This study investigates the effects of wettability and interfacial tension on two-phase flow through porous media for oil recovery. It is found that the pore filling mechanism and oil recovery are influenced by the change in wettability at different Capillary numbers (Ca) values.
Two-phase flow through porous media is important to the development of secondary and tertiary oil recovery. In the present work, we have simulated oil recovery through a pore-resolved three-dimensional medium using volume-of-fluid method. The effects of wettability and interfacial tension (IFT) on two-phase flow mechanisms are investigated using pore-scale events, oil-phase morphology, forces acting on oil ganglia surfaces, and oil recovery curves, for Capillary numbers (Ca) in the range of 1.2 x 10(-3) to 6 x 10(-1). We found that the two-phase flow through oil-wet medium is governed by pore-by-pore filling mechanism dominated by the Haines-jumps. At low Ca values, a change in the wettability from oil- to neutrally wet resulted into the change of pore-by-pore filling mechanism to co-operative pore filling and as the medium wettability changes from the neutrally to the weakly water-wet, the corner flow events begin to emerge. At low Ca values, the invasion through weakly water-wet porous medium is dominated by co-operative filling and results into an increased oil recovery, whereas the two-phase flow through strongly water-wet medium is governed by corner flow events resulting in a low oil recovery. The corner flow events are found to be a function of not only the medium wettability, but also of Ca and are a characteristic of controlled imbibition. Further, we show that a substantial decrease in the IFT results in a fingerlike invasion at pore-scale, irrespective of the medium wettability. Finally, a two-phase flow regime map is proposed in terms of Ca and contact angle based on the two-phase interface morphology.
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