Deep 7 - May 2013 - Subsea 7

04
Recent riser developments
Dr Stuart N Smith, Vice President Technology & Asset Development
Over many years, Subsea 7 has developed a unique suite
of riser concepts and related technologies to meet a wide
range of specific field characteristics, such as water depth,
environmental conditions, host specification, hydrocarbon
composition and client preferences.
The continuous development of our riser technology is of
great strategic importance in enabling our clients to meet the
demands associated with ever-increasing challenges of water
depth, corrosion, fatigue and harsh environments.
Looking to the future, the growing demand for increased
corrosion resistance, high-pressure capacity requirements and
fatigue life is driving the need for new materials. High-strength
steels and composite materials such as carbon fibre are now
being considered as realistic future technological alternatives
to conventional carbon steel. We are actively engaged in
developing and qualifying a number of these novel initiatives
(see page 6).
The following overview provides an update of Subsea 7 riser
developments associated with challenging offshore projects
around the world.
Hybrid Riser Tower (HRT)
The Hybrid Riser Tower concept is a complex
and effective riser system pioneered by Subsea 7
over 15 years ago to gather all carried fluids for a
deepwater or ultra-deepwater field into a vertical
bundle for transfer to an FPSO.
Subsea 7 is currently constructing two HRTs in
Angola for Total’s CLOV project in 1,300m water
depth in Block 17. As part of our continuous
development programme, we are focussed on four
main areas:
• Investigation of the hydrodynamic behaviour
which is sensitive to Galloping, VIV and VIM,
through Basin test campaigns and CFD
computations.
Hybrid Riser Tower
Steel Catenary Risers (SCRs)
• Investigation of the use of non-metallic materials to save
weight and reduce the amount of buoyancy required.
Steel Catenary Risers (SCRs) are a preferred riser system for
many field developments due to their cost efficiency, ease of
installation and track record. Installation can typically be by
all three methods available from Subsea 7: J-lay, S-lay and
reel-lay.
Subsea 7 installed the first-ever metallurgically clad SCR
in Shell’s Bonga development offshore Nigeria by the J-lay
method, followed by Exxon Mobil’s Erha development,
also offshore Nigeria. Installation by reel-lay has also been
performed in Brazil and the Gulf of Mexico.
• Review of our design methodology to increase its
sensitivity and efficiency by the extensive use of global
modelling approaches and fatigue calculations.
• Enhancement of our safety and maintenance
performance by developing a top tower diverless
connection system for flexible jumpers.
The programme deliverables have already produced
benefits on projects such as Total’s CLOV project in Angola,
where the use of polymer materials has been adopted for
the HTR Guiding Frames.
The Steel Lazy Wave Riser (SLWR), an innovative derivative
of the SCR, was also successfully installed on Shell’s BC-10
project off Brazil in 1,800m water depth.
A common requirement of most SCRs is the need for the
highest quality welding and inspection technology, particularly
in the case of installation by reel-lay.
Qualification of the required welding technology for reel-lay
was successfully performed by Subsea 7 to confirm:
DEEP7 May 2013