Ekofisk oil field
| Company type | Oil reservoir |
|---|---|
| Industry | Petroleum industry |
| Founded | 1969 |
| Founder | Phillips Petroleum Company |
| Headquarters | Norway |
Area served | North Sea |
| Products | Crude oil, natural gas |
Ekofisk is an oil reservoir situated in block 2/4 within the Norwegian sector of the North Sea, located roughly 300 kilometers southwest of Stavanger. Discovered in 1969 by Phillips Petroleum Company, it continues to be a significant asset in the North Sea region. This find came after extensive exploration activities spurred by the discovery of the Groningen gas field. Production commenced in 1971, initially utilizing four subsea wells that supplied oil directly to tankers. Plans indicate oil extraction will persist until 2048, with licenses suggesting operations could extend past 2050.
The Greater Ekofisk Area encompasses several fields including Cod, Ekofisk, West Ekofisk, Tor oil field, Albuskjell oil and gas field, Eldfisk oil and gas field, Embla oil and gas field, and Edda oil and gas field. The Ekofisk Center functions as a central platform complex and transportation hub servicing adjacent fields such as Valhall, Hod, Gyda, Ula, Statfjord, Heimdal, Tommeliten, and Gullfaks. This complex consists of 29 platforms.
Extracted crude is conveyed through the Norpipe pipeline to the Teesside Refinery in the United Kingdom, whereas natural gas is transported via the Norpipe gas pipeline to Emden in Germany.
Geology
Ekofisk is characterized by a north–south oriented anticline featuring a central graben, covering an area of approximately 32 square kilometers. It exhibits around 120 meters of vertical closure with a hydrocarbon column extending roughly 270 meters. The structure was shaped by movements of Permian Zechstein salt, which formed salt pillows. Hydrocarbon-bearing zones are located at depths near 3 kilometers, mainly within the Paleocene Ekofisk Formation and the Upper Cretaceous Tor Formation. Both formations consist of chalk reservoirs possessing porosity levels between 30% and 40%. The reservoir rock is a fine-grained chalk composed predominantly of remains from pelagic unicellular algae. Source rocks are identified as Upper Jurassic Kimmeridgian shales.
Seismic reflection methods in the 1960s led to the discovery; however, initial interpretations were challenging due to high gas saturation causing reduced seismic velocities. Nevertheless, the high porosity of reservoir rocks enhances seismic amplitude, facilitating net pay estimation through isopach mapping.
Subsidence
During the mid-1980s, significant subsidence was observed at Ekofisk platforms caused by delayed compactional diagenesis within the chalk reservoir rocks. The reduction in pore pressure from hydrocarbon extraction increased effective stress in the formation, resulting in seafloor subsidence. Attempts to repressurize the reservoir through water injection proved inadequate because chalk saturated with water has a lower compaction strength than when saturated with oil. This led to several meters of subsidence. By the conclusion of Phillips Petroleum’s concession, total subsidence was expected to approach 6 meters, posing risks to platform stability.
Responding to concerns from Norwegian authorities, Phillips enlisted French company Technip to devise a solution. Since five out of seven interconnected platforms needed simultaneous elevation by approximately 6 meters, the approach involved lengthening their steel tubular legs. Large flanges were welded onto these legs before cutting; then hydraulic cylinders lifted all platforms concurrently while extension pipes were inserted between flanges and secured with bolts.
The operation lasted four days and concluded on 17 August 1987 at 11:30 p.m., utilizing 108 hydraulic cylinders coordinated by 14 NUM 760FCNC control systems. Positioning accuracy was maintained within ±5 millimeters per platform and ±10 millimeters between platforms over a continuous period of 38 hours. During flange welding, hydraulic cylinders supported the entire weight load. The hotel platform underwent lifting separately prior to this procedure. The total lifting capacity of about 39,000 tonnes earned recognition in the Guinness World Records as the most substantial jack-up lift ever executed.
Bravo blowout
In April 1977, the Ekofisk Bravo platform experienced a blowout caused by a downhole safety valve that had been installed improperly, resulting in what is considered the largest blowout in the North Sea. The incident was brought under control with the expertise of famed oil well firefighter Red Adair and his crew, who played a crucial role in sealing the well.
Further reading
See also
- List of oil and gas fields of the North Sea
- Commercial offshore diving in the North Sea
- List of oil spills
- Alexander L. Kielland (platform) 1980 disaster