Ekofisk oil field

Ekofisk is an oil field in block 2/4 of the Norwegian sector of the North Sea about 320 km southwest of Stavanger. Discovered in 1969 by Phillips Petroleum Company,[1] it remains one of the most important oil fields in the North Sea. This was the first discovery of oil after the drilling of over 200 exploration wells in the North Sea "triggered" by the Groningen gas field discovery.[2] In 1971, Phillips started producing directly to tankers from four subsea wells.[3] Oil production is planned to continue until 2048;[4] concessions given, yet expected to continue beyond 2050.[5]

The Greater Ekofisk Area consists of Cod oil gas and condensate field, Ekofisk, West Ekofisk, Tor oil field

Subsidence

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 the pore pressure declined and the effective stress increased, leading to subsidence.[12] Water injection was initiated to repressurize the reservoir, but due to the lower compaction strength of water-saturated chalk compared with oil-saturated chalk the seafloor continued subsiding and displacements of several metres were recorded. It was calculated that the total subsidence would almost be 6 m 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 m at the same time. The eventual solution suggested was to extend the steel tubular legs of the platforms. 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 17 August 1987, at 11:30 p.m. thanks to 108 hydraulic cylinders synchronised with a network of 14 NUM 760FCNCs.[13] The position tolerance of the cylinders with each other (+/- 3 mm for a 6 m extension per platform and +/- 100 mm 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 40000 t and was published in the Guinness World Records as being the largest jack-up.

References

The NPD's Fact-pages – EKOFISK] NPD, retrieved 2012-09-14^

Van den Bark, E., and Thomas, O.D., 1980, Ekofisk: First of the Giant Oil Fields in Western Europe, in Giant Oil and Gas Fields of the Decade: 1968-1978, AAPG Memoir 30, Tulsa, American Association of Petroleum Geologists, pp. 195-197^

Ekofisk Center SubseaIQ, Bishop Interactive, retrieved 2010-05-15^

Olje-og energidepartementet. Olje- og energiministerens tale til Olje- og energipolitisk seminar 2022 Regjeringen.no, 2022-05-10, retrieved 2025-01-11^

Ekofisk retrieved 19 September 2013^

ConocoPhillips Gets Go Ahead to Use Norpipe Oil Pipeline Until 2028 Rigzone, 2008-07-22, retrieved 2009-11-10^

Natural gas in the Nordic countries Nordic Energy Perspectives, March 2009, retrieved 2009-11-10^

Sulak, R. M. & Danielsen, J. (1989), Reservoir aspects of Ekofisk subsidence Journal of Petroleum Technology, Society of Petroleum Engineers, 41, 709-716^

Special Ekofisk NUM, October 1987, retrieved 2011-01-26^

Oil Rig Disasters – Ekofisk Bravo Platform^

Red Adair, Oilwell Firefighter, American Hero – His Story... retrieved 15 May 2010^

location map	North Sea
relief	yes
country	Norway
location	Central North Sea
blocks	2/4, 2/7, 7/11
offonshore	offshore
coordinates	56.5492°N, 3.20999°W
operator	ConocoPhillips Skandinavia AS
partners	Petoro Equinor Eni ConocoPhillips TotalEnergies
discovery	1969
start production	1971
oil production bbl/d	127000
production year oil	2013
formations	Ekofisk Formation and Tor Formation (Early Paleocene and Late Cretaceous ages)

Geology

Subsidence

Bravo blowout

Images

Further reading

See also

External links

References