Performance evaluation of novel polymers for CO₂ foam enhanced oil recovery

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.