Ekofisk oil field
Ekofisk is an oil and gas field on the Norwegian continental shelf in the central North Sea. With estimated reserves of 3.8 billion barrels, it is after Statfjord the largest oil field in the North Sea. The discovery of the Ekofisk field in 1969 triggered the oil boom in the North Sea. Current operator is ConocoPhillips Scandinavia AS, other members in the Ekofisk consortium are Total, Norsk Agip, Norsk Hydro and Statoil. The field is about 270 kilometers from the mainland coast, is located in the Central Graben, at just north of the border between the Norwegian and Danish sector of the North Sea.
Geology
The floor above the North Sea Ekofisk field is located in 70 to 74 meters water depth, is relatively flat and consists of fine sand. The Ekofisk plants recover oil mainly from the Ekofisk rock layer, which is approximately 3000 to 3500 meters depth. It consists of secondary chalk. The coccolith deposits from the Late Cretaceous were eroded in Cenozoic and then broke away in today's Ekofisk field. During the deposition encamped on the chalk layer of impermeable mudstone from which later prevented migration of the bound water in the Cretaceous and later the oil upward. This is the pressure in the rock pores at 1.4 times the normal at this depth. The reservoir temperature is about 130 degrees Celsius.
The pressure made sure to keep the pores open. Today, the porosity is close to 50 percent, that is half of the chalk layer consists of pores. Similar rocks have a porosity of 3 to 40 percent, with 10 to 20 percent is the normal case, and even 40 percent is a rare exception value. By means of a salt dome below the vertebrate chalk chalk developed a high permeability. The salt dome stretched out over time, pressed the chalk upwards, this movement set off numerous pores and allied themselves with each other. This exceptionally high permeability allows a good permeability to the crude oil, which contributed to the suitability of the Ekofisk formation as an oil reservoir.
Since 1985, the floor in the Ekofisk field decreases due to this oil production. The pressure caused by the micro pores close after oil is pumped out. This reduction is most pronounced in the eligible area of the North Sea and had not been seen before. It is approximately half a meter per year. To further ensure the safety of oil rigs off a hundred-year wave, the central oil rig had to be subsequently increased consuming and costly. When continuing the reduction, new platforms were built.
History
The Phillips Petroleum Company discovered the field on 23 December 1969, and thus led the first successful exploratory drilling through the North Sea. After the development began in 1971 production. Ekofisk is currently Norway's most important oil deposit and after the Statfjord field, the largest oil deposit found in Norway. It was declared a National Monument in 2001. The area of the Ekofisk field was among the first licensing round in Norwegian waters. This was one of the two rounds, which took place without the direct influence of the state and the only one that was completely run by private companies.
The construction of the Ekofisk tank in 1971 a new generation of drilling began. These were a Erdölsilo, built like a grain silo, which was divided into nine areas, and on an area of 50 meters x 50 meters, 90 meters reached. It was surrounded by a breakwater with 95 meters in diameter. Was produced cement construction in deep but sheltered waters of a fjord from prefabricated sections that were placed on the floating foundation.
Since the Norwegian government did not allow the flaring of natural gas, closed Philipp Petroleum in 1973 a contract with a consortium of Ruhrgas, Gaz de France, Distrigas and Gasunie, who undertook all natural gas from the take off field at a price that was directly coupled to the oil price. A short time later, an identical contract between the same parties came into being for the neighboring Eldfisk field. The gas pipeline that brings gas to the Continent, is the Europipe across the Lower Saxony Wadden Sea to Emden. With a nearly 350 -kilometer pipeline, the field is tied to the refinery since 1980 Seal Sands on the north bank of the River Tees in Northern England.
Mid-1980s, it was found that the Ekofisk oil field, and in particular the Ekofisk platforms began to decrease quite unexpected. Detailed geological investigations showed that this was the result of delayed compaction of the existing of a Chalk Formation oil reservoirs in the rock.
Was produced as hydrocarbon and replaced with water, the chalk began due to microscopic intergranular high-pressure compounds dissolve and formed a new to a more compact, less porous structure. It has been determined a movement of several meters. Calculations from Phillips Petroleum showed that had to be expected a reduction of nearly 6 meters at the end of the compression phase. The Norwegian Government urged Phillips to be active. The French TECHNIP consultant was commissioned to find a solution.
Since 5 of 7 platforms were connected together, they had to be simultaneously lifted about 6 feet. The solution was to extend the tubular steel legs of the platforms. On the legs of the platforms large flanges were welded and then the legs were cut off above the flanges. How could five platforms simultaneously raised in a large-scale operation about 6 feet and then extension tubes are used. After fitting all the flanges, the platform was again safe and stable.
The 4 -day increase was completed on August 17, 1987 at 11:30 clock, thanks 108 hydraulic cylinders synchronized with a network of 14 NUM 760 CNC controls. The position tolerance of the cylinder with each other (3 mm for the 6 meter rise per platform and max. 100 millimeters between the platforms ) had to be kept for 38 hours. While the flanges were welded to the legs, the hydraulic cylinder bore the whole burden. A few days before the hotel platform was raised, which was not connected with the other platforms. The total capacity of all cylinders was approximately 40,000 tons and was published in the Guinness Book of Records as the largest salvage work.
Early 2000s examined the Norwegian Oljedirektoratet whether an enhanced oil recovery would be worth in the oil fields Ekofisk and Gullfaks. But she came to the conclusion that the technology would be economically only at an oil price between 22-33 USD / barrel, while industry estimates foresaw at that time for the future of an oil price 27-33 USD / barrel. The project was then discarded.
Effects
The field was the scene of several serious accidents.
In 1977 at the Ekofisk Bravo One of the largest held blowouts occurred on an offshore oil field. In seven days flowed 23,000 tons of crude oil in the North Sea, spreading over an area of 40,000 square km are. Victims of which were especially seabirds, took very little damage while other marine organisms.
A few years later it came to the then largest disaster in the offshore oil production, as on 27 March 1980, the platform " Alexander L. Kielland " capsized, where 123 people lost their lives. A monster wave hit the platform "Two -Four -delta " in the second year of its existence. The 30-meter wave cost no life, as the Two -Four - Delta was still in the construction stage, but a larger part of the substructure suffered permanent damage.
The Ekofisk field was one of the first in which the effects of drilling platforms have been explored as an artificial reef. In the late 1970s showed pivotal trials with and nets a remarkable concentration of cod in the immediate vicinity of platforms. Their rate fell by half each in 50, 100, and 200 meters from the platforms. The researchers conducted the increased cod stock fall high krill rates that probably accumulated in the vicinity of the platforms due to artificial lighting and circulation changes.