DEEP7 2017 - Subsea 7 - page 14

We have also extended the reach of EHTF
tie-backs by developing efficient subsea
electrical distribution systems, based on
reliable, low-maintenance components,
which supply the EHTF heating elements
at regular locations along a flowline.
This system greatly extends the length
of heated flowlines and offers increased
operational flexibility and reliability, while
also allowing power outputs to be adapted
to changing heating requirements via simple
switching controls.
Another effective technology for enabling
long-distance tie-backs is Direct Electrical
Heating (DEH), which is based on piggy-
backing a heated electrical power umbilical
onto a wet-coated insulated pipeline.
We have a strong track record in this
technology, including the world’s first
implementation of reeled CRA-lined carbon
steel pipe with DEH active heating on
Wintershall’s Maria development in the
Norwegian Sea.
We also installed the deepest DEH system
implemented to date, for Chevron’s Lianzi
Project at a length of 43 km and water
depth of 1070 m.
DEH and EHTF are effective complementary
technologies, covering different ranges
of U-values and Overall Heat Transfer
Coefficients.
Pipeline Bundles
Pre-assembled Pipeline Bundles, in which we
are acknowledged world leaders, are another
extremely effective technology for extending
subsea infrastructure lifespans and reducing
field development costs.
Pipeline Bundles can incorporate hot water
circulated close to the production pipe
within the Bundle cross-section, as fully
preassembled subsea systems containing
multiple flowlines and service lines
packaged inside a carrier pipe.
Multi-bore Bundle-to-Bundle connector
systems are currently under development
to improve the economics for longer
tie-backs by using multiple Bundles.
We are currently assessing the efficiency
of circulated hot water in longer Bundles
in this way, with the longest installation to
date being a 27 km Bundle for BP Andrew
in 2012. Hot water Bundle systems have
the added technical advantage of heating
the Bundle-to-Bundle interconnecting
spools.
Cold Flow Systems
As tie-back distances increase beyond the
effective capability of active heating systems,
the flow assurance strategy moves from
“maintaining the temperature above hydrate
formation temperature” to “transporting
under ambient sea water temperature
conditions”.
Subsea 7’s newWCU is based on already
proven technologies. The WCU offers clients
an cost-effective strategy for achieving a safe
cold flow condition in the development of
remote subsea fields.
We are currently assessing the boundaries
of applicability for Cold Flow Systems for
various tie-back distances and host platform
alternatives, but the concept enables longer
tie-backs at significantly lower cost than with
FPSO or platform-based processing solutions.
Cold Flow Systems have game-changing
potential in remote regions where there is
a lack of existing infrastructure or where
manned processing facilities are not possible.
Future prospects
Tie-backs in recent years have successfully
brought remote resources to existing topside
installations, using non-conventional
technologies such as subsea pump boosting.
For long-distance tie-backs (i.e. greater than
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Technology Magazine from Subsea 7
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