Lufeng 22-1, South China Sea, China

The Lufeng 22-1 oil field lies 250km south-east of Hong Kong in the South China Sea, in 333m of water. Recoverable reserves are estimated at 30 million bbls, representing a recovery factor of approximately 25% of oil-in-place.

Lufeng 22-1 is prone to tropical cyclones that have an average passing speed of 18-22km/h, (50km/h max) and an average duration of 26 hours, which generate waves up to 8m high. The South China Sea is also subject to a cold wave from Siberia, causing force six winds and correspondingly, very rough seas.

FPSO

Statoil selected an FPSO based on a multi-purpose shuttle tanker (MST) for developing the field. The shuttle tanker Navion Munin, built by Samsung Heavy Industries, in Korea, was selected for upgrading to an FPSO.

The Navion Munin is a 103,000dwt multi-purpose ocean-going single-screw tanker, with diesel-electric propulsion. Two electrically driven side thrusters, each 2,000kW, with controllable pitch propeller (CPP) are installed in the bow and two 3,000kW retractable azimuth thrusters are located in front of the pump room.

The hull is designed with the main engine room and accommodation in front, with the cargo/ballast pump room and the engine room housing the electric propulsion motors behind. The cargo tank section consists of 18 cargo tanks, plus two slop tanks with a total cargo capacity of 101,400m³. All cargo tanks are protected by a double bottom and ballast tanks at the sides. There are two longitudinal bulkheads in the cargo section, with one centretank and two sidetanks of equal breadth. The ship is provided with a pump room for cargo and ballast pumps located aft of the cargo section.

The living quarters can accomodate 55 people and are located at the front of the vessel. Electricity is provided by four 5,200kW Wartsila 6R46A engines and one Wartsila 9R20 engine with a generator output of 1,100kW.

PROCESS SYSTEM

Production on-board the FPSO has been designed to process the wide range of oil and water rates expected from the Lufeng 22-1 field, under severe metocean conditions. The design for the Lufeng 22-1 facilities are based on a capacity of a 60,000b/d instantaneous oil rate (for the start of field life) and a maximum throughput capacity of 125,000b/d (as watercut increases).

The production facility includes a first-stage production separator, a second-stage separator, an electrostatic coalescer and crude transfer pumps.

Wellstream fluid arrives on the FPSO via two flexible production risers and is directed to the production separator via the production manifold.

The oil from the crude heater is then routed to the second stage separator, where gas is flashed off. Produced gas from the separation equipment is cold vented. From the separator, oil is pumped by means of two centrifugal pumps, through the coalescer, where water is removed. The water from the coalescer is then pumped back to the first-stage separator by a centrifugal pump.

From the coalescer, oil is cooled to 70°C in a plate cooler. Finally, processed crude oil is routed to storage tanks, where heating coils keep the temperature of the crude oil at 65°C.

SUBSEA

The field is developed with five subsea horizontal production wells drilled through a five-slot template on the seabed. One of these has the longest horizontal section ever drilled off China - it is 2,060m long. The wells produce into an integral manifold, installed on the template.

The FPSO is moored with a conventional catenary mooring system, consisting of six symmetrically spread mooring lines, all connected together at the upper end to a disconnectable STP buoy.

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