Around 1970 the production of natural gas in the US reached its peak and has been slowly declining since then. The degree to which the US economy has grown to depend on natural gas and growing fears of becoming dependent on insecure supplies on the international LPG market has seen a stealthy growth in unconventional technologies to maintain indigenous supplies. The greatest growth has been in winning the useful fuel from ‘tight’ organic-rich shales that are usually regarded as source rocks for conventional petroleum rather than resources in their own right (Kerr, R.A.. 2010. Natural gas from shale bursts onto the scene. Science, 328, p. 1624-1626). The technology relies on drilling methods developed in the oil industry that allow several holes from a single platform to bend to pass at low angles through thin, gently dipping strata. That allows far larger volumes to be tapped than through a single, vertical well. Oil shales are not yet targeted for liquid petroleum because of the cost, but as Richard Kerr, a news writer for Science, reveals they are supplying an increasing proportion of US gas demand: from 1% to 20% since 2000. Being less of a source of carbon dioxide than coal or oil that might seem to be a ‘good thing’ all round, but there are worrying and little known problems with the technology.

To get the gas out demands that the permeability of shale is artificially increased by jacking open joints and fractures using very high-pressure fluids that carry sand to wedge them open when production begins open: this is ‘fracking’ in driller-speak. Not only gas starts to move, but also water locked into the shale for millions of years and often highly toxic. Drillers hope that all the fluids will follow the holes, but that is by no means guaranteed and some may make their way into aquifers and up to the surface. The fluids used in fracking are deliberately full of chemicals that help open up cracks and even biocides that keep them from being clogged by bacterial films: around 15 million litres used per well. Although aimed to be recycled these noxious fluids can escape, sometimes in massive blowouts. Uncontrolled gas and formation water escapes can cause explosions and kill of forested areas by disrupting tree-root biota.