August 6, 2012

expert reaction to frequency of fluid injection-triggered earthquakes

Research in PNAS suggested that fluid-injection operations—such as those used in the production of geothermal power, extraction of petroleum, and disposal of fluid wastes—may cause more small earthquakes than previously reported.

Prof Andrew Aplin, Professor of Petroleum Geoscience, School of Civil Engineering and Geosciences, Newcastle University, said:

“As a result of a US initiative to install sensitive seismic monitoring equipment for scientific purposes, this rigorous study revealed approximately 60 previously undetected earthquakes which occurred over two years in an area the size of England. It is plausible that some of the earthquakes resulted from the lubrication of geological faults by injected water. Whilst the injection of water for disposal is not the same process as fraccing in shale gas, the fault lubrication mechanism is the same as that postulated at the Preece Hall shale gas site. The important fact is that these earthquakes can be barely felt at the surface and have the same magnitude as previously observed and predicted in other gas shale and mining environments. Data such as these are critical to our understanding of risk and indicate the importance of installing similar seismic monitoring equipment in areas of the UK where drilling for shale gas may occur in the future.”

Dr Christopher Green, Director, G Frac Technologies Ltd, said:

“This is a very good paper that helps us better understand the link between sustained water injection (for enhanced oil recovery or water disposal – NOT FRACC’ING) and the potential to induce earthquakes (the references in the first paragraph are what I would consider to be primary references on the subject matter).

“This work reinforces the main recommendations of our DECC report about the induced seismicity due to hydraulic fracturing, at Preese Hall: 1) that there is a need to do a detailed seismic risk assessment before undertaking such developments, and 2) that suitable methodologies should be used during the treatment to be able to monitor and confirm the created fracture dimensions (length and height).

“This research is part of a body of work that is now under way in existing Unconventional reservoirs (UNCON’s – particularly shale) to help us better understand the risks in these developments, with good reservoir characterization and long term production/injection histories.

“Such work will optimize and better define what should then be done for future developments in the UK, but does not affect any of the recommendations made in our report about what needs to be done at the Preese Hall site, should permission to restart be granted.

“Overall, such works are of use in helping us understand what needs to be done to better quantify the risks (potential magnitude and frequency) for seismic events when planning to do similar long term injection projects, as well as shorter term injections, such as hydraulic fracturing.

“This work does indicate that any similar disposal method also needs to be properly assessed for the potential risk of induced seismicity, for future developments in the UK.”

Professor Stuart Haszeldine, University of Edinburgh School of GeoSciences, said:

“Since 2000, and especially since 2007, the oil city of Dallas (familiar to TV viewers) and the adjacent city of Fort Worth have been one of the most intensely drilled areas on earth in the search for shale gas. 14,000 boreholes exist, sometimes only a few kilometres apart. A very few earthquakes, up to magnitude 3.2, have been barely felt in 2008, 2009, 2012. These earthquakes have been linked to deep injection of waste water from drilling.

“This new study shows the scientific benefits of improved earthquake monitoring. By using an extra 25 instruments uniformly spread across a 200 x 300km region the size of central England (London to Scarborough), an extra 67 earthquakes were detected over two years, which nobody had felt at the surface. Although the study author tentatively suggests a link to re-activation of previous geological faults (like that which was proven in the UK at Preese Hall, near Blackpool), that is not conclusively borne out by the data. An equally good link can be made to the location of boreholes injecting waste water from drilling, which is not allowed in the UK.

“This study provides slightly better earthquake monitoring of the shale gas industry, and improves confidence that even in a region intensely exploited for shale gas, no significant earthquakes have been caused during a 10 year period. Lessons for the UK are to enforce better seismic monitoring within a few km radius of shale gas boreholes from the start of exploration drilling, and to continue to refuse deep injection of waste water.”

Prof Peter Styles, Professor of Geophysics at Keele University, said:

“The paper is excellent but it is important to note that the author is correlating seismicity with fluid injection wells, which has already been suggested by Austin Holland of the Oklahoma Geological Survey and, of course, lots of previous work going back to the Rangeley deep disposal wells in Colorado in the 1960’s.
“The author is not correlating these events with hydraulic fracturing per se which is what we have unequivocally in the UK Blackpool scenario.
While relevant and important this is not a contradiction or confirmation of what we have in the UK although the mechanism he suggests is what we postulated for the Preece Hall events.”

‘Two-year survey comparing earthquake activity and injection-well locations in the Barnett Shale, Texas’ by C. Frohlich, published in PNAS on Monday 6th August 2012.