Pore-scale events in drainage process through porous media under high- and low-interfacial tension flow conditions

► In secondary drainage brine advances due to cluster growth with no frontal drive. ► In tertiary drainage surfactant solution penetrates pore bodies without breakup. ► In tertiary drainage surfactant solution may cut off and re-trap the residual oil. ► Surfactant film spreading causes its penetration deep inside the local oil bank. ► Mobilization of trapped oil occurs due to both frontal drive and cluster growth.