The Espadarte floating production vessel was converted from the FPSO VI.
Recent floating production projects in the Norwegian Sea, Far East, and Brazil have been dogged by soaring costs and schedule overruns. EPCI (exploration, production, construction, installation) contractors will not wish to see this pattern repeated in future projects, with so many deepwater developments pending.
However, feedback from two of the region's newer projects is reassuring. Last December, the Kuito development provided Angola's deepest production to date when it came onstream, on budget and within a tight timeframe. Petrobras' Espadarte expansion scheme in the Campos Basin is also shaping up well. In both cases, the FPSO is a converted tanker, with Single Buoy Moorings (SBM) as the lead contractor. SBM claims to be the world's leading specialist in floating production and storage vessel conversions, with 11 leased units operating off Brazil, West Africa, Italy, Sakhalin Island, Thailand, and Vietnam. The firm also supplied one FPSO (floating production, storage, and offloading) vessel to Shell Expro in the North Sea.
The two latest projects, however, represent its biggest test, both in terms of manpower and responsibilities, SBM officials say. In addition to requiring separate project management teams, Kuito was a fast-track, turnkey exercise, while Espadarte is the largest FPSO that Petrobras has ever leased. Having proven the elasticity of its in-house resources, SBM now aspires to manage three such schemes simultaneously.
The Kuito Field floating production vessel was converted from the VLCC Bay Ridge tanker in 14 months.
Kuito was discovered by Chevron's Angolan subsidiary CABGOC in April 1997 in Block 14 offshore Cabinda. The field lies in an average water depth of 400 meters. Chevron and its partners Sonangol, Agip, Petrogal, and Totalfina decided to forge ahead with a development incorporating an FPSO, and invited bids from selected contractors in January 1998.
"At that stage, the development scenario was relatively simple," says SBM's Kuito project manager Chris Davison. "It involved oil pro duction of 50,000 b/d and re-injection of gas - no water injection. But, we then found ourselves continually re-bidding as a result of Chevron's discussions with Sonangol and the continuing exploration effort. The final contract awarded in September 1998 was for a much-expanded FPSO, to be delivered in a tighter-than-normal timeframe (14 months) and achieving first oil offloaded before the end of 1999.
The field development that the partners settled on was a phased development. 1A, the initial production phase, would be based around surface facilities, consisting of a spread-moored FPSO converted from a VLCC tanker, and 12 subsea wells linked to a manifold situated 1.9 miles from the vessel. This manifold would be tied back to the vessel via two 11-in. production lines, a test line, and gas lift/control umbilicals.
Stabilized crude would be pumped to shuttle tankers via a CALM (catenary anchor leg mooring) buoy offloading system moored 1.15 miles from the FPSO and connected to it through two 15-in. ID flexible flowlines. Associated produced gas would be used to provide fuel to the vessel and gas lift, with excess amounts re-injected to avoid flaring. The 1B development phase covered water injection facilities, including a 10-in. flowline and control umbilical tied to an eight-slot manifold. First production from Kuito was realized on December 15, 1999, 15 1/2 months after the contract award with the first offload achieved before year end.
CABGOC's strategy was instrumental in ensuring the project's smooth passage. It appointed a consortium of three main contractors, giving them single point responsibility for the design, fabrication and installation of all the field's production systems:
- SBM, as the lead contractor, was charged with supplying the FPSO (via its joint venture with Sonangol), the associated mooring system, and the export facilities.
- ABB Offshore Systems would provide subsea trees, manifolds, and control systems
- Coflexip Stena Offshore was in charge of flexible flowlines, risers, umbilicals, and subsea equipment installations.
Drilling operations were handled separately by Chevron. According to Davison, this arrangement suited all parties. "Because we were working as a consortium, we paid more attention than usual to the interfaces with our co-contractors vis-a-vis the FPSO, subsea facilities, and the export system. During the negotiation phase, the consortium expended a lot of effort ensuring that those interfaces were properly defined." A cost or schedule overrun would impact all sides, he pointed out.
Quick field tie-ins allowed the Kuito floater to begin production soon after contract.
SBM's strategy is to maintain a VLCC tanker available at all times to cater for short-notice conversion contracts. The vessel of convenience in this case was the Bay Ridge, a 20-year old turbine tanker acquired by the company in 1997 in anticipation of an FPSO order. "Mechanically," says Davison, "its condition was not particularly good, but the steelwork was OK. When we buy a tanker, it's the steelwork that we're interested in primarily."
The vessel had to be adapted to guarantee 10 years' uninterrupted duty on Kuito, with no requirement for drydocking. In its new guise as an FPSO, it was to be 335 meters in length and 44 meters in width, with a deadweight of 228,000 tons. Key capabilities were to include: 1.4 million bbl oil storage capacity; 100,000 b/d oil production at peak; 35,000 bbl/hr export rate; 16 MMcf/d gas injection rate; 36 MMcf/d gas lift rate; 110,000 b/d water injection; and 20,000 b/d produced water.
The refurbishment program featured a complete machinery overhaul, replacement of 400 tons of steelwork in the cargo and ballast tanks, installation of new engine room electrical equipment, and extensive repairs to ballast piping and valves. Life extension work included blasting and coating of the entire hull and deck, ballast, slop, and cargo tanks, and also the installation of new tank anodes.
For the conversion exercise, the vessel's boilers were converted to run on fuel gas and heavy fuel oil - produced steam provides heating to the topsides process plant and cargo tanks. To meet the vessel's power generation/distribution requirements, a new, larger emergency generator was installed, supplementing the two existing steam turbo-alternators, which were considered re-deployable.
Tank venting, cargo, and inert gas piping systems had to be modified to ensure uninterrupted production and simultaneous offloading, in addition to tank gas purging for inspection purposes. The Bay Ridge's inert gas generation/distribution plant had never worked satisfactorily - this type of kit is normally reusable, but SBM moved early on to replace it with a new IG generator, to avoid any delays to the overall schedule.
In the engine room, five electrically-driven seawater lift pumps were added to provide cooling water for the IG generator and heat exchangers, in addition to supplies for the water injection and treatment plant. A new integrated, distributed control system from Moore was also installed, which supervises all process, utility, and safety systems on a continuous basis from the FPSO's central control room. Other changes included a new helideck, a 15-ton Appleton hydraulic crane added to the port side to handle supply boat cargoes, and refurbished accommodation to house up to 68 permanent staff.
Each production flowline feeds produced fluids into a dedicated process train with 60,000 b/d capacity. On arrival, the fluids are processed via heating and three-phase separation. Separated gas is diverted to the main gas compressors or the LP fuel gas system, with separated oil being re-heated. Fluids also can be routed to the FPSO through the test flowline, via a dedicated test heater and separator. Pigging facilities onboard the vessel permit round-trip pigging of all flowlines. Main gas compression is performed in three stages.
- Suction scrubbers remove condensate, which is returned to the oil processing trains, while gas exiting the third stage compressor is sent to the gas dehydration system.
- Dried gas then passes through the gas lift header, either to the gas lift umbilicals or production wells.
- Unused gas is diverted to a single-stage compressor for re-injection.
Surface and subsea layout for the Kuito Field off Angola.
The offloading system is using gas turbine driven pumps in series with the cargo pumps to achieve the required offload rate of 35,000 b/d, using two 15-in. flexible pipelines to feed the export CALM buoy, which is a large SBM standard design unit.
SBM's spread mooring system, which is designed for a 25-year life, consists of four groups of three anchored legs at each quarter of the vessel. The lines are a combination of chain and sheathed spiral strand wire rope terminating in a suction anchor pile.
Installation of the suction piles and anchor legs was performed using SBM's diving support vessel, Dynamic Installer, which was mobilized 89 km from Pointe Noire in The Congo. These were left in situ on the seabed until the arrival of the converted FPSO from the Keppel shipyard in Singapore. The hookup operation required the use of four tugs to control the FPSO, due to very strong surface run-off currents from the nearby Zaire River. The Dynamic Installer had also been deployed early on in the project for seabed soil investigations in preparation for this work.
The CSO Installer and the newly converted DP vessel, Smit Pioneer, were contracted for remaining subsea/seabed installations. The mid-water arches to support the risers were also due to be managed from the Smit Pioneer, using a retainer wire on the FPSO, which was intended to serve as the hold-back point. However, the FPSO was not available at the preferred time for this operation, so the Dynamic Installer assumed the hold-back role instead. All arches were installed prior to the FPSO's arrival, saving 10 days on the original schedule.
"There were some schedule overruns during this project," Davison says, "but they were partly recovered by switching around the installation sequence in this fashion." As another example, the consortium had considered using Chevron's drilling rig to install the manifold. A second Coflexip vessel was brought in for this task, which proved to be a better solution.
FPSO contractors like to discuss client-contractor cooperation. In this case, the consortium agreed with the client, Chevron, that they should be restricted to one resume (update meeting) every six weeks. "We felt that monthly resumes were counter-productive, given the scattered nature of all our operations and the consequent travel involved. These meetings were held in a different project location each time."
Numerous yards in the Far East were subcontracted for the topsides process modules, with the completed skids sent on barges to Sembawang in Singapore. The conversion of the vessel involved the addition of 6,700 tons of new steelwork, plus 400 tons of refurbishment steelwork, 35 km of piping, and 250 km of cabling. "Technically, there is nothing really radical about the FPSO itself," says Davison. "What is unusual about this project is that the consortium took a lot of the interface problems away from the client."
Phase 1B operations, including water injection facilities, should be in place shortly. Front-end engineering studies for Phase 1C, involving a second subsea production center, are in progress. This may also entail expansion of water injection, compression, and reduced water handling in order to prolong the oil production plateau at 100,000 b/d.
After the construction, the FPSO was handed over to Sonasing, the FPSO owner and operating joint venture formed by Sonangol and SBM. As owner and operator of the FPSO, this joint venture has been involved at an early stage in the design.
Espadarte is one of the southernmost of the Campos Basin discoveries, lying 150 km offshore. The field is situated to the south east of the Marimba Field, which is now producing through the P21 semisubmersible. Water depths in the area vary from 700 meters to 1,000 meters.
Historically, Petrobras has pushed for fast-track development of its discoveries as it needs the production revenues. For this reason, it favored conversions over newbuilds for its floating production systems.
Invitations to tender for the Espadarte FPSO were first issued in November 1997. At that time, Petrobras envisaged a 30,000 b/d system, but even the lowest bid proved too costly. Eleven months later, it reactivated the bid process with a new scheme involving a threshold raised to 100,000 b/d (achieved by adding more subsea wells to the development). This drew responses from four consortia - the winner was SBM, in partnership with its two sister companies in the IHC Caland Group, Rotterdam-based IHC Gusto, and Imodco in Los Angeles.
Under the agreement, Petrobras would lease the vessel from SBM and the latter would also manage the vessel in the field. The FPSO Espadarte being a fast track project, Petrobras had agreed to such an arrangement. Normally, it prefers to own and operate its units. The one rider was that SBM would have to interface with Petrobras on subsea aspects of the development.
SBM took overall project management and procurement responsibility in the delivery phase, SBM's remit extended to designing the fluid transfer system for the turret, managing the hull conversion/refurbishment and subsequent fit-out of the process modules at the designated yard in Singapore, followed by installation on the field. Imodco's brief was to engineer the turret mooring system, while Gusto would design the topsides facilities and the vessel conversion.
The completed vessel left Singapore on March 6 and is due to arrive in Brazil in May and will then be hooked up to the pre-installed anchoring system. Eventually, the facility will process oil and gas from 15 producer wells with up to nine water injectors. This will be achieved through satellite subsea production trees tied back to the FPSO via risers including product lines, gaslift lines, and control umbilicals, water injection trees connected via water injection risers, control umbilicals, and in addition, two associated flowlines. A new subsea manifold tying in production from wells on Marimba would replace the semisubmersible currently in service on that field.
Espadarte Vessel history
The Bay Ridge had been a speculative purchase. With that tanker already committed to Kuito, SBM had another vessel in its fleet, FPSO VI, coming off charter after 12 years' shallow water duty for Ashland offshore Nigeria which could be used for the Espadarte FPSO. This vessel had been converted by SBM and was in its day, the world's largest FPSO.
"Due to the work undertaken on this vessel in the 1980s, the scale of the vessel conversion could be slightly reduced for Espadarte" says Jean-Louis Antoine, SBM's Project Manager, Major Systems. The main change would be the construction of a moonpool in what had been the No.1 tank center to accommodate the turret.
Hydrodynamic analysis of the hull took account of the shift to its new environment. "Conditions in the Campos Basin are more severe than off Nigeria," explains SBM's Director of Engineering Tony Mace. "The environmental conditions are moderate and the area is prone to beam seas which introduce a roll motion onto the vessel. That makes it very uncomfortable to be on, and also requires particular design measures for the topsides equipment.
"Petrobras had reported this phenomenon on their other vessels, including the SBM-built FPSO II. An extensive study was carried out on that vessel's roll behavior. To minimize motions, we designed and model tested various bilge keels, and these were subsequently fitted to the FPSO II in a Brazilian drydock. After the vessel had re-entered service, a marked improvement in its roll behavior was reported reducing roll motions in Brazilian conditions to a very acceptable level."
In view of the strict delivery schedule for Espadarte, planning procedures had to be firm from the outset. "Very early on, we had to decide where to take the vessel to from Nigeria," says Antoine. Inquiries were issued to yards in Europe, the Middle East, and Korea. Keppel won the vote. That choice was influenced partly by the topsides configuration. "We wanted to employ fabricators that would be in the area where the ship was being assembled," says Mace. "The modules would have a maximum weight of about 500 tons. That suited the capability of the module yards around Singapore, as well as the shipyard."
SBM had a largely free hand in its choice of equipment vendors, although "SBM maximized Brazilian content by procuring the mooring lines, including anchors, chains, and mooring ropes and some process mechanical equipment, from Brazilian suppliers," Antoine pointed out. Monthly meetings were held with Petrobras during which these matters were raised, along with the evolution of the design, well operations, and other matters.
The FPSO VI had been built originally as a tanker in Norway in 1975, and was operated for two years. It was acquired by SBM in 1984 and converted to an FPSO the following year in a Spanish shipyard. In its new role on Espadarte, it has been designed for a 16-year productive life.
"The hull was in good condition, but we still decided to change out a lot of the plates, partly due to pitting," Mace explained. "That amounted to 350 tons of new steel along both sides of the hull." Some brackets were also modified as part of the life extension program. Anti-corrosion measures included an extensive paint system as well as an impressed current cathodic protection system.
The converted vessel was 344 meters in length, 52 meters in beam, with a depth of 29 meters and a draft of 22 meters. Oil storage capacity is 1.9 million bbl, with a tandem hose arrangement for offloading - this operation will be performed every 10 days via a shuttle tanker moored at the FPSO's stern. Offloading should take around 24 hours. "Petrobras uses 150-meter long hawsers, which are longer than those used elsewhere, says Mace. "They also favor bow loading, which is common in the North Sea, but again, not elsewhere - that's because they operate dedicated tankers. For Espadarte, we chose dual-carcass hoses, as this is an environmentally sensitive area." Key features of the production facilities are: oil production - 100,000 b/d, produced water treatment - 50,000 b/d, gas compression/treatment - 88 MMcf/d, and water injection - 110,000 b/d.
The topsides process, designed by Gusto, features 17 separate modules. "That might sound like a lot of hook-up," says Mace, "but we designed a central piperack system to ease installation." The modules were ordered early in April 1999, and all were delivered to Singapore last October. Then ensued a two-week campaign of lifts onto the vessel, using a floating crane, followed by four months for installing cables, tie-ins, associated tests and equipment commissioning.
The modules and the moonpool also had to be in place before the turret (built in Abu Dhabi) could be fitted. The turret's lower section was delivered mid-September with the superstructure arriving mid-December. The turret was 30 meters high, 17 meters in diameter, and weighs over 1,000 tons. The turret is situated in the vessel's bow and is designed to accommodate up to 45 flexible risers.
At one point, Petrobras had considered experimenting with a steel catenary riser for this project. The technology was proven, but an installation technique still needed further study. Also, the SCR would have entailed modifications to the turret, which was already under construction.
Espadarte's turret is moored to the seabed by 10 chain/polyester rope lines which are in turn secured by 32-ton anchors. Two bearings - one at the top, the other at the turret's base - allow the vessel to weathervane in response to prevailing environmental conditions. Swivels at the top of the structure divert the incoming commingled wellstream to the topsides separation and process modules.
Modules 1 and 2 provide primary and secondary separation of oil, gas, and water. Separated oil is stored in the cargo tanks in readiness for offloading. Separated water is processed further to remove dissolved gas and any residual oil before being discharged overboard. Gas treated in the first separation phase is compressed in Modules 4-7; it then passes back through swivels in the turret for subsequent re-injection into production wells for lift purposes. Gas is used for fuel for the FPSO and any surplus is fed to shore through an existing pipeline. A fifth compressor module re-compresses LP gas separated from the crude in Module 2 to a pressure at which it can be commingled with produced gas from Module 1.
HP gas from the compressors is dehydrated using glycol in Module 3. Circulation of hot water for process heating and cold water for gas compressor cooling is provided by Module 11, while Module 12 contains two 4.4 MW gas turbines used to generate electricity. Power is distributed by switching gear situated in Module 13 and in a forward equipment room in the forecastle of the vessel.
"The FPSO is equipped to use electric submersible pumps (ESP) in some of the wells," says Mace. "In the event this was not followed through, but the power generation system could be deployed to take ESPs later on. We have variable-frequency drives for the subsea pumps and an electric swivel in the turret."
Seawater pumped from the FPSO machinery space is delivered via the cooling medium system heat exchangers on Module 11 to a fine filtration system and then to a vacuum tower to remove all traces of oxygen. A gas turbine water injection pump on Module 10 pumps the treated water to a high pressure, before routing it back through the turret swivels for re-injection. Module 14 contains chemical storage and pumping equipment, while Module 16 houses flare gas scrubbers and the subsea well hydraulic power unit.
Pigging facilities have been designed in part to remove wax from the flowlines. "Petrobras has shared with us its expertise on residence times and heating temperatures for processing," says Antoine. "In the case of wax/hydrates, they have developed a heat-generating technique called SGN, in which a fluid can be used to clear wax/hydrate. We have facilities onboard to pump this fluid into flowlines."
According to Dick van der Zee, SBM President, Operations, the firm is aiming to bring FPSO deliveries in the future down from the current minimum of 15 months to a period of 12 months. "Basically," he says, "a project's schedule is dictated by the lead items of the equipment involved. To shorten schedules, we need to form alliances with equipment vendors. For FPSOs, that means being able to cover different ranges of compressors, water injection, and power generation modules, so these are available as soon as we gain an order. In addition, the yard needs to be informed precisely when the required materials are scheduled to arrive.
"One of the longest lead time items is the mooring system. In response, we have developed a turret to take a certain number of risers, which allows us to order bearings before embarking on a project. To a great extent, the vessel conversion is insensitive to the contract. Much of it is pre-defined - we could even start the conversion without having an order confirmed."
As for shipyard cooperation, SBM now has experience in floater projects in the Far East with Sembawang, Jurong, and Keppel. "But we're also looking at other possibilities in the Middle East," he says. "Basically, yards are good at supplying labor, but management of the project needs to come largely from our side. Yards can handle conversions, but they have problems with a fully integrated FPSO, so we have to put our own management team in place. Yards need to have the scope of their work strictly defined."
SBM derived satisfaction in being involved in the definition phase of Kuito "We also like having responsibility for full development of a field after drilling is completed," said SBM's President Francis Blanchelande. Following problems with FPSOs in other parts of the world, mainly in the North Sea, he believes oil companies will impose stricter performance demands on individual contractors. "But, I still think that EPIC contracts are the most economic way of delivering these vessels."
Blanchelande sees FPSOs becoming a commodity, like drilling rigs. The onus may shift increasingly onto the contractor to invest speculatively in hulls, as SBM did on Kuito, in order to compete for FPSO contracts. SBM has only one small FPSO available currently, Jamestown, which is being targeted for an early production role. "We have had requests from certain oil companies to produce general purpose FPSOs," he adds, "but that doesn't work. It's always better to make the unit fit for purpose for the field development in question. That also brings the cost down.
"On a leased project, you have the investment, the lease period, and the residual value of the unit. You can depreciate your asset a lot or a little. You must also have in place strong project management to ensure that the estimated capital expense is maintained, and also to negotiate any modifications with the client."
Van der Zee sees two 100,000 b/d production systems concurrently as the optimum for SBM. However, Blanchelande believes the company could manage three conversions simultaneously, assuming that man-hour requirements could be kept to around 400,000, as was the case with Espadarte.
Jacques Burger, SBM Production Contractors' Senior VP, Business Development, believes that the best prospects for deepwater FPSOs may come from Angola, and Brazil, now that the oil companies are joining Petrobras as operators. "In this regard, Espadarte is important, because it is a large, complex unit built in record time. Complex units must comply with the highest standards and the best industry practices. Only a limited number of contractors have the technology and know-how necessary to properly design and build such complex units." SBM says its strategy is to be involved in supply, either of turnkey or leased facilities that require a good deal of technology.