The stability study of CO2 foams at high pressure and high temperature

CO2 foam is effective for mobility control and blocking of high permeability channels in the process of CO2 flooding for enhanced oil recovery. CO2 foams are much less stable than nitrogen foams due to the specific properties of CO2, and selection of surfactants as foaming agents is important for foam performance under harsh reservoir conditions. In this study, different surfactants and their mixtures were tested to evaluate their performance as CO2 foam agents, and the experiments were conducted using a visualized foam meter and a core flooding facility at high pressure and high temperature conditions. The influences of temperature, pressure, salinity and the HLB value of surfactants on CO2 foaming capability were investigated. The synergistic effect of the surfactants was also evaluated in order to increase high temperature tolerance of the foams. The experimental results show that the performance of CO2 foams at high temperature is greatly dependent on the types of the surfactants used. For nonionic and anionic-nonionic surfactants, there is a critical or optimum HLB value for best foam performance. Pressure has a positive effect on the stability of CO2 foams but dependent on the HLB value of the surfactants. Combined or mixed surfactants have a synergistic effect that can significantly improve the performance of CO2 foams and increase the foam's stability at high temperatures.