For the second time in four days, fracking company Cuadrilla halted and restarted its fracking activities at its Preston New Road site in Lancashire because of seismic activity, leading to many โearthquakeโ headlines in theย media.
But who decides when fracking needs to stopย and can be restarted? DeSmog UK unpacks the monitoring and real-time decision-making process behindย fracking.
The process is based on the company monitoring, reporting and assessing the cause and size of the tremors and is overseen by the Oil and Gas Authority. However, it remains unclear how or if a seismic event could lead to halting all fracking activity, as it did inย 2011.
โEarthquakesโ
In the fortnight since Cuadrilla began its fracking operations at the site on the October 15, the British Geological Survey recorded 26 small seismic events in the Blackpool area โ including three events above the 0.5ML (local magnitude) threshold above which fracking activities must beย suspended.
The largest tremor detected by the British Geological Survey took place on October 29 around 11.30am and was of magnitude 1.1ML on the Richterย scale.
In a statement, Cuadrilla confirmed that it had suspended its fracking activities for 18 hours while seismic activity continued to be monitored by the company and the Oil and Gasย Authority.
On October 26 and 27, two other seismic events were recorded at 0.8ML โ also above the 0.5MLย threshold.
While regular seismic activity has taken place around the Blackpool area since fracking began, these small tremors remain of low intensity and are usually not felt by people. Large seismic events induced by hydraulic fracturing are generally rare.
However, because people cannot feel such seismic events does not mean they should be ignored. And the Oil and Gas Authority (OGA), which regulates onshore hydraulic fracturing operations, is responsible for managing the risks linked to seismicย activity.
In the US, scientific studies have shown the link between fracking activities and an increase in seismic activity. In the states of Texas, Oklahoma and Ohio, hydraulic fracturing and the use of fracking wastewater disposal injectionย has been repeatedly found as the primary cause for the increasing frequency and intensity ofย earthquakes.
In Texas, just 13 percent of earthquakes larger than 3ML since 1975 were the result of natural causes alone, according to a paper in the journal Seismological Research Letters.ย In Oklahoma, the US Geological Survey estimated a 5.5ML-or-greater quake was potentially due to fracking operations.
What happens when a tremor isย recorded?
Before fracking can begin, companies need to present an hydraulic fracturing plan that has to be reviewed and agreed by the OGA.
The plan would typically ensure the company monitors seismic activities at the site and that it operates a real-time โtraffic lightโ system so that any operations can be quickly paused and reviewed if unexpected levels of seismic activity isย detected.
The company is also expected to do additional monitoring closer to homes and other building structures near the site. This Hydraulic Fracture Plan (HFP) provides detail of what needs to happen in response to seismic activity and has to be agreed by the OGA and the Environmentalย Agency
Seismic events of up 0.5ML are considered amber on the traffic light scale, with the company able to continue its fracking operations โwith caution, possibly at reduced ratesโ and with intensified seismicย monitoring.
The OGA considers this to be โfar below what would cause a perceptible event at the surface but is greater than the level expected to be generated by the fracturing of the rockย itselfโ.
Image credit: The traffic light system/Oil and Gasย Authorityย
A tremor above 0.5ML while fracking is taking place constitutes a โred lightโ and the fracking company must suspend its activities immediately and for 18 hours for further monitoring of seismicity to takeย place.
In its statement confirming the suspension of activities on October 29, Cuadrilla said that the 1.1ML earthquake was โclassed as a โredโ event as part of the traffic light system operated by the OGAโ but added โas we have said many times this level is way below anything that can be felt at surface and a very long way from anything that would cause damage orย harm.โ
Fracturing activities are suspended only if the tremor was recorded at the time hydraulic fracturing is takingย place.
Following the 0.8ML tremor on October 27, Cuadrilla said that the seismic event was โnot a red incidentโ under the traffic light system because the company was โnot pumping fracturing liquid as part of our hydraulic fracturing operations at theย timeโ.
If activities are suspended, the company has to determine whether the seismicity was natural or induced and act according to the agreed hydraulic fracture plan. Ground motion also has to be assessed to identify potential damage to nearbyย buildings.
If the assessment confirms the assumptions and predictions set out in the plan, the company is allowed to resume operations subject to any mitigation or other measures it has to take according to what has been agreed with the OGA and the Environmentย Agency.
The entire process is overseen by the OGA.
Fracking tremors inย context
Fracking requires the injection of high pressure fluids and chemicals into the rock to crack it open and release shale gas. The cracks grow as a result of tiny seismic events and allow the trapped gas to be extracted. These seismic events are usually very small inย scale.
The injected fluids in the rock can also affect pre-existing cracks and faults in the rock. Any seismic activity that results from this is known as a triggeredย event.
In 2011, a 2.3ML earthquake, considered to be a triggered event led to the halting of all fracking activities. DeSmog UK is still waiting for the OGA to clarify what intensity of tremor could lead to a similar decision being made in todayโsย circumstances.
The British Geological Survey (BGS) says that fracking is generally accompanied by microseismicity, which it describes as โvery small earthquakes that are too small to beย feltโ.
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According to BGS, earthquakes with magnitude less than 2ML are not usually felt by people and earthquakes with magnitudes under 1ML are hardly everย felt.
The BGS adds that on average there are around 20 to 30 earthquakes with a magnitude of 2ML in the UK or across its immediate offshore area everyย year.
โThat means we should expect several hundred earthquakes with a magnitude of 1.0ML or above and several thousand with a magnitude of 0ML or above,โ itย said.
A spokeswoman for the BGS told DeSmog UK that it only played โan observatory roleโ regarding the monitoring of seismic events near frackingย sites.
โWe record what we observe,โ she said. โOperators [fracking companies] have their own monitoring process inย place.โ
A spokesman for the Department of Business, Energy and Industrial Strategy (BEIS) said that OGA was responsible for running and overseeing the traffic light system.ย ย
Lowering of seismicย standards
The current traffic light system, which was introduced in 2014 to regulate fracking companiesโ activities during seismic events, includes aย caveat.
In its fracking guidelines, the OGA states that the 0.5ML threshold above which companies have to suspend hydraulic fracturing โmay be adjusted upward if actual experience shows this can be done without compromising the effectiveness of theย controlsโ.
Speaking to The Times, Francis Egan, Cuadrillaโs chief executive, said the threshold for a red light that requires fracking to stop should be raised from 0.5ML to 2ML.
Egan said the 2ML benchmark was appropriate because according to the British Geological Survey tremors of that magnitude were not usually felt by people and that anything below 2ML was consideredย microseismicity.
He said this would โprovide more than adequate assurance that no harm or damage could arise from frackingโ and compared the UKโs traffic light system with the US system where a red light is given between 2.7ML and 4.5ML depending on theย state.
Egan added that the UKโs current traffic light system was allowing every tremor above 0.5ML to be โtreated as major newsโ and was โheightening publicย concernโ.
Earlier this month, Greenpeaceโs investigative unit Unearthed revealed that energy minister Claire Perry suggested that the government could weaken seismic activity standards at fracking sites.
Unearthed obtained a letter sent to Kevin Hollinrake, Conservative MP for Thirsk and Malton, in which Claire Perry said the traffic lights system is โset at an explicitly cautious level but, as we gain experience in applying these measures, the trigger levels can be adjusted upwards without compromising the effectiveness of theย controlsโ.
Following criticism from anti-fracking campaigners, the government said that it had โno plans to make changesโ to the traffic light system forย now.
Image Credit: Horia Varlan/Flickr/CC BYย 2.0
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