INSIGHT: Earthquakes challenge 'fracking' and shale gas future

10 November 2011 16:56  [Source: ICIS news]

By Joe Kamalick

WASHINGTON (ICIS)--Two reports about possible links between hydraulic fracturing and earthquakes have raised new concerns about the drilling technique that is critical for shale gas development and abundant natgas feedstock supplies for US chemicals.

British energy firm Cuadrilla Resources said that a study it commissioned found that minor earthquakes that occurred in April and May this year where it was drilling for shale gas resources in Lancashire in northwest England were very likely the result of hydraulic fracturing (“fracking”) operations at the well site.

Fracking operations were underway at Cuadrilla’s Preese Hall-1 well about 3.5km (2.2 miles) east of Blackpool when a minor quake of 2.3 on the Richter scale was detected on 1 April and a smaller seismic event of 1.5 magnitude was recorded on 27 May.

Cuadrilla said that an independent study of the two events by European specialists “concludes that it is highly probable that the fracking at Preese Hall-1 well triggered the recorded seismic events”.

However, the UK energy company also said that the analysis showed that the minor quakes were “due to an unusual combination of factors, including the specific geology of the well site coupled with the pressure exerted by water injection”.

Basically, according to the report commissioned by Cuadrilla, the combined water, sand and chemicals slurry injected into the well under high pressure entered a pre-existing and “critically stressed” seismic fault line and triggered the fault failure, resulting in the two quakes.

“This combination of geological factors was rare and would be unlikely to occur together again at future well sites,” Cuadrilla said.

If the rare confluence of fracking operations and a failure-ready seismic fault line was to occur again, the resulting quake would not likely exceed magnitude 3 on the Richter scale, the company said.

If felt at all, a magnitude 3 quake would be likened to tremors caused by a passing truck.

The second report was issued by the Oklahoma Geological Survey, which analysed a rash of nearly 50 minor earthquakes that took place over a 24-hour period on 18 January this year near Elmore City, Oklahoma.

That report, completed in August but just recently released, said that the 43 measurable quakes ranged in magnitude from 1 to 2.8, and the majority of them occurred within 3.5km of a shale gas well being worked in the Eola Field in southern Garvin County in south central Oklahoma.

The Oklahoma Geological Survey report said that the series of quakes began about seven hours after the first and deepest fracking stage started at the Picket Unit B well 4-18.

“The strong correlation in time and space as well as a reasonable fit to a physical model suggest that there is a possibility these earthquakes were induced by hydraulic fracturing,” the state agency report said.

However, the report does note that “the uncertainties in the data make it impossible to say with a high degree of certainty whether or not these earthquakes were triggered by natural means or by the nearby hydraulic fracturing operation”.

While the Oklahoma incident is less clearly tied to fracking than the UK example, both reports have triggered new concerns among environmentalists about the safety of hydraulic fracturing.

The Natural Resources Defense Council (NRDC) in the US referred to the two Lancashire seismic events as “relatively large earthquakes” and said those incidents and the Oklahoma quakes have caused “researchers and the public to become increasingly interested in the potential for fracking to cause large earthquakes”.

The 5.6-magnitude earthquake that struck east of Oklahoma City on 5 November, causing serious damage to some homes and other buildings but no fatalities, was significant because the state is considered seismically stable.

The last Oklahoma quake of comparable intensity was in 1952, when a 5.5-magnitude trembler rattled the Oklahoma City area.

There has been some speculation that fracking operations in the state may have stimulated or weakened existing fault lines, triggering the 5 November quake.

Not so, according to the American Petroleum Institute (API).

“The extent to which there is any correlation between hydraulic fracturing and reported seismic activity is not known,” said API spokesman Reid Porter.

“We are not aware of scientific research that ties hydraulic fracturing to seismic activity, or that suggests there is any risk to human health or homes or structures,” he said.

“The overwhelming majority of hydraulic fracturing operations, even including hydraulic fracturing in high-activity development plays for both natural gas and oil, take place without any reported seismic activity whatsoever – and this over a 60-year history of fracking operations,” Porter added.

“Even in the isolated instances where hydraulic fracturing activity is alleged to have played a role in seismic events... we have not seen evidence of harm to human health or to homes and structures,” he said.

The Independent Petroleum Association of America (IPAA) has also challenged any links between fracking and quaking.

The association, whose member firms drill more than 90% of US oil and gas wells, noted that while Oklahoma has not seen an earthquake such as the 5 November trembler since the 1950s, the Oklahoma Geological Survey study itself pointed out that lower-intensity quakes in the 1 to 3 magnitude range are common in the state’s south central area.

IPAA was also critical of NRDC for calling the two UK quakes “relatively large”, noting that both of the Lancashire earthquakes, of magnitude 1.5 and 2.3, would be classified by the US Geological Survey as “minor” and are so mild that they are rarely felt by people.

The drillers group also pointed out that hydraulic fracturing has been employed in some 1.2m oil and gas well developments in more than 25 states over nearly 65 years.

But the environmental advocates at NRDC and elsewhere are not persuaded.

“In an attempt to allay concerns about the unknown risks related to hydraulic fracturing, representatives of the oil and gas industry often state that fracking has been used for over 60 years,” NRDC said, adding: “Yet these and other incidents make it clear that there is still a great deal that is not understood about this process.”

Fairly or not, the earthquake issue serves to add another layer of concern to the fracking process, which is already under scrutiny by federal and state lawmakers and regulators over the technique’s use of, and possible contamination of, water supplies.

Those uncertainties may complicate the future of shale gas development in the US, although they are not likely to halt it.

By: Joe Kamalick
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