Publications

The North Sumatra Basin has been long recognized as an area possessing high overpressure condition. The top of overpressure in this basin is mostly located near top of Baong Formation. The previous researchers notice the difficulty of predicting the magnitude of overpressure within the Baong Formation. They always overpredict the overpressure in this formation. Our comparison with some compaction trend from western Indonesia’s sedimentary basin shows that there is a strong indication that the present normal compaction trend in this area has shifted towards highly compacted area. Consequently, the direct usage of this normal compaction trend to estimate overpressure magnitude in the overpressure sequence will result in severely overprediction of the magnitude. We suggest that the cause of the shifting in the normal compaction trend is a shallow cementation. The possible cause of the cementation in this relatively shallow depth thus low temperature environment is carbonate cementation widely distributed in this sequence. Clearly, this hypothesis needs to be tested by examining petrographical works in the normally pressured strata. To predict overpressure in this area, we suggest to use normal compaction from other nearby area or from other Indonesia’s sedimentary basin where the shallow cementation is not intensive. Our trial of using normal compaction trend from Mahakam Area, Lower Kutai Basin, to estimate overpressure in this area shows a reasonably good match of overpressure magnitude. Keywords: North Sumartra Basin, normal compaction trend, shallow cementation, overpressure estimation