--> ABSTRACT: Inside Auk--Anatomy of an Eolian Oil Reservoir, by Alan P. Heward; #91022 (1989)

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Inside Auk--Anatomy of an Eolian Oil Reservoir

Alan P. Heward

Auk field is located in the central North Sea, UK sector, and produces from Permian Zechstein carbonates and the underlying Rotliegend sandstones. Thirty wells have been drilled at spacings between 70 m and 3.6 km.

The Rotliegend is about 300 m thick and can be divided into five possibly distinct phases of desert sedimentation; the upper three of these are oil bearing with eolian slipface sands forming the main productive horizons. (1) The earliest deposits are localized fluviatile conglomerates which infill topography on the unconformity with the Devonian. (2) The overlying highly porous sands from a large wedge-shaped body onlapping the Devonian. They comprise predominantly eolian slipface sands with slipfaces oriented toward the southeast. (3) This interval represents a change in eolian deposition with a marked increase of tighter wind-ripple laminated sandsheet, dry interdune, and dune apron sands. This unit fluctuates in thickness by about one-third over the field area. Stacked dune slipfac sands are oriented toward the east and cannot be correlated over a few hundreds of meters across wind. (4) An even greater proportion of wind-ripple laminated deposits are contained in this interval. Its geometry is that of a depositional mound 100 m thick and 7 km across wind. Dune and possibly dry slipface sands, oriented east, occur where it is thickest. Fine-grained eolian sands are banked up on its northern flank. (5) Finally, waterlain mass-flow sands partially infill depositional lows and appear to represent rainfall reworking of a largely abandoned erg.

The marine Zechstein transgressed and draped remaining topography.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.