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1 Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, Copenhagen K DK-1350, Denmark; finns{at}geo.ku.dk
2 Noreco ASA, Kongevejen 100 C, Holte DK-2840, Denmark; skj{at}noreco.com
3 DONG E&P, Agern Allé 24-26, Hørsholm 2970, Denmark; micen{at}dongenergy.dk
Finn Surlyk has been a professor of geology with special emphasis on sedimentary basins at the University of Copenhagen since 1989. Prior to that, he worked for the Geological Survey of Greenland where he was the head of the petroleum geology section. Before that, he was employed by the Geological Museum in Copenhagen. He obtained his Ph.D. and Dr. Scient. degree at the University of Copenhagen in 1971 and 1978, respectively. His main research has been focused on the evolution, dynamic stratigraphy, and sedimentology of the early Paleozoic Franklinian Basin in North Greenland, the Late Permian–Cretaceous rift basins in East Greenland, and the Late Cretaceous–Danian chalk sea in northwestern Europe. He is a member of the Danish Royal Society of Science and Letters and is an honorary fellow of the Geological Society of London. He is currently the president of the International Association of Sedimentologists.
Solvejg Kolbye Jensen obtained her M.Sc. degree at the University of Aarhus in 1998. She worked with Schlumberger in Stavanger in 1998–2000, with Denerco Oil AS from 2000, and she is currently a senior geophysicist with Noreco ASA. She has worked with company interests in the German, Dutch, British, Norwegian, and Danish North Sea sectors.
Michael Engkilde obtained his M.Sc. and Ph.D. degrees at the University of Copenhagen in 1990 and 1994, respectively. He has studied the sedimentology and sequence stratigraphy of the Middle Jurassic shallow-marine sandstones in East Greenland, which are excellent field analogs to the Middle Jurassic hydrocarbon reservoirs in the North Sea and mid-Norway shelf. After his Ph.D. he was employed by Denerco Oil AS and from 2006 by DONG E&P as a senior production geologist mainly working on the modeling of Paleogene remobilized and injected sandstone reservoirs in the Danish North Sea. He was appointed as the area exploration manager in 2007.
ABSTRACT
Reflection seismic lines from the Schillgrund High in the German North Sea sector show that the sea-floor deposition of the Upper Cretaceous–Danian Chalk Group was extremely irregular. The Cenomanian–Campanian part of the group is up to 600 m (1968 ft) thick and is dominated by pelagic, relatively horizontally deposited chalk. It was tilted toward the southwest close to the Campanian–Maastrichtian boundary time and was overlain by up to 800 m (2625 ft) of onlapping Maastrichtian–Danian chalk that was eroded and reworked by powerful synsedimentary bottom currents. A north–south to north-northwest–south-southeast–trending slope-parallel multistorey channel system, branching toward the northwest into smaller, laterally directed arms, was developed in Maastrichtian–Danian times. It was more than 200 km (124 mi) long, up to 15 km wide (9 mi), and 200 m (656 ft) deep. The main channel system was eroded by powerful contour-parallel bottom currents, interpreted as having flowed toward the southeast based on the depositional geometry of the channel fill. Successive channel axes were systematically shifted downslope, leaving a series of slightly offset, nested slope-parallel channels. The channels were filled laterally, obliquely, or longitudinally by chalk drifts. Sediment gravity flows were a factor locally but were not integral parts of the depositional system. Erosion, winnowing, sorting, and redeposition by the bottom currents are interpreted to have resulted in channel-parallel porosity-permeability zones. The seismic data indicate that the chalk adjacent to the main channels retained high porosity calculated from logs in an exploration well drilled in 2005. The chalk is of excellent reservoir quality with effective porosity averaging 37%, reaching 50%, and some levels are completely unconsolidated. The influence of powerful syndepositional bottom currents on the anisotropy of reservoir properties of chalk is only now beginning to be realized, chalk having traditionally been considered a monotonous and uniform rock type.
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