American Oil and Gas Reporter - July 2020 - 45

SpecialReport: Proactive Chemistry
drilling, completion or remedial workovers.
Bacteria are found in oil and gas production in two basic states, either planktonic (free floating) or sessile (attached).
Although planktonic bacteria make some
contribution to corrosion, the greatest degree of corrosive attack occurs when the
bacteria become sessile and attach to the
metal surface. During normal operations,
the velocity of the produced fluid moving
through the lateral and up the tubing
string limits bacterial corrosion. While
some bacteria have a stronger affinity for
attachment (becoming sessile), all benefit
from a stagnant fluid.
In addition, most operators monitor
bacteria levels in production operations
and apply an Environmental Protection
Agency-registered biocide to sanitize
the produced well, surface vessel or
tankage when bacteria numbers reach a
certain level.
Past shut-ins of conventional production
taught the industry about the corrosion
potential of bacteria present in wellbore
brines. To offset or limit this corrosion,
fluids used to circulate a corrosion inhibitor
prior to the anticipated shut-in have been
treated with a biocide compatible with
the corrosion inhibitor. These usually
were based on quaternary ammonium
compounds (quats), or blends of quats
with glutaraldehyde. Including these
chemicals in the circulated fluid prevents
or severely limits the growth of bacteria
in the wellbore during the shut-in period.
Again, given the circumstances at
the time, it is unlikely that shut-in unconventional oil wells were treated properly with a biocide pill. If bacteria have
been known to be a problem in these
wells or their surface equipment and
tankage in the past, it is likely that bacteria will grow and become more sessile
in the wellbore fluids. To limit damage
to downhole tubulars and the integrity
of surface separation equipment and
tankage, wells returning to production
should be treated down hole with a biocide pill of an EPA-registered biocide
mixed with clean lease brine (assuming

the brine is bacteria free) or 2% potassium chloride. This treatment can be in
conjunction with surfactant/corrosion
inhibitor treatment.
A biocide known to be compatible
and harmless to the corrosion inhibitor
film should be selected and applied at a
rate of 500-1,000 parts per million. Posttreatment, the well brine should be tested

for bacteria concentration to determine
if a second sanitation is necessary.
Paraffin Waxes
The crude oils produced from unconventional wells often contain some
percentage of paraffin waxes, organic
compounds typically composed of 1870 linear or branched carbon molecules.

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American Oil and Gas Reporter - July 2020

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