Review on Foam-Assisted Gas Injection in Fractured Carbonates for Enhanced Oil Recovery

Foam-assisted gas injection in fractured unconventional reservoirs has garnered considerable attention as a result of its potential to address challenges associated with gas flooding, such as gas fingering, breakthrough, and gravity override. Foams can enhance gas mobility and conformance control by diverting gas flow from high-permeability zones (fractures) to low-permeability zones (matrices), leading to significantly improved oil sweep efficiency. However, foam capacity, stability, and propagation hinge on two primary factors: reservoir characteristics and operational parameters. Reservoir characteristics include permeability, adverse wettability, fracture connectivity, degree of heterogeneity, pressure, temperature, and salinity. On the other hand, operational parameters include injection rate, gas fractional flow, foaming agent formulations and their concentrations, foam stabilizers, gas type, and injection strategy. This review offers a comprehensive analysis of foam-assisted gas injection in fractured carbonates for enhanced oil recovery (EOR). Fundamentals of foam behavior in porous media, particularly fractured rocks, are presented together with the most efficient foaming agents and stabilizers. Furthermore, the factors influencing foam performance in porous media in terms of foam capacity and stability are provided from different aspects. The physics of foam displacement mechanisms during several field trials are also discussed. Lastly, this review pinpoints challenges and knowledge gaps associated with foams and proposes strategies for incorporating experimental insights into performance evaluation and simulation models. The ultimate goal is to enhance the current understanding of foam EOR projects and their potential applicability in fractured carbonates.