CO₂ storage in Residual Oil Zones: Field-scale modeling and assessment

Residual Oil Zones (ROZs) are formed as the result of secondary tectonic activities which trigger extensive oil remobilization after the primary petroleum migration. The ROZs are attractive targets for CO₂ Enhanced Oil Recovery (CO₂-EOR) and storage: first, because in many cases, the thickness of the ROZ ensures an overall recoverable volume of oil comparable to that of the Main Pay Zone (MPZ) and second, because the ROZ has favorable containment and capacity for large-scale and long-term EOR-storage projects. This stud are qualitatively discussedthe study demonstrates thatthe,y investigates one of the underlying theories of the ROZ formation, called, the Altered Hydrodynamic Flow Fields (AHFF). The impact of the AHFF process on the formation of ROZs is specifically investigated using a field-scale simulation model for a Permian Basin San Andres reservoir. The simulation model is tuned and verified by validating the ROZ's characteristics, such as the thickness of the ROZ, the shape of the saturation profile, and the tilt of the OWC. The tuned Permian Basin San Andres reservoir model is used to simulate the primary recovery and the secondary waterflooding phases in the MPZ. Depending on the CO₂ availability and ROZ development strategy, six different development scenarios are specified beyond the waterflooding phase. The corresponding simulations are performed to find the optimum EOR-storage strategies for the MPZ-ROZ through the extensive comparison of key performance parameters, including the cumulative oil recovery, CO₂ storage and net CO₂ utilization. The results confirm the technical viability of CO₂-EOR and storage in the ROZ. The most favorable expansion strategy in terms of oil production and CO₂ storage is the simultaneous development of the MPZ and the ROZ from the beginning of EOR-storage process. Most importantly, that the volume of the utilized CO₂ has a substantial effect on the success of the EOR-storage. While other expansion strategies such as sequential development also provide reasonable oil production response and CO₂ storage potential, early project expansion into the ROZ without sufficient investment in CO₂ resources is shown to be detrimental to the economics of the project. Finally, several important technical considerations for CO₂ storage, including assessment of the ROZ storage capacity, saltwater disposal requirements, and reduced risk of CO₂ leakage in the ROZ.