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Introduction
The injection of waters, both aquifer and seawater, is extensively
used to support and maintain the production of oil and gas.
The main physical treatments of injection
water are:
- Filtration
- De-oxygenation
Filtration is performed to remove particulates,
macro-invertebrates and organic matter down to less than 5
microns in size. De-oxygenation of the water is required to
reduce corrosion and aerobic bacterial growth. Primary oxygen
removal is normally either by use of a vacuum tower or a gas
stripping tower. These reduce the level of oxygen in the water
from around 9ppm to less than 50ppb. Further oxygen removal
is achieved by the addition of an oxygen scavenger downstream
of the deaeration vessel.
Chemical Treatments
The main areas
for the application of chemical treatments associated with
water injection systems including the following:
- Injectivity problems
- Bacterial growth and proliferation
- Filtration
- Produced water re-injection
- Oxygen removal
- Erosion and drag reduction
Coagulants and Filter
Aids - these chemicals are applied to improve the efficiency
of the filtration system and aid removal of organic components,
which can contribute to foaming of injection water. Coagulants
and filter aids typically work at very low dose rates.
Oxygen Removal / Corrosion
Control - achieved by deaeration towers and by the
application of oxygen scavengers. It is vital that low oxygen
concentrations are achieved to protect the topsides equipment,
injection wells and subsea flowlines from oxidative corrosion.
Bacterial Control
– achieved by chlorination treatment (electro-chlorination
or hypochlorite addition) upstream of deaeration and batch
biocide addition downstream of deaeration. Depending on which
biocide is used, the biocide may interfere with the oxygen
scavenger and therefore scavenger should be turned off during
batch treatments.
Antifoam – generally
applied upstream of deaeration if required. Roemex have designed
non-foaming biocides for water injection treatments so as
to prevent the requirement for antifoam addition. However
if foaming is not dependent on biocidal constituents Roemex
Antifoam RX-5505 is a chemical of choice being active at low
concentrations and being environmentally friendly.
Injectivity
- in order to maximise injectivity and sweep efficiency where
no spare injection capacity exists, a polymer flow improver
/ drag reducer can be applied.
Roemex’s Range of
Water Injection Chemicals
Roemex have developed a range of products for treatment
of injection water. All chemicals have been designed to
be highly effective at low treatment rates. Roemex believe
that water injection plants should be considered in totality
and that proper chemical management and application be in
place from start up. On stream monitoring for critical factors
such as dissolved oxygen content, residual chlorides and
sulphites, plus routine bacterial population monitoring
should be applied to optimise chemical dose rates.
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Water
Injection 
