Geological Concerns

DRILLING INTENTIONS

Aurora Energy Resources is planning to site a well pad near Great Altcar, West Lancashire. The potential extent of the subsurface works is shown as a dotted red line on their map extending both east and west of their site.

Aurora Site II

Well DesignThe intention is to drill two vertical boreholes: the first to a depth of 3,200m; the second to a depth of about 2,200m. The second borehole will then be drilled laterally for a distance of 1,500m but Aurora has not yet indicated in which direction.

The rock structure underneath Aurora’s site has been studied on many occasions over the years and is known to contain a proliferation of fault lines. The major surface faults broadly run on a north/south axis.

Downholland Fault

A cross section of the regional underground fault lines shows they interconnect and lead up to or near to the land surface.

Formby Faultlines

ross SectionThe main strata are thought to be ‘castellated’, meaning that the shale seam only runs for short stretches at different levels between the faults. Similar labyrinths of fault lines and strata conditions occur right across The Moss (sometimes known as the Formby Basin) and under much of the UK. No such faults are found in the geology of the USA or Australia.

(Key: Brown=Sandstone, Purple=Shale, Blue=Limestone)

Oil WellsAurora’s scoping request indicates that their well site is located approximately 900m south east of the Formby Oilfield in which about 80 wells were sunk, largely between 1939 and 1965. Whereas most of these wells were dug at shallow levels (one only 50m north of the proposed site), at least one other was dug to a depth of 2,200m.

 

The development currently being proposed is estimated by Aurora to cost at least about £10.5m but appears not expected to produce any gas for sale. The company clearly intends to obtain a commercial return on its initial outlay by harvesting large quantities of gas from further vertical and lateral wells on the Great Altcar pad and other sites close by.

Fracking StagesLateral Multi-Wells

This probably means drilling in a radial pattern (above left) but in view of the likely thickness of the shale seam, it may also be necessary to drill many wells laterally at multi levels (above right). Most fracking wells are shut down anyway after two or three years because the harvest drops off significantly. New shafts then need to be drilled to access other parts of the gas field.

THREATS AND RISKS

About 40% of the fracking fluid flows back to the surface and presents a major problem of safe disposal for an operator – in this case, Aurora. Having absorbed chemical elements of the shale, it will be toxic, carcinogenetic, flammable and slightly radioactive.

If the remaining 60% of the fluid gets near to and lubricates fault lines, it poses the threat of induced seismicity (earthquakes) due to stress changes. Fault lines also provide pathways and conduits, so fracking in their vicinity poses the threat of the fugitive migration of unrecovered gas and fluids upward into groundwater sources and eventually onto the local land surface and into local waterways.

These prospects are clearly magnified when fault lines exist adjacent to disused oil and gas wells, like those on the old Formby oilfield site. Most of these wells were capped off 50 years ago (using standards then applying), and the shafts and seals may well have corroded, shrunk or cracked since then. Aurora has itself indicated that the ongoing presence of oil slicks on the surface of local drains is clear evidence of leaks from these disused wells.

Politicians are fond of claiming that they will not allow fracking where there is a risk to people, property or the environment. However, the government agencies responsible for regulating fracking in the UK merely say they will try to minimise these risks as far as is reasonably practicable. Clearly therefore there is a risk to residents living near to fracking sites, and judgements are to be made by the regulators as to the manner and extent they can be mitigated.

MITIGATION MEASURES

The regulatory agencies have developed a number of theoretical measures designed to mitigate these threats and risks. For example, fracking operators are now required to conduct 3D seismic surveys over wide areas of their PEDLs, to try to ensure that the location of all fault lines is identified at the outset. The results of Aurora’s local 3D seismic surveys will no doubt feature in its impending application for planning permission.

Before fracking is allowed to start, operators must agree with the regulators a hydraulic fracture plan. This will include the safe distance ratios considered appropriate between the planned extent of the fracturing and its proximity to fault lines. It also details the pressure stages that will be employed, and the seismic methodology to be used to monitor the fracturing process.

The regulators place great reliance on a ‘traffic light warning system’ which is designed to prevent large scale seismic events. Under this system, facking operators are required to suspend and review their operations if readings reach pre-determined levels of seismic activity. Thereafter they may only proceed with caution.

Regulators and fracking operators are adamant that they are not aware of any plausible pathways that exist for the fugitive migration of fluids and gases. They regard the various faults, and a mudstone cap rock of Manchester Marl, that occur locally, as forming an adequate barrier and seal to prevent this from happening, at least for many years.

The Moss Alliance has researched these mitigation measures and concluded that each is flawed. We intend to develop our reasons for this view and put them in an objection to the impending planning application by Aurora.