On the Connectivity of Point Bars

Donselaar, Marinus Eric¹, Irina Overeem¹ (1) Delft University of Technology, 2628RX Delft, Netherlands

Point bar deposits form an important architectural element in fluvial reservoir models. Point bar geometry and permeability distribution are well constrained by detailed lithofacies studies. However, it is remarkable that point bar sandstone bodies are typically considered as isolated reservoir elements, because they are not the exclusive locus of sand accumulation in meandering rivers. Inherent to the process of bed load sediment transport, the entire channel floor of a meandering river is covered with sandy megaripples.

Outcrop studies of Miocene fluvial deposits in the Ebro Basin (Spain) show that preservation of elongate channel floor sandstone ribbons is common. The channel floor deposits form extensive, continuous ribbons that create sand-to-sand connectivity between successive point bar accumulations on both sides of the channel. The ribbons have an average thickness of 2 m and consist of well sorted fine to medium grained trough cross bedded sand. They connect with the lower parts of typically crescent-shaped, 4-6 m thick sandy point bar bodies. The ribbons are continuous in outcrop over a length of more than 2 km, and successive channel positions amalgamate to an elongate, low-sinuous belt of over 100 m wide.

Our outcrop results stress the preservation potential of channel floor sandstone bodies and their importance in connecting point bar units in a downstream direction. It is of vital importance to develop new functionality in fluvial reservoir architecture modeling which allows the connectivity between channel floor and point bar architectural elements in reservoir realizations, because this may greatly impact the estimated reservoir volumes.