Reservoir Characterization of Lacustrine Sediments from the Late Triassic, Beryl Field, UK North Sea

Jaqueline Bond and Joann E. Welton

Located on the western flank of the Viking Graben, the Beryl Field has been producing from the Late Triassic Lewis reservoir since first oil in 1976. The Beryl A Triassic contains an estimated STOIIP of 256 mmstb, with a cumulative production of 31 mmstb (8/95) (12% recovery). Low recovery to date, coupled with high remaining reserves potential, necessitated a new simulation model and optimized development program for the Lewis reservoir. This paper summarizes the revised reservoir description of the Beryl A Triassic, a complex lacustrine and fluvial system, and its integration with the reservoir simulation.

The Triassic reservoir is subdivided into four zones: Lewis Units I, II, III and IV. Six lithofacies associations are identified in core: offshore Iacustrine lacustrine sandflat, marginal lacustrine, floodplain, sheetflood/overbank, and fluvial. Detailed petrological studies were conducted which confirmed that both depositional and diagenetic processes influenced reservoir properties and quality. Optimal reservoir quality is preserved in fluvial and Iacustrine sandflat deposits. Argillaceous floodplain and lacustrine facies are non reservoir and form barriers to vertical fluid migration. Calcrete lags (concentrated at the base of fluvial channels) and carbonate paleosols forn baffles to flow.

Field-wide correlation of core and log facies resulted in the identification of 27 genetic flow-units. This geologically-based layering scheme was integrated with production data to generate the framework for vertical zonation for the new reservoir simulation. The simulation studies produced as accelerated development program for the Beryl A Triassic Reserves have increased as result of optimizing secondary recovery.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California