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Cracking the quakes mystery

Readinch

As China begins to sketch out plans for developing its potentially lucrative shale-gas reserves, officials would be wise to consider some recent findings by scientists in the country’s great energy rival, the United States.

In a paper to be delivered next week at the annual meeting of the Seismological Society of America (SSA), the US Geological Survey (USGS) notes that “a remarkable increase in the rate of [magnitude 3.0] and greater earthquakes is currently in progress” in the country’s mid-section.

Beginning in 2001, the USGS says, the average number of such quakes – large enough to have been felt by many people, while small enough to rarely cause damage – grew significantly each year, “culminating in a six-fold increase in 2011 over 20th-century levels”. Such a development raises an important question: are the quakes, which come at a time of significantly increased shale drilling, natural or man-made?

In search of an answer, a USGS team analysed changes in the rate of seismic occurrences since 1970, then examined the rates in areas where energy-production activities have changed in recent years. Key among those changes is “fracking”, the blasting of chemical-laced water and sand underground to break rock apart and release natural gas. Fracking – or hydraulic fracturing – increases shale’s permeability so that gas can flow through the rock mass and be extracted via production wells.

Preliminary findings
, according to David J Hayes, deputy US interior secretary, “do not suggest that hydraulic fracturing, commonly known as ‘fracking’, causes the increased rate of earthquakes”. But, Hayes adds, “at some locations the increase in seismicity coincides with the injection of wastewater in deep disposal wells.”

Deepwell injection is a method of getting rid of the wastewater that is a by-product of oil and gas extraction in tight shale formations and coal beds. (For more on the link between deepwell fluid injection and triggered earthquakes, see here.)

In their early findings, says Hayes, USGS scientists cite “a series of examples for which an uptick in seismic activity is observed in areas where the disposal of wastewater through deep-well injection increased significantly”. Most of those areas are in the central US energy-producing states of Colorado, Texas, Arkansas, Oklahoma and Ohio.

A published study is forthcoming, while an abstract of the findings to be presented on April 18 is available here.

Writing on his respected ClimateProgress blog, Joseph Romm – a physicist and former US energy department official – quotes the subscription website EnergyWire as explaining: 

“The study found that the frequency of earthquakes started rising in 2001 across a broad swath of the country between Alabama and Montana. In 2009, there were 50 earthquakes greater than magnitude-3.0 … then 87 quakes in 2010. The 134 earthquakes in the zone last year is a sixfold increase over 20th century levels.

“The surge in the last few years corresponds to a nationwide surge in shale drilling, which requires disposal of millions of gallons of wastewater for each well. According to the federal Energy Information Administration, shale-gas production grew, on average, nearly 50% a year from 2006 to 2010.”

As for the associated increase in earthquakes, the USGS scientists said that “a naturally occurring rate change” of the magnitude shown by their data “is unprecedented outside of volcanic settings or in the absence of a main shock, of which there were neither” in the central United States.

Their conclusion: “While the seismicity rate changes described here are almost certainly man-made, it remains to be determined how they are related to either changes in extraction methodologies or the rate of oil and gas production.”

The absent “main shock”, then, along with much more research, lies ahead.

For now, says Romm – who testified last year before an energy department panel that examined fracking’s environmental impacts – it’s time to “start developing national standards to minimise these earthquakes”.

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新闻更新——2012年4月13日

据路透社报道,美国总统奥巴马刚刚颁布了一项行政命令,成立一个内部小组监管页岩开发,其中包括“水压裂法”开采事宜。该监管小组由至少13名联邦机构和环保部门代表组成。——玛丽安·贝德

News update - 13 April 2012

Reuters reports that US president Barack Obama has just issued an executive order creating an interagency group to oversee shale-gas development, including "fracking" issues. The group is to include representatives of at least 13 federal agencies, including the defense, interior and energy departments and the Environmental Protection Agency. -- Maryann Bird


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