Residual Oil Zones: Review of current practice and experience

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.