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Akpo – A Giant Deep Offshore Development
Rig Specialisation pipelines. Considerable effort is dedicated to preparing for the offshore
The Akpo development wells will be drilled and completed by two fifth- installation campaign, first to ensure as much installation work is
generation dynamically positioned drill ships, which have been completed as possible before the FPSO arrives, and second to reduce
contracted to perform Akpo development drilling. The Transocean the SCR and umbilical connection time to the FPSO.
Deepwater Discovery spudded the first well of Akpo development in
early August 2006 and is dedicated to drilling operations only, the wells Floating Production, Storage and Offloading
being temporarily abandoned after the drilling operations. To further The FPSO is at the heart of the Akpo development. A consortium of
optimise the operations, riserless phases are drilled in batches of five TECHNIP France and Hyundai Heavy Industries (HHI) was contracted
wells. The Global Santa Fe Jack Ryan will be upgraded to accommodate to perform the detail design, engineering, procurement and
the Akpo-specific drilling equipment/tools and will complete each construction of the FPSO. TECHNIP has the responsibility for the detail
of the wells. engineering of the topsides and HHI for the detail engineering of the
hull and the fabrication of the FPSO in their yard in Ulsan, Korea.
Deepwater Discovery Dynamic Positioned Drill Ship
There are several main benefits of such a specialised rig strategy, The hull is a purpose-built vessel of impressive dimensions measuring
including savings on costly rig upgrades as only one rig will be modified 300m long, 61m wide and 31m high (keel to hull deck) The hull has 13
to run the completion and trees, progressive start-up of drilling off-cargo tanks (dispatched in three rows along the hull) to store the
operations to efficiently set up all human, services and logistic supports, stabilised Akpo condensate in addition to the usual storage for diesel,
a better learning curve on each specialised rig and improved efficiency methanol and ballasting requirements. Total displacement weight is in
of offshore crews, who will rapidly become familiar with a reduced excess of 400,000 tons at full capacity. The accommodation module
number of complex operations. All of the above will contribute to has capacity for up to 240 people and a helideck.
improved drilling performance and deliver the planned 22 wells at
start-up of Akpo facilities. The hydrocarbon production facilities and support systems are
encapsulated in 15 topside modules. Due to the large inventory of
Umbilical Flowlines and Risers Akpo high-pressure gas, the topsides process equipment is heavier
As an integral feature of the development and at the onset of the than other FPSOs of similar size. Consequently, this has resulted in
project, the SCR concept was selected. The basis for the selection the need to closely control the weight, centre of gravity, floatability
was to implement a sufficiently generic proven technology to attract and stability of the FPSO during the project.
competition for its implementation. However, the SCR technology
requires careful design, in particular in terms of the fatigue life of the The topside processing facilities are large but relatively conventional.
riser sections and more specifically for the flexjoints connecting They include a single train of four-stage separation and an
the risers to the FPSO and the touchdown section on the seabed. electrostatic dehydrator to meet the bottom sediment and water
(BS&W) specifications. The unstabilised condensate is heated (using
Not surprisingly, the fatigue life of the SCRs is very much influenced by hot water produced from waste heat recovery units) between the
the hydrodynamic behaviour of the FPSO to which they are connected. first and second stages of separation to achieve a Reid vapour
It is for this reason that the engineering, procurement and installationof pressure (RVP) of 10psia. The reservoir water, extracted from the
both the FPSO and the offloading buoy mooring was included in production separators and electrostatic dehydrator, is treated to
the scope of the umbilical flowlines and risers (UFR) contractor. The UFR achieve an oil-in-water content of <30ppm.
package was awarded in April 2005 to SAIPEM of France. The complete
scope of the work included the engineering, procurement, Although the production separators operate at HP (first stage at
construction, installation and commissioning of the following subsea 80bar, second stage at 24bar, third stage at 8bar, fourth stage at
facilities, including production and injection flowlines (approximately 2bar), these pressures and the size of the separators (e.g. first stage
110km), 14 steel catenary risers, production and injection umbilicals 4.4m inside diameter [ID] x 15.8m long) have resulted in the
(approximately 65km), offloading buoy with two x 16-inch offloading accumulation of large inventories of hydrocarbon gas and
lines, system (12 mooring lines, plus all deck equipment), gas export condensate on the FPSO.
line (16 inches, approximately 150km) tied back to the Amenan AMP2
facilities in shallow water. The UFR contractor scope also included the The safety design required installation of passive fire protection
actual mooring operation of the FPSO and the installation of 10 insulation on the large separators to extend the depressurisation
manifolds provided by the SPS contractor. period in the event of an emergency shutdown (ESD) situation.
Similarly, the application of heat shielding is required on selected
The main technical challenge has been the qualification of an areas around the FPSO to cope with radiation from the flare. Indeed,
automatic ultrasonic testing (AUT), which is technically advanced and one notable feature on Akpo is the vertical flare stack. At 128m high,
accurate enough to satisfactorily inspect the pipeline field welds during the stack is one of the tallest structures to be installed on any FPSO.
the offshore installation campaign. The benefit of AUT is that it will
allow fast and accurate assessment of weld defects, minimising the risk There is a dedicated test separator to perform well testing. A notable
of false calls and their associated slowdown of the pipe-laying process. feature is that it is designed to operate in either HP or LP mode to
Due to the achieved accuracy of the automated process, weld provide operational flexibility. The associated gas from separators is
procedures can be developed more efficiently and greatly increases compressed and dehydrated via a glycol (TEG) contractor in order to
confidence in achieving the predicted fatigue life of the completed minimise the risk of hydrate formation in the gas export pipeline and
EXPLORATION & PRODUCTION – VOLUME 7 ISSUE 2
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