Fracking for Shale Gas ‐ Risks and Concerns Professor Robert Mair
CUEN Annual Conference Jesus College 9th June 2014
What is shale and what is shale gas? Shale is a very fine‐grained sedimentary rock formed from clay, silt or mud and is one of the most abundant sedimentary rock types in the Earth’s shallow crust Shale gas is mostly composed of methane (CH4), otherwise known as natural gas, and can be recovered from shale using hydraulic fracturing i.e. fracking A shale outcrop in the UK
Source: British Geological Survey
Public perceptions
Key concerns • Seismicity Small earthquakes occurred in Blackpool area April‐ May 2011 associated with hydraulic fracturing
• Environmental Widespread concern in USA following incidents of contamination of groundwater and drinking water supplies
Report can be downloaded from http://royalsociety.org/policy/projects/shale‐gas‐extraction/report/ or http://www.raeng.org.uk/news/publications/list/reports/Shale_Gas.pdf
Royal Academy of Engineering and The Royal Society Report on Shale Gas extraction in the UK
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Independent review of the risks undertaken for the UK Government Chief Scientific Adviser, Sir John Beddington: www.raeng.org.uk/news/publications/list/reports/Shale_Gas.pdf
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Committee Members: Professor Robert Mair CBE FREng FRS, University of Cambridge (Chairman) Professor Michael Bickle FRS, University of Cambridge Dr Dougal Goodman OBE FREng, The Foundation for Science and Technology Dr John Roberts CBE FREng , Chairman, Royal Bank of Canada (Europe) Professor Richard Selley, Imperial College Professor Zoe Shipton, University of Strathclyde Professor Hywel Thomas FREng FRS, University of Cardiff Professor Paul Younger FREng, University of Glasgow Dr Dougal Goodman
Terms of reference • Requested by Sir John Beddington FRS, Government Chief Scientific Adviser • Independent review of scientific and engineering evidence • What are major risks associated with hydraulic fracturing to extract shale gas? ‐ geological, ie seismicity ‐ environmental, eg groundwater contamination
Shale Gas Exploration in USA Drilling site
Shale gas exploration in Wyoming (Jonah Field) J. SARTORE/National Geographic Stock
Density of Drilling Operations In the USA: 3.5 platforms / km2 On average 6 wells per platform platforms
1-1.5 km (potentially longer)
Source: Wood et al., 2011; University of Manchester
Shale Gas Production
Production site
Source: Caudrilla Resources
Wellhead
Environmental Risks: Possible causes of groundwater contamination • Surface operations: inadequate treatment of wastewater or spillage of chemicals • Faulty well construction • Fracture propagation or migration of solutes or methane through ground
Well integrity • Importance of preventing shale gas
from leaking out of the well by isolating it from other subsurface formations • A series of holes (‘wellbores’) of decreasing diameter and increasing depth drilled and lined with steel casing, joined together to form continuous ‘strings’ of casing • Cement provides structural support as well as isolation of different rock formations ‐ pumped down wellbore and up between casing and rock until it reaches surface
Briskin (2012)
Briskin (2012)
Passive seismic reservoir monitoring: Microseismicity • Monitoring stress state of the reservoir. – hydrocarbon migration, fluid pressure, borehole breakout.
• Many applications from conventional earthquake seismology. • Relatively new oilfield technology. P
S
Comparisons of fracture growth and depth of overlying water sources (aquifers or water wells) (Fisher and Warpinski, 2012)
