City Perspectives: Hydraulic fracturing (fracking), energy needs, safety and the environment
By Professor Philip Thomas, Professor of Engineering Development
The process of hydraulic fracturing
Natural gas is held in underground rock reservoirs that may be either permeable or impermeable. The extraction of gas from permeable rock is relatively simple because the gas can flow easily to the gas/well pipe. However, due the impermeable nature of the shale rock, pathways have to be created in the rock matrix if the gas is to reach the extraction duct. A well is sunk vertically into the shale bed deep underground and then a horizontal channel is drilled into the shale seam. Shaped charges in a "perforation gun" may be used to induce local fractures in the rock along the channel and these or pre-existing fractures are extended using pulsed, high pressure water - a process known as hydraulic fracturing or "fracking". These fissures, which are kept open by sand that is added to the water, provide the necessary pathways for the gas to reach the horizontal collection channel once the pressure pulsing has ceased.
Shale gas and energy needs in the UK
The UK's self-sufficiency in oil and gas came to an end in 2004. The continued prosperity of the UK is dependant on the discovery of new and secure sources of energy. As well as the carbon-free sources (nuclear, wind power), there is a continuing need for fossil fuels, of which natural gas is the cleanest. There is a lot of shale gas in the North of England: ten percent of the estimated reserves found there is enough to provide the UK with all its gas for 40 years at the current rate of consumption. Further major reserves have been located in the South of England, from Dorset to Sussex.
Economic benefits of shale gas
Shale gas now makes up about a third of US natural gas production, a figure set to double in the next seven years. The US economy has been stimulated by both new jobs and lower fuel prices as a result. The UK's shale gas could contribute a similar fraction of the country's energy use, suggesting a comparable economic benefit.
Environmental, health and safety issues
Concerns have been raised over earth tremors associated with fracking testing in the UK, although the effects are less than those caused by coal mining. Care needs to be taken, though, with the typically ten additives present in fracking water, including acids for rock dissolution, petroleum distillates for friction reduction and anti-bacterial agents. UK fracking safety will be regulated by the Health and Safety Executive, while environmental performance will be monitored by the Environment Agency.