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ABSTRACT: Integration of sequence stratigraphy and sedimentology in an intracratonic setting, Tartulla field, Cooper basin, Australia

Hughes, Tina1, Simon C. Lang2, and Nick Hall1
(1) Santos Ltd, Brisbane, Australia 
(2) University of Adelaide, Adelaide, Australia

Sedimentology and high resolution sequence stratigraphy are vital tools for prediction of size, geometry and connectivity of reservoir facies, but few studies have integrated these tools in entirely non-marine intracratonic basins. This study shows the utility of sequence analysis as an aid to reservoir development at Tartulla Field in the intracratonic Cooper Basin, central Australia. Sedimentology of cores and interpretation of wireline logs from the Permian Toolachee-Patchawarra Formations, indicates the reservoir succession comprises small, narrow, sandy fluvial distributary channels, and crevasse splays. Distal splays, floodbasin and peat mire deposits act as seals and baffles.

Key surfaces (sequence boundaries and extensive lacustrine flooding surfaces and coals), when used in combination with vertical stacking patterns, allow recognition of alluvial depositional systems tracts within unconformity-bounded sequences. The unconformities were formed by tectonic uplift events, and are overlain by amalgamated, sand-prone fluvial reservoir facies (lowstand systems tracts) with optimum reservoir connectivity. The overlying succession typically contains increasingly isolated fluvial reservoir facies associated with extensive coals, topped by a regionally correlatable lacustrine maximum flooding surface formed during maximum accommodation (alluvial transgressive systems tract). The overlying fluvial deposits are associated with an upward increase in channel and splay amalgamation as the rate of sediment supply outstripped accommodation (highstand systems tract). Net to gross trends within each systems tract can be used to predict reservoir facies distribution and likely connectivity not only within the field, but also between adjacent fields.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia