The total dispersion method was developed to simulate first-contact miscible displacements performed in the laboratory. Simulations applying this method add sufficient dispersivity to the numerical dispersion inherent in finite differencing methods so the sum approximates the actual physical dispersion. This paper describes the application of this technique to model three floods taken from the literature and three displacements performed in a CT scanner.

A key variable for modelling miscible displacements is dispersion. Numerical dispersion for both 1-point and 2-point upstream weighting was characterized as a function of grid block size and throughput for an IMPES simulator. After quantifying numerical dispersion, three floods reported in the literature were simulated to confirm the total dispersion method. Recovery curves for two displacements dominated by viscous fingering and one exhibiting gravity override were modelled with good agreement.

Our next objective was to determine if concentration profiles as well as recovery curves could be matched in a well characterized rock. First, longitudinal convective dispersion was measured for Bentheimer sandstone by a series of tritiated water displacements. Two matched density floods were performed. A unit mobility flood showed that the rock is highly uniform. The spider web pattern distributor at the inlet of the core introduced a slight bulge in the initial concentration profile.

At an adverse mobility ratio of 10, a single finger developed and moved through the center of the core. Simulation of this latter flood included the influence of the distributor and provided a good match of both recovery and concentration profiles.

A single gravity override finger developed in the final displacement. Both the total dispersion method with 2-point upstream weighting and the extrapolation method with 1-point weighting predicted the recovery curve. The total dispersion method with 2-point upstream weighting matched the concentration profile. Based upon its ability to predict concentration profiles, the total dispersion method is preferred for laboratory scale simulations.

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