Waterflooding permeability reduction

Review of the literature resulted in several references relating to the use of emulsions as agents for causing permeability reduction. McAuliffe (2) demonstrated that injection of externally produced oil-in-water emulsions at 24 C effectively reduces the water permeabilities of sandstone cores. These laboratory findings were later substantiated by a field test of emulsion injection followed by waterflooding in the Midway-Sunset Field (3). 

In ASP flooding, alkaline, surfactant, and polymer have different effects on relative permeabilities. Table 13.2 shows our attempt to summarize these effects compared with waterflood. From Table 13.2, we can see that the effect of alkaline flood in terms of emulsification is similar to the polymer effect, whereas its effect in terms of IFT is similar to the surfactant effect. Less rigorously, we may say that only polymer reduces k, and only surfactant reduces IFT. In ASP flooding, the viscosity of the aqueous phase that contains the polymer is multiplied by the polymer permeability reduction factor in polymer flooding and the residual permeability reduction factor in postpolymer water-flooding to consider the polymer-reduced k effect. Then we can use the k curves (water, oil, and microemulsion) from surfactant flooding or alkaline-surfactant flooding experiments without polymer. 

In one experiment, emulsion injection was begun after waterflood, and in the others emulsion injection was begun after tertiary recovery. The number of pore volumes of emulsion injected was 10, 7, and 8, respectively. The reductions in effective permeability, 52, 33, and 56%, were significant, but not as high as those when using oil-free cores. 

In the third test, the core was not saturated with oil before waterflooding, and the oil saturation was only 34%, resulting in higher initial permeability. Under this condition, the reduction in effective permeability increased to 43%. In all three tests, oil-in-water emulsions were produced from the core which had droplet size distributions appropriate to cause blockage of pore throats. These three tests illustrate that it is difficult to simulate in a one-dimensional model the conditions which exist in an actual reservoir after a steamflood, but that it is possible to create "emulsion blocks" in situ under appropriate conditions. 

As a result, the permeabilities in these domains within the formation become more uniform. Reduction in permeability in the more permeable domains improves the mobility ratio of waterflood. Premature breakthrough is thus reduced, and the efficiency of the waterflood is improved (Boston et al., 1969). Poorly cemented clay particles, such as kaolinite and illite, can become detached during aqueous flow, especially when flowing brines become fresher. 

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