Wettability Alteration Study for Two Phase Flow in Porous Media

Wettability of pores plays an important role in two-phase flow in porous media. In the case of oil recovery, it has been found from both laboratory experiments and field tests that deviation of reservoir wettability from strongly water-wet conditions either can increase or decrease in oil recovery efficiency which indicates a possible range of wettability change [1]. In this present work, the effect of wettability alteration on the two-phase flow is studied based on a two-dimensional network simulator model of a porous medium developed by Aker et al. [2] with later extensions by Knudsen et al. [3] and Ramstad and Hansen [4]. The wettability alteration mechanism is introduced here in the model. The model is on the pore scale level with simplified mesoscopic description of pore networks. Biperiodic boundary conditions are considered which allows to study steady state flow dominated by complex bubble dynamics. Depending on the relative affinity of the pore surface to one of the immiscible fluids, the system can be defined as purely water wet or purely oil wet. The system can also be mixed-wet where a fraction of the pores or channels are wetting to the fluid which is non wetting in other pores of the system. Wettability of petroleum reservoir rocks generally altered by changing the brine composition, e.g., lowering salinity or adding surfactants [5]. Here we change the wettability condition from purely wet to mixed wet by altering the wettability of a fraction of pores randomly. The direction of the capillary forces are then reversed in those pores. The fractional flow is measured as a function of wettability alteration and saturation for different capillary numbers. The difference of the steady state fractional flow due to the wettability alteration is investigated. Interestingly, a continuous change in the fractional flow has been observed. Moreover, the change is found non-