Determination of Field Scale Dispersivities by Mathematical Modeling

Dispersion in heterogeneous porous media results from the simultaneous action of a mechanical phenomenon and molecular diffusion. The mechanical contribution ari-ses from discrepancies in flow streamlines caused by inhomogeneities within the system. A two dimensional computer simulator based upon the moving point method was written. This method accura-tely described all levels of numerical dispersion. Observation well data from the El Dorado field in Kansas were effluent history matched with corresponding simulator runs. Longitudinal dispersivities ranged from 12 ft to 20 ft while transverse dispersivities ranged from o.oo ft to 0.06 ft. An "ideal" sampling scheme is pro-posed for future field wide dispersion tests, enabling more accurate determinations of history matched disper-sivities. The Lake and Hirasaki method of grouping layered systems producing effective one-dimensional disper-sivities, was found to be a relatively quick, approximate, procedure. This method takes into account the oftentimes important relative spatial ordering of reservoir layers.