Refinement of relative permeability measurements by accounting for viscous fingering in coreflood experiments

Relative permeability (kr) is a critical input data for any calculation involving multiphase flow in petroleum reservoirs. Normally, kr curves are obtained by performing coreflood experiments as part of SCAL measurements or EOR studies. The results of the experiments are then used to obtain kr values often by either analytical models (e.g. JBN) or ID history matching techniques. These models are based on the Buckley-Leverett displacement theory, which is not applicable to unstable displacements. In this paper, we present a simple method to calculate the relative permeability from coreflood experiments in which the displacement front could be unstable, for instance due to adverse viscosity ratio. The method proposed here modifies the JBN technique, and hence is referred to as modified JBN (MJBN), by including a viscous fingering term (rj) in the oil fractional flow. In order to calculate tj, we have developed a correlation between the viscosity ratio and the displacing fluid's viscosity. The correlation was obtained by producing viscous fingering with a known relative permeability and an unfavorable viscosity ratio. The relative permeability obtained by this method was then compared with the results obtained using history matching by commercial software widely used in laboratories. The results show that rj is function of viscosity ratio and displacing fluid viscosity. This means that tj can be used for a wide variety of cases, with different kr, core properties or fluid properties, just by using the same plots of rj versus viscosity ratio versus displacing fluid viscosity to estimate 17. ID history matching was compared with modified JBN (MJBN) for an experiment with unstable flow, resulting in a considerably better match using MJBN. This work provides new insights into the often overlooked issue of viscous fingering, its impact on multiphase flow, and a simple way of correcting kr data for the adverse effects of viscous fingering in kr measurement experiments. The proposed method can be easily adapted by service companies and researchers interested in measuring relative permeability in order to improve the quality of measurements and the accuracy of this crucial data.