Carbon Dioxide (CO2) foam has been widely studied in connection with its application in EOR. This paper reports an experimental study concerning CO2 foam propagation in a surfactant saturated Bentheim sandstone core and the subsequent liquid injection with the aid of X-ray Computed Tomography (CT). The experiments were carried out under various system backpressures. It is found that CO2 foam flows in a characteristic front-like manner in the transient stage and the water saturation keeps at relatively high level at the outlet of the porous media due to CO2 solubility and capillary end effect. The subsequent surfactant solution injection shows a significant fingering behavior, accompanied by a low flow resistance over the core. It is also found that CO2 foam flow shows higher liquid saturation near the outlet and lower pressure drops under higher system backpressures. This can be attributed to the solubility of CO2 in the liquid phase. The results indicate the advantage of using foam in EOR process such as water alternating foam (WAF), where foam flow has higher sweep efficiency and stronger mobility control ability compared for instance to WAG. Nevertheless, care should be taken during water injection stage in order not to favour the fingering.

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