Environmental Engineering Reference
In-Depth Information
Pennsylvania and Ohio south-westwards to Texas, requiring the early wells to
wait several days for these formations to de-gas. Later wells have required
expensive steel casing to contain the generally overpressured gas. It was not
until the 1980s, with indigenous conventional-reservoired gas supplies de-
clining, that in the USA these were considered as a potential resource.
5,6
Early exploitation of gas from these shales was limited generally to for-
mations containing natural fractures, usually with short-lived production, a
notable exception being the Ohio Shale Big Sandy Field in Kentucky, USA,
which has been on production since the 1920s.
7
Antrim Shale production
followed in the 1930s from the Michigan Basin, but it was the advent of
hydraulic fracturing in the late 1940s which aided this development, al-
though not until the mid-1980s did entrepreneurs such as the late George
Mitchell actively target shales as a source of gas. Large-scale hydraulic
''fracs'' were developed but the sought-after breakthrough occurred when
they were used sequentially in horizontal well-bores drilled within the gas-
rich shale intervals.
8
This has led to the current boom in shale gas and oil
production in the USA (see Figure 3). However, whether this success will be
replicated in Europe and elsewhere in the world is yet to be seen, with the
ever-present attendant environmental concerns generally foremost to any
reasoned debate.
Figure 3 Map of major US shale plays.
(Source: U.S. Energy Information Administration).
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