This Record forms part of a study under the Exploring For The Future (EFTF) program (2020-2024). The Residual Oil Zone Project was designed to understand and identify residual oil zones in Australia, with the aim of developing this potential hydrocarbon and CO2 geological storage resource through CO2–Enhanced Oil Recovery. The work presented here is a collaborative study between Geoscience Australia and GeoGem Consultants. Residual Oil Zones (ROZ) represent a new and potentially viable oil resource for Australia, while at the same time providing a means to use and store carbon dioxide (CO2) through the application of CO2 enhanced oil recovery (CO2-EOR). These naturally water-flooded and water-saturated reservoirs, which contain a moderate amount of residual oil, can be associated with conventional fields (brownfields) or occur with no associated main pay zone (greenfields). Both types of ROZ are currently produced commercially through CO2-EOR in the USA, and are of growing interest internationally, but have not yet been explored in Australia. CO2-EOR has been in widespread practice in the USA since the oil shocks of the 1970’s. While tertiary CO2 injection usually targets oil remaining in fields that have been subject to water-flooding, there has been a parallel adoption of practices to recover vast amounts of paleo-oil that existed when many of these reservoirs were much fuller, before relatively recent (in geologic time) events caused structural and seal changes, resulting in natural water-flooding and/or migration of much of the oil out of the reservoir. The Permian Basin in Texas contains many examples where such Residual Oil Zones (ROZ’s) were found beneath conventional oil reservoirs. These ROZ are unproductive to conventional water flood operations but offer the possibility of an extra 9-15% recovery (of the ROZ OIP at discovery). This work reviews the lessons or insights that can be gained from the USA regarding ROZ field developments.

This report represents the first output from a study designed to understand and identify residual oil zones in Australia, with the aim of developing this potential resource using CO2 –EOR techniques. This work is part of the Residual Oil Zone (ROZ) module in the Exploring For The Future (EFTF) programme, which runs from 2020-2024. The work presented here is a collaborative study between Geoscience Australia and CSIRO. ROZ potentially represent a new and viable oil resource for Australia, while at the same time providing an additional CO2 storage avenue through application of CO2 enhanced oil recovery (CO2-EOR). These water-saturated reservoirs, which contain a moderate amount of residual oil and resemble water-flooded conventional oil fields, can be associated with conventional fields (brownfields) or occur with no associated main pay zone (greenfields). Both types of ROZ are currently produced commercially through CO2-EOR in the Permian Basin, USA, and are of growing interest internationally, but our understanding of ROZ in the Australian context is lacking. The first section of this report identifies and discusses the key parameters and factors that influence the efficiency with which ROZ can be produced. These include fluid-rock and fluid-fluid interactions, which may affect injectivity and sweep of hydrocarbons. We also discuss the effects of reservoir heterogeneity as it relates to flow dynamics and also the effects of pore space configuration. The first section concludes with a discussion of CO2 storage associated with ROZ development. In the second section, we discuss two different injection strategies with which to develop ROZ; carbonated brine injection and water alternating gas injection. The final section outlines details of the workflow that will be applied in the EFTF ROZ module over the coming years. Our proposed workflow is a three pronged approach which involves core flooding experiments, pore scale modelling and petrophysical analysis to identify potential ROZ in key Australian basins. In addition to plain CO2 injection, two other promising EOR techniques namely CO2-WAG and carbonated brine injection are also considered in this workflow. The main objectives of this workflow are to: • assess and identifying estimated oil recovery potential from a target ROZ by either of three EOR injection strategies, • identify the best injection strategy for a ROZ • identify the CO2 storage and utilization potential

CO₂ enhanced oil recovery (CO₂-EOR) is a proven technology that can extend the life of oil fields, permanently store CO₂, and improve the recovery of oil and condensate over time. Although CO₂-EOR has been used successfully for decades, particularly in the United States, it has not gained traction in Australia to date. In this study, we assemble and evaluate data relevant to CO₂-EOR for Australia’s key oil and condensate producing basins, and develop a national-scale, integrated basin ranking that shows which regions have the best overall conditions for CO₂-EOR. The primary goals of our study are to determine whether Australia’s major hydrocarbon provinces exhibit suitable geological and oil characteristics for successful CO₂-EOR activities and to rank the potential of these basins for CO₂-EOR. Each basin is assessed based on the key parameters that contribute to a successful CO₂-EOR prospect: oil properties (API gravity), pressure, temperature, reservoir properties (porosity, permeability, heterogeneity), availability of CO₂ for EOR operations, and infrastructure to support EOR operations. The top three ranked basins are the onshore Bowen-Surat, Cooper-Eromanga and offshore Gippsland Basins, which are all in relatively close proximity to the large east coast energy/oil markets. A significant factor that differentiates these three basins from the others considered in this study is their relatively good access to CO₂ and well-developed infrastructure. The next three most suitable basins are located offshore on the Northwest Shelf (Browse, Carnarvon, and Bonaparte Basins). While these three basins have mostly favourable oil properties and reservoir conditions, the sparse CO₂ sources and large distances involved lead to lower scores overall. The Canning and Amadeus Basins rank the lowest among the basins assessed, being relatively immature and remote hydrocarbon provinces, and lacking the required volumes of CO₂ or infrastructure to economically implement CO₂-EOR. In addition to ranking the basins for successful implementation of CO₂-EOR, we also provide some quantification of the potential recoverable oil in the various basins. These estimates used the oil and condensate reserve numbers that are available from national databases combined with application of internationally observed tertiary recovery factors. Additionally, we estimate the potential mass of CO₂ that would be required to produce these potential recoverable oil and condensate resources. In the large oil- and condensate-bearing basins, such as the Carnarvon and Gippsland Basins, some scenarios require over a billion tonnes of CO₂ to unlock the full residual resource, which points to CO₂ being the limiting factor for full-scale CO₂-EOR development. Even taking a conservative view of the available resources and potential extent of CO₂-EOR implementation, sourcing sufficient amounts of CO₂ for large-scale deployment of the technology presents a significant challenge. <b>Citation:</b> Tenthorey, E., Kalinowski, A., Wintle, E., Bagheri, M., Easton, L., Mathews, E., McKenna, J., Taggart, I. 2022. Screening Australia’s Basins for CO2-Enhanced Oil Recovery (December 6, 2022). <i>Proceedings of the 16th Greenhouse Gas Control Technologies Conference (GHGT-16) 23-24 Oct 2022</i>, Available at SSRN: <a href="https://ssrn.com/abstract=4294743">https://ssrn.com/abstract=4294743</a> or <a href="http://dx.doi.org/10.2139/ssrn.4294743">http://dx.doi.org/10.2139/ssrn.4294743</a>