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Analysing Geobody Geometries and Architectural Elements Within Fluvio-Deltaic Depositional Systems: A Case Study from the Mungaroo Formation, NW Australia


The Triassic fluvio-deltaic Mungaroo Formation is the main reservoir in the multi-TCF gas play offshore Northern Carnarvon Basin, NW Shelf, W. Australia. The research utilised a high resolution 3D seismic volume, covering approximately 17,500Km2, located NW of the Exmouth and Barrow sub-basins on the broad NW shelf of Australia, integrated with a full suite of well log data from 21 wells and conventional core from 8 wells, which has enabled characterisation of the stratigraphically complex Mungaroo Formation depositional system, including reservoir architecture and geobody geometries. The dominant facies and facies associations deposited on the Triassic continental shelf include; fluvial channel sandstones, overbank mudstones and siltstones, coal intervals and intercalated, bioturbated mudstone and very fine grained sandstones indicative of lagoonal/ restricted embayment facies and periodic marginal marine depositional settings. Well correlations across the basin have been produced following the integration of core and wireline log analysis which has further enabled the development of a sequence stratigraphic model for the Mungaroo Formation. The results allow the spatial and temporal characterisation of the depositional environment; defining alternating periods of transgression and regression, within an overall transgressive system. Seismic attribute analysis has enabled high resolution imaging of this evolving fluvial succession. A range of geobody morphologies and dimensions can be identified; which, when integrated with core-wireline log studies, allow the generation of seismic facies GDE maps of the Mungaroo Formation through time, and the development of refined depositional and sequence stratigraphic models. The research also examines the control and influence of climate and base-level changes on the observed sedimentary architecture through time, and the significant implications for building predictive 3D reservoir models.