Flexlilfe, the subsea support company, has achieved a major milestone by overseeing the successful installation of a 6.7km pipeline bundle at Apache's Bacchus field development.
In 2009, Apache awarded Flexlife a subsea engineering and pipeline operational support contract to oversee the management of Forties subsea projects and routine maintenance of subsea pipelines and subsea infrastructure.
Via Apache's main Bacchus contractor Subsea 7, Flexlife managed the engineering, procurement, fabrication and installation of the pipeline bundle and a riser caisson. Integrated with towhead fabrications at each end (weighing 190-tonne and 106-tonne), the 6.7km, 40.5-inch diameter pipeline is one of the longest elements of North Sea infrastructure installed in recent years.
The Subsea 7 contracted bundle comprises two insulated 6-inch piggable production lines, two insulated 4-inch heating/produced water reinjection lines, a gas lift line, scale inhibitor and control system lines. The latter include electrical power and instrument cables, high and low pressure hydraulic lines, a chemical injection line and a methanol line.
Subsea 7 fabricated the bundle at its Wester site facility in the north east of Scotland. After the towheads were integrated to the pipeline bundle, there was a 4-week programme of onshore tie-ins and testing followed by a site integration test programme to prove control system functionality.
A specialist fleet of vessels mobilized to Sinclair's Bay near Wick to undertake the bundle launch. Under control of site based Launchmasters, the launch commenced with two leading tugs being connected to the large 190-tonne Bacchus towhead via pre-installed wire rope pennants. When weather and tide conditions were suitable, the 6.7km long bundle assembly was pulled into the sea via a launchway specifically installed on the beach.
With the bundle floating several meters above the seabed, a trail tug was connected, the site holdback winch released and control passed to an ROV support and command vessel. The move to the field commenced with the tugs applying sufficient power to place the bundle into a suspended catenary known as the Controlled Depth Tow Method.
The command vessel towmaster was provided with real time information on bundle position, depth, shape and catenary via an acoustic link with the bundle's in-built "data highway". This allowed tow parameters to be adjusted to maintain full control of the bundle to compensate for effects of movement, weather and tide.
Arriving in the field, the bundle was laid down in a pre-surveyed parking area where final checks and weight control adjustments were made before the tow fleet was reconfigured by placing one of the two large tugs at each end for the final "off bottom" tow to the installation area. In off-bottom tow the bundle floats 4 to 5 meters above the seabed and is moved at between 1 and 2 1/2 knots to its final destination, being a pre-surveyed area with a target box at each end. The acoustic monitoring system was again deployed to ensure accurate positioning of both bundle ends.
Later this year, over a number of diver interventions, the bundle will be tied in to the platform and the three new wells and then tested. Tie in to the platform is achieved via the 149-tonne, 48" diameter riser caisson that the project safely installed in September 2010. The riser caisson houses riser pipelines, chemical injection and control tubing as well as control cables.
Andrew Hoggarth, Flexlife's Bacchus project manager said: "Compared with an individual pipeline concept, the bundle solution is a cost-effective means of controlling pipeline temperature to yield field-life corrosion, hydrates and wax management benefits. It yields significant vessel time cost savings by avoiding multiple individual pipelay installations. The piggable lines enable production rates to be optimized throughout field-life and allow individual wells to be routed to the test separator when necessary. Additional subsea connections are provided to facilitate installation of potential future tie-backs to maximize hydrocarbon recovery."
In support of the Bacchus development, Apache awarded Petrofac a contract for brownfield engineering, procurement, fabrication and offshore construction of the topsides modifications. The scope includes tie-ins to process and utilities systems, new subsea control, emergency shutdown, fire and gas and safety systems.
Weatherford Production Optimisation was awarded the contract to provide the subsea control system, comprising tree and manifold mounted control modules, hydraulic power unit and a spare tree set. GE VetcoGray is overseeing the modification and testing of the subsea horizontal trees.
Discovered in May 2005 in UK Central North Sea block 22/6a, Bacchus field development is based on recovering significant quantities of oil and gas. The field is operated by Apache (50%), partnered by Endeavour (30%) and First Oil (20%).
The Bacchus field has an anticipated 15-year life and peak production is estimated to be 18mbopd and 5.7mmscf/d gas. The Rowan Gorilla VII jack-up rig is expected to arrive at the Bacchus location in June to start drilling the three producing wells.
Flexlife is an industry leader in delivering subsea integrity management and subsea project management.
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