Publications

Basin developments in western Indonesia’s sedimentary basins share a similarity in general. They were started by syn-rift deposit, and then followed by sag deposit (deep marine sequence), and fluvial – shallow marine at the uppermost sequence. This basin development has a strong correlation with overpressuring in this area, which also shares similarities. We found that top of overpressure is mostly located near top the sag deposit. It can be very well understood since the sand sequence starts to deficit in the sag deposit, favouring for ovepressure to be occurring due to ineffective dewatering within this sequence. Further analysis shows that there is a strong correlation of overpressuring in the western Indonesia’s sedimentary basins with clay diagenesis. The top of ‘hard’ overpressure in several areas is located on the onset of smectite-illite transformation. However, we cannot rule out disequilibrium compaction as the possible mechanism generating overpressure in this area, since the shale is still located in the transition zone from mechanical and chemical compaction. Therefore, disequilibrium compaction may still contribute to the overpressuring. It is interesting that almost all carbonate build-up located below the sag deposit in the study area possesses low overpressure to normal hydrostatic pressure regime. We suggest that this is caused by the presence of good porosity carbonate build-up due to karstification experienced by the carbonate in the past. Keywords: Western Indonesia’s basin, overpressure, sag deposit, clay diagenesis, carbonate build-up