Environmental Engineering Reference
In-Depth Information
Figure 2 Distribution of (a) shale and (b) aquifers across England and Wales.
England and Wales is underlain by potential shale gas source rocks and 50%
by geological formations designated as Principal Aquifers (see Figure 2).
The principal groundwater issues thought to be important when con-
sidering shale gas exploration and extraction are considered in the following
sections. These have arisen from the experience that has emerged from
elsewhere in the world, especially the United States where shale gas ex-
ploitation is now well established.
3 Water Resources
The drilling and completion of shale gas wells can require large quantities of
water, as drilling the vertical and horizontal components of the well require
water for maintaining hydrostatic pressure, lubrication and cooling of the
drill bit, and to return the cuttings to the surface. A further larger volume of
water is then needed to carry out the hydraulic fracturing process.
A review of literature associated with shale gas well drilling and stimu-
lation indicates a wide range in the values reported for water use. This
variation generally reflects the complexity of the drilling, the geological
conditions encountered, total depth of the well and length of the horizontal
sections and the number of hydraulic fracturing stages. Estimates of the
water requirements for drilling and hydraulic fracturing in different shale
gas areas (plays) in the United States, are shown in Table 4.
10
For com-
parison, the figures quoted by Cuadrilla for the drilling and hydraulic frac-
turing of their Preese Hall exploratory well in Lancashire are also shown.
11
These figures are lower than those from the United States because they only
