| Ekofisk | |
|---|---|
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| Country | Norway |
| Location | Central North Sea |
| Block(s) | 2/4, 2/7, 7/11 |
| Offshore/onshore | offshore |
| Coordinates | |
| Operator(s) | ConocoPhillips Skandinavia AS |
| Partners | Petoro Statoil Eni ConocoPhillips Total S.A. |
| Field history | |
| Discovery | 1969 |
| Start of production | 1971 |
| Production | |
| Producing formations | Ekofisk and Tor chalk formations (Early Paleocene and Late Cretaceous ages) |
Ekofisk is an oil field in the Norwegian sector of the North Sea about 200 miles (320 km) southwest of Stavanger. Discovered in 1969[1], it remains one of the most important oil fields in the North Sea. Production began in 1971[1] after the construction of a series of off-shore platforms by Phillips Petroleum Company. Oil production is planned to continue until at least 2050.
Ekofisk reservoir consists of Cod, Ekofisk, West Ekofisk, Tor, Albuskjell, Eldfisk, Edda and Embla oil fields. The Ekofisk Center is a vast complex of platforms and structures creating a transportation hub also for surrounding fields such as Valhall, Hod, Gyda, Ula, Statfjord, Heimdal, Tommeliten and Gullfaks. The whole complex consists of 29 platforms.[2] Produced oil is transported by the Norpipe oil pipeline to the ConocoPhillips Teesside Terminal in the United Kingdom.[3] Natural gas is transported by the Norpipe gas pipeline to Emden in Germany.[4]
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In the mid-1980s the Ekofisk field as a whole and the platforms in particular were found to be suffering from an unexpected degree of subsidence. Detailed geological investigation showed that it was the result of delayed compactional diagenesis of the Chalk Formation reservoir rocks. As hydrocarbons were produced and replaced with water, the Chalk began to re-dissolve due to high-pressure inter-grain contacts and redeposit in a more compact, lower porosity configuration. Movements of several metres were recorded, and it was calculated that the total subsidence would almost be 6 metres (20 ft) at the end of the concession of Phillips Petroleum, too much to keep the platforms secure.
The Norwegian government pressed Phillips to take action and the French company TECHNIP was ordered to find a solution. As 5 of 7 platforms were interconnected, they had to be jacked-up by about 6 metres (20 ft) at the same time. The solution was that the steel tubular legs of the platforms would be extended. Subsequently large flanges were welded to these legs and when all flanges were welded and the legs cut, five platforms would be lifted simultaneously in one operation then extension pipes would be mounted in between the flanges. After bolting all flanges the platforms would be safe again.
The four days lifting was completed on August 17, 1987 at 11:30 pm thanks to 108 hydraulic cylinders synchronised with a network of 14 NUM 760FCNCs[5]. The position tolerance of the cylinders with each other (+/- 3 millimetres (0.12 in) for a 6 metres (20 ft) extension per platform and +/- 100 millimetres (3.9 in) between platforms) was to be kept for 38 hours. During the welding of the flanges to the legs, these hydraulic cylinders took over the entire load. A couple of days before this great jack-up, the hotel platform was lifted, as it was not interconnected with the others. The total lifting capacity of all these cylinders was approximately 40,000 tonnes (39,000 long tons; 44,000 short tons) and was published in the Guinness book of records as being the largest jack-up ever.
In April 1977, an oil well blowout occurred at the Ekofisk Bravo platform, due to an incorrectly installed downhole safety valve.[6] At an estimated 80,000–126,000 barrels (13,000–20,000 m3) total, this is the largest blowout in the North Sea. Red Adair and his crew assisted with capping the blowout.[7]
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