By Jason Palmer
Scientists have linked the underground injection of oil-drilling wastewater to a magnitude-5.7 earthquake in 2011 that struck the US state of Oklahoma. Wastewater injection from drilling operations has been linked to seismic events in the past, but these have typically been much smaller quakes.
They also have tended to occur in the first weeks or months of injection.
The study in Geology suggests that “induced seismicity” can occur years after wastewater injection begins.
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 is correlated to an increase in seismic events.
A comprehensive review in 2012 by the US’ National Academy of Sciences found 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.