What’s in a Channel? The Influence of Channel Morphology on Reservoir Compartmentalisation

Payenberg, Tobias H.D.¹ (1) University of Adelaide, Adelaide, Australia

The accurate prediction of external sand body geometry and internal sand body architecture are paramount for building static 3D geological models that are used for fluid flow simulations. Most depositional environments contain some form of channelised flow, and channels in fluvial, shallow marine and deep marine depositional environments all constitute important reservoir facies. Despite similarities in the external channel geometry of many channelised sand bodies, the internal architecture is often quite different.

For example fluvial distributary channels are typically isolated reservoirs, laterally and vertically sealed by delta plain and abandoned channel mudstones, and thus form excellent stratigraphic traps. If formed by mixed-load systems, they are commonly rectilinear channel segments found only on the delta plain between the head of passes and the depositional mouthbars. Fluvial distributary channel sand bodies are typically elongate sidebars attached to the morphologically rectilinear channel wall. The sidebars form by both lateral and downstream accretion resulting from flow in a confined, but low-sinuosity thalweg, which produces elongate sand bodies typically 10 times longer than wide. On the other hand high-sinuosity channel sand bodies are mainly sandstone deposits of meander pointbars, which are more circular in shape, but typically much larger. Width-thickness ratios for meandering fluvial channel reservoirs have width-thickness ratios typically >100:1, while fluvial distributary channel reservoirs are on average 50:1 (range 15:1 to 100:1), In both cases the thalweg may be filled with organic mud following channel abandonment, thus forming compartments within the overall channel form.