Investigation of Gas/Oil Relative Permeabilities: High-Permeability Oil Reservoir Application

Abstract

ABSTRACT Gravity drainage can result in a high recovery efficiency for high permeability oil reservoirs with low viscosity oil and low interfacial tension. In order to make reliable field wide performance predictions of this production mechanism, it is necessary to obtain accurate determination of gas-oil relative permeabilities and residual oil saturation. Gas-oil relative permeabilities have been extensively investigated, by performing: –displacement experiments in various conditions (differential pressure, interfacial tension, connate water or not, short or long core, room or reservoir conditions).–dynamic capillary desorption experiments. Special emphasis has been given to the actual physical meaning of the residual oil saturation and the way it is reached. The main results are: –Gas-oil displacement experiments performed in laboratory conditions (high interfacial tension) with various pressure drops give the same relative permeability if interpreted taking capillary effect into account. The final experimental oil saturation, which depends on the maximum acceptable injection pressure (turbulent flow problems) is different from the "true" ROS (corresponding to kro = 0).–Capillary desorption experiments in lab conditions with numerical interpretation of the transient production, may be used to determine ROS and oil relative permeability at high gas saturation.–Interfacial tension (in the range 0.6 – 30 mN/m) has little influence on the relative permeabilities.–Presence of connate water has little influence: oil and water behave as a single liquid phase.–Relative permeabilities obtained from laboratory conditions (short core) and reservoir conditions (long core) experiments are very close.–The final desaturation (ROS around 5 %PV) is reached very slowly, due to the very low level of oil relative permeability (about 10−5). A reliable method to determine relative permeabilities in laboratory conditions has been established, by performing both displacement and capillary desorption experiments.