دانلود رایگان مقاله اندازه گیری مستقیم نفوذ پذیری نسبی در سنگها از پروفیل های اشباع حالت ناپایدار

Abstract

We develop a method to measure liquid relative permeability in rocks directly from transient in situ saturation profiles during gravity drainage experiments. Previously, similar methods have been used for sandpacks; here, this method is extended to rocks by applying a slight overpressure of gas at the inlet. Relative permeabilities are obtained in a 60 cm long vertical Berea sandstone core during gravity drainage, directly from the measured unsteady-state in situ saturations along the core at different times. It is shown that for obtaining relative permeability using this method, if certain criteria are met, the capillary pressure of the rock can be neglected. However, it is essential to use a correct gas pressure gradient along the core. This involves incorporating the pressure drop at the outlet of the core due to capillary discontinuity effects. The method developed in this work obtains relative permeabilities in unsteady-state fashion over a wide range of saturations quickly and accurately.

7. Conclusions In this work, we extended a relative permeability method to directly measure relative permeabilities during gravity drainage experiments from unsteady-state in situ saturation profiles in consolidated rocks. We injected gas at the inlet of the core at pressures higher than entry pressure of the rock to allow liquids to drain by gravity to (a) apply a gravity drainage method to consolidated rocks, and (b) extend measurements to larger saturation space. From this work, the following conclusions can be drawn: • The gravity drainage method allows calculation of relative permeabilities quickly over a large saturation space and provides many points on relative permeability curve. • The obtained relative permeabilities from this method have high accuracy due to direct measurement of relative permeabilities from unsteady-state in situ saturations. In addition, it is assured that the data are not compromised by capillary entry and end effects. • Extremely small relative permeabilities (10−4 − 10−5) can be obtained from this method. • It is essential to incorporate the correct gas pressure gradient into the relative permeability calculations by removing the pressure drops at the outlet of the core due to capillary effects. • No prior knowledge of the Pc curve is needed because capillary pressure is negligible if the mentioned criteria are met.