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Quake rocks UK shale gas drilling

Steve Marshall

UK shale gas explorer Cuadrilla Resources has postponedhydraulic fracturing as part of its drilling activity in

Lancashire after another earthquake struck last week.

The 1.5 magnitude quake that hit the Fylde coast on 27 May is the second in the region

since Cuadrilla started fracking activities in March at its Preese Hall drilling site near

Blackpool.

The earlier tremor, with a 2.2 magnitude, struck on 1 April and was also centred on

Poulton-le-Fylde, only about two kilometres from the drill site in the Bowland Shale.

A Caudrilla spokesman said the company has now put shale gas fracking in the area onhold as part of a precautionary process.

It is not a halt but a pause. We have not been forced into anything, he said.

There has been some very small seismic activity. We are currently carrying out

monitoring around the drill site and downloading the data to see what this tells us.

There is no conclusive proof that there is a connection between what we are doing and

seismic activity.

The British Geological Survey (BGS) said it has been monitoring the effects of fracking

at the site.

Fracking is the process by which a mixture of water, sand and chemicals is pumped at

high pressure to shatter tight rock formations, allowing gas to flow to the wellbore

through the cracks.

Shale gas drilling in the US has sparked controversy over possible contamination of

water aquifers by fracking chemicals.

However, a UK parliamentary select committee recently gave its backing to shale gas

development, saying that environmental concerns could be overcome by tighter

regulation and monitoring.

Now experts are looking at whether seismic activity may be another environmental riskof shale gas exploration.

In a report on the April quake, the BGS said: Any process that injects pressurised

water into rocks at depth will cause the rock to fracture and possibly produce

earthquakes.

It is well known that injection of water or other fluids during the oil extraction and

geothermal engineering, such as shale gas, processes can result in earthquake activity.

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Typically, the earthquakes are too small to be felt, however, there are a number of

examples of larger earthquakes occurring.

However, it said it could not be determined whether the earlier quake was related to

fluid injection at the Preese Hall site as the nearest seismograph at that time was

located 80 kilometres away.

Instrumentation much closer to the site, as well as a detailed record of dates and

times of injection are required to identify any relationship between the injection

process and any seismic activity in future, the BGS report said.

The Caudrilla spokesman said the company would be discussing its findings from data

gathered at the site with the BGS and Keele University, which is carrying out

monitoring on its behalf.

13:20 GMT 31. May 2011 | last updated: 12:02 GMT 01. June 2011

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