We study a new vertical sweep efficiency correlation for reservoirs with non-uniform layers and compare the effect of permeability autocorrelation on these estimates. Vertical sweep efficiency correlations are important because, in spite of sophisticated numerical simulators now available, there still remains a need for rapid estimates of oil recovery. The vertical sweep efficiencies are calculated using the chemical flooding simulator UTCHEM for a two-dimensional vertical cross-section with one injector and one producer, both also vertical.
As measures of heterogeneity we use the Dykstra-Parsons coefficient (VDP) in the case of a strictly layered reservoir and the Gelhar-Axness coefficient (HI) in the case of a nonlayered reservoir. We validate a strictly layered case and predict the vertical sweep efficiency in cases with nonuniform layers. We show that for mobility ratios greater than one, the effluent concentration of the injected fluid (in this case, polymer) oscillates because of viscous instability.
For unlayered cross sections, we show that the Gelhar Axness coefficient is a better vertical sweep efficiency estimator than the Dykstra-Parsons coefficient, because it accounts for spatial correlation (autocorrelation) as well as for heterogeneity. The vertical sweep efficiency decreases as we increase HI for the same VDP.