Wettability effects in gas gravity-Assisted flow as related to displacement instability

The drainage of oil under gravity forces is an efficient method because it can farther reduce the remaining oil saturation to below that obtained after water flooding. This paper describes a series of visual experiments under forced gas invasion with special attention to the effects of wettability. From oil production history and image analysis, we examine a threshold criterion for displacement stability that is consistent with the results of gradient percolation theory. The effect of the destabilized front velocity on oil recovery and residual saturation is investigated for both wettability conditions. Different recovery rates occur with different fluid morphologies, which depend on the matrix wettability and the balance between gravity and viscous and capillary forces. The dimensionless capillary and gravity numbers are used in analyzing the results. It has been shown that oil production decreases with displacement instability; however, this behavior would extremely depend on the wetting state. In addition, results indicated that the oil recovery depends linearly on the ratio of the gravity to viscous forces; however, the slope of this relationship in oil-wet porous media is more than twice of the water-wet system.