Architecture and sequence stratigraphy of Pleistocene fluvial systems in the Malay Basin, based on seismic time-slice analysis

Abstract

The Malay Basin is underlain by a productive, gas-prone, nonmarine Cenozoic section. Exploitation of the gas reserves is largely based on three-dimensional (3-D) seismic surveys, which have also gen erated much data from the nonproductive, near-subsea Pleistocene section. Seven seismic time-slice images at 12 ms two-way travel time (TWTT) spacings that document the 29-86 m sub-sea-floor section of this Pleistocene succession in the northern Malay Basin are analyzed here. These images reveal at least five types of fluvial systems of widely varying style and cross section dimensions, rang ing from braided systems with channel-belt widths of more than 4 km to small-scale meandering systems with meander-belt widths of a few hundred meters. An incised-valley system estimated to be 40 m deep is intersected by five of the images and forms the basis for an interpretation of one of two sequence boundaries revealed by this data set. The wide variation in channel style and scale in the project area contrasts with the rather uniform fluvial styles that are assumed in many production models for nonmarine oil and gas fields and should serve as a warning against making simplistic as sumptions about the consistency of these parameters during archi tectural and reservoir modeling and paleohydraulic reconstruction.