1st March 2016
“Taking the stress” out of fracking
Scientists at the British Geological Survey (BGS) have today published ground breaking
research that will reduce the risk of earthquakes and borehole damage caused by
Fracking for shale gas has proven controversial in the UK. This controversy intensified after the tremors, caused by fracking, occurred near Blackpool in 2011. All rocks in the UK are under stress and when this is released it can result in an earth tremor. As a result of the tremors, the UK government ordered an expert panel from the Royal Society and Royal Academy of Engineering to investigate the safety of fracking in the UK. A key recommendation from the panel was to undertake a complete review of stress data for the UK, and the BGS was best placed to undertake this review. BGS has totally overhauled the available data for the UK, and is recommending that all new boreholes drilled for shale gas are logged by borehole imaging tools to better understand in-situ stress.
In the early 1990s mapping of the UK in-situ stress orientation, was hampered by the limited data and computing power available at that time. In the intervening period the coal and oil industries have begun collecting a new type of data called borehole imaging which scans the entire inner circumference of the borehole. This allows zones of the borehole wall that have been widened by in-situ stress (borehole breakouts) to be identified. The new data allows breakouts to be imaged much more clearly and so we can interpret much smaller features allowing breakouts to be identified in many more wells under UK stress conditions.
BGS now has access to data from over 90 of these boreholes from the coal and oil industry and has identified features in 37 of these which stretch from the Peak District to the Scottish Border. The BGS compared this new data with the 1990s data and, although we have not changed the basic stress orientation, we have massively decreased the uncertainty of borehole breakouts. This will help to assess the in-situ stress orientation, ensuring that regulators assessing well safety have the best data available to allow them to make properly informed decisions about borehole integrity. The BGS hopes this will allow the Department of Energy and Climate Change (DECC) and the Oil and Gas Authority (OGA) better information to properly assess the risks of any fracking proposed in new boreholes.
Professor Mike Stephenson, Director of Science and Technology at the BGS, commented “ This research is crucial to the regulators and the oil and gas industry as it is an easily applicable technique that can highlight parts of boreholes that may contain evidence of stress that is already present in rocks before fracking.”