Converted tanker & production semi integral to phased Marlim development

Brazil's soaring energy needs are driving an intensive deepwater development program. Petrobras is striving to virtually double the country's current oil production to almost 1.5MM b/d by the year 2000.

Monohulls and semisubmersibles are the favored production medium off Brazil, and two such units have recently been converted at the Cádiz yard of Astilleros Españoles. This was also the yard's first offshore assignment for the Latin American market. Previously it had converted the Bluewater-owned tanker Uisge Gorm for Amerada Hess' Fife development in the UK North Sea.

The latest conversions are both destined for the ongoing Marlim Field development, where estimated reserves have been upgraded this year from 1.6 to 2.5 billion boe. Production will come from three semisubmersible platforms moored in waters over 1,000 meters deep, one of which will be the P-26 supplied by Cádiz. Oil will be exported 16km to Cádiz's P-32 FPSO, anchored in more conventional depths of 170m away from the field.

Semi overhaul

P-26 has an interesting lack of history. It was originally built, but not completed, in Viborg, Russia in 1991 to act as a drilling semi submersible. The unit included a special deck for pipe storage, and a moonpool. Both had to be modified or ripped out for the new production role.

This added to the complexities of the job for the Cádiz yard, which had never before handled a conversion of a platform. Hauling it into the yard's 66 meter drydock was not easy either - although the lower part of the semi was within the width limit, at 64m, the upper part in places measured 74-76m across. However, Astilleros engineers devised a solution which involved bringing the unit in at an incline on its side.

The main tasks for the P-26 (ex-Iliad) included installing new transversal pontoons and blisters around the columns to increase capacity and stability - lowering the platform's gravity allows a greater load to be placed on the deck.

Steel reinforcements have also been added to many parts of the platform's substructures to house kit needed for production purposes, such as turbocompressors and water injection modules. Below the main deck, a `spider' deck has been installed accommodating connections for the manifolded flowlines.

The Brazilian client designed a protection structure for the risers which terminates inside the platform, thereby avoiding the risk of damage from passing vessels. The new mooring spread uses a centralized system of gears to manage the various anchors, with only one windlass - normally winches have to be deployed for each anchor/mooring chain.

Cádiz' brief extended to totally rebuilding the accommodation area to house 88 personnel. It also installed a new helideck, a communications tower, three turbocompressors on the port side and three emergency generators starboard. Other responsibilities included the 140 ton steel flare tower, new ballast, valve control and tank ventilating systems, power and electrical equipment and a centralized, 12,000 point ECOS control system.

Many aspects of the work were new to the Cádiz yard. For previous conversions, it had installed relatively small process items, but on the P-26, a whole new set of process plant had to be installed on 14 separate skids, piece by piece.

Pipework fabrication proved to be more complex than expected. New TIG orbital welding machines had to be brought in, and welding procedures new to the yard had to be formulated rapidly to offshore industry standards to meet the approval of project certifier DNV. And Brazilian installation guidelines turned out to be very different from those applicable in the North Sea, involving more paper work, much of it delayed until towards the end of the project. This in turn impacted certain aspects of the design.

More than 6,000t of special steel were employed in the conversion, compared with the original plan of 2,400t. And more than 300km of cable had to be installed on the platform.

The completed P-26 is a 25,000t semi submersible with an operational life of 25 years. Production capacity will be 100,000b/d of oil and 3mcm/d of gas.

Cairu

Marlim's P-32 FPSO conversion, performed concurrently with the semi, was completed several months ahead of schedule at the end of June. The converted VLCC - formerly known as the `Cairu' - was a 282,750dwt vessel measuring 320 meters long, 54.5m wide and with a draught of 27.8m. It was 21 years old on reception in 1995, but had to be refurbished for a further 20 years service on Marlim. There it will be capable of processing 100,000b/d of oil which will be offloaded periodically to shuttle tankers.

Among the major changes, a new five-point, weathervaning turret was installed with a thruster-driven, drag chain system for fluid transfer. The design, by Bluewater, is purposely less complex and therefore less costly than the Uisge Gorm turret, because conditions off Brazil are milder than in the North Sea.

Elsewhere on the vessel, accommodation had to be upgraded substantially to house 40 people, compared with 30 in VLCC mode. At the front, a new steel helideck with an aluminum base was fitted.

Due to the vessel's age, all existing engine room valves were for manual operation. These too had to be upgraded for integration with the ECOS system, which has 6,000 points of control on the P-32. On the plus side, the vessel was generally in good condition, so only 200t of new structural steelwork was needed.

The process plant is not typical for an FPSO, as there is no gas to process. This was an important consideration for the project cost. The main function of P-32's process plant is therefore to separate water produced with oil from one of the Marlim deepwater semis - the other two output oil only. Some of this oil is sent directly to the P-32 engine room for fuel. New seawater pumps have also been installed there.

The Brazilian client insisted on rigorous inspection of all thicknesses of steel plate. Specialists were brought in from The Netherlands to Cádiz for this purpose, which involved installing special scaffolding on the vessel and around the hull as well as emptying of tanks.

The entire hull was blasted externally to 2.5 ASA while the onboard tanks were being painted - not an easy task. All hydraulic systems were completely overhauled, with valves sent to a company in Madrid for restoration. Any valve, piping or hydraulics in bad condition could have prevented full production of the FPSO.

Co-operation

For both Marlim assignments, 30 Petrobras people worked full-time alongside Astilleros staff in Cádiz. Astilleros reciprocated by sending its engineers to Rio, and also to Houston, for preliminary work on the Cairu, and to The Netherlands to work with Bluewater on the turret.

"If we feel we can't do a job, we hold our hand up and tell Petrobras," says Cádiz area director Francisco Gallardo. "It's a good situation - we never lie to them. They in turn are very happy with us. There has been in this way a very close co-operation."

That was borne out by the reaction of Petrobras' P-32 project manager, Jorge Alberto Sales de Lina, on receiving the completed FPSO. "This delivery marks the starting point for placing further orders with Astilleros Españoles." The latter's chairman, Antonio Mendoza, confirms that negotiations are being held with Petrobras on future oilfield installations.

Before these jobs and Uisge Gorm, Cádiz was known as a repair yard. But Uisge Gorm established its reputation as a specialized offshore conversion site. "The FPSO was approved by ABS, it works, and it works very well," says Gallardo.

"These conversions have transformed our way of working, have broadened our know-how for resolving problems. This allows us to tackle increasingly complex conversions. We have a reputation now above other yards for flexibility, and we are more oriented towards projects - the client's project team and our construction team always work face to face.

"You have to be in daily contact with the client. In turn, the client gets more sensitive to the needs of Astilleros Españoles. These may sound like semantics, but in fact they are absolutely vital."

Nigeria floater re-equipped for Ukpokiti and third party storage

Following a strategic review by Astilleros Españoles, the Cádiz yard is now totally focused on offshore conversion work. So much so that it was able to handle a third floating unit alongside the two for Petrobras.

This was in fact a sister VLCC to the Cairu, the Independence, owned by Conoco. It is being upgraded in stages for floating production duty on the marginal Nigerian Field Ukpokiti under a novel working arrangement. Conoco wants to employ the vessel on the field for eight years, renting out spare storage capacity to a third party user as Ukpokiti production declines.

Prior to the latest work, Independence had sailed into the Cádiz yard in the summer of 1995 for replacement of 500 tons of bottom steel plates. At the same time, Conoco commissioned Astilleros also to blast the entire hull and then to paint the internal tanks. Conoco called this pre-conversion - getting the dirty tasks out of the way to shorten the duration of the main conversion work at a later date.

The turret-less Independence will be moored in only 40 meters of water on Ukpokiti by a splayed, four-pair anchored mooring system. Production will be via flexible risers located beside the hull, linked to a manifold. A metering system and other riser connections will also be installed.

Processing plant will be divided into three or four modules providing a capacity of 20,000b/d. Ukpokiti oil will be offloaded every 100 days from the bow to a shuttle tanker.

There will be normal water and gas separators, with wing tanks for water treatment. Gravity will send water to one tank, with the field's associated gas diverted to the Independence's boiler for fueling purposes, with remaining gas flared. In the bow another system will handle seawater, which will be directed first to the process plant and then into the well for stimulation.

A new crane has been installed in the FPSO's starboard side, and there is also a new helideck. Up to 60 people can be housed onboard.