Three-phase capillary pressure, hysteresis and trapping in mixed-wet rock

The distribution of gas, oil and water on the pore level in reservoir rocks depends on the pressure differences across the fluid interfaces (i.e., capillary pressures) and the wetting preference of the rock surfaces. These properties are required to assess gas- and water-based methods for enhanced oil recovery (EOR) in the field, as they will affect the ability of the fluids to flow through the reservoir rock (i.e., relative permeability). The relation between capillary pressure and fluid saturation is irreversible as it depends on saturation history and the direction of saturation change. Such hysteresis effects are reinforced by pore-scale displacement mechanisms that lead to trapping or remobilization of isolated fluid compartments and different residual fluid saturations. This project will develop improved techniques based on mathematical methods to simulate the displacement of gas, oil and water directly on imaged three-dimensional pore structures. Images of experimental fluid distributions at the pore level will be acquired during three-phase experiments in porous media (utilizing advanced techniques) and compared against simulations. The validated pore-scale model will be used directly on imaged sandstone and carbonate rock samples to gain increased insight into three-phase capillary pressure and relative permeability, hysteresis and trapping behaviour (including the structure and amount of residual oil) in three-phase EOR processes at mixed-wet conditions. We will also include water chemistry effects to investigate the impact of interfacial tension and wettability change during cycles of water and gas invasion processes. Simulation results obtained with the novel pore-scale model can be used subsequently to develop practical and reliable three-phase capillary pressure and relative permeability correlations that can be implemented in reservoir simulators to improve the predictions of three-phase EOR processes in the field.