Wettability and spreading: Two key parameters in oil recovery with three-phase gravity drainage

The objective of this paper is to show that the porous medium wettability and the spreading characteristics of the fluid system hold the key roles in three-phase gas injection, and to study to which extent these two parameters affect oil recovery and phase distributions. To this end gravity assisted inert gas injection experiments have been performed in water-wet, oil-wet and fractionally-wet porous media for spreading and nonspreading conditions. The experiments are simulated and the oil and gas relative permeabilities for three-phase flow are calculated by history matching. It is proved that the existence of wetting and spreading oil films-caused by wettability and spreading-greatly affects the flow mechanisms and consequently the recovery kinetics and the process efficiency. The results are interpreted in terms of physicochemical parameters on the basis of pore scale mechanisms.