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Seismic events triggered by UK fracking

The UK’s complex geology and fracking rules pose challenges for Cuadrilla and other companies that may be interested in developing the country’s shale resources

After the UK Oil & Gas Authority (OGA) ordered Cuadrilla Resources to cease hydraulic fracturing operations over seismicity concerns, the area around the company’s Preston New Road site experienced its largest tremor yet. Cuadrilla, which is targeting gas from the Bowland Shale, had resumed fracking in mid-August after shutting down in December 2018 due to a 1.5-magnitude quake. The 2.9-magnitude quake happened on August 26.

Seismicity issues in the area cannot be avoided if fracking operations are to continue (see chart 1). Peter Styles, professor emeritus of applied and environmental geophysics at Keele University, pointed out to Water in Oil that the geology of the UK is much more complex than in the USA.

SEISMIC CLOSE-UP
SEISMIC CLOSE-UP

SEISMIC CLOSE-UPLeading up to and after Preston New Road’s largest earthquake, several seismic events exceeded the UK’s 0.5ML threshold.

Cuadrilla Resources

“We’ve had a lot of tectonic events happen very close to where [Cuadrilla is fracking], so the rocks have pre-existing faults. In the Permian Basin, you probably haven’t had any great tectonic events since the Laramide orogeny,” Styles explained.

The UK’s geology is also even more complex than local experts had realized before tremors began during Cuadrilla’s 2011 fracking tests at the Preese Hall site. “A seismic survey in the UK […] cannot resolve a fault which has a displacement of less than 5 meters, and some of these faults have a displacement of only 1 meter,” Styles said. “We’re finding out where the faults are by fracking rather than knowing where they are beforehand.”

After studying the Preese Hall earthquakes, a group of scientists including Styles, designed a “traffic light” monitoring system to guide fracking operations and presented it to the UK government in 2012. The system initially called for an assessment after a 0.5ML event and abandonment of the particular fracking stage after 1.5ML, but the system the government adopted stops all fracking operations when a seismic event of 0.5ML or greater is registered (see chart 2).

DIFFERENT APPROACHES

A 0.5ML event is enough to stop fracking operations under the UK traffic light system, while in Oklahoma, where most oil & gas industry-related seismic events have occurred, the threshold has been set at 2.5ML.

LocationMagnitudeAction
UK≤ 0.5Operator must suspend injection, reduce pressure and monitor seismicity and ground motion for any further events before potentially resuming.
0.0 – <0.5Injection proceeds with caution, possibly at reduced rates. Monitoring is intensified.
< 0.0Injection proceeds as planned.
Oklahoma, USA≥ 2.5Operator must pause operations for at least six hours.
2.0Operators must take unspecified actions.

Source: UK OGA and Oklahoma Corporation Commission

Styles told Water in Oil that the Preese Hall studies were some of the first to categorically demonstrate the association of fracking and induced seismicity. “That work and our subsequent work on anthropogenic earthquakes actually set the scene for people to look much more carefully at fracking and, particularly, water injection [into disposal wells].”

Following the most recent earthquakes at Preston New Road, Styles sees a slim chance for produced water disposal in wells. “If we can actually produce seismicity by just fracking, then it’s quite clear that we can probably do much more damage by reinjecting wastewater,” he said.

Cuadrilla carries out slickwater fracks composed of 99.95% water and sand and 0.05% polyacrylamide, which is used as a friction reducer. The company has said that a portion of the produced water would be recycled for new frack stages, while the rest would hauled by tanker truck to a waste treatment facility approved by the Environment Agency.

Both Cuadrilla and the OGA declined to comment, citing the ongoing investigation into the seismic events that occurred in August.

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