Contrasting Contemporaneous Fluvial Styles in a Tropical Depositional Basin—Implications for Modelling of Hydrocarbon Reservoirs

Abstract

Understanding fluvial styles and their deposits is crucial to improve characterization of fluvial petroleum reservoirs, which host significant hydrocarbon accumulations, such as in the fluvial reservoirs of the Mungaroo Formation, North West Shelf, Australia. Here, we present an investigation of two anabranches in the same river system; one a highly sinuous meandering channel, the other a low sinuosity fixed channel, occurring within 10 – 40 km of each other. The investigation of these contrasting fluvial styles in such close proximity offers a unique opportunity for a process-based approach to investigating the relationship between fluvial style and sand-body geometry. We present channel geometry measurements and sand-body geometry data of both highly sinuous and fixed channel anabranching fluvial deposits of the tropical Magdalena River, Colombia. Data collection occurred over two field seasons, the location of topographic and sediment surveys was aided by the analysis of remotely sensed data. Preservation potential in this basin is high; more than 1000 m of fluvial deposits have been preserved during the last 5 Ma. The examination of these two contrasting yet connected channel systems provides an excellent opportunity for investigating the relationship between fluvial style and sand-body geometry at field and reservoir scales. The meandering reach is dominated by lateral accretion, and the fixed-channel reaches are dominated by avulsion. Data indicate that the fixed channel system is presently the dominant fluvial conduit, and that the meandering reach was dominant in the recent past. Both still transmit significant volumes of water and sediment. The existence of such different fluvial style and resultant sand-body deposit geometry in different reaches of a connected river system, active at the same time, within just tens of km, has relevant implications for subsurface interpretation, petroleum reservoir characterization and reservoir modeling. It illustrates that it may not always be necessary to invoke a dramatic climate or tectonic change for explaining lateral changes in fluvial style in the rock record.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015