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Akpo – A Giant Deep Offshore Development
maximise the efficiency of methanol packing during a cool-down offshore environment. Thirteen selective completions are planned in
scenario, and it facilitated the retrieval of the trees or manifolds the Akpo development. The main challenges include the integration of
without having to lift the spools or jumpers. completion design and equipment with the intelligent hardware in
each type of sand control and the qualification and development of the
The subsea equipment is designed with the ever-present threat of completion equipment and their successful installation to assure their
hydrate formation. Insulation requirements are demanding, and the reliability during field life in Akpo pressure and temperature conditions.
high wellhead flowing temperatures have prompted the use of
phenolic resin insulation. In the event of any item of equipment failing, Well Architecture
there is a high level of redundancy in the control systems and greatly The well architecture is based on the lessons learned from the
assists in ensuring the availability of equipment. exploration wells drilled on OML 130, and takes into account
the constraint of the well completion designed to meet the production
The equipment is modular designed, which means that trees can be objectives. Akpo development architecture includes four casings: 36-inch
separated from the wellheads, leaving the downhole completion intact. CP, 20-inch surface casing, 14-inch technical casing and the production
All chokes, subsea control modules (SCMs), distribution units on the liner. The production liner has a 10
3
⁄4-inch outside diameter (OD) for oil
manifold, accumulator packages, flow-line jumpers and electrical and producers and gas injectors to accommodate selective completions, and
hydraulic flying leads are individually retrievable. For each SCM, there
are two independent control paths: electrical and hydraulic. No two
trees share the same two lines.
The Akpo development is the
CAMERON is the SPS contractor and provides the engineering,
first TOTAL deepwater-operated
procurement and supply of Akpo SPS. This was a worldwide operation,
with the wellheads being manufactured in Singapore, Xmas trees and production in Nigeria.
connectors in Leeds (UK), manifolds in Berwick (US) and Wari (Nigeria)
and the control system in Celle (Germany).
The implementation of strict quality-control processes and procedures a 9
5
⁄8-inch OD for water injectors. The 20-inch surface casing is set above
during the manufacturing stages is paramount. The cost to the project the top gas occurrence. The 14-inch casing is set where a sufficient FIT
of discovering and rectifying defects during the manufacturing stage is can be obtained to drill through the reservoir. The liner is run to total
considerably less than having to deal with failures in service. Each depth (TD) in the Frac Pack wells or to the top targeted reservoir in wells
component is subjected to a series of factory acceptance tests. Each completed with open hole sand control. High casing specifications have
assembly, such as a complete tree or a complete manifolds is subjected been selected to resist the loads generated by HP and temperature
to an extended factory acceptance test. Finally, a one-off site conditions. In addition, pressure mitigation means are integrated in the
integration test of a representative part of the complete tree manifold architecture of the well producers and gas injectors to limit the loads
control system is also carried out. It is only after all these tests are created during production/clean up by the annuls pressure build-up (APB)
satisfactorily completed that you can say with confidence that the in closed casing annuli.
equipment will perform as intended in service.
The pressure mitigation means includes the choice of a production liner
Well Architecture and Development Drilling Strategy to minimise the number of close annuli, syntactic crushable foams
around the 14-inch casing and pressure burst disc in the 20-inch
Well Philosophy casing. All of them have been through an extensive qualification and
The reservoir development plan is based on multizone reservoir targets testing process to match Akpo pressure and temperature requirements.
intersecting several channel complexes or lobe compartments to optimise
the number of wells. This strategy calls for selective completions in Well Trajectory
producer and gas injector wells, allowing monitoring and control The wells have 3D trajectories and are J- or S-shaped or horizontal,
of production from subreservoirs with different dynamic behaviours. depending on reservoir target inclination. The dog leg severity is
maintained below 3º/100ft and the inclination of the slant section is
Well Completion maintained >50º where possible to allow wire line intervention.
The reservoir sands are unconsolidated and heterogeneous, requiring Horizontal drains are 1,200m long and are drilled with horizontal
three different sand-control technologies – stand-alone screens, departures up to 3,000m.
expandable screens and Frac Pack – depending on well type and
trajectory. Selective zone isolation in open holes at the Subsea Positioning
reservoir–wellbore interface is provided by an open hole packer, which The wellhead positioning tolerance circle of 2.5m radius requested by
is run with the sand-control systems; innovative annulus barrier tools flowline installation constraints and SPS for well connections requires
have been specifically developed for Akpo applications. an advanced and reliable subsea positioning system. The Akpo strategy
includes the use of a long baseline (LBL) positioning system in
The selective completions will include downhole valves remotely combination with a pre-installed calibrated transponder stand subsea
actuated from the FPSO with hydraulic lines. This intelligent completion array, which is the common reference used by all of the offshore
design will help to minimise costly well interventions in the deep installation spreads and drilling units working on the Akpo field.
EXPLORATION & PRODUCTION – VOLUME 7 ISSUE 2
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