VGP Technical Report 57 - Fault and top seal integrity in the Mussel Platform and the nearshore eastern Otway Basin.
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Product description:About the Victorian Gas Program: The Victorian Gas Program (VGP) is a comprehensive science-led program, incorporating geoscientific and environmental research to assess the risks, benefits and impacts of potential onshore conventional gas exploration and production. The program is also investigating the potential for further discoveries of onshore conventional and offshore gas in the Otway and Gippsland geological basins and assessing the feasibility of additional onshore underground gas storage in depleted reservoirs around the Port Campbell area. The VGP includes an extensive, proactive and phased community and stakeholder engagement program, through which the results of the scientific studies are being communicated. Executive summary: As part of the Victorian Gas Program (VGP), the Geological Survey of Victoria (GSV) is studying petroleum systems components (reservoir, seal and source), to assess the hydrocarbon prospectivity of the Victorian Otway Basin and to estimate the potential for further onshore and offshore discoveries within Victoria’s jurisdiction. This report is part of a series of studies undertaken by CSIRO as part of a collaborative research program with the GSV. This report investigates the impact of faults on hydrocarbon prospectivity on the Mussel Platform and in the nearshore eastern Otway Basin. The behaviour of faults over geological time influences the distribution of hydrocarbons in a petroleum system through migration, entrapment, and leakage. A 3D structural model was constructed to investigate the complex geometry and timing of the Late Cretaceous and Cenozoic stratigraphic units to provide structural insights into fault evolution, reactivation and interaction with regional top seal intervals. Fault analysis was performed to highlight the fault architecture and evolution in the region and generate a relative containment potential map. The map reflects the potential for faults to provide cross- and up-fault seal, demonstrating confidence in structural trap integrity in a structurally complex area. In the study area, the most widely distributed sealing facies are the Belfast and Skull Creek mudstones. The seals are well developed with an overall thickness increasing from the north-east to the south-west, reflecting the structural evolution of the margin. The Belfast and Skull Creek mudstones represent effective top seals for several gas accumulations in the area. An assessment of sediment juxtaposition patterns and membrane seal capacity suggests that structural closures are expected to rely primarily on juxtaposition seal, with reservoirs of the Waarre and Flaxman formations juxtaposed against seals of the Belfast or Skull Creek mudstones expected to impede lateral flow. This sealing scenario is observed in the nearby Halladale, Pecten, Netherby, Martha and Henry gas discoveries. This configuration is expected to provide adequate trapping mechanisms for tilted blocks and horsts in the study area. A relative containment potential map, generated from fault seal analysis, reflects the potential for faults to provide cross- and up-fault seal on the Mussel Platform and in the nearshore eastern Otway Basin. The map was derived from key controlling parameters such as the distribution and thickness of the top seal interval, lithofacies variation and strain distribution. The map illustrates an adequate probability of structural trap integrity, with the gas discoveries on the Pecten Anticline associated with a moderate probability of structural trap integrity. This indicates likely containment of hydrocarbons on the Mussel Platform and in the nearshore eastern Otway Basin. Bibliographic reference: Langhi, L., Swierczek, E. & Strand, J., 2021. Fault and top seal integrity in the Mussel Platform and the nearshore eastern Otway Basin, Otway Basin, Victoria. VGP Technical Report 57. Geological Survey of Victoria, Department of Jobs, Precincts and Regions. Download: The downloadable version of this report is supplied in PDF format (38 MB) & Att A1 (ZIP 1.3 GB). | ||||||
