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Chemical Technology • July 2015
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since chlorocarbons are considered an environmental pol-
lutant. As with chlorocarbons, the presence of quantities
of organobromides has a potential health effect since they
cause malfunctioning of the nervous system and cause
damage to organs such as liver, kidneys, lungs, and cause
stomach and gastrointestinal issues [30].
Conclusions
What are the implications for shale gas produced water
treatment? In presenting the variation in composition and
particular chemicals analysed, we can make a number of
statements about produced water from shale gas wells with
regard to re-use and disposal, as well as guide research-
ers in future treatment efforts. In particular, given the salt
content correlates with the concentration of hydrocarbon,
it will be important to determine if the salt content and ion
ratios within actual shale connate waters (water trapped
in rock pores containing mineral ions) provide a link to
explaining the presence of higher concentrations of some
of the organics that are observed.
The low permeability nature of shale means that when
they are introduced to under-saturated water, solubilisation
will occur of salts, organics and other minerals that were
at equilibrium in the connate waters. After fracture treating
shale, the recovered water volume peaks in a few days (5 to
15 days is common) and then sharply declines. This short-
lived burst of water recovery describes a rapidly changing
flow environment. When the salinity profile is compared,
the produced water quickly moves from: a base frac fluid
to a mixture of base fracturing fluid and connate water to
a rich leachate and then sharply decreases in volume, salt
and mineral content to a purer connate composition with
very low recovered volumes.
Our data highlights a few issues that should be taken
into account when developing treatment strategies for
frac and produced waters to allow for their reuse. The
first issue is that unlike coal bed methane produced wa-
ters, no polyaromatic hydrocarbons (PAH) are observed,
meaning that the general toxicity of the produced (frac
flowback) water is potentially lower for shale plays. This
is important since many PAHs have serious health effects
in the >0,2 µg L
-1
level.
The second issue is that while many of the chemicals
used in the frac process are identified as being present in
the produced water, they are lower in concentration than
those that were naturally present in the connate waters
within the shale. Thus, subsequent treatment of shale
produced (and flowback) water should concentrate on the
removal of saturates rather than the remaining aromatic,
resin and asphaltene groupings. This analysis should also
be used as a guide for creating a ‘standard’ or ‘idealised’
shale produced water so that the efficacy of any treatment
may be measured.
The presence of chlorocarbons and organobromides
is, we believe, most probably due to the interactions of
produced water with the salts used in hydraulic fracturing
and drilling or the chemical treatments (and pre-treatment)
of produced water.
At present, due to the high bacteriological content of
natural waters (and also produced water upon standing in
ponds which is blended with ‘fresh’ water), chemical treat-
Figure 3 The relative saturate, aromatic, resin and asphaltene (SARA) composition for
produced water: (a) neutral and (b) acid extraction.