Critical foaming oil saturation

In addition to the mobihty control characteristics of surfactants, critical issues in gas mobihty control processes are surfactant salinity tolerance, hydrolytic stabihty under reservoir conditions, surfactant propagation through the reservoir, and foam stabihty in the presence of cmde oil saturations. 

In most applications of CO2 as an oil recovery agent, the CO2 exists as a supercritical fluid above its critical pressure (7.4 MPa) and temperature (32°C), while its solutions in oil are liquids (5). Hence, the dispersion types of most direct interest are supercritical-fluid-in-a-liquid (for which no specific name yet exists) and emulsions of oleic-in-aqueous liquids (which may be encountered at low CO2 saturations). However, for historical reasons (described below), all dispersions used in research on gas-flood mobility control are sometimes called "foams," even when they are known to be of another type. 

The close match between experimental and simulated data does not continue when the same fractional flow curve is used to simulate the experimental pressure drop results at a slower frontal advance rate (2 m/day, oil free). A new fractional flow curve had to be constructed to give a closer match. In Figure 10 the experimental pressure drops are compared to the simulated curves and in Figure 9 the contrast between the new and old fractional flow curves is made clear. Due to the shear thinning nature of the foam, at slower frontal advance rates a steeper fractional flow curve is required at the same critical water saturation, = 0.35. 

Experimental evidence [35] snggests that, in the presence of foam, the irreducible phase saturations of water and oil (S rg, Soj.g) can be lowered significantly. Thus, the irreducible water saturation, Swrg, can actnally be lower in the presence of foam than the measnred valne of 46%, determined from the gasAvater relative permeability experiment (Appendix). For all of the foam simnlations, an irreducible water saturation of 30% was chosen. Since the in-sitn water saturation was not measnred, the critical water saturation valne (set to 0.35) conld not be determined accurately. 

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