Inferred reservoir quality from modern fluvio-aeolian sediments: Umbum Creek, Western Lake Eyre Basin, Central Australia

Abstract

Reservoir qualities of subsurface reservoir rocks are primarily controlled by their composition, texture and grain size. The ability to quantifiably predict such porosity and permeability is a significant factor in reservoir quality forward modeling. Sand composition, texture and grain size are functions of hinterland processes: provenance, tectonic setting, climate, sand evolution and transportation, and the depositional environment.

Sands from the modern dryland Umbum Creek, western Lake Eyre Basin, Central Australia reflect the nature of the hinterland region and drainage basin. Evolution of sand composition throughout the river course is mainly related to the changes in the relative proportion of bedrock lithologies. Six petrographic provenances were identified and established in the Umbum Creek drainage basin: upstream Palaeoproterozoic and Neoproterozoic provenances supply lithic grains and metamorphic minerals to the stream's sand, whereas quartz is mainly sourced from reworked older sedimentary units further downstream.

Initial rock compositions such as mineralogy, texture and grain size are the main influence on diagenetic processes such as cementation, quartz overgrowth, mechanical and chemical compaction, grain breakage and pressure solution. In the case of the Umbum Creek sands, the medium to coarse grain size, 88-92% of quartz, less than 2% of feldspar and less than 10% of lithic fragments, together with subrounded to rounded grains, moderately well sorting and very little in clay content, leads to a suitable candidate for good reservoir quality, if buried. A similar analysis of the hinterland of a petroleum basin could lead to a better assessment of reservoir quality prior to drilling.