Deltaic and Shallow-Marine Seismic Geomorphology of the West Natuna Basin: Implications for Reservoir Architecture and Basin Evolution

Jed M. Flint and Lesli J. Wood
University of Texas at Austin, Austin, TX

Quantitative seismic geomorphology and morphometric analysis of modern and paleo-landforms are powerful tools for extracting data about geologic history, processes, and fill architecture of terrestrial and marine basins. This study of the hydrocarbon-rich West Natuna Basin of Indonesia combines 3,154 km2 of 3D seismic and analysis of 15 well logs to explain how 3D reservoir shape, size, and distribution evolve and are preserved within deltaic and shallow-marine environments. The study also addresses how these characteristics vary in response to changes in sediment load, discharge, and base level.

Statistically robust, morphometric measurements of channel form and character were made using both Workstation and GIS software; where well logs have penetrated channels, lithology and calculated sand percentages were determined. The area has a variety of channel morphologies, ranging in sinuosity from 1.1 to 3.4 and varying in width from 45m to 8750m. Geometries range from single thread to wide, multithread. Crevasse splays and interdistributary creeks and lakes lie adjacent to channels. Sand percentages vary greatly between element types, and many multikilometer-scale elements show complex accretionary architectural composition.

The combination of morphometric measurements with lithologic characterization results in a predictive model that strengthens the relationship between channel form and sediment content. Architectural and sedimentologic changes have been assessed in the context of the basin's tectonic, climatic, and sea-level history. Results of this study apply not only to development of the study area, but to explaining how reservoir shape, size, and distribution evolve and are preserved within deltaic and shallow-marine environments.