The application of foam in the upstream petroleum industry has gained significant interest in the past few years. Foam usage can mitigate challenges associated with the gas flooding; it simply reduces the gas’s mobility, which could significantly enhance the sweep efficiency. Foam is generated using CO2 or N2 and stabilized by different materials such as surfactants, nanoparticles, polymers, or a combination thereof. The success of foam injection mainly depends on the stability of the flowing foam; the harsh reservoir conditions is one of the major challenges in this regard. Historically, surfactants have been used to generate and stabilize foams. However, recently, nanoparticles have gained attention due to their higher adsorption energy at the gas–liquid interface. In this paper, foam stabilizers such as surfactants, nanoparticles, and polymers are reviewed. Relevant advantages/disadvantages of different foam stabilizers and associated challenges are also highlighted. The results obtained in previous studies are discussed, and conflicting findings are highlighted and critically analyzed. Field applications of CO2 foam are also discussed in this Review. There are only a few field trials using surfactant stabilized foam. However, nanoparticle stabilized foam has not been tested in the field.

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The oil recovery from foam flooding mainly depends on the stability of the foam flow in porous media. At severe reservoir conditions, CO2 foam becomes unstable due to water drainage and gas diffusion through the lamella. The petroleum industry is using several foaming agents to produce and stabilize the CO2 foams. These are mainly water-soluble surfactants, CO2 soluble surfactants, nanoparticles, and water-soluble polymers. Addition of a water-soluble polymer in a conventional foam can increase foam stability, viscosity, and oil tolerance. Most of the previous studies utilized partially hydrolyzed polyacrylamide (HPAM) for CO2 foam stabilization. However, the data on CO2 foam stabilization using other polymers is limited. In this work, CO2 foam stability was assessed using several novel polymers. The foam was generated using alpha olefin sulfonate (AOS) surfactant at a constant concentration. These polymers were mainly acrylamide-based sulfonated polymers that contain thermally stable monomers that increase salt tolerance and thermal stability. The foamability, foam stability, foam diameter and bubble count per unit area of different foaming systems were measured using a dynamic foam analyzer. The result showed that the addition of polymers enhanced foam stability and reduced liquid drainage. Novel sulfonated polymers showed much better performance compared to the conventional HPAM polymer. Reduction in liquid drainage rate was much higher for sulfonated polymers compared to the conventional HPAM due to viscosity of the foaming solutions. For HPAM, the viscosity of the solution reduced at high temperature in presence of salts whereas sulfonated polymers maintained a high viscosity in the presence of salts that resulted in less liquid drainage and enhanced foam stability. The foam stability was also assessed using foam structure analysis. This is the first systematic study on the application of sulfonated polymer with varying molecular weight and structure for CO2 foam stabilization. This study helps in understanding the role of polymer molecular structure, molecular weight, and degree of hydrolysis on foam stabilization for CO2 -EOR.