Publications

Sequence stratigraphic analysis was conducted for the Paleogene Ngimbang Carbonate Reservoir in Pagerungan Utara Offshore, Kangean Block, East Java to evaluate the depositional styles and reservoir distributions of carbonate rocks, which were previously interpreted as a reef build-up. Examinations of core facies, well-log successions, and seismic sequences using existing two well data and eleven 2D seismic sections revealed that the Paleogene Ngimbang Carbonate in the area showed not a reef but an isolated platform, consisting mainly of shoal complexes. The Ngimbang Carbonate Reservoir in the isolated platform can be divided into two 3rd order depositional sequences: the lower sequence and upper sequence. The lower to middle part of the Ngimbang Carbonate Reservoir belongs to HST of the lower sequence, and the upper part of the Ngimbang Carbonate Reservoir to TST of the upper sequence. On the seismic sections, the sequence boundary between the two depositional sequences can be recognized as an onlap surface traced as the sidewall of the isolated platform. Mapping of core/seismic facies information revealed the following depositional process model. During deposition of HST of the lower sequence (the lower to middle part of the Ngimbang Carbonate), two shoal complexes were developed with progradational and aggradational patterns at the western to central part and eastern part on the isolated platform. At the time of lowstand of relative sea level, topographic highs at the center of the shoal complexes might be exposed, and the sequence boundary was formed. Subsequent relative sea level rise resulted in TST carbonate (TST of the upper sequence: the upper part of the Ngimbang Carbonate) deposition only on the isolated platform with upward fining/deepening facies succession patterns, and finally it was covered by hemipelagic shales (Ngimbang Shale), when the rate of relative sea level rise exceeded the rate of carbonate production.