THE STRUCTURAL DEVELOPMENT AND PETROLEUM POTENTIAL OF THE ROEBUCK BASIN

Abstract

The Roebuck Basin is a sparsely explored, frontier province located between the Carnarvon and Browse basins on Australia's North West Shelf. Mapping of the main structural and depositional elements of the basin has led to the identification of new features and elucidated the basin's tectonic history.

The newly-identified Oobagooma High is a 25 km wide north-south oriented, elongate structure that separates the Oobagooma and Rowley sub-basins at the Palaeozoic level. This structure links with the Bedout High to form a major hinge zone that stretches across the entire basin.

In the study area, three sub-divisions of the Fitzroy Movement are observed which have been termed Fitzroy Movement I, II and III, of Middle Triassic, Late Triassic and Early Jurassic ages. A previously unidentified breakup event linked to Fitzroy Movement III in the Early Jurassic is inferred from the stratal geometries in the basin.

The region lacks a source rock equivalent to the Upper Jurassic Dingo Claystone of the contiguous Carnarvon Basin. However, Lower Triassic marine shale and deltaic sands are well developed in the Bedout Sub-basin and based on the results of forward stratigraphic modelling using SEDPAK™ software and sequence stratigraphic correlations these sediments, have high source potential over most of the untested Rowley Sub-basin. Possible Jurassic source rocks in the Roebuck Basin were deposited under fluvio-deltaic conditions during waning thermal sag. Thinly developed sapropel zones exist in the Bedout Sub-basin but potential exists for greater thicknesses in the Rowley Sub-basin. This potential is suggested by the seismic character, sedimentary architecture and sedimentary modelling of Lower Jurassic rocks in the basin. Preliminary thermal modelling indicates that source rocks would have generated significant hydrocarbons from Middle Jurassic to the present. Timing of generation is favourable for trap formation.