Factors controlling tight gas sandstone reservoir quality in the Whicher Range gas field, Southern Perth Basin, Western Australia

Abstract

There are limited studies characterising the Willespie Formation, a Permian tight gas sandstone in the southern Perth Basin of Western Australia. Consequently, the main factors controlling the reservoir quality, lateral reservoir connectivity and fluid flow mechanism remain unknown. Available data from five Whicher Range wells—including wireline logs, seismic, core data, well reports and petrographic data—were studied to define the syn-depositional and post-depositional events affecting the reservoir rock quality. Based on analysis of the aforementioned data, the Willespie Formation is interpreted to have been deposited under predominantly fluvial conditions in an ancient rift basin of continental origin with no marine influence. The sedimentary environments were laterally varied, as inferred from discontinuous facies formed by meandering channels, crevasse splay and flood plain settings that were mainly controlled by the Permian tectonic setting. Extensive compaction due to ductile grain deformation, as well as clay and calcite cements—filling pores and replacing grains—are the main post-depositional factors affecting the reservoir quality of the medium–coarse-grained, poorly sorted litharenitic sandstones of the Willespie Formation. Combined syn-depositional parameters—controlling the composition and the texture of the sandstone—and post-depositional diagenetic events have had a critical control on the distinctive poor porosity (8% average) and very low permeability of this tight gas sandstone reservoir.