Detailed analogue dipmeter measurements have been made along a 430 m roadcut in the Upper Namurian Rough Rock at Elland in Yorkshire. A series of 21 vertical sections were measured with dip and azimuth (dip-log) readings taken every 0.2 m, which were calibrated to previously described sedimentological sections and recordings of surface natural gamma ray profiles.
The inter-relationship between the scale of sedimentary structures and dipmeter processing parameters is shown by dip-log measurements in medium scale, crossbedded sedimentary structures. The analysis of grouped dip-log data is seen to give palaeocurrents very similar to those measured by traditional methods at outcrop. The relationship between sedimentological facies and ‘dip-log facies’ is applied to reservoir characterization, and statistical analysis of dip-log data is demonstrated to be an aid to inter-well comparisons.
Analysis techniques, mainly computer based and applicable in the subsurface, are applied to the outcrop data and the implications for subsurface dipmeter studies are stressed.
A widespread, slumped, redeposited, uppermost Cretaceous chalk interval, up to 60m thick, immediately below the Cretaceous-Tertiary (K-T) boundary, recognised in oil company boreholes across the central North Sea and a major hydrocarbon reservoir, we re-interpret as the result of a single, catastrophic event caused by secondary effects related to the bolide impact at Chicxulub. A thin, dark clay bed immediately above the redeposited chalks, we suggest correlates to the outcropping, Iridium rich, Danish 'Fish Clay', rapidly deposited after the impact. Physical effects on sea-floor sediments, caused by the K-T bolide impact, have not previously been interpreted in the North Sea.
FMS (Formation MicroScanner) electrical images in a single well from a familiar, deep marine North Sea Palaeogene section are illustrated. More than 900 m of good quality images were acquired through an interval from the Palaeocene Ekofisk Formation to the Eocene Grid Formation in a well from the centre of the South Viking Graben, Norwegian sector. The information that was obtained from these images is illustrated and discussed in terms of lithology, sedimentary structures, stratigraphy and petrophysics. The information on this deep marine, mainly gravity deposit succession, is considerably enhanced using image interpretation. Lithological information includes an improved net-to-gross ratio and an understanding of lithological heterogeneities. Sedimentary structure information includes the geometrical and lithological characterization of slumped intervals and a detailed description of evolving gravity deposit sequences. In terms of stratigraphy, illustrative images are shown of the Balder, Lista and Sele Formations. Some of the key surfaces of the Palaeogene interval, used for correlation and sequence stratigraphy, are shown in detail, especially the surface at the base of the Balder Formation and the boundary between the Lista and Sele Formations. The effect of hydrocarbons on the images is illustrated and used qualitatively in petrophysical terms to define the hydrocarbon-water contact.
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