Journal of Petroleum Geology, Vol.18, No.4, pp. 421-438, 1995

©Copyright 2000 Scientific Press, Ltd.

NUMERICAL MODELLING OF DIAGENETIC QUARTZ HYDROGEOLOGY
AT A GRABEN EDGE: BRENT OILFIELDS, NORTH SEA

A. M. Mullis + * and R. S. Haszeldine*

* Department of Geology and Applied Geology, University of Glasgow, Lilybank Gardens, Glasgow G12 8QQ.

+ Current address: School of Materials, University, Leeds LS2 9JT.

Abstract

Oilfields in the Middle Jurassic Brent Group of the East Shetland Basin contain abundant quartz cement, which reduces porosity by 10-15%. This quartz cement is believed to have started to grow at depths of around 2-3km. Oxygen isotope signatures in diagenetic quartz imply that it grew from meteoric pore waters; however, fluid inclusion temperatures are 30-50°C higher than temperatures which should have prevailed at the inferred palaeo-depth. Large-scale circulation of hot water has been proposed to explain this "temperature anomaly", but this is geologically difficult in terms of heat and fluid budgets. Finite-element fluid-flow models of a generic fault-block rift-basin stratigraphy are used to evaluate two alternative hydrogeological models for deep quartz diagenesis in Brent Group sandstones: