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SUBPRO Subsea Production and Processing
Sequential separation
The main topic to be studied in the sequential
separation subproject is the quality of the water
and oil phases from several separation stages,
with a focus on the water quality. Adding additional
subsea oil polishing steps as described in the “All
subsea” and “Subsea Factory” visions entails a
more complex separation system for both phases.
The composition and properties of the well stream
Project manager and PhD
supervisor, Prof. Johan
Sjöblom
PhD candidate,
Are Bertheussen
will change over the lifetime of the installation,
which also affects the water and oil quality at
different separation stages. To predict how inlet
conditions will affect the oil and water quality
at the different stages of the separation, more
knowledge is needed about the compounds that
affect the separation. The compounds of interest
in this subproject are the indigenous polar crude
oil compounds which display surface active prop-
erties, focusing on the resin fraction. This mostly
entails acidic molecules like naphthenic acids or
basic molecules like pyridines. These compounds
partition themselves between the oil and water
and affect the emulsion stability by adsorbing at
the oil-water interface. We will study the partition-
ing kinetics of acids and bases of different sizes,
and how parameters like pH and water cut affect
the partitioning.
device will be used which matches the shear rate
conditions present in the sub-sea production
system. Figure 12 shows a cartoon of the cold
finger device, which provides improved matching
of heat transfer, mass transfer and momentum
transfer conditions in comparison to traditional
cold finger designs. The development of the wax
deposition simulator will be informed by the
experimental wax deposition measurements.
Paraffin wax deposition may occur in subsea
production systems. Paraffin wax deposition
occurs because of wax crystal precipitation as
waxy crude oil is cooled during pipeline trans-
portation and subsea processing. When warm
waxy crude oil flows past a cold surface, thermal
gradients drive deposition of paraffin wax on the
cold surface. Build-up of wax deposits in a pipe-
line results in reduced cross-sectional flow area
in the pipeline, restricting fluid flow. At extended
tie-back distances, wax deposition may become
a more severe problem due to greater thermal
losses.
A new simulation model is under development to
provide improved forecasts of wax deposition rates
applicable to extended tie-backs and sub-sea
processing units where the bulk fluid temperature
drops below the wax appearance temperature
(WAT). The simulator will predict the build-up of
wax deposits as well as aging of wax deposits. The
simulator will provide predictions for untreated
fluids as well as fluids treated with polymeric wax
inhibitors.
A cold finger apparatus is used to experimentally
measure wax deposition rates. A cold finger
Modelling of wax deposition
Project manager and PhD
supervisor, Associate
Prof. Kristofer Paso
PhD candidate, Jost
Ruwold
Figure 12. The coldfinger apparatus, with cold and
hot water flows labelled with blue and red arrows.
Researcher, Dr. Sebastien
Charles Simon