Ottesen D.,Exploro AS |
Dowdeswell J.A.,University of Cambridge |
Bugge T.,Det norske oljeselskap ASA
Marine and Petroleum Geology | Year: 2014
The North Sea Basin has been subsiding during the Quaternary and contains hundreds of metres of fill. Seismic surveys (170000km2) provide new evidence on Early Quaternary sedimentation, from about 2.75 Ma to around the Brunhes-Matuyama boundary (0.78 Ma). We present an informal seismic stratigraphy for the Early Quaternary of the North Sea, and calculate sediment volumes for major units. Early Quaternary sediment thickness is>1000m in the northern basin and >700m in the central basin (total about 40000km3). Northern North Sea basin-fill comprises several clinoform units, prograding westward over 60000km2. Architecture of the central basin also comprises clinoforms, building from the southeast. To the west, an acoustically layered and mounded unit (Unit Z) was deposited. Remaining accommodation space was filled with fine-grained sediments of two Central Basin units. Above these units, an Upper Regional Unconformity-equivalent (URU) records a conformable surface with flat-lying units that indicate stronger direct glacial influence than on the sediments below. On the North Sea Plateau north of 59°N, the Upper Regional Unconformity (URU) is defined by a shift from westward to eastward dipping seismic reflectors, recording a major change in sedimentation, with the Shetland Platform becoming a significant source. A model of Early Quaternary sediment delivery to the North Sea shows sources from the Scandinavian ice sheet and major European rivers. Clinoforms prograding west in the northern North Sea Basin, representing glacigenic debris flows, indicate an ice sheet on the western Scandinavian margin. In the central basin, sediments are generally fine-grained, suggesting a distal fluvial or glacifluvial origin from European rivers. Ploughmarks also demonstrate that icebergs, derived from an ice sheet to the north, drifted into the central North Sea Basin. By contrast, sediments and glacial landforms above the URU provide evidence for the later presence of a grounded ice sheet. © 2014 The Authors.
Napoli G.,University of Palermo |
Nigro F.,Italian National Institute of Geophysics and Volcanology |
Favara R.,Italian National Institute of Geophysics and Volcanology |
Renda P.,University of Palermo |
And 2 more authors.
Journal of Geodynamics | Year: 2015
The Sicilian fold-and-thrust belt is located in the central Mediterranean area, and it represents the south-eastern arcuate segment of the Apennine-Maghrebide orogen. The tectonic evolution of the Sicilian belt is documented after outcrop analysis of small-scale structural features carried out throughout the region. Results are consistent with the following four main deformation stages having affected the study area, from the oldest to the youngest: (i) multilayer weakening; (ii) folding-and-thrusting, (iii) extension, and (iv) renewed thrusting. The first deformation stage included three different substages (layer-parallel shortening, bed-parallel simple shear and fold nucleation), the second one by both thrusting and fold amplification and tightening. The third deformation stage involved re-activation of the pre-existing mechanical discontinuities and formation of low-to-high angle normal faults. Out-of-sequence thrusting postdated the aforementioned extensional stage, and formed the latest orogenic deformation stage that affected the Sicilian belt. © 2015 Elsevier Ltd.
Hammer E.,Statoil |
Hammer E.,Lundin Norway AS |
Brandsegg K.B.,Exploro AS |
Mork M.B.E.,Norwegian University of Science and Technology |
Petroleum Geoscience | Year: 2012
A new methodology for robust, high-resolution correlation of reservoir sandstones in highly compactable depositional sequences is proposed. Quantitative sequential re-burial modelling has been successfully applied on real data from seven wells covering the heterogeneous fluviodeltaic Åre Formation in the Heidrun Field, offshore mid-Norway. The methodology is based on ten interpreted lithofacies classes derived from core descriptions and wireline logs signatures, in addition to interpreted sequence stratigraphic surfaces, i.e. flooding surfaces. Analysis of decompacted sedimentary columns, with emphasis on studies of shallow compaction effects tied to uniquely calculated compaction curves, has revealed several new correlatable horizons within the Åre Formation. These include laterally extensive coals and several laterally correlatable fluvial sandstones enabling a reinterpretation of parts of the Åre stratigraphy. The results from the present study demonstrate the benefits of correcting for the effects of differential compaction in well-to-well correlation of heterogeneous reservoirs comprising highly compactable sediments. The methodology outlined here has widespread applicability to other stratigraphic successions and could potentially help in the correlation of highly compacted sediments in the subsurface. © 2012 EAGE/Geological Society of London.
Brandsegg K.B.,Norwegian University of Science and Technology |
Brandsegg K.B.,Exploro AS |
Hammer E.,Norwegian University of Science and Technology |
Sinding-Larsen R.,Norwegian University of Science and Technology
Natural Resources Research | Year: 2010
Multivariate analysis is employed to investigate the structure of variations within highly heterogeneous data. Traditionally, principal component analysis (PCA) is run by analyzing the entire wireline log and using PCA scores to characterize variability within and between lithologies. In this paper, we propose a technique using only specific subsets of all well records to quantify reservoir heterogeneity due to second order lithological variability. These subsets are chosen from uniform lithofacies parts of the wireline log in order to reduce the variability in the correlation matrix that otherwise would cause lithological changes. The purpose is to assess the efficiency of structured PCA in analyzing small-scale heterogeneity that is captured by wireline logs but often masked by traditional PCA approaches. This paper shows that a structured PCA procedure based upon special lithological units is superior to an unstructured PCA, when the focus is within lithology variations. This structured procedure is applied to data from the Heidrun field, offshore mid-Norway. The results demonstrate clear benefits from added insight into the variability of a complex fluviodeltaic heterolithic sequence that poses great challenges to hydrocarbon development. © 2010 International Association for Mathematical Geology.
Marello L.,Geological Survey of Norway |
Marello L.,Norwegian University of Science and Technology |
Marello L.,Exploro AS |
Ebbing J.,Geological Survey of Norway |
And 2 more authors.
Geophysical Journal International | Year: 2013
We present a new 3D geophysical model for the Barents Sea that highlights the basement properties and crustal setting. The model results from the modelling of gravity and magnetic field anomalies and is based on a large number of seismic and petrophysical data. The set up consists of a water layer, sedimentary units that incorporate density variations associated with depth and time of deposition (Cretaceous-Cenozoic, Triassic-Jurassic, Late Palaeozoic and deeply buried sediments), upper and lower basement and an upper mantle. The upper crust is considered as the major source of the magnetic anomalies and has been divided into a number of units characterized by constant densities and magnetization, which show a good correlation with the main structural elements of the Barents Sea. The Southwest Barents Sea crust is an aggregation of allochthonous Caledonian terranes and autochthonous Archaean and Palaeoproterozoic complexes. We interpret the different crustal blocks in terms of distinctive lower, middle, upper and uppermost allochthonous terranes that can be linked with the major nappes onshore. The largest part of the North Barents Sea is distinguished from the rest of the shelf by its low-magnetic properties and its large crustal thickness. These differences are compatible with a geodynamic scenario in which an independent crustal block (Barentsia, not corresponding entirely to the island of Svalbard) was located between Baltica and Laurentia and became attached to the shelf during the Caledonian orogeny. To the east, the basement underlying the large mega-sag East Barents Basin, is an assemblage of Precambrian rocks deformed during the Timanian and Uralian orogenies. The basement is characterized by an alternation of high-magnetic and low-magnetic units that mimic the arcuate shape of Novaya Zemlya. In the Southeast Barents Sea, the crustal units are linked to the onshore geology of the Timan-Pechora region and are mostly the result of Timanian orogenesis. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.