Usan Oilfield, Nigeria

In February 2008, Total was given approval from the Nigerian Government to begin the development of its offshore Usan field. Discovered in 2002, Usan lies in licence block OPL 222, around 100km south of Port Harcourt, in water depths ranging from 750m to 850m.

The field is operated by Elf Petroleum Nigeria (20%) on behalf of equity partners Chevron Petroleum Nigeria (30%), Esso Exploration and Production Nigeria (Offshore East) (30%) and Nexen Petroleum Nigeria (20%).

Proven and probable reserves of Usan were put at in excess of 500 million barrels of oil. Usan is expected to come onstream in 2012 and to ramp up quickly to a plateau production of 180,000bpd of oil. The associated gas will be reinjected in the reservoir.

Usan field development

The development of the Usan field involves 23 production wells and 19 water and gas injection wells connected to a two-million-barrel capacity floating production, storage and offloading (FPSO) vessel by subsea lines and risers. The processing capacity is around 150,000bpd. First oil is planned for 2010.

The Usan-1 discovery well encountered significant net oil pay. It was production tested at a restricted rate of 5,000bpd. The nearby Ukot field was discovered in 1998 and also encountered significant net oil pay, testing at a rate of 13,900bpd.

This was followed by Usan-2, which was located approximately two miles west of the discovery well and tested an up-dip portion of the fault block. Usan-3 was drilled approximately one mile north-west of the discovery well and tested a separate fault block.

The Usan-3 well was production tested and produced 5,600bpd under restricted flow conditions. Ukot-2, an appraisal well on the separate Ukot discovery, spudded in 2008.

Usan-4, located 5km south of the discovery, was drilled in 2003. It flowed at the rate of 4,400bpd from the first interval and 6,300bpd from the second interval. Usan-5 well was located 6km west of the discovery.

Usan-6 appraisal well was drilled around 4km south of Usan-5 in water depths of approximately 850m. During the well test Usan-6 flowed at a rate of 5,800bpd under restricted flow conditions.

In 2005, Usan-7 and Usan-8 confirmed an eastern extension of the Usan field. Both wells were drilled using Transocean's semisub MG Hulme.

FPSO

The construction of the FPSO for the project was started by Hyunday Heavy Industries in 2008. The vessel wil be 320m long and 61m wide, and will weigh 114,000t. The construction of the FPSO is expected to be completed by late 2011.

Usan contractors

Cameron was awarded a contract with a value of approximately $650m to provide subsea systems for the initial phase of the 44-well Usan subsea development.

Under the $1.3bn contract, Cameron will provide subsea systems engineering and project management along with subsea Christmas trees, production and intervention control systems, manifolds, flowline connection systems, installation support and associated spares for Total's Nigerian subsidiary. Further, Cameron subcontracted Acergy to provide fabrication, assembly and testing of eight manifolds and associated structures. Saipem was awarded the contract for the umbilicals, flowlines, risers and oil loading terminal activities.

The contract work includes the engineering, procurement, construction, installation and pre-commissioning facilties. In addition, it also requires Saipem to assist in the commissioning and start-up of the subsea umbilicals (72km), flowlines (61km) and risers connecting the 42 subsea wells to the FPSO, along with the oil-loading terminal, consisting of an offloading buoy and two offloading lines and part of the FPSO anchoring system.

Fabrication will be carried out locally in Nigeria, mainly in Saipem's Rumuolumeni yard. The offshore installation will be carried out by the highly specialised vessels Saipem FDS and Saipem 3000, in water depths ranging from 730m to 850m, between the fourth quarter of 2010 and the fourth quarter of 2011.

West Capella drilling rig

West Capella drilling rig was built by Samsung Heavy Industries at Samsung's South Korea shipyard. The rig can operate at 10,000ft underwater and has a maximum drilling capacity of 37,500ft. The rig was positioned at the field in April 2009.