Abstract: A Sr Residual Salt Analysis (SrRSA) Study to Investigate the Connectivity of the Brent Group Reservoir of the Dunbar Field, UK North Sea

John J. Mcbride, Jean-Marc Feroul, Euan W. Mearns

The Middle Jurassic Brent Group reservoir sequence of the Dunbar oilfield in the UK Northern North Sea consists of interbedded fluvio-deltaic sandstones, mudstones and coals. This sequence occurs within rotated fault block structures on the western margin of the North Viking Graben.

Strontium Residual Salt Analysis (SrRSA) has been performed on 254 core samples from 9 wells in the Dunbar Field. SrRSA data are ⁸⁷Sr/⁸⁶Sr ratios from residual salts (and/or water) extracted from reservoir cores. These data reflect the ⁸⁷Sr/⁸⁶Sr ratios of irreducible waters at the time they were trapped by hydrocarbons. Profiles of variation of SrRSA ⁸⁷Sr/⁸⁶Sr ratios with depth were integrated with sedimentological, structural and petrophysical data to assess compartmentalization within and between the study wells. The results of this study suggest that certain coal and mudstone beds are laterally extensive sealing barriers which isolate flow units within the Brent reservoir. In addition, these data have also indicated hat other barriers - which may be sealed faults - are present between certain wells in the field area.

The results of this study have confirmed some aspects of the pre-existing reservoir model and thus enhanced confidence in the interpretations. The SrRSA data have also highlighted previously unexpected aspects of reservoir connectivity and thus enabled informed decisions to be made on the optimum production strategy. The integration of SrRSA with the geological and reservoir engineering database during the development phase may thus have helped optimize production from the Brent reservoir of the Dunbar Field.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France