Large-scale development of the mid-Norwegian shelf over the last three million years and potential for hydrocarbon reservoirs in glacial sediments
Published:January 01, 2012
Dag Ottesen, Julian A. Dowdeswell, Leif Rise, Tom Bugge, 2012. "Large-scale development of the mid-Norwegian shelf over the last three million years and potential for hydrocarbon reservoirs in glacial sediments", Glaciogenic Reservoirs and Hydrocarbon Systems, M. Huuse, J. Redfern, D. P. Le Heron, R. J. Dixon, A. Moscariello, J. Craig
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About 3 million years ago, major ice sheets developed over Scandinavia and began to deliver large volumes of sediment to the mid-Norwegian shelf. The shelf was built out in a prograding pattern towards the west, and more than 1000 m of sediments was deposited over large areas on the middle/outer shelf. The dominating large-scale depositional pattern is a series of prograding wedges and flat-lying, sheet-like units mainly of glacial origin. On top of these units are flat-lying till units deposited during the last few glaciations, commonly separated from the underlying units by one or several erosional unconformities. The lithology of these layers is generally fine-grained, mainly clay and silt, but with sporadic clasts up to boulder size. Based on regional and detailed bathymetry, the ice-flow pattern from the last glaciation has been reconstructed on the shelf. This involved a very dynamic ice sheet with fast-flowing ice streams in the transverse, cross-shelf troughs, separated by more passive ice domes on the intermediate shallow banks. The ice streams appear to follow the cross-shelf troughs from glaciation to glaciation, but occasionally they switched to new flow paths. The thick Quaternary sediments on the outer part of the mid-Norwegian shelf represent a challenge for hydrocarbon exploration. Several large slides have occurred from the shelf break and down the continental slope. During the last few years there has been an increased focus on investigating the Quaternary succession in order to search for hydrocarbon prospects. The potential for finding reservoirs in these sediments is discussed, and a few examples of gas discoveries are shown. The Peon gas field (c. 250 km2) is located in the glacially eroded Norwegian Channel above the Upper Regional Unconformity (URU) separating flat-lying glaciogenic sediments from dipping sedimentary units. The reservoir is developed in glaciofluvial sands a few hundred thousand years old, and sealed by flat-lying glaciomarine sediments and till units.
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Glaciogenic Reservoirs and Hydrocarbon Systems
Glaciogenic reservoirs and hydrocarbon systems occur intermittently throughout the stratigraphic record, with particular prominence in Neoproterozoic, Late Ordovician, Permo-Carboniferous and Late Cenozoic strata. Recent interest in glaciogenic successions has been fuelled by hydrocarbon discoveries in ancient glaciogenic reservoirs in North Africa, the Middle East, Australia and South America. Glaciogenic deposits of Pleistocene age are noteworthy for their content of groundwater onshore and potentially prospective and/or hazardous gas accumulations offshore. The abundant imprints of Pleistocene glaciations in both hemispheres can be used to reconstruct complex histories of repeated ice cover and retreat, and glacier-bed interactions, thus informing our view on the dynamics of older ice caps and predictions of future glaciations. This volume aims to provide a better understanding of glaciogenic processes, their stratigraphic record and reservoir characteristics of glaciogenic deposits. The book comprises 3 overview papers and 16 original case studies of Neoproterozoic to Pleistocene successions on 6 continents and will be of interest to sedimentologists, glaciologists, geophysicists, hydrologists and petroleum geologists alike.