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Chemical Technology • July 2015
and the well begins to produce hydrocarbons, the water
that comes to the surface is now called ‘produced water’.
Generally this water has far lower or no amounts of the
engineered components that were added to the frac water
initially. However, the chemical make-up of the production
water may still include quantities of chemicals and materi-
als, such as inorganic salts, bacteria and organic molecules,
with the organic molecules being either naturally occurring
or a residue from the added components. Shale gas wells
produce most of their water within the first few weeks of
production. Subsequently, a few barrels a day are com-
monly produced.
Given that projections of cumulative net water used in
all shale plays during the next 50 years totals 4 350 Mm³,
there is an incentive to reuse frac flowback and produced
water for hydraulic fracturing. Unfortunately, produced
water is often unsuitable for reuse in frac fluids due to
high dissolved salts and high organic content, including:
hydrocarbons, greases, and biological matter. Furthermore,
produced water discharges offshore have been shown to
be toxic to marine organisms [10, 11] and hence it is illegal
for recovered waters from shales to be released into rivers
or groundwaters. However, concerns still linger with regard
to accidental spillage and exposure.
In an attempt to eliminate exposure of waste produced
water to the environment, companies use enclosed fluid
capture systems. One common disposal practice in the
Barnett Shale production area of Texas involves re-injecting
the wastewater fluids back into the ground. Unfortunately,
this is not a long-term solution, and it will be necessary to
clean produced water for reuse in hydraulic fracturing. The
chemical and physical characteristics of produced water
from conventional and unconventional oil and gas reservoirs
worldwide and the potential treatment options for the waters
have been reported [12–14]. However, in most cases the
organic content has been described by the total organic
content (TOC) rather than the individual species present. A
detailed study by Orem
et al
has investigated the identity
of organic compounds in produced water for coalbed gas
wells [15] but this source presents different issues to those
WATER TREATMENT