Heriot-Watt University scientists have revealed that shale gas extraction was geologically challenged by fault networks at all the drill sites attempted in Lancashire.
Using Cuadrilla Resources’ seismic data which was made public in January 2018, the team created 3D images of the 100km2 area of the Fylde Peninsula and published the findings in the journal of Petroleum Geoscience.
These images enabled the scientists to find that one significant fault line appears to have been misrepresented in Cuadrilla’s previously published material.
The team claims this is significant because faulting places significant limits on the picking of optimal drill sites as they increase the risk of generating induced seismicity during hydraulic fracturing operations.
This may have contributed to the earthquakes that led to a suspension in such operations at the Preese Hall site in 2011.
If the fault line’s accurate position had been mapped in the first instance, the scientists have speculated that the site would not have been chosen as a candidate for exploratory drilling or hydraulic fracturing.
These claims are supported by a 2012 report commissioned by the UK Government’s Department of Energy & Climate Change (DECC), the precursor of the Oil & Gas Authority (OGA).
Professor Peter Styles, Professor Emeritus at the University of Keele is a global authority on induced seismicity and author of the DECC report said: “This is a very significant and impactful paper in the context of UK unconventional gas exploitation.
“As the authors ably demonstrate, this was an area which had significant geological complexity and that shale gas development would pose extraordinary challenges.”
This comes in light of the UK Government’s decision to lift the ban on fracking in England, a move that Business and Energy Secretary Jacob Rees-Mogg claims is in the interest of energy security following Russia’s invasion of Ukraine
Professor John Underhill, Professor of Exploration Geoscience, explains: “We believe our research demonstrates the need for detailed, forensic mapping of the subsurface to be carried out as a prerequisite for shale gas exploration, not just in Lancashire, but in any area where shale gas extraction may be attempted.
“This will allow the subsurface geology to be fully understood and the risk of seismic hazard evaluated in advance of drilling. It is clear that there is much more structural complexity and many more faults in the subsurface than evident at the surface.
“The understanding, identification and accurate mapping of faults is vital in any shale resource assessment and when seeking to evaluate the risk of intersecting critically stressed fractures, upon which seismicity might be induced.
“Our structural interpretations suggest that this particular shale gas reserve, known as the Bowland Shale gas play, remains highly challenged with significant uncertainty in its resource estimates, the planning of well site locations, horizontal wellbore pathways and risk of induced seismicity on faults that are seismically resolvable and those that are sub-seismic scale.”
Iain Anderson, a post-graduate student who led the data analysis as part of his PhD project, added: “Due to shale’s low permeability, it is necessary to hydraulically fracture the rock at multiple points along a horizontal well in order to initiate the flow of gas from the shale. Our mapping has demonstrated the severity of seismically resolvable faulting underneath the Fylde region which would limit the locations in which hydraulic fracturing could occur.
“The occurrence, size and dimensions of the compartments between the faults place limits on shale resources, the optimal location of well sites and on horizontal well bore lengths. The accurate mapping of faults prior to drilling and hydraulic fracturing of wells may, in the future, help reduce the risk of fault reactivation and induced seismicity.”