NW Borneo reservoir characterisation based on sedimentological evaluation of turbidite facies

Borneo was positioned in an exceedingly dynamic tectonic area throughout the Tertiary at the edge of an Early Cretaceous continental fragment and is surrounded by the Sunda Shelf, South China Sea, Sulu Sea, Celebes Sea, the narrow Makassar Strait and the Java Sea. Throughout this period of time, the Northwest Borneo basin and other adjacent basins (sedimentary and marginal) were formed and deformed as a result of the subduction and extension of the surrounding plates. The Northwest Borneo basin is distinguished by a steep slope from shelf to basin floor and shows high flow rates of turbidite sediment. The study areas include the Northwest Borneo Basin (offshore; 10.6 to 8.2 Ma) and the on-shore area covered by the Crocker Formation (Eocene to Early Miocene) on northwest Borneo and Gaya Island near Kota Kinabalu, East Malaysia. The Crocker Formation covers an area from 115o 58’E to 116o 09’E longitude and 05o 46’N to 06o 01’N latitude. All the study areas display characteristics of sediment deposited during lowstand systems tract (LST) and illustrate type II turbidite depositional systems consisting of proximal and distal turbidite deposits. The turbidite sediments accumulated in small lobes and are usually found deposited in the distal parts of the distributary channels. Ta-Tb-Tc-Td-Te Bouma sequences are present in all study areas but, commonly the base, middle or top of the sequences are absent. Other facies identified are massive sandstone, wispy sandstone and chaotic interbedded sandstone and mudstone sequences (Sm, Sw and Sa facies).