A plan to use CO2 to replace the water used in controversial energy technique fracking has been met with a mixed reception by experts contacted by The Register.
New Scientist reported on work done by Andres Clarens and his team at University of Virginia, Charlottesville, to pump CO2 into fracking sites, which could act as a form of carbon sequestration, and so be a better solution than the water currently used.
The story reports that using CO2 would prevent fracking chemicals from contaminating drinking water supplies.
However, Mark Linder from global PR outfit Bell Pottinger, who has worked with a number of oil and shale companies, told The Register: “Fractures don't come close to aquifers. Also there's no evidence at all of fracture contamination."
"Yes, it is possible that casing could burst during a frac, releasing fluid into the aquifer. But this would be extremely rare, and today's frac fluids are simple. In the UK they are required to be non-toxic," he added.
"Subsurface fluid injections associated with geologic carbon storage or hydraulic fracturing are likely to lead to increases in pore pressure that would drive transport into overlying formations," said Clarens.
"We are working to develop a fundamental understanding of how interfacial properties at the gas-brine interface and at the gas-brine-mineral interface could impact buoyancy-driven flow through porous media. Mass transfer between gas (e.g. CO2) and brine and CO2 phase change will mitigate leakage," he added.
However, experts have questioned how useful this is. Richard Davies, a petroleum geologist at Newcastle University in the UK, told the magazine that technique now being talked about was “unnecessary [and] fractures rarely extend past a few hundred metres above the shale reservoir".
Colin Scott, a geologist working on oil rigs and an independent oilfield consultant with 40 years of experience in directional and horizontal drilling, told us that there were some merits, but not from any perceived dangers in fracking.
“It sounds very interesting and the potential is there – we already pump CO2 into wells in the North Sea as a way of disposing of it,” he said.
But he agreed with Davies on the issues around groundwater contamination: “Fracking is done way lower down than aquifers and as long as the casing in the wells is well cemented, no fracking fluid can escape. There is a way of testing the cement 'bond' which is foolproof and verifiable, so the worry is just not there. But as a method of CO2 disposal, it would be great,” he said.
New Scientist reported that Clarens' team has mirrored conditions in the Marcellus shale, the Appalachian Basin site of fracking activity in and around Pennsylvania, encompassing over 100,000 square miles, and the largest source of natural gas in low-permeability shale in the US, with production still growing.
It seems that the team found that half the CO2 injected in the simulation was converted into solid carbonates within a day.
Linder took a different view on the merits: he saw it as one of reassurance and managing perception. "Where does the CO2 come from? It would have to be captured and transported to the site. So this is not an economic behaviour. And the problem it is supposed to prevent is not a problem ... though the perception is there!" he explained.
Hydraulic fracturing, known as "fracking", splits rocks thousands of feet below ground using high-pressure liquid, to collect shale gas. The UK recently gave the go-ahead for further exploration of the UK's shale gas reserves. ®