PBIOS - October 2021 - 128

throughout development of the field. "
With oxidative biocides, Proaño says
it is easy to test waters for demand and
residual biocide concentrations during
the completion process to verify the bacteria
in the water have been mitigated. He
indicates field tests with conventional
biocides are not practical.
Treating surface waters is not enough.
" Bacteria can be reintroduced to the
water when it is mixed with proppant, "
Proaño warns. " To further complicate
matters, bacteria that are indigenous to
the reservoir can bloom after the frac because
friction reducers and other completion
chemicals have nutrients that
stimulate their growth. "
To address downhole bacteria, many
operators use biocides that can survive
and remain effective for an extended period.
" One of the challenges with these
long-lasting biocides, which can be
called extenders, is that many were designed
for freshwater. They work well in
that environment, but they lose most or
all their potency in brines. Others get absorbed
into the shale rather than staying
in the water, " he says.
Cudd has a proprietary biocide that retains
its potency even in high TDS water,
Proaño mentions. He says the base chemistry
originates in the aerospace industry
and has been used widely in the pharmaceutical
and food and beverage sectors.
" We are extremely proud of this technology,
one of the few biocides in the
market that can provide both short- and
long-term protection at an affordable
cost, " Proaño says. " Additionally, we are
working with microbiologists to develop
next-generation formulations that should
be even more effective. "
Sampling's Importance
Treating produced water efficiently but
effectively requires thorough sampling,
says Coby Reynolds, a Midland-based
chemical engineer with SwiftWater, a
TETRA Company.
" Even in an area as well-understood as
the Permian Basin, produced water quality
can vary widely, " he explains. " A treatment
process that works well on water from one
formation or bench may prove inadequate
if it is applied to a new area without confirming
the water quality is similar. "
Reynolds stresses that treatment plans
should be based on samples from several
water sources. " One of the most common
mistakes we see is designing an entire
program around one sample, even though
most of the water that will end up in a
frac pond comes from different zones,
wells and areas, " he says. " This can lead
to significant problems.
" To understand how, remember that
during completions, there is always a
chance the well will connect to and begin
producing from an unintended zone, " he
continues. " If that zone happens to be the
Bone Springs, the flowback from the well
might have 2% H2S, which can be hazardous
and has a huge effect on how the
water needs to be treated. "
To minimize unnecessary treatment
costs, Reynolds advises operators to limit
how long water sits in pits. " The longer
the water is in the pit, the more time bacteria
and other contaminants have to
grow, " he warns. " Produced water tends
to be warm and salty, so it is a friendly
environment for the sulfate-reducing bacteria
that create H2S. "
By introducing ambient oxygen to the
water, aeration systems can make the
pond hostile to SRBs while supporting
more benign aerobic bacteria. These bacteria
generally have more aggressive lifecycles
than SRBs and often outcompete
them for nutrients.
" When evaluating aeration systems,
look for systems with small bubble sizes
rather than focusing solely on turnover and
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PBIOS - October 2021

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