Fracking 'linked to Oklahoma quake'

27 March 2013 Last updated at 07:45 ET By Jason Palmer Science and technology reporter, BBC News

Scientists say wastewater injection from hydraulic fracturing was linked to a magnitude-5.7 earthquake that struck the US state of Oklahoma in 2011.

Fracking, as it is known, injects water and chemicals into petroleum wells in a bid to extract trapped natural gas.

Opponents of the practice say that it risks causing seismic events and contaminating groundwater.

The study in Geology shows that "induced seismicity" can occur years after wastewater injection begins.

Most seismic events linked to fracking have been markedly of smaller magnitudes, and have tended to occur in the first weeks or months of injection.

By contrast, fracking wastewater was first injected into Oklahoma's Wilzetta oilfields, near the town of Prague, some 18 years prior to the November 2011 series of quakes that included three of magnitude 5 or greater.

The new study adds to an increasing body of evidence that the injection of wastewater from fracking - rather than the wellhead injection that extracts gas or oil - is correlated to an increase in seismic events.

A comprehensive review in 2012 by the US' National Academy of Sciences found that "the process of hydraulic fracturing a well as presently implemented for shale gas recovery does not pose a high risk for inducing felt seismic events", but that "injection for disposal of waste water derived from energy technologies into the subsurface does pose some risk for induced seismicity".

However, the report said the number of such documented events over several decades was small compared to the overall number of operations carried out.

In April 2012, a study by scientists at the US Geological Survey of the interior of the US found that events of magnitude 3 or greater had "abruptly increased in 2009" from 1.2 per year in the previous 50 years to more than 25 per year - although a number of gas and oil extraction methods may be implicated in the rise.

'Unexpectedly large'

But the authors of the new study focus on the significantly larger and delayed events in Prague, which they wrote "necessitate reconsideration of the maximum possible size of injection-induced earthquakes, and of the time scale considered diagnostic of induced seismicity".

Study co-author Geoffrey Abers of Columbia University said that "there's something important about getting unexpectedly large earthquakes out of small systems that we have discovered here, " adding that "the risk of humans inducing large earthquakes from even small injection activities is probably higher" than had been believed.

But seismologist Austin Holland of the Oklahoma Geological Survey said while the study showed a potential link between the earthquake and fracking, "it is still the opinion of those at the Oklahoma Geological Survey that these earthquakes could be naturally occurring".

"There remain many open questions, and more scientific investigations are underway on this sequence of earthquakes and many others within the state of Oklahoma," he said.

The topic remains hotly debated in the scientific literature, and between lobbyists and policy-makers, particularly in the UK.

Links between fracking in Blackpool and tremors in the region led to a government ban on the practice, which was lifted at the end of December 2012.

Source: http://www.bbc.co.uk/news/science-environment-21952428#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa

veep los angeles kings earth day timothy leary jonathan frid pujols watchmen