Visund was developed using a semi-submersible steel drilling, production and quarters platform, connected to a subsea completion system.
The wellheads for 21 wells are installed under the platform, with a separate template for two other wells, located 8km away to the north of the platform. The field began its gas production and exportation on 7 October 2005.
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StatoilHydro is the major stakeholder in the field with a 53.2% share. The other stakeholders are Petoro 30%, Norske ConocoPhillips 9.1% and Total E&P Norge 7.7%.
StatoilHydro plans to temporarily shutdown the Visund field along with another 20 fields, for expansion and maintenance.
In June 2009, StatoilHydro discovered oil in the Norwegian Sea’s Tampen area, which is located north-east of the Visund field production centre. Two wells 34/8-13A and 34/8-13S have been drilled on the Titan structure of the area.
It is estimated that the wells contain five to 12.5 million recoverable barrels of oil equivalent. They will be tied-back to Visund.
Visund field location
Located roughly 140km west of Sogne Fjord, Visund comprises four reservoirs. It lies in licence 120, blocks 34/7 and 34/8.
The licence was awarded in late 1985 in the tenth round. Visund lies 27km away from the Gullfaks field in a water depth of 335m.
Visund field well production
For the overall field development, a total of 24 wells were drilled in the vicinity of the platform. These can be broken down into 14 oil producers, two water injectors, six gas injectors and one gas producer. There will also be two spare slots.
Two further oil producers will be drilled 8km to the north-east. Overall reserves in the field are estimated at 304 million barrels of oil and 51 billion cubic metres of gas.
Reservoirs
Visund is developed from two reservoir groups called Statfjord / Amundsen and Brent.
Statfjord / Amundsen reservoir
The depth to the Statfjord / Amundsen reservoir is 2,900m and that to the oil / water contact is 3,095m. The depth to the gas / oil contact is 2,811m.
The reservoir has recoverable reserves of 13.5 million cubic metres of oil. The oil column is 150m-high and the gas column 90m-high. The reservoir has a 266m³ / 512m³ gas-to-oil ratio.
The reservoir pressure is 450bar and its temperature is 115°C.
Brent reservoir
The water depth to the Brent reservoir is 2,900m and the depth to the oil / water contact is 2,820m. The depth to gas / oil contact is 2,904m.
The field has recoverable reserves of 35 million cubic metres of oil. The oil column is 40m-100m and the gas column is 110m.
It has a 180m³-230m³ gas-to-oil ratio. The reservoir pressure is 425bar and the temperature is 115°C.
Tampen area oil reserves
The first 13A well has a small oil column in Upper Jurassic sands and the second has found oil in Brent group. It is drilled 2.7km to the south-east.
In October 2008, the drilling of 34/8-13S well conformed the delineated Pan / Pandora gas and oil columns.
The well 34/8-13 A is the 23rd well while 34/8-13 S is the 24th well in Visund’s licence PL120. The depth of 13A is 3,108m and is terminated in the Statfjord formation, while the depth of 13S is 3,258m and is terminated in the Hegre group.
The oil found in eastern direction is delineated by the 34/8-14D well, whose drilling was completed in the first quarter of 2009. The oil and gas columns in indicating concurrent hydrocarbon contacts were conformed by the well.
In December 2008, the drilling of 34/8-14A appraisal well was completed, while the sidetrack 34/8-14S will be drilled from 34/8-14A. The well 34/8-14C will be drilled in the lower flank of the segment.
Visund field development strategy
Due to the overall economics and the operational flexibility needed to handle the complex reservoir conditions, as well as to operate in water 335m-deep, Norsk Hydro selected a semi-submersible production / drilling / quarters (PDQ) facility for the Visund development.
The platform is located directly above the subsea completed wells. It is 121m-long and 95m-wide. The height to the upper deck is 27m and that to the lower deck is 20m. It has a 21m draught and a displacement of 52,600t.
The platform has a topside weight of approximately 25,000t, including process facilities for both oil and gas.
The Visund semisubmersible has enough space for 28 risers on the production side, as well as the capacity for ten non-hazardous risers in the living quarters area. The processing facilities have a design capacity of 16,000 cubic metres a day (m3/d) of oil and 28,000m³/d of liquid. It has a water-injection capacity of 18,000m3/d.
Gas production is rated at ten million cubic metres a day and gas injection is ten million cubic metres a day. The total gas-production capacity is 18 million cubic metres a day.
Visund living quarters
Visund has a maximum capacity for 120 people in its living quarters, although it will normally house just 28 people during normal operations. The living quarters are a modular aluminium structure, located above the utility module.
The construction of the Visund platform was carried out under an under an engineering procurement and construction (EPC) contract with Umoe. An Umoe / GVA 8000 semi-sumbersible design was selected in March 1996, based on functional specifications and process data.
The structure was fabricated at three locations. The substructure was fabricated by Kvaerner Rosenberg in Stavanger. The living quarters were built by Leirvik Sveis at the Stord Island yard and the remaining two deck sections were fabricated at the Haugesund yard.
Visund field pipeline systems
A 16in ID riser was delivered to Visund by NKT Flexibles I/S in April 2005. NKT also supplied important accessories, including fire protection, tether clamps, buoyancy modules, bending stiffeners and hang-off systems.
The gas from the Visund floating production unit is transferred to a subsea tee at the Kvitebjørn gas pipeline by means of NKT riser and a new 34km-long, 20in pipeline.
