Robert McGovern, Greg Miller
R.J. Brown-CMPS
Chatswood, N. S.W., Australia
First oil from near Lake Kutubu in Papua New Guinea began flowing in June (OGJ, June 29, p. 44) through pipelines and marine facilities recently installed by Chevron Niugini Pty. Ltd. (Chevron).
Chevron reported that production of light, sweet crude oil eventually will reach 100,000 b/d and possibly as much as 140,000 b/d.
Export facilities consist of a 162-mile pipeline and an offshore platform and single-point mooring (SPM) in the Gulf of Papua.
Production facilities were built near Lake Kutubu (Fig. 1). The export pipeline was laid from the central production facility to landfall on the Kikori River - approximately 171 km (106 miles) away - and then another 56 miles to a platform in 66 ft of water in the gulf.
From the platform, an oil-loading line extends about 2.4 miles to the SPM in 83 ft of water where tankers will load oil at an initial design flowrate of 157,000 b/d.
KUTUBU PROJECT
Chevron, acting as operator for a group of six oil companies, discovered commercial quantities of oil in the lagifu-Hedinia and Agogo fields in the southern highlands of Papua New Guinea.
Work on route selection, survey planning, and engineering began in 1988.
Chevron examined several options. The company decided to use the river system as a pipeline corridor only after considerable study had shown the feasibility of routing the pipeline along the channels of the Kikori and Nakari Rivers and the technical inferiority and expense of routing it to the coast through permanently flooded marshland.
Deciding where the onshore pipeline would become a marine pipeline - a key decision - had to be made early.
Anyone familiar with the coastal terrain around the Gulf of Papua will readily appreciate the problems faced. Although the terrain is relatively flat for about 93 miles inland from the Nakari River estuary, there exists a transition zone between ground which is reasonably firm, at least during the dry season, and ground which is permanently wet and marshy.
This transition area occurs about 28 miles inland from the coast and was selected for the landfall on the Kikori River.
The other major focus for study during the conceptual design phase was the selection from a number of options of the marine terminal concept. The options included SPM and floating storage and offloading (FSO) systems in a variety of water depths.
An optimization matrix which addressed the major design variables-flowrate, tanker capacity, and storage required-led to the selection of an SPM as the loading system with storage provided at the central production facility at Moro.
An ANSI Class 600 loading line to the SPM is provided to allow for potential future upgrade to an FSO should this become required by flowrates increasing beyond the present design maximum of 280,000 b/d.
In December 1989, the pipeline design concept had been largely established, and the final design began in February 1990. Similarly, preliminary design of the platform began at this time.
Construction bid documents were issued in May 1990 for the marine pipeline and SPM installation and the jacket, deck, and module fabrication and installation.
In September 1990, bid documents were issued for SPM design and fabrication. In parallel, the detailed design of the platform was completed.
By January 1991, all major contracts were in place, and jacket procurement and fabrication had commenced on Batam Island, Indonesia.
Fabrication of the SPM was completed in December 1991 at the Sembawang yard in Singapore; installation of the buoy commenced in February 1992. The jacket fabrication was completed in January of this year with installation and piling being completed in February (Fig. 2).
The decks and modules were loaded out in March and hook-up and commissioning of the platform have just been completed.
Installation of the marine pipeline was completed in January. Such associated activities as trenching, impressed-current installation, PLEM installation, and expansion spool installation have been carried out subsequently.
Hydrotesting was completed in June.
MARINE FACILITIES
As stated, the marine facilities consist of the pipeline, the platform, and the loading system.
The total length of the marine pipeline from the landfall to the platform, and to the SPM, is 58 miles.
The pipeline enters the Kikori River about 2.5 miles upstream of the village of Kikori, which is the entry point for personnel flying into the principal fixed camp at Kopi, approximately 15.5 miles upriver from Kikori.
An insulation joint electrically separates the land pipeline from the marine pipeline, and an impressed-current station provides cathodic protection to the section of the pipeline in the river. With the possibility of lateral spreading under seismic loading at the landfall, the pipeline is trenched to a depth equal to that of the river bed and then brought up to ground level by two 90 bends and a vertical "riser.,,
The pipeline is routed down the channels of the Kikori and Nakari Rivers for about 30 miles, where it enters the Gulf of Papua in the vicinity of Banana Island (Fig. 3).
Generally, the pipeline route follows the deepest part of the river channel to provide maximum protection from any vessel impact, alleviate pipelaying difficulties, and reduce trenching requirements.
The pipeline is 508 mm (20 in.) OD, 11.1 mm (0.437 in.) W.T. Grade X-60 SAW (submerged arc welding) pipe from Japanese mills (named later) and coated with 0.5 mm (20 mils) of fusion bonded epoxy (FBE) corrosion coating and 50 mm (2 in.) of high-density concrete weight coating.
Although currents in the river can be high during periods of heavy rainfall in the wet season, these currents will generally parallel the pipeline axis and will cause no stability problems.
The pipe is designed to have slight negative buoyancy in fluidized river bed material and will therefore tend to self bury with time.
River traffic along the pipeline route is generally infrequent in terms of large vessels.
The maximum draft of any vessel capable of navigating the river is 3.0 m.
Hence, the pipeline has been trenched at locations where the extreme low water depth is less than 4.0 m.
This trenching criterion for the pipeline has resulted in approximately half of the river pipeline being trenched.
IMPRESSED-CURRENT SYSTEM
Cathodic protection (CP) of the pipeline in the river is provided by impressed current with three stations located, respectively, at the landfall and at two sites 27 and 40 km downstream from the landfall.
A sacrificial zinc-anode system starts at kilometer post (KP) 46.2 (with reference to the landfall) and continues out to the platform and SPM.
Impressed current is used for corrosion protection in the river because most of the river consists of fresh water during periods of high river discharge in the wet season. This fresh water has a high electrical resistivity.
Consequently, in the upper reaches near the landfall, anodes will not work and, farther down the river, anodes would work but be too large and too numerous to be economically viable.
The CP units are driven by general purpose, sealed gel batteries which, in turn, are recharged by an 8-kva diesel generator.
Electrical connection to the pipeline is by way of a four-core armored cable which is buried 2 m. Test points are installed between the impressed-current stations so that system performance can be monitored.
As the marine pipeline passes Banana Island and enters the Gulf of Papua, water depths are still quite shallow, on the order of 10 m. Consequently, the hydrodynamic effects of waves and currents are quite pronounced and result in a requirement for additional concrete weight coating to ensure stability of the pipeline.
Between KP 49 and KP 83, the concrete coating thickness is 90 mm (3.5 in.).
When the pipeline reaches the platform at KP 89.6 it is connected to the base of the incoming riser by a dogleg expansion spool which is 35 m long.
The expansion spool is necessary to absorb movements in the pipeline during hydrotest, under extreme hydrodynamic loads, and under seismic loading.
Water depth at the platform is 20 m, and the platform risers are supported by two clamps; the upper one is a deadweight anchor flange and the lower a sliding support.
The risers were preinstalled at the fabrication yard and protected by neoprene coating from the top of the splash zone to the spool-piece connection flange.
CONVENTIONAL STRUCTURE
The platform (Fig. 4) is a conventional four-leg, piled structure with two principal decks (main deck and cellar deck) and two partial decks (mezzanine and subcellar deck).
Since all processing and storage of the crude oil takes place at the CFP, the functions of the platform consist of: pressure reduction, metering, emergency shut down, surge control, pipeline monitoring and control, pollution response, accommodations, and maintenance for the loading system.
The jacket structure is designed for in-service conditions, including extreme storms, seismic events, fatigue, vortex shedding, workboat impact, and wave slam.
The platform utilizes a conventional structural design except that the weak soils at the platform site necessitated that the piles be driven 80 m deep. That is considerably deeper than would normally be expected for a jacket of this size in this water depth.
Mudmats were used to support the jacket after it was set on the seafloor, and piles were then driven, shimmed, and welded to the top of the jacket legs.
Two modules have been installed on the jacket, one for accommodations and the other for utilities.
The accommodation module has bunk space for 14 and includes galley and kitchen, recreation area, office, control room, first-aid room, laundry, dry storage, refrigerated storage, and HVAC.
The utilities module includes store room, workshop, generator room switchgear-motor control center, spill-response equipment, SPM spare parts storage, and laboratory and battery room.
Other features of the platform include a boat landing on the north face, a 20-ton capacity pedestal crane, and a helideck capable of accepting a Bell 219 helicopter.
The metered crude is delivered to the SPM through a 3.85 km (2.4 mile) long, 508 mm (20 in.) OD loading line which is designed identically to the marine pipeline.
Although the loading system is designed to ANSI Class 150, the pipeline and pipeline-end manifold (PLEM) consist of ANSI Class 600 pipe and fittings so that an FSO can be installed should future oil flows require an expanded offloading facility.
The PLEM is a simple gravity structure which incorporates two concentric reducers, a 14-in. ball valve for isolating the downstream loading system, and a 12-in. outlet flange for attachment of the underbuoy hose.
The SPM buoy is moored in a water depth of 25 m with chains of unequal lengths and sizes to 48-in. diameter anchor piles.
The facility is designed to serve a range of tanker sizes from 50,000 dwt to 150,000 dwt.
A 12-in. diameter floating hose will deliver the crude oil into the tankers from the SPM.
The hose is connected to the buoy pipe arm and equipped with a manually operated full-bore butterfly valve at the discharge end.
The loading operation is controlled from the platform, and the platform control valve will be used to start and finish the loading sequence.
Should the outlet valve on the floating hose be closed in an emergency, pressure-monitoring devices will relay to the platform to close the ESD valve. Any resulting surge in the loading line will be accommodated by a surge tank located on the platform.
UNIQUE ELEMENTS
Several features in the Kutubu export system make the project unique.
The routing of the pipeline along the bed of a river for some 45 km is the first-ever use of such an approach, the authors believe.
Requirements for long-term integrity, constructability, and cost effectiveness posed many considerations for the selection of the pipeline route in the river.
Because of frequent high currents in the river, the pipeline was routed, as stated previously, parallel to the current flow as far as possible.
Shallow water and sand banks were other problems which had to be solved by careful routing to avoid excessive trenching and to provide sufficient water depth for the loading.
Also, because the river channel becomes narrow and tortuous in some areas, a route had to be selected that could be physically laid with a shallow-draft pipelay barge.
Horizontal curvature was limited to a radius of 650 m (2,145 ft), and the pipeline is routed no closer than 50 m (165 ft) to the bank so that the barge can deploy its breasting anchors.
The river bed is known to be extremely mobile and, after a major flood, its topography can change significantly. This problem has been addressed, first of all, by routing the pipe in the deepest channel where possible and by designing the pipe to be slightly negatively buoyant in the fluidized river bed material.
This means that the pipe will tend to settle into the river bed and, after time, will self bury over most of its length.
The problems of CP design for the pipeline were unusual in that, for the majority of the route in the river, the water could be completely fresh or completely saline depending on the volume of river discharge and the state of the tides.
The electrical resistivity of fresh water being about 25 times that of sea water presented a unique CP design problem.
CORROSION COATING
After extensive analysis of all potential solutions, it was decided to proceed with a combination of impressed-current protection together with a very high quality corrosion coating.
With normal design levels of coating breakdown, a large number of impressed-current stations would have been required in the river at a high cost.
Consequently, a zero-holiday corrosion coating was specified. Additionally, the coating contractor was required to prove during a series of tests that the conCrete-coating operation would not damage the FBE corrosion coating.
To achieve this requirement, the coating contractor had to design a high-density concrete mix for impingement which would meet specifications and which had a maximum aggregate size of only 2 mm.
Taking these measures to reduce coating breakdown levels permitted the number of impressed-current stations required to be limited to three.
Landfall design presented some problems because of the probability of liquefaction and lateral spreading of the soils under seismic loadings. So that the pipeline not be affected by such an event, the landfall was constructed in a sheet pile cofferdam and the pipe kept below riverbed level until well back from the river bank.
The sheet piling was left in place to add to the long-term stability.
The platform, although relatively simple, has some unusual features in its design and operation.
A combination of relatively high seismic loading and very weak soils strata at the platform site resulted in unusually stringent piling requirements. The resulting piles are 100 m long (80 m penetration), 1,067 mm OD (42 in.), and 45 mm thick at the mud line.
Evidence of the poor soil is shown with the large platform excursion during the 100-year storm where the lateral displacement at the mud line is approximately 27 CM.
Another requirement was to have a large deck area available for maintenance and the ability to handle the SPM hose for maintenance on the main deck. As a result, the modules are cantilevered well out from the main deck, and diagonal braces are used to prop the cantilever beams.
The meter-prover piping is ANSI Class 300 for future expansion of the facility. Provision for an additional riser was also included in the design.
MONITORING, CONTROL
Emergency shutdown on the platform will be handled by an ESD valve on the incoming pipeline which has a closure time of 10 sec. Shutdown will be initiated by high pressure in the ANSI Class 150 system, detection of fire, local hand switching, high level in the surge-relief tank, and low pressure in the outgoing pipeline.
A control valve will also be used as the normal loading termination valve which can be closed by the pipeline monitoring and control system (MACS). An emergency shutdown will initiate a pipeline shutdown via the MACS which will stop product inflow at the central production facility (CPF).
The MACS, with master stations located on the platform and at the CPF, will monitor and control the entire export system. Initially, it will be programmed for operation of the pipeline under nominal gravity flow conditions with only the CPF low-head pumps.
It will be capable of being configured to include monitoring and control of future high-head main line pumps at the CPF and at the Kopi valve station (Fig. 1). The MACS will control normal start-up and shutdown operations for tanker loading.
Telecommunications on the platform will provide for data transmission to the CPF control room, pump station, and all remotely operated facilities. Voice communications will be provided between the platform, CPF pump station, permanent pipeline facility sites, and SPM-tanker.
There are also several levels of backup communication; for example, Inmarsat.
A pressure-relief system has been incorporated on the platform and protects the ANSI Class 150 system from potential over pressure. A relief tank averts the possibility of any local pollution.
The outlets of all pressure safety valves on the platform will be directed to the relief tank which will have a volume equal to 100% of the expected relief flow during an emergency shutdown. The tank will also be used as storage for crude oil which will be used as fuel for the electric generators.
The metering system on the platform will be used for custody transfer and has an input to the MACS. All real time data and stored constants used in metering calculations will be available for display on the MACS.
The metering system will include the following:
- Metering runs with flow computers capable of metering to better than 0.5% accuracy.
- A bidirectional, spheroid displacement meter prover and controller. Double block and bleed valves will be provided to ensure that no bypassing occurs.
- Automatic sample collection and storage system.
- Pressure and temperature transmitters.
BIDS, AWARDS
Early in the project, it was decided to reduce the number of fabrication, procurement, and construction contracts for the export system and, as far as was practical, to proceed on fixed lump sums based on performance specifications.
It was originally intended to let the platform contract on the basis of design, supply, fabrication, and installation. In order to maintain close control of the design of the platform facilities and to improve the project schedule, however, it was decided to retain the design function in the EPCM contract of R. J. Brown-CMPS under subcontract to Williams Bros.CMPS.
Consequently, in mid-to-late 1990, bids were called for the following packages:
- Platform fabrication (including procurement)
- Design and fabrication of the SPM
- Coating of the marine pipeline
- Installation of pipeline, PLEM, platform, and SPM.
In December 1990, the platform fabrication contract was awarded to DeLong Hersent S.A., Singapore, with the work being carried out in its yard on Batam Island, Indonesia (Fig. 5).
Except for the metering and meter prover skids and the communications equipment, all equipment on the platform has been supplied by the contractor in accordance with the drawings and specifications which R. J. Brown-CMPS prepared on behalf of Chevron.
In early 1991, the design and fabrication contract for the SPM was awarded to Bluewater Terminals S.A., Leiden, Holland. The design work was carried out there with fabrication in the Sembawang yard, Singapore. All materials required for the SPM, including hoses, swivels, bearings, and anchor chains, have been contractor-supplied.
The marine pipeline-coating contract was awarded to Bredero Price, Malaysia, in December 1990, and the work was completed in its Kuantan yard in August 1991.
The work scope entailed FBE coating, fabrication of Pri-Grip shear bands to ensure adequate shear strength between the FBE and the concrete, application of "Heavicote" concrete, and installation of zinc anodes.
Bredero Price was to fabricate the somewhat complex pipe-to-cable connections for the impressed-current stations and test points. A 30-m cable tail was left on these pipes for the installation contractor to connect into with the armored cable to shore.
The main installation contract was awarded to Bouygues Offshore Singapore Pty. Ltd. in December 1990. The contract's scope is installation of the pipeline system, PLEM, platform, and SPM; it includes hook up, testing, and commissioning of the platform facilities.
For the marine pipeline system, almost all materials are company-supplied including the coated line pipe, subsea flanges, ball valves, and all equipment for the impressed current facilities.
The major procurement packages for the marine facilities (and their suppliers) were:
- Line pipe (Marubeni acting for a consortium of four Japanese mills: Nippon, NKK, Sumitomo, and Kawasaki)
- Subsea ball valves (Cameron Iron Works, Scotland)
- Subsea flanges (MGI, France)
- Metering and meter prover (Smith Systems Operation, Corpus Christi, Tex.)
- Communications equipment (Alcatel, France)
- Impressed current stations (Northern Power Systems, Moretown, Vt.).
START-UP
By June, installation of the marine facilities was essentially complete.
Hook-up, fit out, and precommissioning of the platform topsides and all work on the marine pipeline system was complete.
The river pipeline was installed with the barge TAK 300 which was rigged up as a shallow-water pipelay barge.
Trenching of the pipeline in the river was carried out by the pipeline trenching machine Granceola, which is owned and operated by the Italian company Sadarincop and under subcontract to Bouygues.
The machine underwent full scale trials in France in July 1991 which confirmed that it could achieve the required trenching depth and that it could operate under conditions of strong currents.
The Bouygues derrick lay barge BOS 355 installed the offshore section of the marine pipeline, the jacket, and modules. The shear leg, Semco 1501, was used to perform the deck lift.
Copyright 1992 Oil & Gas Journal. All Rights Reserved.
