Wettability heterogeneities in gas injection: experiments and modelling

We carried out experiments to study the effect of wettability heterogeneiti es on: (1) displacement mechanisms, (2) sweep efficiency and (3) trapped oi l quantities and fluid distribution in three-phase gas injection and develo ped a theoretical simulator. Secondary gas injection experiments was conduc ted in transparent glass micromodels of heterogeneous wettability. Oil-wet patches in a water-wet matrix were obtained by selective silane grafting on the glass surface. Different heterogeneity patterns were considered for th e same oil-wet over water-wet surface ratio. Displacement sequences were vi deo-recorded and fluid saturations determined by image analysis. A theoretical model of three-phase flow in a porous structure was developed . In this model the porous medium is simulated as a network of interconnect ed pores. The model permits an imposition of heterogeneous wettability by a ssigning different water-oil contact angles according to the desired wettab ility pattern. The calculation of flow within the network takes into accoun t the flow of oil through wetting and spreading films and the displacement mechanisms observed in the transparent micromodels. Comparison between experimental results and simulations shows that the size and distribution of wettability heterogeneities strongly affects microscop ic and macroscopic behaviour during gas injection.