Carbon Capture and Storage (CCS) involves injecting carbon dioxide into underground geological reservoirs for long term storage, and is a major part of the global strategy for reducing greenhouse gas levels. It is already used in several oil and gas fields as a technique to prevent gases from entering the atmosphere, however in order to significantly reduce emission levels CCS would need to be scaled up massively to store more than 3.5 billion metric tons of CO2 a year.
Unfortunately a new paper written by two geophysicists from Stanford University, Professors Mark Zoback and Steven Gorelick, and published in the journal Proceedings of the National Academy of Sciences, found that CCS may actually cause earthquakes.
CCS is intended as a method to remove carbon dioxide from the atmosphere for thousands of year, so any chance of triggering earthquakes, which could allow the gas to escape to the surface, needs to be thoroughly researched. The plan to use CCS as the backbone of our greenhouse gas reduction strategy will have to be reconsidered.
Zoback said that “almost all of our current climate mitigation models assume CCS is going to be one of the primary tools we use. What we’re saying is, not so fast.”
The earthquakes created by human activity tend not to be as large as naturally occurring earthquakes at the boundaries between tectonic plates. They occur far from the boundaries as pressure within the earth’s crust is increased to such a level that local faults can slip. Last year, storing wastewater from fracking under high pressure induced small quakes in Arkansas, Ohio, Colorado, and New Mexico.
The quakes themselves are generally not destructive, but they could break the seals on the reservoirs storing the CO2, releasing the gas into the atmosphere. Zoback and Gorelick state that even a fault slip of a few centimeters could allow stored CO2 to reach the surface; a problem considering the whole point of CCS is to bar the gases access to the surface.
Another hurdle facing CCS is that the formations where it can be utilised have a very specific geological profile. The reservoirs themselves are formed from weak, porous rock that slows down pressure build ups, and are isolated from the surface by an impermeable rock layer, such as shale.
Zoback and Gorelick believe that in order to significantly reduce CO2 emissions by CCS, roughly 3,500 such formations will need to be discovered, and the worry is that there are not enough; although scientists disagree about that number. Sally Benson, professor of energy resources engineering and director of Stanford’s Global Climate and Energy Project, argues that only 600 such sites need to be found and that many already exist in Texas, the Gulf Coast, the Middle East, the North Sea, and Western Australia. She also suggests that the pressure build-up can be easily managed by controlling the injection rate, and carefully designing the well.
Zoback is still doubtful as to the viability of using CCS as a large scale carbon emission reduction method. “For the U.S. and the world to be considering CCS one of the potential solutions to the greenhouse gas problem—it’s a very high risk endeavor,” he said. “We need options that are practical, don’t cost literally trillions of dollars and aren’t vulnerable to moderate size earthquakes.”
By. James Burgess of Oilprice.com