The Influence of Tectonic Regimes and Age on Growth Styles of Eocene-to-Recent Carbonates, Offshore and Onshore Sarawak, Malaysia: Implications for Carbonate Play Exploration

Adams, Erwin W.; Besems, Ronald E.; Gough, Simon J.; Kosa, Eduard
Sarawak Shell Berhad, Lutong, Malaysia.

Historically, in Sarawak, Malaysia, carbonate exploration has focused primarily on the renowned Middle to Upper Miocene Central Luconia Province carbonates. With this play becoming mature in Central Luconia, exploring for other plays is warranted. Thus, a regional play-based exploration study was carried out resulting in the establishment of a framework connecting the evolution of tectonic regimes and basin fill with carbonate occurrences and growth styles since the Late Eocene. This predictive contemporary framework provides the basis for a play-based assessment of the remaining exploration potential of carbonate plays in Sarawak. Upper Eocene-Lower Oligocene carbonates have been found in southeast Sarawak and developed speculatively as isolated platforms atop basinward propagating thrusts developing in front of the Rajang accretionary wedge. During the Late Oligocene, a relatively stable, regionally extensive shelf system was established and continued developing until present day. The Sarawak shelf succession can be subdivided into four lower-order sequences. At the end of Sequence 1, the aerially most extensive shelf system developed. At the onset of Sequence 2, in the Early Miocene, the clastic shelf system retreated to the southwest, while widespread passive shelf-margin carbonate deposition occurred in the distal shelf area including the development of a pronounced high-relief platform margin. Eventually, prograding shelf clastics smothered most carbonates. The base of Sequence 3 demarcated a time of major flooding in the Middle Miocene during which many of the Luconia Province carbonates initiated. A major extensional event ending in the early Late Miocene amplified and differentiated several structural domains with fault-block carbonate platforms developing on horsts and keep- and give-up pinnacles in tectonic lows. During Sequence 4, Pliocene and younger carbonates locally developed, while distally located platforms continued to grow until present day. In summary, since the Eocene, the tectonic evolution and basin fill history in Sarawak interacted with different styles of carbonate growth while several global evolutionary trends influenced the type of carbonate being deposited and hence the potential for variable reservoir quality. The present study demonstrates how play-based exploration and the placing of carbonate occurrences in a tectonostratigraphic context enables explorers to understand and derisk carbonate plays in complex settings.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012