Publications

Two petroleum systems are identified for the Conoco West Block 'B' PSC Indonesia. The two petroleum systems are: (1) coals and coaly shales of the Arang and Gabus formations and (2) the lacustrine synrift sediments of the Belut or Gabus Formations. The petroleum systems are identified from measured data and/or inferred from oil chemistry using geochemical inversion. The synrift organic facies are divided into ",deep", lacustrine and shallow lacustrine characterized by a range from predominantly oil prone algal organic matter to mixed algal and terrestrial organic matter, respectively.Hydrocarbon generation and expulsion modeling indicates that early synrift sections expel as early as 29-19 mya, and the progressively shallower and more gas prone synrift sections expel from 26-12 mya and 23-0 mya. Generation from the deep parts of the synrift petroleum system is exhausted early, the shallower intervals were switched off during inversion (i.e. during development of Muda unconformity 12-10 mya) and potentially switched on again in the last 4-5 mya due to burial associated with deposition of the Muda Formation.The coals and coaly shales in the Arang and Gabus are composed of mixed gas and oil prone macerals, or kerogen having hydrogen index (HI) cumulative probability distribution P,,, P,, and P,, of 470, 305 and 210 mgHC/gOC. The amount- of oil expulsion from coals is estimated from the ratio of free hydrocarbons to organic carbon content (S UTOC mgHC/gOC). Expulsion from coal and coaly shale petroleum system occurs at depths below approximately 7,500 ft (2,300 m) (0.7% Ro) suggesting that charging started 8 mya until present. An integrated study of the spatial and temporal relationships . between hydrocarbon charge, development of structural traps and formation of potentially breaching unconformities can assist in both dry hole post-mortem evaluations and risk analysis of new prospects.Late formed traps (<,20 mya) are more likely to be charged from more gas prone synrift facies or syninversion coals and coaly shales. Their prospectivity for oil will be less than early formed traps that are more likely to drain more oil prone synrift facies.