ABSTRACT: Synsedimentary tectonic control upon Miocene stratigraphic sequences in two petroleum provinces of Borneo

Snedden, John W.¹ and J. Frederick Sarg²
(1) ExxonMobil Exploration Company, Houston, TX
(2) Mobil Technology Company, Dallas, TX

Recent exploration in the Kutei and Sarawak basins of Borneo provides an opportunity to assess viability of sequence stratigraphic correlations in areas of complex tectonics. The basins are about 1000 km apart and contain substantial quantities of discovered hydrocarbons. Stratigraphic surfaces were identified from regional seismic data, well logs, cores, palynology, biostratigraphy, isotope dating, and structural restorations.

Three sequence boundaries, associated with major tectonic events, are most prominently developed here: Messinian-2 (Top Miocene), Serravallian-4 (basal Late Miocene), and Langhian-2 (basal Middle Miocene). In spite of considerable differences in tectonic style, these surfaces can be traced from coastal-plain paleoenvironments into the deep marine basin. Recognition of these horizons is critical to understanding basin history and evaluating reservoir, seal, and source rock quality.

Establishing the proper chronostratigraphic framework is important in determination of timing of maturation and migration. In Sarawak, long-term shift of deposition to the south following the Langhian-2 lowstand prevented sufficient burial of underlying Miocene source rocks until Plio-Pleistocene progradation of the Rajang-Lupar delta (post-Messinian-2). Thus, maturation and migration of hydrocarbons is quite recent or in some areas has not occurred at all.

In the Kutei Basin, updip inversion and basinward tilting following the Serravallian-4 lowstand generated the sediment supply and accommodation space, respectively, for a thick succession of Late Miocene and Pliocene siliciclastics in the offshore region. Hydrocarbon maturity and migration thus follow the prograding depocenters, younging basinward. Hence, most areas of the offshore Kutei basin have attained hydrocarbon maturity. Exploration success in the Makassar Straits confirms this model.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia