Simulation Interpretation of Capillary Pressure and Relative Permeability from Waterflooding Laboratory Experiments in Preferentially Oil-wet Porous Media

Summary In preferential oil-wet porous media, water flooding laboratory experiments are prone to capillary end effects. The wetting oil phase will tend to accumulate at the outlet where the capillary pressure is zero and leavea high remaining oil saturation at steady state (defined by stable pressure drop and zero oil production rate) compared to the residual oil saturation. Andersen et al. (2017a) derived analytical solutions describing how capillary pressure and relative permeabilityof water (the injected phase) could be determined based on pressure drop and average saturation at steady states obtained at different water injection rates. Plotting these values against inverse rate reveal linear trends at high rates, with slopes and interceptsthat directly quantify the saturation functions in the range of negative capillary pressures. The method is similar to Gupta and Maloney0027;s (2016) intercept theory, but quantifies entire functions rather than a single point and provides the trends also at lowrates, thus utilizing all the information. Our aim is to demonstrate how pressure drop and oil production at steady state for different water injection rates can be used to derive relative permeability and capillary pressure from water flooding. This is done inthree ways. First, synthetic waterflooding tests are generated (using the commercial software Sendra) applying the same saturation function correlations as assumed in the analytical solution. Then, more general correlations are assumed when generating thesynthetical data with Sendra. This , to test the robustness of the analytical solution of producing similar functions as the ‘true’ ones. Finally, we perform a waterflooding experiment in the lab on a high permeability (3 Darcy) Bentheimer sandstone core, alteredoil-wet using Quilon solution. The core was saturated with ~90 % n-decane oil and ~10 % brine. Spontaneous imbibition yielded << 1 % recovery. Forced imbibition of brine followed, starting from 0.4 PV/d, then increased stepwise after approaching steady stateuntil 12 rates had been applied, varied overall by a factor ~ 1000 to yield states governed by capillary forces and states governed by advective forces. The results were interpreted using both Sendra and the analytical solution. The experimental procedure and model demonstrate that only water relative permeability and capillary pressure determine the steady state during water flooding and hence can be estimated accurately. The analytical solutioncould match the trends and magnitude simultaneously of steady state pressure drop and production with injection rate to give an estimation of the saturation functions. The estimates were as good as full history matching.