Operations at the Preston New Road site are currently paused following the latest in a series of minor seismic events.
To date, four events have exceeded the seismic magnitude 0.5ML limit for caution, with the most recent on Sunday, 4 November which recorded a magnitude of 0.66 ML at an approximate depth of 2.3 km.
This threshold is set at a level far below what could be perceptible at the surface and following any event that exceeds the threshold, the operator is required to immediately pause, reduce pressure and monitor for any further events.
During these pauses, the OGA compares the location, magnitude and ground motion of these minor seismic events to the operator’s approved Hydraulic Fracture Plan (HFP). The OGA must be satisfied that events are in line with the geological understanding set out in the HFP and that the risk of induced seismicity is being appropriately managed.
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. There are several thousand minor seismic events like these occurring naturally in the UK every year and can only be detected at the surface with specialist equipment.
“We are taking a cautious approach and have strict controls in place so that even this low level seismic activity results in a pause in operations to allow us to review the event and ensure that the operator’s approved plan is still valid.”
Notes to editors
- For more information on HFPs and the OGA’s traffic light system for monitoring operations, click here
- A Hydraulic Fracture Plan (HFP) sets out the steps that the operator will take to minimise seismic risks and the ways in which the operator will monitor and control the hydraulic fracturing process. The HFP must be approved independently both by the OGA and by the Environment Agency (EA), with the Health and Safety Executive (HSE) having had the opportunity to comment. The OGA requires detailed geological studies to be undertaken by an operator to assess the risk of seismic activity, and to prevent any hydraulic fracturing operations taking place near identified geological faults. The OGA must also be satisfied that controls are in place to minimise the risk of a seismic event or any disturbance to those living and working nearby.
- A graphic/image describing the traffic light system can be found here.