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2.1.2 The Early Days of North Sea Seismic Surveying


In April 1965, Norway announced the country’s first concession round for oil and gas exploration on the shelf: Norway’s oil age had started! Te first exploration well was Esso’s well 8/3-1,


a


drilled in 1966. Te well confirmed reservoirs, cap rocks and potential source rock but no hydrocarbons were found and it was abandoned as a dry hole. Te second well, 25/11-1, drilled in 1966–67 by Esso, was located on the Utsira High in the northern North Sea. It encountered gas and live oil in early Eocene sands, and the first litres of oil from the Norwegian continental shelf were brought to the surface by a formation interval test. However, the reservoir rocks were too thin and the geology too complex, so the well was abandoned as a non-commercial oil discovery. Seismic data at the time was inadequate to investigate the lithology of this portion of the North Sea Basin. Five years later, in 1974, well 25/11-5 discovered the Balder Field when it encountered a 25m oil column in the Paleocene, demonstrating the potential for a commercial accumulation, but it took a total of 18 exploration and appraisal wells and two seismic 3D surveys (1979 and 1988) before Esso decided to develop the field. With the completion of the 10th well, 7/11-1, in June 1968, the first Norwegian commercial discovery was made – the Cod gas-condensate field – but further drilling disappointments led to a reduction in drilling in 1969, as by then companies had already drilled 33 dry holes and spent NOK 750 million on the Norwegian shelf. But then, in August 1969, Phillips started drilling well 2/4-1, which eventually led to the discovery of Ekofisk – the first billion-barrel oil field in Western Europe. Tis was also the first commercial discovery of oil in the whole of the North Sea, despite the drilling of more than 200 exploration wells.


b


Figure 2.5: Photos from a 1966 article by Birger Rasmussen (Institute of Marine Research) published in the journal Norsk Natur (Norwegian Society for the Conservation of Nature). (a) The recording vessel is to the left and the shooting vessel in the middle. The high spurt of the water column (typically 15–45m) is a result of the explosive being detonated at quite a shallow depth (1–1.5m). (b) The explosive was contained in a pail which hung from a plastic balloon with electric cord to the vessel. It was fired approximately one–two vessel lengths behind the ship. The explosives varied from 2–25 kg, and were detonated at shallow depths to avoid bubble pulses. When high-explosive dynamite and TNT were forbidden due to the steep and high pressure front of the pressure wave, they were replaced by ammonium nitrate, which burns less rapidly and produces a smoother pressure front with smaller amplitude than dynamite.


Drilling for oil requires acquiring seismic, which was mainly


Figure 2.6: Havbraut I sailing from Middlesbrough Dock in August 1966. She was completed in Flensburg in 1949 as a steam trawler. In 1942 she was bought by Austevoll Shipping and rigged as a purse seiner fishing boat. Her length was 157 feet and she had cabins for 20 men. Havbraut I can be considered to be the first cultural meeting place between American oil explorers and Norwegian seamen. Onboard Norwegian waffles with brown cheese and coffee would be served.


done by specialist service companies like Geophysical Services International (GSI), Seismograph Service Ltd (SSL), Prakla, Compagnie Générale Géophysique (CGG), and Western Geophysical Co. In the North Sea the first commercial


seismic surveys took place in 1962. GSI acquired data offshore eastern Great Britain and Scotland, whereas Prakla undertook the first ones on the German shelf. From 1963 to 1965 almost 20,000 km of seismic lines were shot over the Norwegian sector of the North Sea for the oil companies Shell, Phillips, BP, American Overseas Petroleum Limited (Norsk Caltex Oil), Superior Oil, Petronord (a joint venture between French oil companies and Norsk Hydro), and Te Norwegian Oil Consortium (a group of Norwegian industrial companies). More than 50 vessels were involved. In the whole of the North Sea, it has


been estimated that around 210,000 km of seismic lines were acquired during the same time span (Johansen, 2012).


60


Teesside branch of the World Ship Society – Albert Weller Slide Collection


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