It has been a shaky start for shale gas exploration in the United Kingdom, but Cuadrilla Resources Ltd. is looking to regain its footing.
Just a few months ago, in late September, Cuadrilla announced that it had happened upon huge shale gas resource potential – 200 TCF – in Blackpool and South Lancashire, an area of the UK desperately in need of economic activity. In addition to over 50 years of gas, there were hopes that shale gas production there could create several thousand jobs as well.
But earlier, in the summer, the company stopped its hydraulic fracturing activities in the wake of minor seismic activity, even though there was no definitive proof that it had been caused by fraccing. At the beginning of November, however, following an independent study initiated by Cuadrilla and submitted to the UK’s Department of Energy and Climate Change (DECC), Cuadrilla came clean, admitting that hydraulic fracturing activities at its Preese Hall I site were to blame, because of a number of rare geologic factors that rendered the subsurface unstable.
At Shale Gas World 2011 in Warsaw, Poland, Cuadrilla Resources COO Eric Vaughan recalled: “We were trying to show that there was gas in place, and we also wanted to prove that we could actually fracc the shale. We also wanted to know if gas would actually come out if we fracced it and it does.”
While Cuadrilla is now waiting for the go ahead from DECC to resume exploration at Blackpool, Vaughn described the company’s method of mitigating seismic activity.
“If the seismicity becomes too strong, then we can modify our treatment; we can change what we’re doing in the well depending on what we’re seeing on that.”
“The maximum magnitude event actually happens after you’ve stopped pumping,” he explained. So if we want to stay below a certain level – in this case 2.6 – then we have to stop our pumping at a lower magnitude before that, because based on the information from the appraisal well and also some experience from some the geothermal work, we’re probably looking at a 0.9 units difference between what we’ve seen while we’re pumping and what will come later.”
He presented a “traffic light” approach to dealing with the seismic activity associated with hydraulic fracturing – green, amber and red codes for evaluating the monitoring of real time seismic events.
He explained: “It’s not the same as fracc mapping, where you’re looking at the little stuff. We’re really concerned with stuff above zero, so as long as we either can’t see it because it’s too small, or it’s in the below zero range, you can carry on with regular operations – you don’t have to do anything different.
“If we start seeing seismic magnitudes in the zero to 1.7 range, then we’ll be able to continue with the actual pumping that we’re doing, but when we shut down on that one, we’ll probably start flowing it back because we have to monitor it for a couple of days and get it down where we’re less than two events in that range for at least two days.”
More movement, he explained, could send Cuadrilla into the dreaded red zone.
“If we were to see something bigger than 1.7, then we would stop the operation, stop pumping at that time and then go immediately to a flow back, which we’d have to monitor, so there’s no events for about 10 days.”
Mr. Vaughn explained that part of the study – which is available on Cuadrilla’s website – was about determining what the chances were for more seismic activity occurring. “The chances of it actually happening are fairly low, mostly because the seismicity relies on a few key things: you have to have a critically stressed fault – it’s pre existing; the fault must be able to accept a large amount of fluid; and the rock has to be brittle, has to be able to fail seismically.”
One conference delegate asked Vaughan what effect the seismic tremors had had on public opinion in the UK.
“We do quite a few talks with local groups, and anti shale groups. The seismicity issue does come up,” he admitted, “but it is dwarfed by water and water contamination issues.”
Another attendee asked if Cuadrilla’s activity was building up underground stress and whether or not that would be a worry for locals.
“The stress is already there,” said Vaughan. “We’re relieving the stress in the rock – that’s the problem.”