Why doesn’t the fracking moratorium cover acidising too?

The surprise announcement of a moratorium on fracking in England earlier this month left many people confused about which operations had been banned.

Campaigners across the Weald received celebratory messages from people overjoyed that proposed drilling at Horse Hill, Balcombe and elsewhere would be stopped in its tracks. Sadly that’s not the case.

The moratorium (not a ban) only applied to fracking – short for high-volume hydraulic fracturing – which is defined in the Infrastructure Act 2015 as using 1,000 cubic metres of fluid per stage or 10,000 cubic metres in total. The type of drilling we see in the Weald (and also at West Newton, Wressle & Ellesmere Port) uses lower volumes of water, so is not counted as fracking and is not included in the moratorium.

“It’s not possible to predict the probability or magnitude of earthquakes that fracking might trigger”

The government’s decision to halt fracking was based on a report by the UK Oil and Gas Authority on earth tremors at Preston New Road in Lancashire, the UK’s only currently active fracking site.

Current rules mean that fracking must be suspended for 18 hours if any tremor over 0.5 magnitude is detected. The largest tremor at Preston New Road measured 2.9 magnitude, and the report warned that it was not possible to predict the probability or magnitude of further earthquakes that fracking might trigger.

Meanwhile, in Surrey, there has been a swarm of earthquakes up to 3.1 magnitude, very close to the oil drilling sites at Horse Hill and Brockham. So why doesn’t this merit a moratorium too?

Professor Peter Styles, emeritus professor in applied and environmental  geophysics and a former government adviser on fracking, addressed the question in a guest post on the news website Drill or Drop.

Fracking and acidising explained

Professor Styles explained that fracking and acidising are both methods used to increase the permeability of rocks where oil and gas are trapped. He said, “If, as is common, the rocks are shales, fine grained sediments, then this is usually done by hydraulic stimulation or fracking.

“This is done by injecting high-pressure water with a limited number of chemicals so that new fractures and pathways form and these are kept open by injecting a proppant, either sand or a synthetic material…

“If the rock is strongly cemented, so that the pores are blocked by calcite (calcium carbonate) or silica, or is itself a limestone, then the permeability can be increased somewhat by dissolving these cements or matrices with acids (hydrochloric for calcite, or hydrofluoric for silica). This is known as acidizing or acid stimulation.

“It is also possible to combine these two stimulation techniques by injecting the acidic solution at a high enough pressure to fracture the rock as well. This is known as acid fracking.”

Fracking – only attempted twice in the UK

Fracking has only been attempted twice in the UK – at Preese Hall and Preston New Road in Lancashire, both by Cuadrilla. These fracks caused ‘induced seismicity’ – stimulating movements of pre-existing faults – and resulted in numerous seismic events.

Professor Styles wrote: “The other, up to now rather less noticed, UK onshore oil and gas exploration is in the leafy landscapes of the Weald, south-west of London, particularly around Horse Hill and Brockham in Surrey and also in Sussex, in younger Jurassic rocks: the Portland Sandstone and Kimmeridge Limestone amongst others.

“Here the jury is out as to whether acid fracking, (the more aggressive combined acid and hydraulic stimulation process) is also actually banned under the recently-announced moratorium, as it generally uses lower volumes than the 1,000/10,000 limits.

“[In Surrey] there are faults which could potentially be further destabilised by hydrocarbon-related activities”

“There is additional concern because a sequence of earthquakes up to magnitude 3.1 ML have occurred around Newdigate in Surrey, just south of Brockham and very close to Horse Hill over the last year.

“Although the British Geological Survey and some university researchers appear to have ruled out a link to a recommencement of activity at Brockham or activity at Horse Hill, the existence of this seismicity does indicate that there are faults which could potentially be further destabilised by hydrocarbon-related activities.

“There is, to say the least, considerable local concern and calls for the moratorium to be clarified/extended to categorically encompass acid-fracking processes.”

The Weald Action Group is one of those voices calling for the moratorium to be extended to other forms of oil and gas extraction, which aren’t defined as fracking, but which carry many of the same risks, including earthquake risk.

Our member Brockham Oil Watch launched an open letter to regulators calling for a ban on all well stimulation for oil and gas exploration and production, and, in the interim, to ensure that requirements applicable to fracking apply to all well stimulation treatments.

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