Chemical flooding has been successfully applied in sandstone reservoirs using surfactant-related formulations due to their abilities to reduce interfacial tension (IFT) between injection fluid and oil. This scheme need to be modified to fit the requirement of effective application in carbonate reservoirs that present preferably oil-wet or mixed wet. In this case, the wettability alteration should be triggered by a kind of surfactants that can change the wettability towards water-wet and induce the spontaneous imbibition of injection fluid into the carbonate matrix for higher oil recovery. In this study, 16 surfactant samples were screened aiming at an Arabian carbonate reservoir, among which 3 surfactant samples were selected for spontaneous imbibition experiments using Amott cells at 95°C. The experimental results presented the imbibition was induced by the surfactant solutions compared to effect of the brine. It also showed that brine imbibition recovery decreases with the increase of permeability and initial water saturation. Surfactant can effectively improve imbibition recovery, and cores with higher permeability show better increased imbibition recovery. Imbibition can be divided into three types based on the value of bond number, and recovery as well as recovery rate can also be correlated with bond number. The imbibition model is validated by two imbibition modes – surfactant imbibition and brine imbibition then surfactant imbibition – using UTCHEM simulator. This paper demonstrates the effect of surfactant induced spontaneous imbibition on oil recovery, which should be taken into account in the chemical flooding application for carbonate reservoirs.

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