Most of the previously reported work for extracting relative permeability and capillary pressure data has been indirect and based on reservoir core history matching which requires iterative numerical solutions of inverse problems until a satisfactory match is obtained. The direct methods are based on integral formulations of the equations describing the fluid pressures and saturations for laboratory cores and they do not require numerical solution methods for differential equations involved in the indirect methods. Therefore, the numerical stability and accuracy and the history matching problems associated with the indirect methods are eliminated.

In the present study, a new direct method for determination of relative permeability and capillary pressure data from unsteady-state non-Darcy fluid displacement in laboratory cores is presented. The new method takes advantage of the internal fluid displacement data that can be obtained by noninvasive techniques in addition to the usual external fluid rate and pressure data. The mathematical interpretation method developed in this study enables the determination of relative permeability and capillary pressure simultaneously without the inherent limitations of the previous methods. It is also computationally more convenient, based on a semi-analytic solution of an algebraic formulation of the flow through porous media. Because it is an algebraic formulation it also provides a numerically more accurate interpretation of laboratory core data. The method is applied with typical gas/brine data to demonstrate its capability.

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