Detailed mapping, three-dimensional modelling and upscaling of a mixed-influence delta system, Mitchell River delta, Gulf of Carpentaria, Australia

Abstract

Data from satellite imagery, field measurements and analogues were used to construct a three-dimensional (3D) geocellular facies model of the Mitchell River Delta, Australia; a modern mixed-influence delta system. Detailed mapping identified 16 different facies elements and classified the delta as tide dominated, fluvially influenced and wave affected. The 3D model was subjected to varying degrees of upscaling of the horizontal and vertical dimensions and allowed comparison of volume and connectivity changes throughout. The upscaling process, to coarser grid cells up to 100 m horizontally and 4 m vertically, created false compartmentalization of facies bodies and significant changes in facies bulk volumes. The vertically upscaled models produced greater changes when compared to the horizontally upscaled models. Key changes in reservoir facies connectivity and bulk volume due to upscaling are associated with the facies architecture, including the elongate and thin morphology of beach ridge and channel facies in this mixed-influence delta system. Recognition of the defining reservoir features and incorporation into reservoir modelling methodology can improve volumetric estimation and allow for better predictions of reservoir connectivity in ancient delta systems.