<div>We have investigated whether water-saturated residual oil zones (ROZs), sometimes associated with conventional Australian hydrocarbon plays, could provide a CO2 storage resource and supplement depleted field storage. 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. Presented at the Australian Energy Producers (AEP) Conference & Exhibition (https://energyproducersconference.au/conference/)

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.

<div>The “Australia’s Future Energy Resources” (AFER) project, funded under the Government’s “Exploring for the Future” (EFTF) program has been completed. The project’s four modules have evaluated a mixture of energy resource commodities, including natural gas, hydrogen, subsurface storage opportunities for carbon dioxide and hydrogen. They are complimented by several targeted basin inventories which outline the current geological knowledge of energy resources in underexplored, data-poor regions. Several publicly available data sets have been generated and published under the AFER project, including 3,750&nbsp;line-km of reprocessed 2D seismic data, acquired in the Pedirka and western Eromanga basins, of which key lines have been interpreted and integrated with geological and petrophysical well log data. Relative prospectivity maps have been produced for five energy resource commodities from 14&nbsp;play intervals to show the qualitative variability in prospectivity of these resources, including quantitative resource assessments where warranted. Results from the AFER project have helped to identify and geologically characterise the required energy resource commodities to accelerate Australia’s path to net zero emissions.</div> Presented at the Australian Energy Producers (AEP) Conference & Exhibition (https://energyproducersconference.au/conference/)

<div>Geoscience Australia and CSIRO have collaborated, under the Exploring for the Future program, to investigate whether water-saturated residual oil zones (ROZs), sometimes associated with conventional Australian hydrocarbon plays, could provide a CO2 storage resource and enhance the storage capacity of depleted fields. This product is part of a larger project that includes, among others, a reservoir modelling component. </div><div>This report focuses on our petrophysical module of work that investigated the occurrence and character of ROZs in onshore Australian basins. Our findings demonstrate 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.&nbsp;</div><div>For more information about this project and to access the related studies and products, see: https://www.eftf.ga.gov.au/carbon-co2-storage-residual-oil-zones. </div><div><br></div>

<div>Geoscience Australia and CSIRO have collaborated, under the Exploring for the Future program, to investigate whether water-saturated residual oil zones (ROZs), sometimes associated with conventional Australian hydrocarbon plays, could provide a CO2 storage resource and enhance the storage capacity of depleted fields. This product is part of a larger project that includes, among others, a petrophysical study to identify and characterise ROZs. </div><div>In this report, we model the formation of a residual oil zone in an Australian setting and the subsequent injection of CO2 using a 5 spot well pattern. The reservoir is built as an archetype example of the Hutton Formation from the Cooper-Eromanga basin. The reservoir interval is populated with "permeable sandstone” and “impermeable baffle” facies and a sealing layer at the top of the model is created and assigned properties such that it can be made to leak oil by capillary failure, as part of the process used to create a residual oil column. The static model is them imported into CMG-GEM software for the reservoir flow simulations.&nbsp;We find the scenario, with injectors perforated at the top and a central producing well perforated at the bottom, able to both store the most CO2 and produce the most oil. The storage and sweep efficiencies are high, highlighting the difference with typical CO2 storage scenarios without pressure mitigation.</div><div>For more information about this project and to access the related studies and products, see: https://www.eftf.ga.gov.au/carbon-co2-storage-residual-oil-zones. </div> <b>Data is available on request from clientservices@ga.gov.au - Quote eCat# 149366</b>