Paleo-depositional Environment Reconstruction of Oligocene, Early Miocene Intervals in Northeast Part of Malay Basin

Abstract

Paleo-depositional environment reconstruction is a useful tool to help portray the structural and stratigraphic evolution of a basin. It provides the interpreter with a “picture” of the depositional setting from which to predict reservoir beyond that observed in wells. Cores, well-logs and 3D seismic data were integrated to construct seven paleo-geographic maps of four sequences and three sub-sequences in Oligocene to early Miocene intervals of the Northeast Malay Basin. Sequence 1 deposition is controlled by formation of the initial syn-rift basin and is dominantly fluvial/alluvial environments. An uplift in the centre created two isolated lakes to the North and South of the high basement. The increase in sediment supply and sedimentation rate during this period resulted in development of extensive alluvial fans and braided rivers flowing into lakes. A significant rise in lake level combined with a low subsidence rate created a sediment starved basin in Sequence 2 of middle Oligocene age that accumulated thick lacustrine shale deposits. Sequence 2 is divided into three sub-sequences and the two lakes were connected. In late Oligocene of Sequence 3 and early Miocene post-rift of Sequence 4 regional drainage systems became better developed and delivered more sand rich sediments into the lakes. The depositional environment was dominated by an extensive alluvial plain characterized by a complex fluvial system consisting of multiple channels. Sequence 4 is a transitional environment to shallow marine.