THE TECTONIC FRAMEWORK AND ASSOCIATED PLAY TYPES OF THE WESTERN OTWAY BASIN, VICTORIA, AUSTRALIA.

Abstract

A regional seismic interpretation was carried out over the onshore Otway Basin in western Victoria to produce two-way time formation top and thickness images and a structural elements map showing the ages of faulting. This interpretation improved the understanding of tectonic events controlling the evolution of the basin and associated hydrocarbon plays.

The early development of the basin involved rifting due to NE–SW extension in the Late Jurassic–Early Cretaceous, producing a number of half-grabens. The rifting conforms with established rift development models, in which half-grabens of alternating vergence are separated by transfer zones displaying complex folding and faulting patterns. Within the northern margin of the basin these half-grabens were filled and rifting ceased prior to the Aptian.

An unconformity in the Wangerrip Group has been identified in the basin, corresponding to a change in Southern Ocean spreading rates from slow to fast (52Ma).

Compression, resulting in right-lateral wrenching and inversion of previous faults, occurred during the Miocene–Recent.

A number of hydrocarbon play types were identified based on the structural mapping carried out. These play types include anticlines associated with transfer zones, tilted fault blocks, buried basement highs, stratigraphic traps, post-Albian horst structures, syndepositional roll-over structures and post-Oligocene normal and reverse fault related structures.