Professional Engineering

The UK is facing an energy crisis, and the recent discovery of shale gas in north-west England is heralded by some as one way of becoming self-sufficient and obtaining sustainable power supplies. But others disagree, saying that a shale gas industry could have environmental impacts and is not a long-term solution to the problem.

Shale gas is extracted by a process called hydraulic fracturing. This involves drilling into shale rock formations that lie thousands of feet beneath the earth’s surface. A series of steel tubings are cemented into the ground, to contain the well. The end of the steel tubing is then perforated by a small electric charge to give access to the shale formation.

A combination of water, sand, and small quantities of a friction reducer and biocide, known as fracking fluid, is pumped down the well. The pressure forces the fluid through the perforations and into the shale bed where the rock is prised open to create tiny fractures that migrate in all directions. These fractures are held open by the sand particles in the mixture, so when the fluid is pumped out the gas trapped within the rock escapes to the surface. A typical frack lasts around three hours.

Fracturing has been used in the oil and gas industry since the 1940s. But the use of fracking in shale formations was pioneered by the Mitchell Energy and Development Corporation in the Barnett shale, Texas, during the 1990s. 

Over the past 20 years, the US shale gas industry has boomed. In 2011, the US Energy Information Administration (EIA) reported that US shale reserves harboured 862 trillion ft³ of recoverable natural gas, double the estimate published the previous year and comprising 34% of the country’s total natural gas base. The EIA believes estimates are likely to increase in the future, with shale gas comprising 46% of the country’s natural gas by 2035.

Although the US boom has transformed the energy landscape, it has brought with it some unwanted environmental effects. An Oscar-nominated documentary, Gaslands, famously shows residents setting fire to the water coming out of their taps after the shale gas companies have come to town. In other scenes, homeowners draw brown and murky water from their taps. 

Late last year, the US Environmental Protection Agency published the first formal findings of groundwater contamination caused by fracking. Draft findings from an investigation in Wyoming reveal that local groundwater had probably been contaminated with synthetic chemicals associated with fracking, and had high levels of benzene and methane gases. The exact mechanism behind the contamination remains unclear. 

The controversial practice has now arrived on UK shores. Last year, independent energy company Cuadrilla began exploratory work to better understand the prospects for natural gas in the Bowland Shale around Lancaster.  

Since the start of the exploratory programme, fracking has barely been out of the headlines. Environmentalists have called for a moratorium, MPs have held an inquiry into its potential effects, and two earthquakes in the area concerned have halted proceedings. 

Further afield, the French and Bulgarian governments have banned the technique, and fracking-associated earthquakes have been reported in the US state of Ohio.

Cuadrilla’s exploratory project in Lancaster remains on hold until the Department of Energy and Climate Change (DECC) looks into the recent seismic activity. A report commissioned by the company and submitted to DECC says that the quakes, measuring 2.3 and 1.4 respectively on the Richter-scale and two months apart, were a result of a well at Preese Hall encountering an existing critically stressed fault.

Paul Matich, well services manager at Cuadrilla, says: “The fault was transmissible, so it would accept large quantities of fluid, and the fault was brittle enough to fail seismically.”

The report says that the opening of the hydraulic fractures is unlikely to have triggered the quakes because they occurred 10 hours after the injection of fracking fluid. Instead, the pressure from the fluid built up on an area of the fault zone over time. The report adds that similar events are very unlikely to happen again because the chances of any one of these factors occurring alone is small, with the chances being even smaller in combination.