Network Modeling of Three-Phase Flow in Porous Media

Abstract

Summary We present a network model of three-phase flow in water-wet porous media. To explain the high oil recoveries in gas injection and gravity drainage experiments, we show that the mechanism for oil recovery is flow through connected oil layers in the pore space that are on the order of a micron thick. We then describe a simple model for the configuration of oil, water, and gas in a single pore and present an approximate expression for the conductance of oil layers. We use this expression to derive the oil relative permeability when flow is dominated by layer drainage. We show that for low oil and water saturations kro∼So2, consistent with the results of several experiments. To predict kro for the full range of oil saturation we use a capillary equilibrium-based network model that can simulate any sequence of oil, water, and gas injection. We introduce a self-consistency procedure to ensure that the correct sequence of saturation changes is used in the network model to compute relative permeability. We then present relative permeabilities and oil recoveries for gas injection into different initial oil saturations, and for waterflooding a reservoir containing gas and oil. We show that the relative permeabilities are strongly affected by the fluid properties and by the type of displacement process.