Multiple Carbonate Outcrops in Onshore Sarawak - Analogues for Various Carbonate Plays and Reservoir Types
The Sarawak Basin is one of the most prolific areas in Southeast Asia for carbonate growth during the Tertiary. About 224 isolated carbonate platforms, ranging from Late Eocene to Late Miocene, have been identified onshore on top of 200 others that have been seismically mapped offshore. The onshore carbonates display a variety of carbonate types, while those offshore show much greater similarity in terms of architecture, facies variability, biota systems and sequence evolution. Some of these exposed carbonates onshore can be used as analogues for offshore and nearby carbonates.
The carbonates are typically located on fault blocks and often display unique depositional patterns, facies variability and biosedimentary fabrics. The Subis Limestone complex which is rich in algae, massive/branching corals and benthic foraminifera, often displays layer cake features. This complex is an ideal analogue for the Central Luconia carbonates since it has similar dimension, morphology, and internal architecture.
The Batu Gading Limestone (Late Eocene - Early Miocene) is typified by massive nummulitic intervals that are occasionally interbedded with matrix-rich limestone, representing the main shoal and distal ramp settings. Based on the shape and size of Nummulites, the limestone can be further divided into five reservoir facies for better reservoir description. In addition, the Suai Limestone complex (Early Miocene) is characterized by fining upward parasequences of larger foraminifera dominated by different Eulepidina spp. In contrast, the Bekenu Limestone is comprised of finely laminated marls rich in planktonic and pelagic foraminifera. These types of carbonates can be used as analogues for carbonates equivalent to Cycles I-II and turbidite carbonate plays, respectively, that are present but yet to be tested in offshore Sarawak.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009