EFFECT OF CAPILLARY PRESSURE ON ESTIMATION OF RELATIVE PERMEABILITY FROM CORE FLOODING TESTS

The following investigation focuses on the impact of capillary pressure on estimation of two phases relative permeability curves. Accurate relative permeability is a crucial parameter for evaluating reservoir performance. The unsteady state core flooding tests, which is considered in this study, is mostly used to measure oil-water relative permeabilities.
The Johnson ,Bossler and Neumann (JBN) method is the conventional method for estimating relative permeabilities from field core. The limitations in the JBN method create an error in relative permeability curves and make it unrepresentative of a typical core flooding test results. There are always capillary pressure effects taking place during core flood tests. Ignoring of capillary pressure by JBN method will influence the calculation of relative permeability curves and final saturation levels.
One dimensional numerical model with uniform initial saturation has been implemented in this study using Eclipse 100 software to understand the relationship between relative permeability and capillary pressure. Pressure drop and recovery data obtained from 1-D numerical simulations are used to estimate the relative permeabilities by JBN method. Many scenarios have been studied by running the simulation at constant injection rate and varying the input capillary pressure.
The results obtained have shown the influence of capillary pressure on estimating relative permeability curves. It is shown that increase in capillary pressure increases the water relative permeability. Furthermore, the results demonstrate that the water flooding curves differ greatly in shape and position according to the corresponding values of capillary pressure.
Comparisons of relative permeability curves have shown that the capillary pressure dominates the displacement process. Capillary pressure gradient will increase the fractional flow of water and this increase in fractional flow of water results in lower frontal water saturation, higher frontal velocity and subsequently leading to a decrease in oil recovery.