Geoscientist explains what is involved with the fracking process

Wells geoscientist William Wills has responded to fears that fracking on the Mendip Hills could set off a dormant volcano.

Mr Wills, who has worked with monitoring oil and gas exploration projects around the world, said: "I am neither an advocate for or against fracking in the Mendips, but I think the record needs to be set straight on what is actually involved with this process and to help ensure the public can be as savvy as possible in identifying alarmist and apocalyptic predicted outcomes of hydraulic fracturing."

Hydraulic fracturing is a technique employed for decades in the USA but has only recently begun to be used in the UK.

This 'unconventional' oil and gas extraction method has become more prevalent as reserves closer to the surface are becoming increasingly rare.

Mr Wills said: "The first key to understanding oil reservoirs is to not think of it as underground caves or pools of oil, but rather the sedimentary rock acting like a sponge with the hydrocarbon molecules trapped in the many microscopic pore spaces within.

"An impermeable layer of geology is required above and around the reservoir rock to allow the hydrocarbons to be trapped and build up over time.

"However, with unconventional gas we are exploiting ultra-high porosity (so lots of microscopic pore spaces containing oil) but ultra-low permeability reservoir rocks.

"This means that we have a 'sponge' full of oil that we cannot extract, unless we artificially make the pathways."

This is achieved by the high pressure pumping of a liquid, often a sand and water gel mix through a well and into the tight rock to fracture. This is where many environmental concerns arise.

Mr Wills said: "How do we know where the fractures are going? What if they reach ground water? Or worse lubricate a fault and cause a small earthquake?

"In the process, micro earthquakes are set off – so small that 10m from the shock they cannot be felt. Geophones – a kind of underground sensor – are also placed underground, to make sure that the only places affected by the micro earthquakes are the hydrocarbon bearing rocks, and nowhere important like dormant volcanos and the source of hot springs."

And to make sure the risk is kept to an absolute minimum, this is done by making sure that the area being drilled is fitted with a series of permanent monitors, which track the fracturing process at every stage and stop the fractures going anywhere they shouldn't.

Mr Wills added: "This is called advanced borehole seismic monitoring technology.

"By having multiple geophones this micro-seismic energy can be pinpointed in three dimensions to its point of origin.

"By plotting these points in 3D in real time, geophysicists can exactly map where the fractures are occurring.

"To add further balance to the argument it should be noticed that the media has repeatedly reported occurrences of ground water contamination in the US, conversely this is less than a handful of incidents amongst thousands of successful and productive fracking operations, making this energy production one of the more environmentally passive techniques.

"I do not wish to understate the possible worst case outcomes of fracking, but we will certainly not be able to induce any unwanted geothermal activity under the Mendips."

The geoscientist advised that key to mitigating any of the small risks of fracturing near geothermal or ground water zones is to have a permanent borehole monitoring system, recording and plotting the microseismic fracture pathway – a common practice in the US.

Mr Wills will be giving a talk on fracking and the fracturing process to the Wells Society of Scientists and Engineers in January at the Wells EMI Social Club.