Fractures have been cited as possible underground pathways for deep sources of methane to contaminate drinking water in underground reservoirs.
Prof Richard Davies, director of Durham Energy Institute at Durham University, told The Engineer: ‘The chances of a rogue fracture extending beyond 600m are exceptionally low. Therefore, a distance of 600m should be seen as an absolute minimum vertical separation distance between the fracking depth and shallower aquifers.’
The analysis is based on thousands of fracking operations in the US and natural rock fractures in Europe and Africa.
‘Where shale fracking in the US has been carried out with vertical separations significantly higher than 600m (for example, 1–2km) then contamination of aquifers cannot be the result of fracking,’ said Davies. ‘We should look for other mechanisms such as poor cementing of casing or even natural seepage.’
During fracking operations, fractures are created by drilling and injecting fluid into the rock strata underground to increase oil and gas production from fine-grained, low-permeability rocks such as shale.
A UK government report recently backed the drilling for shale gas onshore, lifting a temporary ban on the method that was brought into force following fracking-related earthquakes in Blackpool last year.
The researchers hope that governments and shale-gas drilling companies will use the analysis when planning new operations.