This document summarizes a poster presentation about delineating the Upper Jurassic reservoirs in the Witch Ground Graben region of the North Sea using genetic sequence stratigraphy methodology. The study applied this methodology to over 100 wells in the area around the Scott Field, identifying up to twelve regionally correlatable maximum flooding surfaces that constrained five sandstone intervals. Mapping these intervals revealed shifts in the basin's depositional center and effects of syndepositional faulting. The results enhanced understanding of the tectonics, sedimentation, and basin evolution in this economically significant area.

1. Poster Session : Reservoi r Anil Regiona l Geolog y Wednesday
MacLeod 'A '
DELINEATION OF THE UPPER JURASSIC RESERVOIRS, WITCH GROUND
GRABEN, NORTH SEA USING GENETIC SEQUENCE STRATIGRAPHY
METHODOLOGY
McCracken, Jock, Mobil New Business Development, 330 -5th Ave S.W., Calgary, Ab.
Canada T2P 2J7 and David Harrison, Mobil North Sea Limited, Mobil Court, 3 Clements
Inn, London, UK, WC2A 2EB
The Late Jurassic Oxfordian to Volgian sandstones of the Witch Ground Graben have been
attractive and prolific exploration targets since the discovery of oil in the Claymore and Piper
Fields in the early 1970's. More then two billion barrels of oil have been discovered to date.
With exploration reaching its "mature" phase new tools have been developing to further
exploit the more subtle traps within this very rich hydrocarbon province. To further the
understanding of the reservoirs in this area, where close spaced well control and higher
resolution biostratigraphy is abundant, the genetic sequence stratigraphic approach of
Galloway (1989) has been used.
Until recently the Upper Jurassic sequence had been divided into the Piper Formation, a
shallow marine Oxfordian sandstone, overlain by a Kimmeridgian-Volgian package
comprising the organic rich Kimmeridge Clay interbedded with a number of sandstone units
assigned to the Claymore or Galley Formations. Recent workers in the UK North Sea have
been re-examining this interval and have subdivided it into up to thirteen regionally
correlatable marine condensed sections and maximum flooding surfaces (Partington et al,
1993).
This approach was applied to the area around the Scott Field in a regional study using in
excess of 100 wells with detailed biostratigraphy. Up to twelve regionally correlatable
maximum flooding surface "time lines" were identified and used to constrain five sandstone
intervals. These sandstones were then mapped using geological and geophysical control and
as a result, shifts in the basin depocenter and the effects of syndepositional faulting became
Apparent. These results were then used to predict where these elusive sandstone packages
were deposited in this economically significant area.
This study shows that the genetic sequence stratigraphic approach in a mature area can
greatly enhance understanding of the tectonics, sedimentation and basin evolution, and hence
prolong the productive life of a basin.
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© 2010 by the Canadian Society of Petroleum Geologists