A Question of Seismicity
A local resident puts the Oil and Gas Authority to the question.
Will answers be forthcoming?
Oil and Gas Authority
Cc Mark Menzies MP
4 November 2018
Following the recorded seismic events near Blackpool in 2011, Cuadrilla commissioned a report into the seismicity of Bowland Shale. In the summary to this report, the following statement was presented.
“Over the past decades, experience gained from mapping hundreds of hydraulic fracture treatments with downhole geophones has shown that seismic events induced by these fracture treatments normally have a magnitude much lower than 0 on the Richter scale.”
This assertion has subsequently appeared in all documentation produced since the events of 2011.
The Environmental Statement( ) issued by Cuadrilla in support of their Preston New Road development included the following statements.
“The hydraulic events induced by hydraulic fracturing do not typically exceed magnitude 0 ML and very rarely exceed 0.5 ML. Data from the surface array will be used to mitigate the level of induced seismicity from hydraulic fracturing operations so that they are below 1.5 ML.”
“Induced seismicity refers to seismic events, typically of very low magnitude, usually in the magnitude range of -3.0 to 0.0 ML.”
Appendix L of the Environmental Statement( ), which discusses induced seismicity, includes the following statement.
“In the context of shale gas recovery, seismic events in the range of less than 0.0 ML are often attributed to the initiation and growth of hydraulic fractures.”
Information on the management of induced seismicity has also been issued by the Oil and Gas Authority (OGA). The primary vehicle for this information has been an “infographic”, a section of which is reproduced in Figure 1.
From the information in the expanded bubble, it is clear that the expected level of “micro seismic events recorded during hydraulic fracturing” would be <0.0 ML and that any seismicity in excess of this level would be an abnormal event. In relation to induced seismicity, the OGA included the following statement in its supporting documentation.
“Currently, the action level for the traffic light system (the “red light”) is set at a magnitude of 0.5 ML. The OGA considers that this is far 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 rock itself.”
Figure 1. The traffic light system for the management of induced seismicity.
In February 2017, at a public meeting with regulators at the Wrea Green Institute, I discussed the traffic light system with representatives from OGA. Throughout these discussions, I was assured that the traffic light system would ensure that there would be no risk of induced seismicity from hydraulic fracturing operations at the Preston New Road site. A representative of the Environment Agency (EA) further informed me that all seismicity associated with US shale gas operations was due to the reinjection of flowback fluid for disposal and that there was no evidence for induced seismicity from hydraulic fracturing operations. Given that the reinjection of flowback fluid for the purpose of disposal would not be permitted in England, I was told that I need not be concerned.
Given, the previous statements issued by Cuadrilla and their regulators, it would be reasonable to assume that there would be very limited seismic activity associated with the Preston New Road operations and that any measured activity that was detected would be below magnitude 0.0 ML. However, within 2 weeks of hydraulic fracturing commencing at the Preston New Road site, there have been a number of seismic events which have strayed into the amber and red regions. In response, OGA have issued the following statements via their website (27 and 30 October 2018).
“Hydraulic fracturing is known to cause minor seismic events of this magnitude. While the operations at the Preston New Road site have been designed to minimise any disturbance, minor events like these were expected.”
“Operations at the Preston New Road site are continuing following the series of minor seismic events, including three that have exceeded the seismic magnitude 0.5ML limit for caution.”
“OGA Director of Regulation, Tom Wheeler, said: “We knew that very low level seismic events deep underground were entirely possible during fracturing operations and this is what has been happening recently at Preston New Road.”
I have underlined the word caution as the OGA infographic clearly states that “injection proceeds with caution” if a seismic event of magnitude 0.0 ML or higher is recorded and that the “operator must suspend injection” in a response to a seismic event of magnitude 0.5 ML or higher. Several recent events have been well in excess of the limits for caution and the event which registered 1.1 ML has been registered as felt on the British Geological Survey (BGS) database.
The description of seismic magnitude 0.5 ML as the limit for caution is a clear shift in the position of OGA and appears to contradict all previously supplied information. Obvious questions also arise, If OGA fully expected the levels of seismicity observed at Preston New Road, why was this information not shared with the public prior to operations commencing and, why does the traffic light system still show 0.0 ML as the upper limit for normal operations?
The upper limit of 0.5 ML was set to guard against a worst case post-injection magnitude increase of 1.0 magnitude units. Although the recent events at PNR could be taken as evidence that the traffic light system is working, it is clear that, when compared with pre-operational statements, hydraulic fracturing operations are not proceeding as expected. If operations are proceeding in line with expectations, the information provided to the public in relation to induced seismicity was incorrect. It appears that both statements cannot be true and I would be grateful if you could explain which is correct.
The stance taken by the operator and OGA is that seismic activity is at a level which cannot be felt at the surface and that it would be too low to cause any damage. These statements somewhat miss the point of setting limits. Where an operating limit has been set, there is a quite reasonable public expectation that operators will comply with these limits (in this case 0.0 ML for normal operations) and that the role of the regulator is to ensure that they do comply. However, regulators typically adopt a risk based approach to regulation and often take no action against a non-compliance where the potential level of harm is judged to be minor. In applying such a risk based approach, the regulator is placed in a position of having to defend its decision and from the public’s perception, could be accused of defending the operator. When the operator subsequently demands a relaxation of the agreed seismic limits and the regulator appears to be shifting its position in relation to the traffic light system, the perceived collusion appears to have some basis.
I have recently raised similar concerns with the EA who, along with Cuadrilla, described several breaches of Environmental and Hazardous Waste Regulations as “minor non-compliances”. While I can accept that the consequences or potential consequences of these breaches were of minor environmental impact, the operator was clearly guilty of offences under the relevant regulations. It is for the regulator to decide whether any action should be taken against the suspected offence but this action and the reasoning behind the decision should be distinct from the offence. Describing such offences as minor non-compliances trivialises the actions of the operator and in many ways is similar to the stance adopted by OGA in response to seismic events at Preston New Road. The adoption of a common language by the regulator and the operator in describing the seismic events at Preston New Road does little to inspire confidence in the independence of the regulator and I would strongly urge OGA to review its current position.
As I was about to send this email, a further earth tremor of magnitude 0.7 ML has been reported by BGS (04/11/18 at 16:24). Given that this event falls outside the 18 hr post fracturing monitoring period, please could you explain how this event or trailing event fits with the hydraulic fracturing plan for Preston New Road.
I would be grateful if you would forward this letter to Natascha Engel, Commissioner for Shale Gas, as she remains uncontactable via email.