Can we really measure the relative permeabilities using the micropore membrane method?

We have performed experiments and simulations to study the accuracy of Kr determination by the membrane technique. We have developed a numerical simulator and an analytical model which both account for the membranes as a boundary condition. The analytical model is based on the assumption of constant Kr and linear Pc during a small pressure step. These assumptions lead to a saturation equation which can be solved by standard methods used for thermal problems. The conclusions of the experiments and the simulations are the following: (1) for intermediate saturation values, the transient production is governed by membrane permeability, without any real influence of the Kr, when the membrane resistance (thickness/permeability) is larger than core resistance; (2) for oil/water systems, the transient production is controlled by the very small mobility of the fluid at low saturation near the end-points. Its mobility can be determined with good accuracy, especially for very small Kr values. But, the mobility of the other fluid (at the highest saturation) cannot be determined; (3) for oil/gas systems, the oil permeability can be determined, provided that the resistance ratio is smaller than 1 (membrane resistance/core resistance). Our conclusion is that transient production during Pc measurement with porous plate or membrane techniques cannot be used for Kr determination of liquid/liquid systems, except if the two following conditions are satisfied: (1) very low membrane resistance (smaller than core resistance) (2) independent measurement of the Kr(max) at end-points by removing the membranes and using a standard one-phase flow.