Effect of System Wettability on Three-Phase Displacements Saturation Paths and Pore Occupancies in the Immiscible to Miscible Transition

The extended Bartell-Osterhof theory of van Dijke et al. has been applied in previous work to study the physics of three-phase displacements in porous media of non-uniform wettability. The underlying theory has previously been confirmed by experimental data. More recently, the model has been verified by comparing its predictions on three phase pore occupancies with experimental micro-CT image results. These imaging experiments were carried out on water-wet and oil-wet systems and the comparisons were qualitatively good. However, the theory can be applied to any arbitrary wettability distributions in the porous medium to study the effect of the immiscible to miscible transition on three-phase flow in porous media. In this work, nine wettability cases (water-wet, oil-wet, mixed-wet and fractional wet) have been considered to cover all possible behaviour of the rock, and the results of different phase invasion are presented for the immiscible to miscible transition. Although experimental data is not available for several of these cases, a list of clear predictions are made which can be tested in due course.

The results show that gas invasion saturation paths at immiscible condition depends on wettability state of the system, while at near miscible conditions they become similar for all wettability states. Such behaviour is also predicted for oil invasion as well. However, the situation is quite different for water invasion. In case of water injection, no matter what the system IFTs are, in both immiscible and near miscible conditions, saturation paths are predicted to be identical. The details of the physics of this behaviour have been discussed by considering the role of the phase wetting order in three-phase systems.