CAN WE REALLY MEASURE THE RELATIVE PERMEABILITIES USING THE MICROPOREMEMBRANE METHOD

We have performed experiments and simulations to study the accuracy of K-r determination by the membrane technique. We have developed a nume rical simulator and an analytical model which both account for the mem branes as a boundary condition. The analytical model is based on the a ssumption of constant k(r) and linear P-c 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 intermediat e saturation values, the transient production is governed by membrane permeability, without any real influence of the K-r, when the membrane resistance (thickness/permeability) is larger than core resistance; ( 2) for oil/water systems, the transient production is controlled by th e very small mobility of the fluid at low saturation near the end-poin ts. Its mobility can be determined with good accuracy, especially for very small K-r values. But, the mobility of the other fluid (at the hi ghest saturation) cannot be determined; (3) for oil/gas systems, the o il permeability can be determined, provided that the resistance ratio is smaller than 1 (membrane resistance/core resistance). Our conclusio n is that transient production during P-c measurement with porous plat e or membrane techniques cannot be used for K-r determination of liqui d/liquid systems, except if the two following conditions are satisfied : (1) very low membrane resistance (smaller than core resistance) (2) independent measurement of the K-r(max) at end-points by removing the membranes and using a standard one-phase flow. (C) 1998 Elsevier Scien ce B.V.