Enhanced heavy oil recovery via surfactant-assisted CO2 huff-n-puff processes

CO2 huff-n-puff suffers from sharp decrease of recovery factor (RF) after the second cycle. The major objective of this paper was to study the key parameter and mechanism of surfactant-assisted CO2 huff-n-puff process (SACHP) as an enhanced oil recovery (EOR) method after the second cycle. In this study, two kinds of surfactants were used as viscosity reducer and foaming agent. The effects of the key parameters on RF, such as gas-liquid ratio, slug size, order of injections and soaking time were investigated through huff-n-puff experiments. The mechanisms of SACHP were studied by analyzing the produced fluid and oil sand after the SACHP experiments. The huff-n-puff experiments indicated that the combination of foaming agent and viscosity reducer was optimal for SACHP, and can improve ultimate RF by 13% compared to CO2 huff-n-puff. The recommended injection parameters for SACHP were 0.2 PV and 0.1 PV for CO2 and the surfactant solution, respectively. A larger slug size and an excessive soaking time have little effect on the ultimate RF. The SACHP caused the asphaltene content reduction in the produced oil and the asphaltene precipitation in the reservoir. The foaming agent can effectively control CO2 channeling and increase the swept range by 16.7%. The viscosity reducer can improve the displacement efficiency and the mobility of oil by forming emulsion. The synergistic effect of the surfactants and CO2 improved the ultimate RF. Therefore, the results of this study suggested that SACHP is a viable technique for EOR.