Abstract: Reservoir Geological Modeling of the A3/A6.0 Viscous Crude Reservoirs of Bokor Field, Offshore Sarawak, East Malaysia

Lancelot Sering, Ramli Adnan

The late Miocene A3.0/A6.0 sequence (1940-2440 ft ss), comprising four separate reservoirs, is the most prolific unit in Bokor field, with 155 MMstb of oil in place. A detailed geological modeling study was conducted in support of numerical simulation to improve understanding of the reservoir fluid flow in this viscous crude reservoir (oil gravity 19.5 API, average viscosity 10 cP).

Six lithofacies were identified from 323 feet of core: poorly stratified, cross-laminated and bioturbated sandstone, sand- and mud-dominated heterolithic and mudstone. These facies represent deposition by a fluvial-dominated delta complex, which prograded into a muddy marine shelf. Based on reservoir property characterization, the facies were grouped into three reservoir flow units: good (^phgr = 35-40%, k = 1000-2000 md), moderate (^phgr = 30-35%, k = 100-300 md), and poor (^phgr <25%, k <10 md), with mudstones acting as interreservoir seals. These flow units were then determined in 40 uncored wells using a reference set of electrofacies derived from deterministic values of GR/FDC/CNL logs integrated with the core data. This resulted in a detailed nineteen-layered reservoir mod l. Special emphasis was given to the identification and delineation of heterogeneities, ranging from shale intercalations to dolomite-cemented stringers.

The flow-unit properties were computer mapped and used in reservoir simulation models, which have yielded a good history match. Results of the study have significantly improved understanding of the reservoir fluid flow and led to identification of further infill development opportunities.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994