Terra Nova FPSO sets sail for NewfoundlandVessel & ROV News // March 22, 2000
The FPSO will travel through the Indian Ocean, the Suez Canal, and across theAtlantic Ocean, to arrive in late May at the Bull Arm site, Newfoundland. Onceberthed at the Bull Arm site, it will undergo seven months of hook-up andcommissioning work prior to its journey offshore to begin producing oil from theTerra Nova oil field.
Gary Bruce, Chairman, Terra Nova Management Committee and Vice-President,Petro-Canada, Terra Nova's field operator, said, "This is an important milestonefor the project and we look forward to its arrival in Newfoundland. By the timethe vessel arrives all the topsides modules and the upper turret will be in Bull Arm, and we'll begin the next phase of the development - topsides hook up andcommissioning."
"We have come a long way in just over two years but there are still challengesahead for us over the next 12 months," he added. "Our focus remains the deliveryof a top quality FPSO vessel to operate safely and efficiently on the Grand Banks. We are looking forward to the day when the Terra Nova FPSO, once installed offshore, will start production of the second major oil field off Newfoundland and Labrador, further establishing the oil and gas industry here".
The Terra Nova FPSO is 292m long with a breadth of 45m, and from keel tohelideck is as tall as an 18-storey building. It is designed with a productioncapacity of up to 150,000 barrels of oil per day, and a storage capacity of 960,000 barrels.
In the next few weeks, the Water Injection Module (M03), Separation LPCompression Module (M05) and the Upper Turret will also set sail forNewfoundland.
The Water Injection Module (M02), Produced Water/Glycol Module (M04), Power Generator Module (M09), Flare Stack and deck assemblies under construction in Bull Arm will also be completed soon. All modules will be lifted aboard the FPSO after it arrives inBull Arm.
Over the summer and autumn, the FPSO vessel will undergo hook up and commissioning, in preparation for the planned voyage to the Terra Nova field toward the end of the year.
The FPSO topsides facilities contain eight main modules, four of which are scheduled for completion at Bull Arm in April. The M03 and M05 modules are underconstruction in Scotland and the upper turret in Abu Dhabi are scheduled to arrive at the Bull Arm site during April. The accommodation module was included in the vessel fabrication scope.
The Terra Nova owners are: Petro-Canada (operator) (29%), Mobil Canada, awholly-owned subsidiary of Exxon Mobil Corporation (22%), Husky OilOperations Ltd. (17.5%), Norsk Hydro Canada Oil & Gas Inc. (15%), Murphy OilCompany Ltd. (12%), Mosbacher Operating Ltd. (3.5%), and Chevron CanadaResources (1%).
The Alliance consists of: Petro-Canada, AGRA Brown & Root, HalliburtonEnergy Services, FMC Offshore Canada Ltd., PCL Industrial Constructors Inc.,Coflexip Stena Offshore Newfoundland Limited and Doris ConPro Offshore Ltd.The Terra Nova oil field is located on the Grand Banks, 350 kilometres east-southeast of St. John's, Newfoundland. Discovered in 1984, Terra Nova is thesecond largest oil field off Canada's East Coast, with estimated recoverablereserves of 3 70 million barrels of oil.
The unique ice-strengthened FPSO will become operational in the Terra Nova development on Canada's Grand Banks. Located some 350km east-southeast of St John's, Newfoundland, Terra Nova is the second largest oil field off Canada's east coast, and is located in an area of relatively shallow water (approximately 95m) which is subject to particularly harsh weather conditions, high levels of icing, and icebergs during much of the year.
Development of the Terra Nova field therefore required an FPSO with some unique characteristics - the vessel needs to be capable of being relocated as quickly as possible, and if contact with an iceberg cannot be avoided, of withstanding the impact without incurring damage to men and equipment.
As Terra Nova FPSO Project Manager Bob Dunsmore explained, the Terra Nova development effort has taken advantage of many lessons learned from the Hibernia project, but many of the technical challenges of the project were being addressed for the first time.
In the same way that Hibernia - a fixed installation - has provided invaluable experience on the Grand Banks, so the Terra Nova Alliance hopes the Terra Nova FPSO will provide valuable experience for future Grand Banks developments.
Terra Nova will be the first FPSO to operate in North American waters, and the first in the harsh Grand Banks environment. At the same time, the development project is also highly innovative in a number of ways - it will make use of the latest drilling technology, including some horizontal wells, technology that has only become available in the last five years.
Terra Nova will, for instance, use horizontal Christmas trees, making it easier to perform well re-entry. The production facility will have the capacity to produce 125,000 barrels per day initially, increasing to 150,000 barrels per day whilst compressing 300 million cubic feet of gas per day. Crude oil storage capacity on board the 292.2m FPSO will be 960,000 barrels, almost eight days storage at peak production.
However, it is the unique environment of Canada's Grand Banks that really distinguish the project, and present a number of key technical challenges.
As Bob Dunsmore explains, there are three main differences between developing offshore oil facilities for the Grand Banks and developing facilities for most other locations in the world.
Firstly, the area in which the Terra Nova field lies is subject to ice as well as icebergs, a factor that therefore had to be addressed in the design of the FPSO and subsea facilities.
Secondly, the Grand Banks experiences very low temperatures during the winter months. The combination of low temperatures and waves/spray means ships and floating facilities will experience considerable icing of their superstructure. Although icing willnot impede operations, it does have to be considered in the design criteria of the facilities, thus adding to overall costs.
Thirdly, sea states combined with water depth are another challenge. The waves - which can be in excess of 30m - and swells on the Grand Banks, can produce considerable vessel motion. This is further complicated by the relatively shallow water depth (95m), and introduces special challenges in the design of the vessel, turret, the moorings and the riser system.
Having chosen a floating production solution for Terra Nova, the seasonal presence of ice and the possibility of an iceberg encroaching into the field required the design and construction of a vessel that is ice strengthened. It also required a production facility that could be rapidly disconnected from its risers and mooring chains and relocated in order to avoid a collision with an iceberg.
As Bob Dunsmore explains, icebergs migrate into the region annually mainly during the months of March to August - the 'ice season'. They range in size from thousands of tonnes up to several million tonnes, and this is also the time of the year when fog is most prevalent on the Grand Banks.
The Terra Nova development therefore has a comprehensive ice management strategy based on detection, monitoring and deflection to prevent icebergs encroaching into the area in which the FPSO and production facilities are located.
The vessel is equipped with a high-resolution ice-tracking radar. If a large iceberg approaches it the vessel and a collision with the FPSO is likely, a standby vessel will attempt to tow it out of the path of the FPSO. Historical data suggests that thisis a strategy that will be successful about 48 per cent of the time.
However, since it cannot be guaranteed that an iceberg will not threaten the platform, the Terra Nova FPSO has the capability to rapidly disconnect from its risers and moorings and move off location.
According to Brown & Root Energy Services, the FPSO will disconnect in pack ice 0.3m thick and 5/10 cover. Model tests have indicated that the hullform adopted for the FPSO will perform well in pack ice 1.0m thick which covers the surface completely.
If a collision occurs, ice strengthening of the design of the Terra Nova should prevent serious damage. The 'ice belt' on the Terra Nova extends from the turn of the bilge to 24m above the keel in the midships and aft body and from the turn of the bilgeto the lower focsle deck in the forebody.
The midbody and aftbody has a level of ice strengthening equivalent to Baltic 1A. The forebody reinforcement is significantly stronger as it is anticipated that an iceberg collision is more likely in the forebody.
In many respects, however, the Terra Nova FPSO is a conventional floater, with the turret system towards the forward end and the mooring chains and risers connected to the vessel. It shares the classic design requirements of all such ships, and providessufficient weight, space and volume required to carry its payload whilst meeting the needs of stability, structural integrity, sea keeping, propulsion and economy of construction.
Classed by Lloyd's Register, the design of the FPSO is based on the Brown & Root PV150, which was originally developed in 1995 for the Haltenbanken area in the northern North Sea, where wind and wave conditions are not dissimilar to those on the Grand Banks.
The vessel is configured with a forward superstructure and poop deck. The accommodation area of the superstructure is also the temporary safe refuge, and the helideck is located atop the superstructure.
The Terra Nova has two machinery spaces, one forward and one aft, and the main switchroom is positioned aft of the machinery space in the poop deck, immediately aft of the main gas turbine generators on the main deck. The topsides payload is about 12,500tonnes with a combined mooring and turret load of about 5,000 tonnes (in iced-up conditions there is an additional ice load of 2,000 tonnes).
The arrangement includes a cambered deck with a 0.8m camber over half the deck width, the benefits of camber including ice prevention, reduced corrosion, and reduced risk of fire from pool fires and rapid drainage of firewater or spray.
The Terra Nova shares the classic design requirements of all such ships, including the potentially hazardous process plant. The minimum design requirement for Terra Nova is that production should continue in a 1-Year storm, with the design 10-Year stormas a target.
Process equipment is exposed to the weather, and the crew must be protected from wind and from green water whilst maintaining or inspecting plant. With this in mind, there has been a strong emphasis on reducing motions and the incidence of green water.
Crude oil and gas will be processed on board and exported by shuttle tanker whilst the vessel remains fixed on station using a Thruster Assisted Position Mooring System (TAPMS).
With a storage capacity of 960,000 bbl, maximum offloading rate is around 8,000m3/hr. This has been achieved by arranging seven pairs of cargo tanks, divided by a longitudinal watertight bulkhead, such that the number of cargo tanks has been kept to a minimum, consistent with requirements for damaged stability, avoiding sloshing in the tanks.
In order that the size and arrangement of the tanks would form a full double skin, meeting MARPOL requirements and allowing full access to the hull structure for inspection, 33 ballast tanks with a capacity of 460,000bbl have been arranged outboard of the crude oil storage tanks and at the vessel's forward and aft sections. This arrangement produces a buffer zone providing protection to the storage tanks from external penetration resulting from a collision.
Terra Nova crude has a high waxing point and will be stored at 57 degrees C to prevent wax separating out and collecting on the sides and bottoms of the tanks. The ballast tank arrangement selected is designed to minimise waxing by avoiding storage of crude oil and cold ballast water in adjacent tanks.
Of numerous other design features which Brown & Root highlights, attention should also be drawn to the height and length of the poop and focsle, which were chosen to prevent storm crests breaking aboard the vessel.
In addition, the bow profile, sections and waterlines have all been shaped to minimise the effect of storm waves and divert wave crests as far as possible away from the main deck.
The hull design also incorporates a horizontal knuckle running the full length of the hull which allows the hull to be shaped for low motions and green water whilst remaining what Brown & Root calls 'fabrication friendly'.
1.05m wide bilge keels are fitted over 50 per cent of the length of the Terra Nova, predominantly over the parallel midbody. They are sized in order to keep roll angles to a minimum of 7 degrees in all anticipated weather conditions.
Overall, the hullform chosen has been optimised to reduce motions throughout the full range of operating draught of the Terra Nova. The increased depth provided by the required stability characteristics has been used to increase freeboard at the main deck by as much as 20 per cent compared to existing designs.
Rounded transom corners have been used to strengthen the aft end of the hull, thus reducing the risk of damage to the shuttle tanker serving the Terra Nova.
Given the low temperatures and wind and wave conditions on the Grand Banks between December and March, the Terra Nova FPSO has been designed to accommodate up to 2000 tonnes of superstructure icing. The vessel has also been designed to withstand loads imposed on it by icebergs of up to 100,000 tonnes and ice 0.3m thick.
To withstand icebergs and ice, the vessel has been ice-strengthened - more than 3000 extra tonnes of steel have been used - and the vessel is double hulled throughout.
Most of the ice strengthening in the hull is at the forward end of the vessel since in operation it will weathervane into the prevailing weather.
The turret system, which allows it to weathervane, supplemented by five large, 5MW azimuthing thrusters, tow of which are located in the bow and three in the stern and carefully located to ensure good flow into them for propulsive efficiency and to avoidvibration when self-propelled.
The turret, which is designed and fabricated by FMC/SOFEC, is arranged in such a way as to enable the FPSO to be disconnected from the moorings and risers, and is notable both for its sheer size compared to other FPSOs, and the speed with which it can bedisconnected and re-connected.
Numerous positions were examined for the location of the turret before it was decided to locate it forward of the centre of rotation in order to improve heading control, and aft of the FP in order to minimise induced riser and umbilical motions. The final position adopted is about 27 per cent of the ship's length aft of the bow, which will keep the moorings clear of the bow thrusters and provide additional benefits in terms of hull strength and thruster power required.
The turret, which allows the FPSO to weathervane through 360 degrees, is also the mooring point for the FPSO, and remains stationary, whilst the FPSO weathervanes, and provides an interface between the subsea structures and the topsides. Everything passes through the turret-well fluids, injection water and gas and the electrical connections and controls for the subsea systems.
The turret consists of the upper turret, lower turret, spider buoy. The upper turret consists primarily of the manifold decks, swivels, and turret equipment room. This part of the turret structure is similar to other turret structures supplied by SOFEC for FPSOs.
The lower turret carries the riser piping from spider buoy to upper turret. It also contains the bearing to transfer mooring loads and allow weathervaning, and houses the main connector to secure the buoy to the lower turret and the buoy retrieval equipment.
The spider buoy is integral to the disconnect /reconnect operation of the FPSO, and the mooring chains and the risers are connected to it. The spider buoy is approximately 20m in diameter, weighs over 1,300 tonnes, and supports nine anchor chains and upto 19 risers.
The turret weighs over 4,000 tonnes and has an overall height of 70m. It is, as such, the largest disconnectable turret mooring system ever built. A planned disconnect of the FPSO will take approximately four hours to perform but - in an emergency situation - the FPSO can disconnect in just 15 minutes.
Other special design requirements for Terra Nova include the ability to reverse the disconnect procedure at any time prior to actual disconnection, and the need to minimise any release of oil in an emergency disconnect.
As Dunsmore explains, a planned disconnect involves a sequence of production shutdown; flushing all lines; flooding the lower turret to equalise hydrostatic pressure; and disconnecting the main connector to release the spider buoy.
If the FPSO has to be disconnected, the spider buoy settles to a mid-water depth supporting the mooring chains and risers - ready for reconnection when the FPSO returns. Once the iceberg threat passes, the FPSO can return and reconnect, and reconnectioncan be accomplished without any external assistance in seas of up to 2.1m.
Reconnection involves the engaging of the retrieval line with a remotely operated vehicle (ROV), pulling-in the Spider Buoy, de-watering the lower turret, and recommencing production start-up operations.
'Terra Nova will provide the operational experience to demonstrate that this type of disconnectable turret system can successfully on the Grand Banks', says Dunsmore. 'No doubt each of the proprietary turret suppliers will have their own design solution,but Terra Nova will provide actual operational experience'.
Apart from icebergs and freezing temperatures, the sea states and water depths in which the Terra Nova FPSO will operate also present their own challenges, particularly for the design of the riser and mooring system.
'Designing the riser and mooring systems for relatively shallow water with a large variation in sea states was a special challenge for the companies involved in this aspect of the project', says Dunsmore.
Coflexip Stena Offshore is responsible for the riser system design, and PMC/SOFEC for the mooring system. Because of the complexity of the interaction of the vessel, the moorings and the riser systems, the technical co-ordination of this work has been aparticular area of focus for the Alliance.
Significant movement occurs in the risers as a result of sea state, and because Terra Nova has the largest disconnectable riser system in the world, the designers of the riser needed to consider three modes: connected, transient drop, and disconnected.
To produce a riser system that would work in the environment of the Grand Banks, the designers therefore adopted a triple outer sheathing in the touchdown area to provide the required flexibility/bending resistance in extreme conditions.
They also used double sheathing in the upper area of riser for resistance to abrasion and impact protection during system disconnection, and the largest buoyancy clamps produced to date, in order to meet high environmental loading. The mooring system isa particularly stiff system, due to the shallow water depths and large environmental loadings.
The presence of icebergs also means that the wellheads must have protection from scouring action by icebergs. Studies on the Grand Banks have shown that iceberg scour can go as deep as 1.5m, so although Terra Nova is using so-called 'open glory holes' asa means of protection for subsea equipment, a number of other wellhead protection methods are also required.
The methods considered included cased Glory Holes (in which the wellhead and Christmas tree are placed in a steel casing); caisson completion; the construction of external barriers (such as rock berms or structures are placed around the wellhead); open Glory Holes (in which the seabed is excavated to locate the wellhead and Christmas tree below the scour depth of an iceberg).
Open Glory Holes were eventually selected as the preferred option, and excavation on the Grand Banks was completed in September of last year, using the jumbo trailing suction hopper dredger Queen of the Netherlands.
Dry dock construction of the Terra Nova started at Daewoo Heavy Industries on 08 February, although initial fabrication started in August 1998, when the first sheet of steel was cut.