VGP Technical Report 68 - Conventional gas prospectivity assessment and resource estimation, Onshore Gippsland Basin, Victoria.
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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: The conventional gas resources in the onshore Gippsland Basin have been assessed as part of the Victorian Gas Program (VGP). The evaluation has integrated new geoscientific studies conducted under the VGP geoscience program with pre-existing data and interpretations to identify the areas of the onshore Gippsland Basin where future conventional gas discoveries are likely, and the potential volume of conventional gas that remains to be found has been estimated. The assessment is based on the identification and evaluation of related geological circumstances that control the distribution of hydrocarbon accumulations in the subsurface and are known as a play. A play is the timely combination of reservoir and seal rocks with petroleum charge and potential traps to produce hydrocarbon accumulations in a basin. Seven plays, defined by reservoir interval, have been identified in the Mesozoic and Cenozoic rocks of the Gippsland Basin, of which one is at the base of the Seaspray Group, four are in the Latrobe Group (Cobia, Halibut, Golden Beach and Emperor) and two more are in the underlying Strzelecki Group (top Strzelecki and Intra-Strzelecki). Previous exploration has shown the offshore Gippsland Basin to be a prolific hydrocarbon province, but no development has occurred onshore. Previous exploration has demonstrated that the key geological components of each play (reservoir, seal, charge and trap) are present in the landward areas of the basin. The likely presence and effectiveness of each play element has been mapped and combined into a play fairway map which is a spatial assessment of the distribution of the required geological conditions for gas accumulation for each play. Proven play fairways are areas where there is high confidence that all elements of the play are present and are generally characterised by discovered oil and gas accumulations. While this is true for the Latrobe Group plays offshore, it is not the case onshore, although gas has been found in the top Strzelecki play onshore. Those parts of the fairway where the occurrence or effectiveness of one or more components of the play is ambiguous represent a possible play fairway. The geographic extent of the proven and possible fairways is a critical factor in both the assessment and size of the resource potential of the basin. The onshore extent of the play fairways in the Gippsland Basin is chiefly controlled by access to hydrocarbons migrating from mature source rocks located offshore in the Central Deep. Consequently, areas of better onshore prospectivity are adjacent to the coast where the distance and complexity of lateral hydrocarbon migration is reduced. Vertical hydrocarbon migration may occur where the Strzelecki Group is sufficiently mature to be generating and expelling hydrocarbons. The Strzelecki Group plays are also restricted by poor reservoir quality due to burial depth, while the limited onshore extent of the Golden Beach and Emperor subgroups significantly reduces the size of the area in which reservoir might be present. Biodegradation and water washing are likely to have altered the properties of hydrocarbons trapped in the Latrobe Group plays, although these changes are unlikely to significantly affect gas quality. The Cobia play (top Latrobe Group) is assessed as having the largest prospective area and highest probability of success, with the top Strzelecki and Intra-Strzelecki plays having somewhat smaller prospective areas and a lower probability of success. These three plays define the geographic extent of the proven and probable prospective resource areas in the onshore Gippsland Basin. Low, mid and high case exploration and production scenarios were developed from a deterministic assessment of prospective resources that assumed one new gas discovery in each of the seven identified plays. The discovery and production scenarios formed a key input to modelling the risks, benefits and impacts of a conventional upstream gas industry in Victoria (Ernst & Young, 2020). Bibliographic reference: Whittam, D.B., 2021. Conventional gas prospectivity assessment and resource estimation, Onshore Gippsland Basin, Victoria. VGP Technical Report 68. Geological Survey of Victoria, Department of Jobs, Precincts and Regions, Melbourne, Victoria. Download: The downloadable version of this report is supplied in PDF format (44 MB), Att A1 ESRI™ GIS data (ZIP 64 MB) & Att A2 (ZIP XLSX 800 KB). Related products:
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