Publications

Oil - source rock correlations have provided a firm basis for a comprehensive program of basin modelling in the Sunda Basin, offshore SE Sumatra. There is a good match between oils and the Type P kerogens found in lacustrine shales of the upper Banuwati formation. Immature shales have 30 - 40 mg extractable hc/gm rock, and kerogen variations are probably attributable to changes in lake facies. Geochemical data suggest a present day topoil window of 9,500. Maturity and hydrocarbon generation modelling have been carried out with the BasinmodrM software, utilising heatflow and compaction options. Projections to mapped source rock depths were made for modelling purposes in the basin center. The results indicate that significant hydrocarbon generation began at the end of Talang Akar time in the basin center and progressed outwards through time. No regional heat flow changes were evident from the modelling. Volumes generated since Talang Akar time appear to have varied mainly in response to changing rates of basin subsidence and to the source rock areas (volumes) in different depth levels. The kerogen volumes moving into the oil window over time have been, of course, also a function of source rock richness and thickness. The uncertainties surrounding these factors in the deep basin have placed some limits on volumetric calculations.The emphasis on significant generationlmigration at depths below 9500 has led to modifications of the hydrocarbon migration system proposed in earlier papers. Current work suggests that mature source rocks are more limited in areal extent, with vertical migration being crucial close to the generation area, and lateral migration dominating away from it beneath the regionally sealing Gumai shale. Zones of lateral migration convergence and divergence have been identified in plan view.This modelling, coupled with regional mapping, has significant implications for exploration in this basin. The results now permit a better assessment of migration risk for prospects, particularly those located some distance from mature source rocks. Structural timing is now considered to be of minor importance in most prospects in the basin. Calculations of hydrocarbon volumes generated do involve some uncertainty, but they permit an evaluation of the remaining oil to be found in different parts of the Sunda Basin. Drainage areas have been identified and the calculated volumes compared with those already discovered. The results highlight two areas with higher potential than other areas. The boundaries of the Banuwati generation - migration hydrocarbon system delineate the probable prospective areas within the region.