A wide variety of studies have been carried out around the Australian margin to infer or detect natural hydrocarbon seepage. Hydrocarbon seepage can, in selected geological settings, delineate subsurface petroleum accumulations and provide information on hydrocarbon charge type. However, the relationship between near-surface hydrocarbon seepage and subsurface petroleum generation and entrapment is often complex. Rates and volume of hydrocarbon seepage to the surface produce a variety of near-surface geological and biological responses, which require a range of sampling techniques to detect the seepage effectively. Interpreters must firmly grasp these issues to understand the significance of migrated hydrocarbons within near-surface sediments. Thus, it is important to understand the data types that have been used to infer seepage in Australia and the results of these studies, if natural hydrocarbon seepage is to be assumed in this region. Furthermore, the strengths and weaknesses of different approaches need to be understood and the data often need to be set in a global context to appreciate the significance of results obtained. This report is aimed at providing an overview of natural hydrocarbon seepage studies that have been carried out around Australia and to provide information on techniques and approaches that have proved to be successful during studies carried out by Geoscience Australian between 2004 and 2007.
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This investigation provides an increased understanding of seepage detection technologies and techniques, particularly in relation to the Australian environment, and appropriate interpretation of potential seepage indicators in a global context. Consequently, seepage studies can be undertaken with greater confidence in Australia's offshore jurisdiction, in locations and at times that are optimal for effective seepage detection.
