Session 27. Oral Presentation for: The potential for CO₂ storage in residual oil zones in onshore Australian basins

Abstract

Presented on Thursday 23 May: Session 27

Geoscience Australia and CSIRO have collaborated to investigate whether residual oil zones (ROZs), sometimes associated with conventional Australian hydrocarbon plays, could provide a carbon dioxide (CO₂) storage resource and enhance the storage capacity of depleted fields. Our petrophysical study demonstrates that ROZs occur in Australia’s hydrocarbon-rich regions, particularly in the Cooper-Eromanga Basin. ROZs with more than 10% residual oil saturation are uncommon, likely due to small original oil columns and lower residual saturations retained in sandstone reservoirs than in classic, carbonate-hosted North American ROZs. Extensive, reservoir-quality rock is found below the deepest occurring conventional oil in many of the fields in the Eromanga Basin, potentially offering significant CO₂ storage capacity. Multiphase compositional flow modelling was used to estimate the CO₂ storage efficiency of typical Australian ROZs. We developed a novel modelling methodology that first captures oil migration events leading to the formation of ROZs. Modelling CO₂ storage over a 20-year injection period demonstrates that CO₂-oil interactions increase the density and viscosity of CO₂, enhancing CO₂ sweep efficiency and lateral flow, improving storage efficiency. The extent of these effects depends on the quantity and spatial distribution of residual oil in place and the miscibility of CO₂ at reservoir conditions.

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