--> Abstract: The Early Recognition of Compartmentalisation in the Dunbar Oil Field, UK, by T. Coombes, J. J. McBride, and E. W. Mearns; #90937 (1998)

Datapages, Inc.Print this page

Abstract: The Early Recognition of Compartmentalisation in the Dunbar Oil Field, UK

COOMBES, T., Total Oil Marine, Scotland, J. J. MCBRIDE, and MEARNS E. W., Isotopic Analytical Services, Scotland

The Dunbar Oil Field lies 135 km east of the Shetland Islands. UK North Sea. Oil occurs in fluvio-deltaic Brent Group sandstones which are locally overlain by a transgressive shallow marine sandstone (UMS). The Brent part of the sequence comprises interbedded sandstones, mudstones and coals while the UMS comprises a sheet of sandstone that was expected to be continuous. The structure is formed by rotated fault blocks that are separated by normal faults. The main faults were mapped employing 3D seismic providing a first order picture of large-scale compartmentalisation.

During field appraisal it was recognised that owning to structural, sedimentological and diagenetic complexity, the areal connectivity of the reservoir needed further investigation. Pre-production formation pressure profiles defined single gradients in each well and provided no evidence for restrictions toverticalconnectivity. There were however, significant pressure differences between wells. A Strontium Isotope Residual Salt Analysis (SrRSA) program (9 cored wells. 254 samples) was conducted prior to production start up (December 1994) which identified both vertical and lateral connectivity barriers that were not apparent from pre-production pressure data. Certain, but not all, coal and shale beds were inferred to be laterally continuous seals with the geometry to isolate hydrocarbon volumes. This information was used to optimise development well locations and completions.

Conclusions drawn from SrRSA have been shown to be consistent with post-production formation pressures. The acquisition of new data since production started has enhanced the connectivity model and has been particularly useful in demonstrating local connectivity pathways between the main fault bounded compartments.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah