A systematic review of anhydrite-bearing reservoirs: EOR perspective, CO2-geo-storage and future research
KFUPM-KU Joint Research Program ( KU-KFUPM-2020-28, KU-201-004).
Understanding the rock/fluid interaction is key to the success of any enhanced oil recovery (EOR) method. However, EOR methods are significantly affected when the reservoir formation contains calcium sulfate minerals such as anhydrite. Anhydrite is a common chemically reactive sulfate rock/mineral found in both sandstones and carbonates. The presence of anhydrite, its distribution and the associated anhydrite–fluid–interactions are thus important to precisely evaluate the effectiveness of oil recovery techniques. While anhydrite dissolution is the key interaction mechanism in anhydrite-rich rocks, its presence may also lead to a complex rock wetting behavior. Therefore, this review focuses on the factors affecting anhydrite dissolution during EOR such as temperature, pressure, composition of EOR fluids, salinity and pH. We then relate these factors to the interactions of anhydrite with different EOR fluids. The review further presents the implications of anhydrite–fluids–interactions on the overall effectiveness of EOR methods. The prospects and challenges of several EOR applications (e.g. sea water, low salinity/smart water, and CO2/CO2 – brine/CO2-foam floods, and alkaline-surfactant-polymer [ASP]) in anhydrite-containing reservoirs is then discussed. The findings of this review indicate that until now, there is insufficient understanding of the actual mechanism and effect of anhydrite minerals on EOR. Further, the influence of anhydrite in chemical EOR such as surfactant, polymer, and CO2/CO2 – brine/CO2-foam flooding is still poorly understood.