The Use of Polymer Injectivity Data for the Estimation of Porous Media Longitudinal Dispersion

Current dispersion estimation techniques rely on the measurement of a tracer concentration smearing either in-situ or at the outlet. We propose a much easier technique that does not require measuring concentrations. The technique involves the injection of a pure phase followed by the same phase saturated with a non-linear viscosifying agent (or vice versa). This transition in the viscosity of the injected phase will result in a pressure transition. Theoretically, without dispersion, the pressure transition is directly linear with respect to time. However, with dispersion and due to the non-linearity of the viscosity-concentration dependence this transition will further spread. Analyzing this additional smearing and delay of the pressure response would give a direct measure of dispersion. Adsorption of the viscosifying agent also can cause a similar effect where the pressure propagation is delayed. Nevertheless, we could decouple those effects. The proposed procedure of measuring pressures during a viscosity switch is already done in the industry. In the context of polymer flooding, injectivity tests are used to give indication of potential injectivity issues and, explicitly, provide estimates of the polymer solution resistance and residual resistance. Therefore, we can further use injectivity data to estimate water dispersion and polymer adsorption. Injectivity data measured for a polyacrylamide polymer in a limestone core was used to test the method. Our pressure analysis suggest the aqueous phase exhibits a longitudinal dispersivity of 0.02 ft while, at 0.2 wt. %, 10% of the polymer concentration is adsorbed. Both results fall within the ranges reported in the literature. Additional simulation sensitivity results were performed using UT-Chem. The results support the presented theory. The proposed method is simple and could prove helpful in eliminating experimental redundancy and in simplifying dispersion estimation.