The Yoho field lies in Oil Mining Lease (OML) 104, offshore Nigeria. ExxonMobil’s subsidiary MPN holds a 40% interest in the joint venture and the Federal Government of Nigeria holds the remaining 60% interest through the Nigerian National Petroleum Corporation (NNPC).

The completed project incurred a cost of approximately $1.3bn and recovered an estimated 0.44 billion barrels of oil from the Yoho and Awawa reservoirs. These reservoirs lie in a water depth of between 200ft and 300ft.

Yoho serves as a hub for future development of other OML 104 petroleum resources.

ExxonMobil employed a temporary FPSO vessel as the basis for the initial stages of the development. This was used as an early production system (EPS), ensuring that the first oil from Yoho came onstream almost two years ahead of full-field start-up.

Production through the FPSO reached over 90,000 barrels of oil a day. This marked the first deployment using an EPS system in West Africa. The FPSO was operated by Esso Deepwater, an ExxonMobil subsidiary.

The full-field development involved 33 wells over wellhead platforms, a central production platform and a living quarters platform as well as an FSO vessel to replace the EPS. Full-field start-up was scheduled for late 2004, but started in January 2006 with around 150,000bopd produced.

The produced gas is re-injected to eliminate routine flaring and maximise oil recovery.

FPSO Falcon

The FPSO Falcon, formerly the Amazon Falcon VLCC, was installed over the Yoho field offshore Nigeria in a water depth of 64m.

The system was converted from the existing tanker into the FPSO in Singapore and Dubai. The FPSO Falcon registers 315,000dwt and has a storage capacity of 2.2 billion barrels.

It is equipped with an external turret mooring system and production facilities capable of producing 100,000bpd of oil and 100 million cubic feet of gas per day.

The swivel stack can accommodate six 10in risers as well as three umbilicals. On Yoho, the swivel stack can contain two 12in low pressure production streams, two 12in high pressure production streams, a 10in water injection swivel (spare) and a 6in pigging swivel. It also has a low pressure utility swivel, an electric swivel and a 6in gas injection swivel.

The turret can accommodate a maximum throughput of 90,000 barrels oil per day.

The system specification includes a 95 million cubic feet per day of gas injection capacity, a 20 million cubic feet per day of gas lift and export capacity while the water injection system can inject up to 90,000 barrels of water per day. These facilities have been provided by Single Buoy Moorings (SBM).

Classification and certification

ABS was contracted by SBM to provide classification and certification services, including condition assessment of tankers, technical design review, surveys during refurbishment, conversion and hook-up and commissioning of this and two other FPSOs offshore West Africa.

Using the ABS classification society, it was assigned a new class notation +A1 Floating Offshore Installation and issued an IMO MODU Safety Certificate on behalf of the Bahamas Flag administration.

YOHO platform installation

The Saipem and Bouygues Offshore subsidiary Saibos was awarded the contract to develop Yoho. The scope of work included: project management, engineering, procurement, construction, transportation and installation, hook-up and commissioning of one production platform, pipeline laying and the other facility installation.

The vessel Castoro Otto installed the platform and laid the pipelines. The vessel Saipem 7000 installed the deck by 2005.

ExxonMobil is particularly active in Nigeria, with a portfolio including six deepwater blocks covering 3.2 million acres. These discoveries include Bonga and Bonga Southwest in OML 118 (20% equity), Chota in OPL 220 (47.5% equity) and Usan in OPL 222 (30% equity).

The company also has a 56.25% share in Erha located in OPL 209 and a 20% stake in Bolia in OPL 219.