Jotun, North Sea Northern, Norway

Jotun is located on the Utsira High, between the Balder and Heimdal fields, approximately 200km west of Stavanger. Average water depth in the field area is 126m. Geologically, Jotun consists of the Elli, Elli South and Tau West structures.

RESERVOIR

The 4x5km Jotun reservoir lies in a Paleocene basin. The oil/water contact has been located at 2,091m below the seabed. The oil-column thickness in the exploration wells ranges from 18-46m.

Recoverable reserves are estimated at approximately 200 million barrels of oil (32 million m³) and 1.8 billion m³ of gas.

DRILLING

Reservoir development plans call for 11 horizontal oil producers, six water injectors and two wells that will produce injection water. Produced water from the oil processing will also be reinjected into the reservoir so as to provide aquifer support during production. Water-based drilling mud will be used whenever possible, while oil-based drilling fluid will be re-circulated and reinjected. The wells will have a measured depth of up to 7,000m.

FIELD DEVELOPMENT

Jotun is developed by the floating production and storage unit Jotun A and the wellhead/drilling platform Jotun B.

PRODUCTION VESSEL - JOTUN A

The production storage vessel is 233m long and 42m wide. The topsides construction was carried out at the Kvaerner Rosenberg yard at Stavanger, while the hull engineering and construction was carried out by the Kvaerner Masa Yards, in Finland. The production vessel hull has double sides and bottom.

The topsides contain processing, living quarters, power generation, utility systems, safety and emergency systems, support communication, control, instrumentation and electrical systems. The flare will be placed aft.

TOPSIDES - JOTUN B

The wellhead platform consists of an integrated deck with utilities, wellhead systems, a helideck, support systems and complete drilling facilities with derrick and mud facilities. Herema Tonsberg was a main contractor, in consortium with ABB Offshore Technology. The company carried out deck construction and WHP integration. The platform deck engineering and installation of electrical and instrumentation systems, along with the offshore hookup, were carried out by ABB, in Oslo.

The drilling facility was engineered by Bentec in Oslo, while the drilling module was fabricated by Kvaerner, at Teesside. The living quarters, with accomodation for 90 people, were built by Emtunga in Sweden. The total weight of the topsides is 7,800t.

JACKET

The sub-structure consists of a four-legged steel jacket with a piled foundation. The weight of the jacket is 6,300t. The 24 well-slot jacket was built by Aker Maritime at Oslo/Verdal.

RISERS AND FLOWLINES

The flowlines and risers transmit all produced fluids from the oil and water source wells running from the wellhead platform to the FPSO; and all the necessary water injection and gaslift from the FPSO.

Each riser is made of unbonded flexible pipe with a single-layer nylon pressure sheath. These are configured in a 'lazy-S' arrangement, which uses two buoyancy arches, 60m above the seabed. Risers are reinforced to avoid overload at the turret entrance below the vessel.

ACCOMMODATION

The living quarters, located in front of of the turret, were engineered and constructed by Consafe, in Aberdeen. They have accomodation for 60 people, as well as containing offices and recreation rooms.

PROCESSING

The production system contains the necessary facilities for inlet separation, crude-oil stabilisation and dewatering, gas dehydration, hydrocarbon dewpoint conditioning, sales and lift gas compression, product metering, and chemical and water injection systems. It has a design rate of approximately 100,000 barrels of oil a day and a storage capacity of 580,000 barrels.

TURRET

The production vessel will weathervane around the bow turret, which has a swivel system for transferring well-stream fluid/gas, injection water and gas, signals and power between the turret and the vessel. It is designed to accommodate seven risers, an integrated umbilical and a subsea isolation valve (SSIV) umbilical. This is anchored to the seabed using 12 mooring lines. The engineering and project management of the turret was carried out by Bluewater, in Holland.