Transfer of Fluid Components in a Porous Medium at Constant Saturation and Fluid Velocity

Abstract

Abstract When a gas is displaced by another in a porous medium, and there is a relative immobile liquid present, there is a transition zone in which the gas composition varies from essentially that of the original gas to that of the injected gas. The change in extent of this zone with time may be governed by a mixing process in the direction of flow and by the rate of establishment of gas-liquid equilibrium, if the gases are appreciably soluble in the liquid. The relative importance of these two factors in determining the growth of the transition zone is discussed, with appropriate equations and experimental data. Introduction The various solution methods of oil recovery involve a transfer of the components of a mixture, whether within a single phase or between a liquid and gas. The similarity of a natural porous medium to systems used in separation and chromatographic processes makes it seem reasonable that certain concepts used by chemical engineers in "mass transfer" might be applicable to petroleum reservoirs. One approach, the HETP (height equivalent to a theoretical plate), involves a distance or length of time over which equilibrium might be considered as established. Another approach involves direct use of a rate of mixing or rate of establishment of equilibrium. The latter approach has been preferred in relation to production problems. Discussion and Procedure When a gas or liquid in a porous medium is displaced by one of different composition but miscible with it there will be set up a transition zone in which the composition varies from essentially that of the original fluid to essentially that of the injected fluid. If the fluid being displaced is a gas, and there is a relatively immobile liquid present, the transition zone may be defined such that the liquid ahead of and behind this zone is practically in equilibrium with the original and injected gas, respectively. It is the extent of the transition zone which is of primary interest, for, if this is relatively small compared to the whole system approximate recovery calculations can be made purely by an over-all material balance and, if two phases are involved, by equilibrium considerations.