Generating reliable gas condensate relative permeability data used to develop a correlation with capillary number

The authors have previously reported that steady-state relative permeability measurements conducted using condensing fluids will result in relative permeability increasing with increasing velocity. The techniques used, however, can be experimentally demanding, as individual steady-state points are measured and the initial condensate saturation in the core is established by condensation. If the data representative of the flow of condensing fluids could be generated using unsteady-state procedures and conventional gas-oil fluids, as has been suggested in literature, then the duration and cost of the tests would be greatly reduced. To investigate the applicability of conventional techniques to flow in gas condensate systems, a series of tests were conducted using conventional and condensing fluids. For each set of tests, the interfacial tension (IFT) and flow rate were the same, with the only variables being the measurement of steady-state relative permeability when using condensing fluids, and the measurement of unsteady-state relative permeability when using conventional fluids. The main areas of interest were hysteresis in the relative permeability curves between imbibition and drainage, and the degree of relative permeability rate sensitivity. It was demonstrated in this study that conventional methods could produce erroneous results when applied to condensing fluids. The steady-state gas condensate rate sensitive relative permeability data has been used to formulate a new correlation that relates gas and condensate relative permeability to capillary number (the ratio of viscous to capillary forces). The correlation incorporates two major parts, with exponents and coefficients that appear in the correlation being determined by regression of the steady state relative permeability data. Comparisons between the measured and predicted relative permeability curves show a good agreement. The study highlights the need to use condensing fluids when measuring gas condensate relative permeability.