Environmental Engineering Reference
In-Depth Information
projects. The percentage of wastewater that is being recycled is increasing as
companies become more adept at handling this waste and on-site treatment
technologies become more readily available.
2.2.2.6 Greenhouse Gas Emissions
When evaluating the overall merit of any energy source many people look at
the greenhouse gas emissions relative to the energy produced, e.g. the
amount of greenhouse gases produced by burning coal to produce elec-
tricity. In the case of shale gas extraction, concerns have been expressed that
there are significant fugitive emissions of methane associated with the
process of shale gas extraction itself.
A study by Howarth et al. published in 2010 stated ''Compared to coal, the
(greenhouse gas) footprint of shale gas is at least 20% greater''.
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Fugitive
emissions are losses of methane that occur between the well caps and the
end user. These can be as a result of leakage around the site, leaks in dis-
tribution pipelines between the well and the end user, leakage from venting,
etc. Most of these sources would be the same, whether it is a conventional
gas well or a hydraulically fractured gas well. However, the fugitive emissions
from the hydraulic fracturing process are of greater concern, as they have not
been fully examined in detail and could potentially be very high.
After hydraulic fracturing but before the well is capped and the gas piped
away for use, the well will be cleaned by flushing fluid or gas into the bore to
remove debris and also flushing away produced methane that is not prof-
itable to store or transport. In a study based on US Environmental Protection
Agency data, academics from Cornell University have calculated that the
venting of such emissions could mean that shale gas may be actually worse
for global warming than coal (see Figure 5).
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Although coal releases more carbon dioxide per unit energy than methane,
methane is a far more potent greenhouse gas - 72 times more powerful per
unit mass than carbon dioxide over a 25-year period, falling to 25 times over
a 100-year period. In the United Kingdom the Environment Agency believes
that good practice can mitigate such fugitive emissions and is considering
options to monitor air near the site to keep track of any leaks.
Venting in itself is a dangerous procedure, even if it were permitted in the
UK by the Health and Safety Executive. Cuadrilla, which is one of the leading
exploration companies operating at present in the UK, plans to flare the
methane that is produced during testing prior to the production phase.
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In the US there are also concerns about methane emissions and the US
EPA runs a voluntary program, EPA Natural Gas STAR, for companies
adopting strategies to reduce methane emissions. These procedures are
known by a variety of terms, including ''the green flowback process'' and
''green completions.''
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To reduce the emissions, the gases and liquids
brought to the surface during the completion processes are collected,
filtered and then placed into the production pipelines and tanks instead
of being dumped, vented or flared. The gas clean-up during a ''green''
