How safe is shale gas extraction?
Gas exploration companies drill boreholes down into the gas-bearing shales, thousands of metres below the surface; drilling may also continue horizontally.
The borehole is lined with a steel and concrete casing.
A 'perforating gun' is lowered into the borehole to make small holes in the concrete casing at the depth of the shale target.
A mixture of water, chemicals and sand is pumped — at very high pressure — along the borehole and through the perforations which fracture the shale.
The water opens up cracks in the rock, and the sand grains lodge into the spaces and keep them open, allowing the released gas to flow out of the rocks and to travel back up the borehole casing.
How do we know if shale gas is leaking?
The BGS has recently started (2011) a baseline study for groundwater methane in areas likely to be prospective for shale gas. It will involve sampling groundwater from water wells, and determining concentrations of natural methane and its origin (thermogenic or biogenic).
The results will help us to identify any future impacts on shallow groundwater that might result from fracking or shale gas extraction.
The project is part of a wider national programme of groundwater characterisation that includes:
- aquifer characterisation and testing
- chemical, isotope and environment tracer analysis
- groundwater age dating
- conceptual model development
- development of risk screening tools and models
Understanding how shale gas could leak
We need to further our understanding of how shale gas could leak from wells through laboratory studies of fluid and gas movement in shales.
Underground stress states and temperature conditions can be simulated in the laboratory to quantify the following key properties:
- gas permeability
- anisotropy ratio
- capillary entry pressure
- gas permeability function
- fracture transmissivity
Seismic study and monitoring
This involves the study of regional baseline seismicity and stress regimes to understand what events are unusual and how shale gas extraction and fracking water disposal might cause earthquakes.
Monitoring of current fracking operations.
More about the environmental impacts of shale gas extraction
Contact
Contact Prof. Mike Stephenson for further information or enquiries about BGS shale gas consultancy services
