| Three-phase flow in water-wet porous media is studied. The investigation begins at the sub-pore level with a theoretical analysis of hydrocarbon film spreading and stability between water and gas. Hydrocarbon films on flat water surfaces are shown to be of molecular-sized thickness. Displacement mechanisms at the pore scale are described from analysis of micromodel experiments and considerations of capillary equilibrium. Unlike hydrocarbon films on flat surfaces, the corners, roughness, and crevices of the pore space allow for thick hydrocarbon layers between water and gas. The effect of hydrocarbon layers and pore scale displacement mechanisms is incorporated into a three-dimensional network model. The network model calculates capillary pressure, relative permeabilities, and ultimate recoveries, and thus connects pore scale events with macroscopic flow parameters. Network model displacements are performed by specifying a series of changes in capillary pressure. Different capillary pressure paths result in drastically different relative permeabilities and recoveries. However, the capillary pressure path for a given macroscopically defined displacement with particular injection and initial conditions is not known a priori. Thus an iteration procedure has been developed that determines the proper capillary pressure path, and three-phase relative permeabilities, for the particular displacement. Three-phase relative permeabilities for gas injection into oil and water and water injection into a gas condensate reservoir are examined. |
