New Exploration Strategy for the Vlaming Sub-basin of the Perth Basin, Australia

Shige Miyazaki and Steve J. Cadman

The offshore Vlaming Sub-basin is a major Mesozoic depocentre lying within the Perth Basin in Western Australia. Bounded by N-S trending faults between Pre-Cambrian blocks, the sub-basin formed as a rift basin associated with the breakup of Gondwana. Early Neocomian faulting, related to this rifting event, is responsible for the structural grain presently observed in the sub-basin. Faulting was followed by regional uplift, which resulted in a major Neocomian Unconformity.

A total of 16 wells have been drilled in the sub-basin, resulting in the discovery of a non-commercial oil accumulation within a thin, lower Neocomian sandstone. Many of the wells were designed to target structures associated with palaeo-highs on the Neocomian Unconformity. Our dry-hole analysis shows that these plays are vulnerable to leakage through cap rocks of poor quality.

Our new study has revealed that the relatively-unexplored Upper and Middle Jurassic Yarragadee Formation is favourably placed to entrap liquid hydrocarbons. The upper part of the Yarragadee Formation contains highly permeable and porous sandstones even at great depths. Source rocks of the Formation are within the oil generation window and contain 4% of TOC on average. Significantly, seismic surveys sparsely cover the inshore part of the sub-basin, where the Formation lies at relatively shallow depths and appears to be relatively unfaulted.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California