--> Abstract: Stratigraphic Relationships in the Upper Rotliegend Interpretations from Horizontal and Vertical Well Borehole Images, Core and Logs in the Lancelot Area, Southern North Sea, UK, by W. C. Fisher and D. J. Went; #90942 (1997).

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Abstract: Stratigraphic Relationships in the Upper Rotliegend Interpretations from Horizontal and Vertical Well Borehole Images, Core and Logs in the Lancelot Area, Southern North Sea, UK

FISHER, WILLIAM C., and DAVID J. WENT

The Lancelot Fields were developed with nine horizontal wells. Interpretations of core, image and log data in these and vertical wells have yielded important insights into the stratigraphic relationships in the upper section of the Rotliegend reservoir.

The complex stratigraphy of the upper Rotliegend in Lancelot in part results from the marine inundation of an active erg margin. The extensive reworking of the erg featured erosion and fluidisation of the dune sands and produced a remnant eolian topography.

In the Lancelot area the reworked sequence (Unit 4) is characterized by massive sandstones which show increasing cementation up to the overlying Zechstein boundary. The underlying unreworked sequence (Unit 3) comprises generally good quality eolian dune sandstones.

The remnant dune field sandstones of Unit 3 show a mounded geometry which is only partly infilled by the Unit 4 reworked sandstones, resulting in an undulating top to the Rotliegend.

Unit 4 sandstones show variation in sedimentary character, including erosively based massive facies, slumped dune foresets, fluidized sandstones and repeated Kupferschiefer units.

The localized absence of Unit 3 reflects the former position of interdraa areas. These are predicted using models of dune/draa dimensions.

The scales of the cross bedding in Unit 3 mounds varies considerably reflecting either a mixture of dune and draa foresets, or a wide range of sizes of dunes associated with slipfaceless draa.

The above geometries and heterogeneities have important implications for successful targeting of horizontal wells, particularly near the top of the reservoir and for volumetric estimates and reservoir simulations.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria