The approaches to analysing unsteady state displacement experiments in order to determine relative permeability curves are reviewed. A new version of the Welge technique, which incorporates, explicit functional forms for relative permeability is developed. The sensitivity of the production nd pressure history to the shape of the relative permeability curve is analysed The influence of capillary pressure is then predicted by comparing results from the Welge technique and from the numerical simulator. INTRODIXTION Relative permeability measurement methods may be broadly classified into two types: steady state and unsteady state. For the steady state method, the phases are injected at a fixed volumetric ratio until pressure and flow equilibrium have been established. The pressure drops across the core of each phase (,IP8) and the flow rates of each phase (Qa) are then used to calculate the relativ 25-1 permeabilities (kra) bY means of the Darcy equation Qa ua L where lAa is the viscosity. k is the absolute permeability, A-is the cross sectional area of the sample and L is the length of the sample.A saturation of the sample is also required, this is typically determined by weight. The unsteady state method is based on interpreting an immiscible displacement process. This interpretation is based on orie of the two approaches: application of the Welge Theory (see Johnson, Bossler and Naumann or Jones and Roszelle or numerical simulation (see Sigmund and McCaf'fery3). The Welge approach requires the determination of the derivative of fractional flow with saturation. These derivatives are usually found either
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