One of the UK’s leading seismologists says more shale gas wells must be fracked to assess the risk from tremors.
Dr Brian Baptie, a project leader with the British Geological Survey (BGS), was speaking a month after Cuadrilla’s shale gas site near Blackpool caused the UK’s biggest fracking-induced seismic event.
He told a scientific meeting in London last night:
“To really truly understand the risk of this process we’ve got to try it in a few places and probably not just the north west of England but in other plays as well and try and get some data that we can use to try to constrain what the hazard is.”
The 2.9 magnitude tremor on August bank holiday was reported to the BGS by several thousand people. Several hundred people told the BGS it had damaged property.
Replying to DrillOrDrop’s question about whether Cuadrilla could successfully exploit the Bowland shale without causing damaging tremors, Dr Baptie said:
“The Bowland [shale] appears to behave differently from some other analogue reservoirs in the States – you appear to get some quite high seismicity rates.
“To truly understand the hazard we just need more observational data.”
Dr Baptie said the seismicity caused by Cuadrilla was “way too small” to cause structural damage”. But his comments on the need for more fracking data have angered opponents of Cuadrilla’s activities in Lancashire.
A representative for Preston New Road Action Group told DrillOrDrop:
“Back in April, Dr Baptie stated that earthquakes with less than a magnitude of 4ml do not usually cause damage. Recent events have shown this statement to be quite incorrect. He was also advocating that the Traffic Light System should be increased on an incremental basis to allow fracking at PNR to be intensified.
“He is now saying that fracking should be tried out on other communities in other areas of the UK. This trial and error approach, ignoring the impact that it has on people’s lives and wellbeing, is totally unacceptable. Other geological experts have said that the seismicity on the Fylde was predictable given the highly faulted nature of the Bowland Shale.”
A spokesperson for Frack Free Lancashire said:
“We note Dr Baptie’s suggestion that having failed once in the Fylde, the industry should try to get a different result by imposing themselves on another unfortunate community.
“While trying the same thing somewhere else and hoping for a different result might save the industry’s and the government’s blushes for a few more years, it really is time that they admitted defeat and packed up and left.
“There is no place for unabated fracking in UK Net Zero 2050. Exploiting yet another source of fossil fuels is incompatible with these climate goals.”
There’s more detail on Dr Baptie’s comments on damage from Cuadrilla’s induced tremors in a special DrillOrDrop report coming soon.
Changing tremor pattern
Cuadrilla carried out hydraulic fracturing on one well at Preston New Road (PNR-1) in October-December 2018 and on the PNR-2 well in the second half of August 2019.
The BGS online database reported more than 50 tremors from the 2018 fracks and more than 130 from 2019.
Dr Baptie told last night’s meeting the pattern of tremors varied between the two sets of fracks. In 2019, he said, there were many more trailing events. These are defined as tremors measuring more than 0.5ML which happened after fracking.
The 2.9ML earth tremor, on 26 August, was almost three days after the last frack at the site, on 23 August 2019. The most recent tremor recorded at Preston New Road by the BGS’s online database was on 14 September 2019.
Relationships, uncertainties and faults
Previous research has linked the volume of injected fluid to the size of tremor. But Dr Baptie said of the Preston New Road fracks:
“There doesn’t really appear to be a clear relationship between injected volume and seismicity. There is possibly a relationship between the number of events and volume.”
He said research showed that measurement of the magnitude of earth tremors could be uncertain by about 0.1ML. This could have implications for the traffic light system regulations, which requires companies to pause fracking at 0.5ML. This uncertainty should be taken into account by the regulations, Dr Baptie said.
The traffic light system also requires operators to proceed with caution if fracking causes tremors of magnitude 0.0 – the amber level. But Dr Baptie said BGS research showed that surface networks of seismic monitoring may not be good enough to implement this part of the regulations.
Dr Baptie said faults capable of inducing tremors measuring up to 2.0ML could not all be identified by seismic imaging methods.
“There are lots and lots of faults of these dimensions that we just don’t know about and they probably are pervasive.”
Fracking and bedding planes
Dr Baptie also said the seismic data suggested fracking had reactivated what he described as near-optimally oriented faults.
But the American fracking expert, Dr Grant Hocking, told the meeting Cuadrilla had not actually fracked the formation at Preston New Road. Instead, he said, the company had opened slickensided bedding planes and created seismic activity a long way from the well.
“They have not been doing hydraulic fracturing here. They have just been pumping fluids into the formation.
Dr Hocking, said his company, GeoSierra, carried out a review of Cuadrilla’s 2011 Preese Hall frack along with researchers from Halliburton, Imperial College and the Massachusettes Institute of Technology. He said:
“We decided that you virtually couldn’t hydraulically fracture those shales because of the presence of the slickensided bedding planes.
“I’ve been trying to tell the OGA [Oil and Gas Authority] this for a whole year and a bit and the BGS and no one listens.”
Dr Hocking said the traffic light system, which is based on monitoring the magnitude of seismic events, was “not a good handle of the [fracking] technology”.
“Microseismicity doesn’t tell you where the frack is. It definitely doesn’t tell you where the frack fluid is. It tells you where you’ve had slip due to pore pressure changes.”
Dr Hocking said surface tilt metre monitoring should be mandatory because of the slickensided bedding planes. For more on this issue, see DrillOrDrop report from August 2019
Reporting from the meeting, hosted by Society for Earthquake and Civil Engineering Dynamics, was made possible by individual donations from DrillOrDrop readers.