Opponents of drilling at Bury Hill Wood near Leith Hill in Surrey. Photo: DrillOrDrop

Another report commissioned by opponents of oil exploration, has criticised plans by Europa to drill near Leith Hill in Surrey.

Last week, DrillOrDrop reported that a review, funded through a 38 Degrees petition, concluded that the plans contained “many significant errors, inconsistencies and omissions”.

Yesterday, a second report, commissioned and crowd-funded by the campaign group, A Voice for Leith Hill, said proposals for oil drilling and testing at Bury Hill Wood posed “a serious and unacceptable risk” of contamination to local drinking water aquifers.

The report, by David Smythe, Emeritus Professor of Geophysics at Glasgow University, was submitted to the Environment Agency (EA) as part of a public consultation.

The EA has said it is minded to grant an environmental permit for the proposed operations, including the use of acid in the well. The draft permit would, the EA said, “ensure that a high level of protection is provided for the environment and human health”.

But Professor Smythe said Europa’s permit application contained “incomplete and misleading information”. He said the company had miscalculated geological depths and used out-of-date maps.

He described the application’s understanding of hydrogeology as “seriously defective”. He added that the company had “a poor understanding of the geology and the technical problems that it is likely to encounter in drilling”.

Risk to groundwater

Europa said in its application that the proposals did “not present an unacceptable risk to the water environment”.

It also said the public water supply boreholes at Dorking, which take water from the Hythe Formation aquifer, were “not considered to be at risk” from the proposals.

Professor Smythe disputed Europa’s claim that there was no direct underground pathway from the wellsite at shallow depths to the Dorking boreholes.

He said the Hythe Formation would be inadequately protected from any contamination. The proposed 50m long conductor casing would not penetrate deeply enough to reach the impermeable Weald Clay Formation, he said.

Professor Smythe added that Europa’s understanding of the shallow groundwater flow through the Hythe Formation was “seriously in error”:

“There will be a major risk of outflow from the base of the Hythe Formation to the east into the [River] Mole catchwater and not to the west into Pipp Brook, as claimed.”

Geological faults

Professor Smythe said Europa’s application had “poorly understood surface-mapped faults around Leith Hill”. He said the company had overlooked field evidence of thrust faulting within 50m of the wellsite.

He added:

“The applicant does not have a robust understanding of the faulting in the target area. The applicant needs to commission a dedicated resurvey by the BGS to examine all the evidence”.

Use of acid

Europa had initially proposed to carry out an acid wash to clear any formation damage caused during drilling. This would be followed by an acid squeeze, in which acid would travel up to 14m into the formation and may result in stimulation of oil flow.

The company has since said it intended to clear debris from only within a 1m radius of the wellbore and that pressure used to pump acid into the well would be below that needed to fracture rocks.

Professor Smythe said the EA should restrict the volume and strength of acid to that needed for an acid wash.

Another consultation response, referenced in his report, highlighted that, while Europa had reduced the distance travelled by the acid, it had increased the volume likely to be used. The response also said there were inconsistencies in the definition of acid squeeze and questioned how the EA would enforce different acid techniques.

Deviated well

Europa plans to drill what is known as a “deviated well”, which begins vertically but then bends diagonally or horizontally.

Professor Symthe said the “highly deviated wellbore” was at the limit of what he described as “permissible technology”.

He said it cut through a major fault:

“This will probably give rise to technical problems such as washouts (over-enlargement of the borehole) during the drilling, as has happened with a similarly inclined borehole in similar geology at Broadford Bridge”.

He also predicted problems in sealing the casing of the deviated portion of the wellbore because of its shallow inclination:

“Inadequate cementing of wellbore casings is recognised as a major problem, giving rise to pollution of groundwater aquifers.”

Conventional or unconventional?

Europa has described the operation at Bury Hill Wood as conventional oil exploration.

But Professor Smythe said:

“The Kimmeridge Clay formation, with its tight thin semi-limestone ‘micrite’ bands, is an unconventional target.”

He said the company’s proposals also included unconventional testing by matrix acidisation.

• More than 103,000 signed a petition urging the Environment Agency not to grant the permit. At the time of writing, the EA’s website had 145 published responses to the consultation. Link to A Voice for Leith Hill JustGiving page