Abstract

PULHAM, ANDY, , MIKE BOWMAN, DAVID MacDONALD and COLIN DALY

The Cusiana Field (BP, Ecopetrol, Total and Triton) comprises relatively sand-rich reservoirs that range from late Cretaceous, passive margin deltaic to early Tertiary, early foreland basin estuarine-fluvial. The key reservoir is the Eocene Mirador Formation which comprises ~60% of reserves. Currently (October 1996) the Mirador reservoir is providing nearly all of the 180,000 bopd of production from the Cusiana Field.

The Mirador reservoir comprises a stack of sandy, incised valley deposits. Valleys comprise 50% of the Mirador stratigraphy and contribute the bulk of a moderately high net:gross ratio of 60%. Reservoir pressure data prior to and after the onset of production have all indicated that valley sandstones are well connected across the Cusiana Field. However, the same pressure data and extensive production logs have also indicated, during early depletion of the Mirador, that the reservoir comprises two major compartments and the individual incised valleys behave as strongly layered systems. Both these features of the Mirador owe their origin to textural characteristics of the incised valley sandstones that are stratigraphic in nature.

The two compartments in the Mirador are separated by a major transgressive surface of at least sub-regional extent. The dramatic changes in production characteristics within single Mirador valleys occur across intra-valley flooding surfaces. These stratigraphic features of the Miradot reservoir have implications to the reservoir management of the Cusiana Field. Accurate characterization of the major stratigraphic controls on production could lead to important predictions about the movements of injected gas and water leg encroachment during early field life.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria