Quantitative Seismic Geomorphology of Pleistocene Fluvial Systems in the Malay Basin, Southeast Asia: Implications for Reservoir Modelling

Outcrop data and satellite imagery of modern systems typically provide only 2D and quasi-3D data on the geometry, orientation and dimensions of reservoir sand bodies, which are critical elements for the construction of geologically meaningful, 3D, object-based reservoir models. 3D seismic data can also provide important data, although the ability to collate large, statistically valid datasets is limited by the tools that are available in standard seismic interpretation software packages. We present a new methodology for quantifying planform geometries and dimensions of fluvial channel sand bodies that are imaged in shallow, near sea-bed, 3D seismic datasets. Data capture has been semi-automated using ArcGIS, which allows fast and efficient mapping of these morphometric parameters. We have applied this methodology to a Pliocene-Pleistocene fluvial succession that is spectacularly imaged on a high-resolution, regionally-extensive, 3D seismic survey from the Malay Basin, Southeast Asia, and we focus on the quantification of key channel parameters, such as meander channel width, meander belt width and meander wavelength. We demonstrate that the lower part of each seismic unit is characterised by wide, deep, low-sinuosity channels, which pass gradually upwards into narrower and thinner, high-sinuosity channels at the top. We speculate that a combination of sea-level changes and fluctuations in discharge and sediment load, both of which may have been linked to climate variations, may have controlled the observed stratigraphic organisation. Empirical equations developed on modern rivers have been tested on the channels identified in this study. The results suggest that existing empirical equations cannot be applied to describe the relationships between geometric parameters that characterise the fluvial channels in this particular geological setting. Hence, several new empirical relationships are proposed, which may be more applicable for predicting fluvial channel dimensions in humid-tropical settings. Our data have been used to constrain reservoir models for the deeper, oil- and gas-producing Miocene succession, which contains a large proportion of fluvial channel reservoirs but which is less clearly imaged on 3D seismic data. The study highlights the value of using high-quality, near sea-bed 3D seismic volumes for extracting analogue data on sand body dimensions; datasets such as these are increasingly accessible to researchers from many parts of the world.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California