Girassol FPSO, Luanda, Angola
Girassol is located about 210km north-northwest of Luanda, Angola. It lies in 1,350m of water and has been developed using a subsea facility tied back to an FPSO.
Girassol base-case reserves are around 630 million barrels (bbls) of 32° API crude oil. The field came on-stream in December 2001.
TotalFinaElf E&P Angola is the operator of the $2.8bn project, with a 40% interest. Its partners are Esso Exploration Angola (20% interest), BP (16.7%), Statoil (13.3%) and Norsk Hydro (10%).
Subsea exploration and production system
The subsea production system consists of 39 wells, including 23 producers.
In January 2011, FMC Technologies was awarded an $80m contract to provide subsea production system for the GirRI (Girassol Resources Initiative) project.
FMC will suplly three subsea production trees, six wellheads and various flowbase and jumper systems under an option three agreement.
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Hull of the floating production, storage and offloading (FPSO) unit
The bare hull was built in the Hyundai Heavy Industries (HHI) shipyard in Korea and moved out of dry dock in July 1999. It can store two million barrels of crude oil and support processes with a capacity of 200,000b/d.
It has an overall length of 300m, a moulded breadth of 59.5m, a moulded depth of 30.5m and a design draught of 22.77m. The design life of the hull is 20 years without dry docking.
Deadweight is 343,000t which includes 98% of cargo capacity and 50% of slop tanks.
The hull features a double-sided construction with 12 ballast wing tanks measuring 7m wide, as well as two fore-peak and two aft-peak ballast tanks. In total, it has 12 cargo tanks.
Topsides and accomodation
The main contractor, MAR Profundo Girassol - a joint venture between ETPM and Buoygues - was originally subcontracted to build the integrated deck at Fos-sur-Mer in France.
It subsequently re-awarded the contract to Hyundai. This deck is 180m long by 60m wide. It weighs approximately 20,000t.
It contains living quarters, oil treatment facilities, storage, metering and offloading, gas treatment and reinjection facilities.
The process deck is located 7m above the deck of the hull. It contains facilities for produced water treatment at a flow rate of 180,000BPD as well as facilities for three million m³/day gas lift, eight million m³/d gas compression at 285 bars and gas dehydration.
The living quarters unit is located at the aft end of the hull and is designed to accommodate 140 people in 80 cabins.
Mooring, risers and umbilicals of the west African FPSO
The FPSO was towed from Korea to Girassol, where the risers and umbilicals were installed and connected ready for commissioning and first oil.
The FPSO is spread-moored with 16 lines, four at each corner. The anchor lines are a composite assembly of chains and cables connected to 16 suction anchors.
The east side of the FPSO has been designed to receive the umbilicals and risers from three riser towers. Each of the riser towers is connected to the FPSO by a riser, each of which is 1.5m in diameter and 1,250m long, said to be proportionately equivalent to a 1m length of piano wire.
Floats 40m high and 8m in diameter are attached to the tops of the risers, along with flexible pipelines to carry the oil up into the FPSO. Each riser tower consists of 12 tubes arranged around a thick central pipe that acts as a backbone, and the whole assembly is sheathed in epoxy insulating material.
The riser towers were built by UK-based engineering company Acergy in Sonamet, Angola.
In addition, ten umbilicals are connected to the base of the riser towers. The west side of the FPSO is designed to receive further risers and umbilicals if needed.
The FPSO is designed for two offloading systems, one for normal operation with a buoy and one as back-up offloading, in tandem.
Both systems are located at the bow of the FPSO.
The main offloading system includes a loading buoy, located approximately one mile away from the bow of the FPSO. This can accommodate tankers from 80,000 to 400,000DWT, with a nominal offloading rate of 6,000m³/h through two rigid steel catenary 16in lines.
The tandem offloading is a conventional system with a mooring hawser assembly and handling system, and an offloading hose and its handling system. It is designed to accommodate tankers up to 200,000DWT at a nominal offloading rate of 8000m³/hour.
The field came on-stream in 2001. The average production from Girassol is about 240,000 bpd.