concur, if the shale is the primary seal then the CO2
could migrate upwards. However, there is no such
thing as an unfractured, or zero permeability, shale
so the concept of such a formation serving as a
permanent barrier are incorrect. The real problem is
that, for the most part, people think in a human time
scale and not a geologic time scale so while things
that are not possible in the human scale they are
easily possible in the geologic scale.
- 'The process is designed to increase permeability of the rock over a long distance.'
- Once again, No: The permeability if the rock itself
is not changed (except for maybe in a negative sense
per previous comment). The propped fracture is the
high permeability (when compared to the matrix)
conduit over a 'long distance' which is likely
something on the order of a few hundred feet to maybe
as much as 1000 feet.