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Unconventional Shale Oil Evaluation Of Otway Basin Source Rocks

Sobey, James

Weller, Paul

Engineering Honours Degree, 2012

University of Adelaide


Shales are traditionally viewed as the source rocks for conventional oil and gas accumulations. However, advances in drilling, completions and hydraulic fracture stimulation are changing how the energy industry views these shale source rocks. In the United States of America (USA) many shale source rocks are becoming reservoirs and producers of oil and gas. Outside the USA, many countries are beginning to evaluate their basins for potential shale plays. In Australia, several basins (Canning, Cooper Maryborough and Perth) have been highlighted as prospective for shale gas and oil, with gas reserves estimated up to 400 trillion cubic feet (EIA, 2011a). However, other basins are in their infancy and require further study to determine if they hold unconventional hydrocarbons. The Otway Basin in Victoria and South Australia consists of good quality shale source rocks with the potential to produce oil and gas through fracture stimulation. Further geological evaluation is required to determine the full extent of the Otway Basin’s unconventional shale plays. This study represents the first comprehensive assessment of unconventional source rock quality in the Victorian sector of the Otway Basin.

Initial investigations of shale plays are based on historical data available for the play area. This is used to undertake a source rock analysis typically compiled for comparison with already successful analogous shale plays from the USA. This evaluation technique is based on geochemical data from well completion reports and regional studies and is used to determine the shale oil potential of the Laira and Casterton Formations in the onshore section of the Otway Basin in Victoria. The Laira and Casterton Formations were chosen for this study as they are two of the key source rocks for conventional hydrocarbons in the western Otway Basin. South Australian companies Beach Ltd and Cooper Energy Ltd are already looking into the Casterton Formation as a shale play. Although, at this stage limited effort has gone into the shale oil potential of the Otway Basin, particularly in Victoria.

The results from this evaluation study revealed that the Laira Formation has relatively low potential for shale oil, primarily due to its low average total organic carbon content and immaturity. The Casterton Formation displays some highly prospective areas within the Ardonachie, Penola and Windermere Troughs, with good comparison to the USA shale plays in terms of total organic carbon content, formation thickness, genetic potential and maturity. This assessment of the Laira and Casterton Formations is one of the first steps toward development of unconventional resources in the Otway Basin. Recommendations for future work are made with the goal of further appraising the prospective areas of the Casterton Formation. This includes re-investigation of well data, drilling new appraisal wells, determination of stimulation potential and seismic surveying.

Australian School of Petroleum



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