DEVELOPMENT AND PETROLEUM RESOURCE EVALUATION OF THE BOWEN, GUNNEDAH AND SURAT BASINS, EASTERN AUSTRALIA

Abstract

The Early Permian to Middle Triassic Bowen and Gunnedah basins and the Early Jurassic to Early Cretaceous Surat Basin in eastern Australia developed in response to a series of interplate and intraplate tectonic events located to the east of the basin system. The initial event was extensional and stretched the continental crust to form a significant Early Permian East Australian Rift System. The most important of the rift-related features are a series of half graben that form the Denison Trough, now the site of several commercial gas fields. Several contractional events from the mid-Permian to the Middle Triassic are associated with the development of a foreland fold and thrust belt in the New England Orogen. This caused a foreland loading phase of subsidence in the Bowen and Gunnedah basins. Thick coal measures deposited towards the end of the Permian are the most important hydrocarbon source rocks in these basins. The development of the Surat Basin marked a major change in the subsidence and sedimentation patterns. It was only towards the end of this subsidence that sufficient burial was achieved to put the source rocks over much of the basin into the oil window. Based on an evaluation of the undiscovered hydrocarbon resources for the Bowen and Surat basins in southern Queensland, our estimates of the yields of hydrocarbons suggest that significant volumes of hydrocarbons have been produced in the basins. The bulk of the hydrocarbons were generated after 140 Ma and most of the generation occurred in the late Early Cretaceous. Because the estimated volume of the hydrocarbons generated far exceeds the volume of discovered hydrocarbons, preservation of accumulations may be the main risk factor. The yield analysis, by demonstrating the potentially large quantities of hydrocarbons available, should act as a stimulus to exploration initiatives, particularly in the search for stratigraphic traps.