Source to Sink Sedimentation in a Dryland Fluvial System, Western Lake Eyre Basin, Central Australia

Saju Menacherry¹, Simon C. Lang¹, Tobias H. D. Payenberg¹, and William Heins^2
1 University of Adelaide, Adelaide, Australia
² ExxonMobil Upstream Research, Houston, TX

Subsurface porosity and permeability of reservoir sandstones is strongly and systematically related to texture and composition of the initial sediment. Initial sediments texture and composition, in turn, are controlled by the provenance lithotype and transport distance within the sedimentary basin. Therefore the study of a modern system from source to sink in any climatic condition can be used to predict subsurface compositions and textures of reservoir sandstones. Umbum Creek in Central Australia is a modern dryland river flows eastward from the Davenport Ranges (Palaeo-Neo Proterozoic metasedimentary rocks) and drains Mesozoic and Cainozoic sedimentary rocks on its way to the depositional edge on the western side of Lake Eyre. Sediments were sampled from strategically located stream confluences and categorized through petrography and sieve analysis to capture the input of the various provenance lithotypes. Results show that over the 100 km transport distance, the observed grain-size as coarse grained and the sorting is moderate to well. The composition is high in quartz compare to lithics and feldspar, thus making the sediment a good candidate for reservoir quality sand in the subsurface. The modern sand is not only directly proportional to the hinterland bedrock lithology, but also cannibalizes all outcropping bedrock along the transport path. This practically means that no bypass area exists in the system, but that the complete catchment constitutes a source for the sediments, while the sink area is relatively small. This relationship needs to be considered on predicting subsurface sandstone compositions based on a hinterland study.