Medium wettability plays the main role during spontaneous imbibition (SI) in fractured porous media; however, one can rarely find pore-scale studies addressing wettability effects on this process. In present work Cahn– Hilliard phase field coupled with Navier-Stokes equations were solved using finite element method to simulate counter-current SI in a horizontal heterogeneous porous medium containing fracture. Capillary governed fluid displacement in media with different contact angles - θ=π/10 (extremely water-wet) up to θ=π/2 (neutral wet) - were simulated. The simulated models realistically captured micro-scale mechanisms during imbibition process in strongly water wet media, e.g., oil film thinning and rupture, fluids’ contact line movement, water bridging and oil drop detachment. Water capillary fingering through matrix and oil drop expulsion from matrix grains to the fracture were evident displacement phenomena in strongly water wet media. There was a specific grain contact angle, θ=π/4, above it matrix oil recovery was negligible and below it the imbibition rate and oil recovery were significantly increased by decreasing contact angle. For instance, after 5 s, almost 20% of the matrix oil was recovered in the model with θ=π/10, while final recovery of the models with θ>π/4 was less than 10% even after more than 1 min.

Keywords