American Oil and Gas Reporter - June 2017 - 60

SpecialReport: Offshore & Subsea
the produced fluid.
Reservoir energy (source, level and
drive mechanism) plays a large role in
determining whether a subsea processing
or boosting technology is needed. If a
reservoir has low energy or there is a
large pressure drop between the reservoir
and the bottom hole because of the formation's low relative permeability/porosity
or depth, a boosting or artificial lift technology may be needed.

Fluid characteristics such as pressure/volume/temperature properties, gas-to-oil ratio,
viscosity, water production and emulsion
tendency dictate in large part the kind of
boosting technology to be deployed. For
instance, if a reservoir fluid has a low
GOR and remains undersaturated while
flowing through subsea flowlines, a single-phase boosting pump may be sufficient.
On the other hand, if a fluid has a relatively
high GOR and free gas flows along with

liquid phase, care must be taken to overcome
gas locking and other issues associated
with multiphase flow when selecting a
boosting technology. Obviously, a gas
compression technology will be needed if
the reservoir contains only gas.
Cost is by far the most crucial governing
factor in subsea development projects, but
another key consideration is the ability to
deliver equipment on time to assure project
schedules are met and that the time to
first oil is not delayed or jeopardized. The
number of interfaces, equipment suppliers
and subcontractors can make this process
complex and difficult to manage for subsea
processing projects. However, several subsea separation projects have been commissioned fault-free and demonstrate an
availability exceeding that of conventional
topside projects. This only can be achieved
using a disciplined, multifaceted approach
based on reliability engineering in design,
extensive qualification testing and strategies
to minimize risk.
Perhaps the most critical element is
employing a disciplined reliability strategy
throughout the design phase. Using techniques such as reliability, availability and
maintainability analysis, and failure mode
effect and criticality analysis provide
vital insight to inform front-end engineering and detailed system design. Both
operators and subsea system vendors can
benefit from the analysis of field data to
learn lessons that can be applied to
improve the availability and performance
of subsea processing systems.
There also is a strong need to improve
qualification testing processes. An extensive qualification program can help
evaluate the functional, environmental
and reliability performance of the system.
The goal of qualification testing is to
help maintain a high level of operability
for subsea systems to avoid unplanned
shutdowns and mitigate the need for
costly interventions that add incremental
HS&E risks.
Continued Future Growth
Subsea technology has expanded into
water depths approaching 10,000 feet
with tieback distances now pushing 100
miles and pressures as high as 15,000 psi
at the seabed. Longer tie-back distances,
demands for improved recovery and flow
assurance, as well as reduced topside
processing requirements all will contribute
to the continued growth of subsea processing solutions in the future.
The benefits of subsea processing-in-

60 THE AMERICAN OIL & GAS REPORTER

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American Oil and Gas Reporter - June 2017

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