Forecasting earthquakes caused by fracking is still “a scientific challenge”, the British Geological Survey (BGS) said in a report published today.
The BGS said there was high-quality data in some parts of the UK. But limited exploration data from other areas meant there was “significant gaps” in our knowledge of shale gas formations in England.
More data was needed from some shale gas basins to allow earthquake forecasting methods to be applied more widely, the BGS said.
The report, commissioned by the government in April, said hydraulic fracturing can trigger earthquakes large enough to cause structural damage, which were not predicted in advance.
It did not appear to justify today’s formal lifting of the moratorium on fracking in England or suggestions that the government would review relaxing the regulations on earthquakes.
In August 2019, nearly 200 people reported damage to homes to the BGS from a 2.9ML earthquake caused by fracking by Cuadrilla at Preston New Road in Lancashire.
The moratorium has been in place since November 2019 after ministers concluded that earthquakes caused by fracking could not be predicted or controlled.
The BGS review said:
“Forecasting the occurrence of large earthquakes and their expected magnitude remains a scientific challenge for the geoscience community. This is the case for both tectonic and induced earthquakes.”
Methods used to estimate the strength of induced earthquakes do not account for the possibility of earthquakes that occur after operations have stopped, the BGS said.
The largest earthquakes caused by high volume fracking at the only three wells in the UK all happened after pumping had stopped. These operations were all carried out by Cuadrilla in Lancashire. The earthquakes measured between 1.5ML-2.9ML.
The BGS said adapting methods used to forecast tectonic earthquakes had showed “some promise” in forecasting patterns in fracking-induced seismicity.
But it said more work was needed to understand these methods:
“It remains challenging to identify and characterize faults that could host seismic events of magnitudes up to 3.0 even when using 3-D seismic reflection survey ahead of operations. These may only be revealed by seismicity recorded as HF [hydraulic fracturing] operations are ongoing.”
Gaps in knowledge
The BGS said modelling of faults that could rupture during fracking required accurate mapping and knowledge of rock stresses and pore pressures. It said:
“While this information is available in areas with unconventional hydrocarbon potential such as the Bowland Basin, more data is needed from other basins to apply this more widely.
“Limited exploration data from other basins with unconventional hydrocarbon potential of the UK means that there are significant gaps in our knowledge of sub-surface structure of potential shale resources in these places.”
The BGS said the Bowland Basin in Lancashire was complex with a wide variety of fault styles and scales.
Referring to other parts of England, the BGS said:
“Existing data suggests that these areas share a complex depositional and structural history, with the possible exception of the Gainsborough Trough and Cleveland Basin”
Last week, IGas reported that the Gainsborough Trough, in Lincolnshire and Nottinghamshire, was less complex than other parts of the UK and had a “significantly reduced risk of induced seismicity”.
Traffic light system
The BGS made no specific recommendation on relaxing the traffic light system, which require fracking to pause if earthquakes reach a red-light limit of 0.5ML or above.
It said traffic light systems “remain a useful tool for the mitigation of risks from induced seismicity”.
But it did say red-light limits in other countries usually resulted in a complete cessation of operations in a well, rather than a brief pause, because of the increased risk of larger magnitude events.
It also said:
“red-light thresholds should be chosen to ensure that the probability of the scenario to
be avoided, e.g., disturbing or damaging ground motions, is at an acceptable level. Amber light thresholds should be chosen as much as two magnitude units below the red-light threshold.”
Consistent risk targets
The shale gas industry has frequently complained that its earthquake regulations are stricter than for other industries.
The BGS said consistent risk targets “could be considered for all energy-related industries that present a risk of induced earthquakes”.