Depositional Environment and Prospectivity Assessment using the Cazadores 3D Seismic Survey of the Outer Exmouth Plateau, Carnarvon Basin
Anna L. Maddocks - 2012
Honours Degree of Bachelor of Science (Petroleum Geology & Geophysics)
Australian School of Petroleum,
The University of Adelaide
The northern Carnarvon Basin has not been uniformly explored for hydrocarbons. More extensive exploration has been concentrated in shallower water depths of the more southern Dampier and Barrow sub-basins, with deeper waters of the northern Exmouth Plateau area being relatively under explored.
Extensive drilling, mostly within the southern, eastern and western areas, has shown that the Triassic Mungaroo Formation is extensively deposited across the Exmouth Plateau as a fluvio-deltaic sequence and forms a proven reservoir and source rock. Limited data are available within the northern Exmouth Plateau region with only a few wells drilled on the outer flanks. The Cazadores 3D seismic survey was acquired to further the knowledge of this northern region, thus enabling the analysis of likely reservoir rocks, trap geometries, source rocks and top seals.
The primary focus of this study is to utilise seismic interpretation methods for the analysis of depositional environments and prospectivity of the Mungaroo Formation within the Cazadores 3D survey area. Interpretation of the depositional environment of the Mungaroo Formation are obtained using integration of well log data and sculpted seismic images, the latter displaying discrete amplitudes within the seismic data to highlight channel and other depositional features. The interpretations resulting from these studies place the TR20 Mungaroo Formation level at a marginal marine environment of a lower delta plain with both fluvial and coastal influences. Verification of these interpretations is suggested through integration into the regional gross depositional model.
Prospectivity within the survey area is identified using structural mapping and seismic attributes from sculpted analysis. Volumetric calculations are carried out using area-depth volumes on a prospective four-way horst structure identified in the western region of the survey area. Geological risks and uncertainties relating to this structure are considered, resulting in a 17% probability of success. Hydrocarbon charge within the Cazadores 3D area remains questionable with two dry exploration wells, Belicoso-1 and Dalia South-1. However, some encouraging features have been identified within the seismic data, including pockmarks, chimneys and HRDZs. Source rock, trap and seal integrity studies are recommended to constrain the subsurface uncertainties and help facilitate successful exploration within the northern Exmouth Plateau region.