Insights into viscous fingering effect induced by wettability alteration processes: A fractional flow study

Wettability alteration is one of the promising mechanisms for enhancement of oil recovery from preferentially oil-wet rocks. Many water-based EOR methods containing chemicals (e.g. surfactants) or ions (e.g. low salinity water: Low-Sal) were proposed to alter rock wettability to more water wetness. But, one of the possible challenges to get the full potential of such EOR methods is the occurrence of the viscous fingering phenomena. This could be the case for those of EOR methods in which an oil mobility profile over the flow domain could be formed due to the wettability alteration and thus potentially trigger viscous fingering with a negative impact on the oil displacement. In this paper, we aimed to describe this kind of viscous fingering phenomena by applying the fractional flow theory for the case of a tertiary Low-Sal injection process in a core sample previously flooded by a high salinity water. We explained the fractional flow procedure to obtain the saturation and location of the viscous fingered-region. As to the results, water saturation continuously decreases over the viscous fingered-region from an upstream point located at the Low-Sal region to a downstream point at the High-Sal region. The severity of the viscous fingering phenomena could be well addressed by the location of upstream and downstream saturation points as the proposed model honors these points. The model performance to predict breakthrough time and oil recovery factor was also validated by the previously reported Low-Sal experimental data and we found a good agreement between the model outcome and lab data.