To ensure the physics of multiphase flow in porous media is rightly modelled, the balance between capillary, viscous, and gravity forces need to be understood. Capillary pressure (Pc) and relative permeability (kr) are critical parameters representing capillary and viscous forces respectively. Both are typically determined by special core analysis in the laboratory. The importance of application of proper capillary pressure curves for different processes and the consistency between the kr and Pc input are investigated.
In this study, we used the idea of Numerical Coreflood Experiment (NCFE) where detailed geology and known oil-water relative permeability and capillary pressure curves are used. Various NCFEs' production and pressure data can be generated for different conditions and used to estimate the kr and Pc. Here, we used a commercial application to back calculate a set of relative permeability and capillary pressure that fits the given production and pressure data for the examined cases. Afterward, we compared the resulting kr and Pc curves with those that were used to generate the NCFEs data to begin with.
In this study, we focused on the two-phase oil-water system to assess the process of obtaining a history- matched relative permeability by fitting the core-flood experiment data while setting capillary pressure to zero (ignoring Pc) in the simulation model. We compared different cases that we examined to identify the role and importance of Pc measurements in core-scale and reservoir-scale numerical simulations. The conclusion is that using appropriate input capillary pressure measurement is an essential step to ensure proper representation of the multi-phase flow physics. Ignoring Pc or using inaccurate Pc measurements could lead to inaccurate relative permeability curves and as a results unrealistic production and pressure output.
The results of this study can be used by researchers and practicing reservoir engineers in oil and gas industry. NCFE is an inexpensive and easy-to-use technique to evaluate the current experimental procedures and suggest improvements. NCFE can be extended to cover a wider-range of evaluations including the effect of gravity, injection rate and heterogeneities.