In the early 1990s the oil and gas industry in Texas started to produce gas by drilling into deeply-buried shale layers. They found that creating underground fractures in the layers, later coined ‘fracking’, increased the rates of production and their investments started to make money. This was the start of the shale gas industry in the USA which may now grow in Europe, China and elsewhere around the world.
Hydraulic fracturing is far from being a new technology; it’s been carried out in many wells since the 1940s. But in the last 10 years, its widespread use for recovering gas from shale has led to it becoming extremely controversial. A tipping point may have been when the filmmaker Josh Fox was asked to lease his land for drilling, it resulted in him making the documentary ‘Gaslands’ (2010), with footage of gas coming out of taps being ignited. The potential link between fracturing and the contamination of water supplies with methane was thus made. More followed in 2011 when the UK’s first shale gas well was drilled near Blackpool in northwest England and triggered earthquakes up to 2.3 in magnitude. ‘Fracking’ has quickly become a catch-all term for any shale gas operations.
But what do we actually know about the geological risks? Can fractures created underground really travel much further than we anticipate, intersecting water supplies and polluting them as ‘Gaslands’ suggested? Could the pumping of thousands of cubic metres of water underground cause damaging earthquakes? How much of what we read in the press is scientifically sound? The debate is polarised with claim and counter claim.
There is a lot we already know. Hydraulic fractures can form entirely naturally when pressure builds up as rock is buried over millions of years. Underground seams of minerals in fractures have of course been mined for centuries and the processes involved in fracture formation have been well understood since the 1960s. In the last decade, chimney-like subterranean hydraulic fractures extending vertically for hundreds of metres have been found in many parts of the world.
‘Unnatural’ or stimulated hydraulic fractures are generated by pumping water and chemical additives into rock layers. The orientation of fractures that grow can be predicted approximately. But it’s a little like smashing a pane of glass: where exactly the cracks occur is different every time. It is difficult to predict whether a fracture will extend beyond the intended geological layer. Nor is it feasible to calculate whether or not pumping fluid underground to create fractures will cause small earthquakes that could be felt at the surface.
But what we do have is data – and lots of it. Thousands of fracturing operations have already been completed in the United States and the dimensions of the hydraulic fractures recorded at least for the last ten years. So we can adopt an empirical approach to understanding the chances of a fracture extending further than ever before. Our analysis shows that the chances of a fracture extending further than 500 metres vertically are very small. There are also hundreds of examples of induced earthquakes caused by activities other than ‘fracking’: the filling of dams, fracturing for geothermal energy, injecting water to maintain oil fields pressure and because of subsidence triggered by mining of oil and gas.
It is claimed that companies involved in shale gas are not releasing data about operations – but in fact there are hundreds of papers in the public domain that can be accessed and I’ve spent months pouring over them while producing a paper on the topic. The compilation and reviewing of 20 years of shale gas activity will give us a pretty good steer on the chances of something extraordinary happening. It is the sort of data mining task one of our undergraduates would excel in – some studies have been published, but in the surrounding media hysteria, a lot of basic information has been missed. This would go a long way to informing not just the broader public who are often misinformed by the media, but also industry, academic geoscientists and engineers, regulators, non government organisations and publics about safe shale gas operations in a hyperbole-free way.
Richard Davies is Director of Durham Energy Institute.
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