Deep Water Reservoirs of the Lower Barrow Group (Macedon Member), Eastern Exmouth Sub-Basin, North West Shelf, Australia

Kirsten L. Dahl and Annette D. George
School of Earth & Geographical Sciences, University of Western Australia, Perth, Perth, WA, Australia

The Macedon Member reservoir sandstones of the Late Jurassic-Early Cretaceous Lower Barrow Group form part of a syn-rift succession within the Exmouth Sub-basin of the Northern Carnarvon Basin, offshore northwestern Australia. These problematic reservoirs host commercial hydrocarbon accumulations including the Macedon gas field in the eastern sub-basin. The Macedon field reservoirs have been previously interpreted as submarine fan channel-levee complexes and sand lobes deposited during a third-order lowstand located eastward and down slope of sand-rich slope canyon fills. The cored reservoir intervals in the Macedon field are dominated by fine to medium, poorly to moderately sorted quartz sandstones which are locally glauconitic and organic. Marine deposition is indicated by glauconitic material and ichnotaxa of marine affinity including Helminthopsis and Phycosiphon. The dominant reservoir facies are thickly bedded massive sandstones with mud-clast horizons (debrites) and thickly bedded turbiditic sandstones with normal grading and organic tops. Sedimentological features are consistent with deposition by sediment gravity flows principally sandy debris flows and sand-rich turbidity currents, and are interpreted as sand-rich channel fills. Thinly bedded laminated or bioturbated muddy sandstones record turbidity current deposition in interchannel areas. Similar facies associations are recognized in nearby fields which is significant for establishing distribution and geometry of the fan lobes and overall fan evolution.

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