Sequence stratigraphy of the Lower to Upper Cretaceous sedimentary deposits in the Exmouth Plateau and Exmouth Sub-basin, North West Shelf of Australia.

摘要

The Exmouth Sub-basin and Exmouth Plateau are a portion of the Northern Carnarvon Basin in the North West Shelf of Australia. This basin contains several major oil and gas fields in the Upper Triassic, Upper Jurassic, and lowermost Cretaceous reservoirs. A detailed sequence stratigraphic study of the Lower to Upper Cretaceous strata was done to evaluate their petroleum potential. Interpretation was done using an integrated regional exploration database including 2-D seismic data, wireline logs from six wells.;Nine stratigraphic sequences were defined from the Valanginian through Santonian. Sequences 1-3 (Zeepaard Formation) are part of a large progradational wedge of siliciclastic of slope to coastal plain strata, which show distinct topset-foresetbottomset depositional geometry. Sequences 4 (Birdrong Formation) and 5 (Muderong Shale) backstep and overlie the underlying sequences 1-3. The overlying sequences 6-8 (Gearle Siltstone) thin across the Exmouth Plateau and thicken across the Exmouth Sub-basin, and are characterized by several distinct internal downlap surfaces. In sequence 8, a wedge-shaped interval thickens to the east. Sequence 9 (Toolonga Calcilutite) marks the onset of marine carbonate sedimentation overlying the Gearle Siltstone.;The Lower Cretaceous strata are characterized by two phases of northward progradation of delta (Barrow Group and Zeepaard Formation), caused by the uplift and extensive erosion in the southern Exmouth Sub-basin. A regionally extensive marine transgression developed after the Valanginian continental breakup in the study area, resulting in deposition of the thick Muderong Shale, a regional seal, as far northwest as the edge of the Exmouth Plateau during the Hauterivian and Aptian. A continuous relative sea level rise during the Albian through Turonian resulted in a deepening of depositional environments with the deposition of the Gearle Siltstone. During this interval, there was a significant change in sediments' provenance, which was influenced by various tectonism and eustasy. After the Turonian, stable tectonism with decreased terrigenous influx into the study area resulted in the initiation of widespread deposition of carbonate sedimentation.;Based on this study, several potential plays for future exploration were identified. Potential plays are primarily associated with the stratigraphic traps (e.g. pinchout trap, reefal trap), which are developed in multiple sequences from sequence 2 through 9.