Abstract
There have been numerous papers discussing the advantages and disadvantages of Steady State versus Unsteady State Relative Permeability tests. But, there have been little discussion about the interrelationships between these two procedures. This paper shows how the transient data (pressure drop and saturation changes) during steady state tests can be used to arrive at relative permeability data and, thus, provide coverage for the full saturation domain. The transients occur after injecting at a new water-oil ratio (or gas-oil ratio) begins and before saturations along the core are equilibrated. A numerical simulator was used to model the steady state method. Injection of water and oil was simulated at different water-oil ratios (WOR) in a one-dimensional model. Both the constant injection rate (CIR) and the constant pressure drop (CPD) cases were simulated. The pressure drop and the fluid injection and production data during the transient periods (before stabilization at the next steady state point) were analyzed. These data closely matched the actual relative permeability curves. The new method was further tested by using actual laboratory measured data. The close agreement between the estimated relative permeability data based on transients with those based on steady state suggests the applicability of this new technique to any system. Thus, by using this technique, it should be possible to reduce the time required to conduct a Steady State tests by running fewer WOR (or GOR) cycles.
