AAPG Bulletin, V. 82 (1998), No. 3 (March 1998), P. 497-515.

Controls on Reservoir Quality of an Upper Jurassic
Reef Mound in the Palmers Wood Field Area, Weald Basin, Southern England¹

S. Qing Sun² and V. Paul Wright³

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received September 13, 1996; revised manuscript received January 21, 1997; final acceptance August 25, 1987.
²Carbonates International Limited, 93-99 Upper Richmond Road, London, SW15 2TG, United Kingdom.
³Postgraduate Research Institute for Sedimentology, University of Reading, P.O. Box 227, Whiteknights, Reading, RG6 2AB, United Kingdom. Current address: Department of Earth Sciences, University of Wales, P.O. Box 914, Cardiff CFI 3YE, United Kingdom.

S. Qing Sun would like to thank Petrofina Ltd. (UK) and Cairn Energy for financial support, assisting with access to the subsurface data, and granting permission to publish this paper. The comments of Peter Rowe (Cairn Energy) on an earlier version of this paper were much appreciated. AAPG reviewers P. M. Harris, C. H. Moore, and J. F. Sarg are thanked for their constructive comments. Jill Banham, Alan Cross, and James Watkins are thanked for assistance in preparing the manuscript. 

ABSTRACT

An Upper Jurassic (Oxfordian) reef mound in the Palmers Wood field area of the Weald basin, southern England, clearly shows the relationship of facies, diagenesis, and porosity development to relative sea level changes.

The coral-microbial reef mound was initiated over a drowned oolite shoal during a third-order marine transgression and exhibits changes in coral morphology from base to top as the reef mound caught up with sea level during the subsequent highstand. During the highstand, extensive encrustation of the reef mound took place by microbial, stromatolitic cements, with subsequent porosity loss.

During the following lowstand of relative sea level, extensive leaching of the aragonitic corals took place, and a lowstand wedge accumulated down-ramp. Porosity was lost during burial-related cementation and compaction.

Coral-microbial reef mounds of this type have moderate potential for porosity formation, unlike tighter, deeper ramp reefs in the Jurassic, which are less prone to subaerial leaching and have less potential for secondary porosity development because they are less rich in aragonitic components.

Although the Upper Jurassic reef mound is only a minor contributor to reservoirs in the Palmers Wood field, it may provide a model for other Upper Jurassic reef plays.