Fracking, or hydraulic fracturing, is a technique for getting methane gas out of shale rocks.
The gas, which is a fossil fuel, can then be burnt to provide energy for power stations to generate electricity. Because methane has a lower proportion of carbon than coal and oil and can be burnt more efficiently, many see it as a transitional fuel, allowing continued use of fossil fuels but reducing greenhouse gas (GHG) emissions. This would buy time while alternatives were developed. According to this model, fracking would help by increasing the availability of methane.
There are two types of argument against fracking. One type focuses on threats to local environments, particularly for people living nearby; the other takes issue with the “green” claims made for methane.
Fossil fuels are the remains of plants (mainly trees) and animals (mainly sea creatures) that died hundreds of millions of years ago.
The trees fell into swamps and the sea creatures sank into sediments on the sea-bed; neither rotted due to the lack of oxygen in these environments. Instead, their bodies were subjected to heat and pressure; water diffused away; the fats, carbohydrates, and proteins were converted into impure carbon (in the case of trees) and oils and gases (in the case of sea creatures). Subsequently, some compounds were further broken down, producing more gases, mainly methane.
Some methane has been naturally escaping, giving rise to the will o’ the wisp (also known as jack o’ lantern and ignis fatuus (Lat. “foolish fire”)), which features in folklore worldwide. Here, methane seeping from marshes spontaneously ignites, causing a ghostly dancing flame.
Fossil methane is trapped in reservoirs capped by impermeable rock, sometimes with oil deposits. This is where it is found in conventional gas wells, while it is “flared off” wastefully from oil wells. It is also found “dissolved” in rocks, including “tight” sandstones and shales. These are relatively impermeable and the methane was hitherto unobtainable, except where rocks were naturally faulted. Methane is also “dissolved” in coal and seeps out when coal is mined (‘fire damp’) or through natural faults.
Hydraulic fracturing of gas-bearing shales and “tight” sandstones is a technique that has been developed commercially in the last 14 years. It introduces cracks into the rock to allow the methane to come out through the greatly increased surface area.
This is done by injecting water, sand and various chemicals at enormous pressures into drill-holes. This is enough to overcome the considerable pressures in the rocks at this depth and cause them to fracture. The sand helps prop the cracks open so that the released gas can travel to the surface. The chemicals, some of which are quite unpleasant, form a gel which helps deliver the sand to the cracks. Much water can be lost to the surrounding rocks, together with the chemicals.
Hydraulic fracturing has been used in conventional, vertical, gas wells for 60 years to remove the last bits of gas. It has become more cost-effective for shales with the development of horizontal drilling outwards from vertical drill holes. This makes much more rock available for fracking.
Criticisms tend to be on environmental grounds.
Local complaints include gas coming out of water taps, polluted ground water, and minor earthquakes or tremors. Criticisms on the global scale refer to its greenhouse gas footprint.
Groundwater contamination. Despite complaints from some residents, a report from the University of Texas absolves hydraulic fracturing itself from causing groundwater contamination, hardly surprising since it takes place typically between 1.5 and 6 km depth. Contamination from the drilling process seems no worse than for conventional oil and gas extraction on land. However, this is not to be ignored and communities should demand that companies use less dangerous chemicals and take greater precautions to prevent leaks. Also, fracking has not been going on for very long and it is possible that worse problems may emerge.
Flaming water taps. The Texas report concluded that examples of tap water saturated with methane were probably natural, though there was little evidence to compare the situation before and after fracking.
It is worth mentioning that natural methane seepage from coal seams has been known for a long time. Older readers may remember the Abbeystead (Lancashire) water pumping station disaster 28 years ago. Methane seeping from coal deposits 1 km deep had built up in an empty water pipe and then been driven into the main hall by the pressure of the pumps. It exploded, causing 16 deaths and 28 serious injuries.
Fire damp has been known since coal-mining began. Methane builds up in mines and can be ignited by any spark, the reason why taking lighters and matches into mines is a criminal offence. In the US, 128 miners have died in methane explosions in the last 30 years (compared with 43 deaths attributable to Chernobyl).
Earthquakes. It’s official! Fracking caused two tiny earthquakes near Blackpool last year.
Of magnitude 1.5 and 2.3, they were caused when water injected into shale rocks lubricated faults, allowing them to shift by about a centimetre at a depth of 2 km. These are really trivial: 1.5 would not usually be detected and 2.3 would usually only be detected by sensitive seismometers. For comparison, I have survived a magnitude 3.5 ‘quake in Nottinghamshire. This released about 70 times as much energy as the 2.3 ‘quake and all I noticed was a bang like a skip falling off a lorry and the windows rattling. A slightly bigger one that occurred at night failed to wake me.
There are about 15 magnitude 2.3 earth tremors in Britain per year. Subsidence due to mining is a far more common problem (notably in Northwich, Cheshire, due to salt mining) but … fracking has only just started here!
The US Geological Survey reports a rise in earthquakes greater than magnitude 3 which coincides with the introduction of hydraulic fracturing. While these are small, it is not impossible for larger tremors to be triggered.
Cheaper and more widely available methane is going to encourage its use to generate electricity.
This involves burning lots of it and therefore releasing carbon dioxide, a “greenhouse” gas. In principle, this is just as bad as burning any other fossil fuel. In fact, methane is only 75% carbon, compared with heavy oils and coal at about 90% carbon. Also, gas-fired power stations are about 50% more efficient than other fossil fuel power stations. All other things being equal, switching to gas would reduce carbon dioxide emissions and help mitigate climate change.
This has led some to see it as a bridging power source, taking us towards a lower-carbon future. However, methane is itself a potent greenhouse gas, some 70 times worse than CO2, and it escapes from fracking operations.
This has been analysed by researchers at Cornell University, NY, who conclude that hydraulic fracturing releases substantially more methane than conventional gas wells and that, over 20 years (when we need to greatly reduce GHG emissions), it would have a much worse impact even than coal, let alone ordinary methane and oil.
To sum up, the adverse effects on local environments of fracking seem to be exaggerated, though evidence is limited. However, switching to shale gas would make global warming worse and on those grounds alone it should be opposed.