--> Resource Optimization through Facies-Based Characterization of a Braid-Delta Sandstone Reservoir, Tirrawarra Oil Field, Cooper Basin, South Australia, by S. H. Hamlin, S. P. Dutton, N. Tyler, J. S. Yeh, R. J. Saggie, P. Lansom, and G. B. Asquith; #90986 (1994).

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Abstract: Resource Optimization through Facies-Based Characterization of a Braid-Delta Sandstone Reservoir, Tirrawarra Oil Field, Cooper Basin, South Australia

Scott H. Hamlin, Shirley P. Dutton, Noel Tyler, Joseph S. Yeh, Robert J. Saggie, Peter Lansom, George B. Asquith

The Tirrawarra Sandstone is an important oil reservoir in Cooper Basin, but recovery efficiency is <11% at Tirrawarra field, where the resource base exceeds 150 MMbbl. Previous reservoir descriptions were unable to simulate primary and EOR production patterns until a depositional-facies-based flow-unit model proved crucial to understanding past reservoir behavior and to identifying opportunities for incremental development. A comprehensive subsurface data base, including 1,000 m of core from 29 wells, was used to develop the flow-unit model.

The Carboniferous-Permian Tirrawarra Sandstone reservoir, which was deposited in a proglacial intracratonic setting, is 30 to 50 m thick and comprises 4 facies assemblages that record progradation of several fluvial-deltaic systems across a lacustrine basin. A braid-delta facies assemblage, dominated by bed-load channel-fill sandstone, forms the core of the reservoir and is bounded by more lithologically heterogeneous facies. Prodelta, delta-front, distributary-channel, and channel-mouth-bar facies underlie the braid-delta facies, which are truncated and overlain by braidplain facies.

Because depositional environment proved to be the primary control on reservoir properties and productivity, each facies assemblage was subdivided into reservoir flow units according to fluid transmission abilities. Stratigraphic analysis established flow-unit architecture and delineated flow barriers. Petrographic and petrophysical analyses quantified flow-unit-specific properties such as porosity, permeability, and water saturation. The facies-based flow-unit model accounted for historical reservoir performance and showed that Tirrawarra field has considerable potential for reserve appreciation. Future reservoir simulation studies of Tirrawarra field will be based on this model.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994