--> Tithonian Sand-Dominated Marine Gravity Flow Deposits and Related Hybrid Flow Deposits in Producing Fields in the Dampier Sub-Basin, North West Shelf of Australia

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Tithonian Sand-Dominated Marine Gravity Flow Deposits and Related Hybrid Flow Deposits in Producing Fields in the Dampier Sub-Basin, North West Shelf of Australia

Abstract

The Tithonian-aged Angel Formation in the Dampier Sub-basin has produced to date some of Woodside's most successful producing oil and gas fields (Wanaea, Cossack, Angel, Lambert, and Hermes). The key reservoirs in these fields comprise massive, high quality sandstones with excellent permeabilities that are interpreted to have been deposited by large gravity flow events into a deep marine setting that existed over the sub-basin during Tithonian time. These reservoirs are also interbedded with hybrid flows of lesser reservoir quality. These hybrid flows are interpreted to have been created through the downslope transition of the sand-dominated gravity flows into slower and increasing cohesive, slurry-like flows that contain contorted and sheared sedimentological fabrics. They are interpreted to have been created through the erosion, incorporation and resultant breakdown of mud clasts within the flow. These hybrid flow deposits tend to dominate both the distal and the lateral settings of composite fan systems in both analogue outcrop and field examples worldwide and correctly identifying these flow deposits in core in the Dampier sub-basin makes them a useful tool to understand how the deep marine depositional system was building out at any one time. Due to the significant difference in permeability between the sand-rich gravity event beds and the hybrid event beds, correctly identifying this hybrid facies in core will allow for the application of adequate architectural analogue data to reservoir field models which in turn will impact field history matching and the prediction of future field performance.