The behavior of miscible displacement patterns at laboratory scale is strongly affected by the structure of the porous medium. This report covers both the experimental and mathematical approaches employed to investigate the effect of small scale heterogeneity on miscible flood tests. Experimental computerized techniques have been used to measure the detailed variation in rock sample properties. The experimental results indicate that there are significant nonuniformities in permeability and porosity at small scale level. The results showed that the spatial variability of permeability and porosity values has a clear impact on the miscible displacement performance.

The interaction of the nonuniformity of rock properties and dispersion can be mathematically described by a set of isoconcentration surfaces that move through the porous rock. This paper presents the analysis of the growth and decay rates at which the irregularities of these surfaces change as a function of the spatial variability of rock properties and the fluid diffusivity. Based on the experimental and theoretical observations, the conventional one-space dimensional models of miscible displacement cannot properly describe laboratory corefloods. In this paper, a new alternative model is proposed, based on the correlation length and overall variance (the major geostatistical descriptors of the variability of rock properties). A major consideration for a proper interpretation of the impact of nonuniformity of rock properties on mixing in the porous medium is the relative importance of correlation length and core dimensions.

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