VGP Technical Report 53 - Geomechanical analysis for the Underground Gas Storage project, Onshore Otway 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 opportunity for further underground gas storage (UGS) in depleted gas fields in the onshore Otway Basin is being investigated as part of the Victorian Gas Program (VGP). There are currently three depleted gas fields used for UGS in Victoria. These sites are in the Port Campbell area in the onshore component of the Otway Basin. The Geological Survey of Victoria (GSV) engaged SEAL Energy Pty Ltd (SEAL Energy) to carry out a suite of technical studies to investigate the potential for further underground gas storage at depleted gas fields in the onshore Otway Basin. Six sites (depleted gas fields) were selected through a ranking process (Bagheri, 2019) for static and dynamic modelling. The sites are Croft, Fenton Creek, McIntee, Mylor, Penryn and Tregony. This report describes the geomechanical analysis of the six depleted gas fields. A modelling workflow was developed to generate one-dimensional Mechanical Earth Models (MEMs) to simulate the geomechanical impacts of injection and withdrawal on underground gas storage. The MEMs were constructed for six wells; one well from each of the six depleted gas fields. Stress profiles and the rock elastic properties from the MEMs were key inputs for subsequent geomechanical analyses on cap rock integrity, fault stability and surface deformation. The study identified no likelihood of cap rock failure and no likelihood of fault instability for all the modelled fields during the simulated injection and withdrawal cycles. Fault stability analysis demonstrated that none of the analysed faults were predicted to fail. Surface deformation analysis, based on two analytical models, predicted minimal amounts of surface movement for the six fields. From the modelling, the greatest amount of surface uplift predicted was approximately 2 mm for Mylor, and the largest surface subsidence predicted was approximately 4 mm for Tregony. This is less than the 4 -12 mm vertical displacements modelled for the operational Iona underground gas storage site (Tenthorey et al., 2013). The geomechanical modelling demonstrates there are no structural integrity concerns for the six depleted gas fields when operated as underground gas storage sites following the dynamic modelling injection and production scenarios. Bibliographic reference: SEAL ENERGY., 2021. Geomechanical analysis for the Underground Gas Storage project, Onshore Otway Basin, Victoria. VGP Technical Report 53. Geological Survey of Victoria, Department of Jobs, Precincts and Regions, Melbourne, Victoria. Download: The downloadable version of this report is supplied in PDF format (15 MB). | ||||||
