Environmental Engineering Reference
In-Depth Information
industry. We must not look back in 20-30 years and regret not taking
the actions we have the opportunity to take now.
1 Introduction
With the increasing demand for gas in the UK, declining North Sea gas re-
serves and the drive for greater energy security, attention is turning to al-
ternative domestic sources of gas. One of these is shale gas. Resource studies
for the UK are not yet complete, but early indications are that the UK may
possess considerable reserves.
1
However, very little exploration has taken
place and so its potential as an economically viable source of gas has yet to
be determined. Over the next decade it is expected that exploration activity
will significantly increase as a pre-cursor to exploitation and an even greater
level of industrial activity.
There are significant technical challenges ahead for an industry that has
no track record in the UK and these will apply during both the exploration
and exploitation phases. The process of shale gas extraction (which, for the
purposes of this chapter, includes both exploration and commercial ex-
ploitation) involves accessing gas-rich shale at considerable depth below the
ground surface and then hydraulically fracturing ('stimulating' or 'fracking')
the rock. This controlled fracturing significantly increases the permeability
of the shale by creating fissures and interconnected cracks in material that
naturally has extremely low permeability. As a result, gas trapped in the rock
is released and can flow into the well and then to the surface.
Hydrogeological considerations play a very important role in shale gas
extraction for a number of reasons. Significant volumes of water are required
to drill and hydraulically fracture the shale and some of this will need to be
sourced from groundwater. The drilling of wells from the surface to depths
of typically a kilometre or more requires penetration through geological
formations near to the surface that contain freshwater (groundwater). This
groundwater may be used as a source of water for drinking, for industry
(including food production and agriculture) and for supporting stream flow,
groundwater-fed wetlands and their associated ecosystems. The drilling ac-
tivity itself may impact on the quality of groundwater if not managed ef-
fectively, but the greatest concern arises from the potential contamination of
groundwater (and the wider environmental impact) by the constituents in
the fluid used to hydraulically fracture the shale, the water that returns to the
surface after the fracturing operation ('flowback' or 'produced water') and
the constituents of the shale gas.
Whilst there are already well-developed regulatory regimes in the UK for
hydrocarbon operations and for groundwater protection, it is not yet clear
how effective they will be for a new and unproven shale gas industry in the
UK. This chapter examines some of the key considerations for shale gas
extraction in the UK in relation to groundwater management and protection,
taking into account experience elsewhere in the world where the industry is
already established.
