Foam displacement in porous media: Experiment and mechanistic prediction by the population balance method

Although foaming injected gases with aqueous surfactant solution has proven to be a technically viable method for controlling gas flow mobility in porous media and improving oil reservoir production, modeling of foam displacement has been frustrated because the conventional continuum and Newtonian description of oil reservoir fluids is inadequate for foam. Foam in porous media is discontinuous on a length scale that overlaps with pore dimensions. This foam-bubble microstructure determines the flow behavior of foam in porous media, and in turn the flow of gas and liquid.; The primary goal of this research is to formulate a numerical description of foam displacement that incorporates the pore-level mechanisms of foam generation, destruction, and transport. More importantly, a general framework is established for the inclusion of additional physical mechanisms as knowledge of foam matures. A simultaneous experimental and mechanistic simulation study is reported where both transient- and steady-state foam behavior in porous media are elucidated by a population balance on foam bubbles.; Since the flow mobility of foam in porous media is strongly dependent on foam microstructure, rate expressions for the generation and destruction of foam are developed directly from the dominant pore-level mechanisms. These rate equations depend on gas and liquid velocity, aqueous phase liquid content, and surfactant concentration. Upon combination of the rate equations with expressions for bubble convection, accumulation and flow resistance, a conservation equation is formed for the number density of foam bubbles that is analogous to the usual continuum equations describing the flux of mass and energy in porous media.; A gamma-ray densitometer is used to investigate in-situ, transient, and steady aqueous phase liquid content in one-dimensional porous sandstones, under conditions where the rock is initially saturated and free of surfactant. Transient pressure profiles are measured with a conventional pressure transducer. The total superficial velocity of the gas and aqueous surfactant solution is constrained to less than 1 m/day to be relevant to oilfield flow rates. Both our experimental and model results show that foam generation is rapid and foam displacement is efficient where surfactant is available. Excellent agreement is obtained between model and theory. We find that the bubble population balance is the only current means of describing all flow modes self consistently.