Publications

The Belida Field was discovered in November, 1989 Sandstones of the Lower Arang and Udang Formations fonn the productive reservoirs. which arc pressure isolated by a regionally extensiwe shale unit. the Barat Formation Recent studics have allowed the three major lithostratigraphic units to be subdivided into seveii fourth-order depositional scquences, which define the reservoir architecture and control resenoir performance.The Belida accuinulat~oni s controlled by pronounced middle Miocene structural inversion of a minor extensional s> stem. located between and en-echelon to the regional West Natuna and Penju Oligocene rift systems The approximately 200 m thick gross interval, which includes the producing reservoirs. ranges in age froin late Oligocene to early Miocene Thc depositional en1 ironment was predominantly noninarinc to marginal marine and precise age dctennination is problematic Syndepositional tectonic control on relative sea level and stratigraphic architecture includes the effects of differential compaction over the original extensional system and the late onset of subtle inversion. Low average accumulation rates for the gross interval of 4 cm/1000 years are attributed to limited accommodation space and extensive reworking. Productive reservoir facies include storm and wave-dominated lacustrine shelf, wave-dominated lacustrine delta front, and tidal and wave-dominated marine shoreface sandstones. The lithostratigraphic formations can be considered as the systems tracts of third-order depositional sequences. The Udang Formation displays lowstand affinities in that it is dominated by non-marine facies and high frequency depositional sequences, characterized by major basinward shifts and subaerial exposure. The producing units of the Lower Arang Formation consist of stacked marginal marine parasequences of thirdorder transgressive and highstand systems tracts. Major differences in reservoir and aquifer performance between the Lower Atang and Udang sandstones can be attributed to the different stratigraphic architecture and depositional processes within the third-order systems tracts.