by Barry Colam

The UK government recently agreed to the resumption of exploratory drilling for shale gas near Blackpool using the controversial process of hydraulic fracturing, or fracking. So what does this process consist of and why is it so controversial?

The stores of natural gas in conventional reservoirs are dwindling in many parts of the World as well as often being in countries which are politically unstable and/or unreliable. World demand is rising and so alternatives are being sought. Gas is also found in more compact rocks such as fine-grained limestone and shales but from which extraction is more difficult as the gas is more tightly trapped.

The major breakthroughs have been the developments of horizontal drilling and hydraulic fracturing. The shale beds which contain the gas are only tens of metres in thick but hundreds of metres wide, so once a vertical borehole has reached the layer, the drill bit is turned to drill horizontally along it. The bore is lined to form a gas-tight seal with the surrounding rock. The lining of the bore hole is perforated at intervals and then several million gallons of water containing sand and chemicals are pumped in at high pressure to form cracks in the rock, held open by the sand particles. Gas flows through the cracks into the well bore and up to the surface for processing.

However, of the millions of gallons of water pumped into the well, only around 30% is recovered after fracking is complete and stored in surface ponds, the rest remaining underground. Little information is available about the chemicals used, the companies claiming “commercial confidentiality”. What we do know is that while some of them are relatively benign, even harmless, like table salt and citric acid, others are less so. Benzene and other volatile organics, known carcinogens, have been identified by investigators and these will evaporate from the storage ponds.

The companies maintain that these additives only make up 5% of the total volume, but it does amounts to 80 to 300 tons for each fracking operation, and a well can be fracked up to 18 times. Concerns around contamination of groundwater have so far proved groundless but there is increasing evidence that it is a possibility in the longer term. Another concern is that of leakage of methane, either into aquifers or into the surrounding rock due to inadequate sealing of the bore pipe, and there is evidence that this has happened. But the famous “flaming tap” was due to a farmer hitting a gas pocket as he drilled a water well and nothing to do with nearby fracking!

And finally, what about the risk of earthquakes, one of which was the reason for the Blackpool drilling shut-down. While it is clear that it was the fracking process that caused the earth tremors, the risks are considered small provided safety regulations are strictly followed. In the USA earthquakes have also been caused when waste water from fracking has been disposed of down empty wells.

The cost of gas in the USA has fallen markedly with the development of hydraulic fracturing, but don't imaging we'll get the same benefit over here. Not only will our fracking be on a much smaller scale but the geology of the UK shale gas roscks is very different.

Update 1st March 2014. The UK lobby group for the shale gas industry has drawn up guidelines encouraging companies to disclose the chemicals they use in fracking – but they are entirely voluntary!