Hydrocarbon Processing - November 2021 - 67

Water Management
M. YANG, TÜV SÜD National Engineering
Laboratory, Glasgow, Scotland
Impact of inaccurate water-in-oil measurement
Water-in-oil content is an important
Measurement of water-in-oil can be carparameter
for both the upstream and
downstream sectors of the oil and gas industry.
Water is co-produced during oil
and gas production as a byproduct, and
as oilfields mature, water production often
increases as a result of water injection
for reservoir pressure maintenance. The
increasing presence of water in production
fluids can lead to process capacity
issues, which affect oil/gas/water multiphase
separation and, consequently, the
quality of oil and gas for export. The presence
of water in an export crude oil and/
or gas can not only impact the sales value,
but also lead to operational issues such as
pipeline corrosion or hydrate formation,
as well as problems in downstream refining
and refinery operations.
For the upstream oil and gas industry,
water-in-oil content is also referred to as
water cut and is included in multi-phase
flow measurement for production monitoring,
allocation and well testing operations.
Knowledge of the proportions of
oil, gas and water from individual wells
helps to maximize the production rate
and, ultimately, the overall recovery of
the oil and gas from a particular field.
For custody transfer and/or allocation,
water-in-oil content must be determined
accurately and discounted, as
it is not a commodity. Here, water-in-oil
is usually low and is measured as part of
basic sediment and water (BS&W), a
key quality parameter in custody transfer
and crude oil sales.
Accurate measurement of water-in-oil
is therefore essential for the oil and gas industry,
both upstream and downstream.
Inaccurate measurement could lead to
production process problems, transportation
issues, pipeline integrity concerns
and loss of revenue from the sales of commodity
oil and/or gas, as well as refinery
operations problems.
ried out by sampling and subsequent laboratory
analysis using standard methods. It
can also be achieved using online waterin-oil
measurement devices-at least four
techniques are known to have been commonly
used and are discussed here.
Production,
allocation,
transportation
and custody transfer. In oil and
gas production, well fluids containing a
mixture of oil, gas, water and solids are
brought to the surface where production
separators are used to separate the
mixture into gas, oil and water and solids
phases. The gas separated is then compressed,
dehydrated and exported (or
flared, as an option), while separated oil is
sent for export. Solids accumulated inside
the separator are periodically removed,
cleaned and discharged-if this is permitted-in
an offshore environment. Separated
water then goes through a treatment
process where oil and solid contaminants
are removed. The cleaned water is then
either discharged for disposal, re-injected
for reservoir pressure maintenance, or reused
for agriculture, irrigation or hydraulic
fracturing operations purposes.
Production fluids can come from wells
in the same oil and gas field, but they can
also come from different fields owned
by separate operating companies. Therefore,
well testing using a test separator, as
shown in FIG. 1, is periodically carried out
to establish the rate of oil, gas and water
produced by the individual wells. Knowledge
of the rate and proportions of various
phases in the individual wells allows for
the overall production to be optimized.
In cases where well fluids from different
operating companies are processed, it is
essential that the total rate of oil, water and
gas are correctly calculated and " allocated "
back to the individual wells and their owners
to ensure each obtains a fair share of
the production fluids. Allocation is a process
rooted in the need to distribute the
FIG. 1. Schematic of production and well test arrangement.
Hydrocarbon Processing | NOVEMBER 2021 67
Hydrocarbon Processing - November 2021

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