The article provides the findings of studying the physical properties of formation fluids at oil fields under high pressure drawdown due to the extraction of separated gas from the wellbore annulus. The porous media were prepared using the centrifugation method because of its greater accuracy and less labor intensity compared to capillary impregnation or semi-permeable membrane methods. Creating a recombined (gas-saturated) sample of reservoir oil and its gradual degassing made it possible to determine the degree of reduction in oil viscosity and density. Every sample of partially degassed oil was examined within the monophase domain in the range of pressures: oil saturation pressure of that stage - reservoir pressure. As the pressure decreases, the density and viscosity of the monophase oil decrease. By comparing the values of density and viscosity at saturation pressures of each partially degassed reservoir oil sample, it has been established that during gas release the density and viscosity of oil increase with each stage, the density increases by 0.7%, the viscosity - by 23%. The dissolution of gas does not produce a significant (multiple) reduction in the density and viscosity of the sample. This is due to the fact that the degassed oil is originally bituminous (the density is above 895 kg/m3) with low gas content and saturation pressure. It has been discovered in the course of the research that at some values of permeability (less than 2·10-3 μm2) the oil relative permeability connate water saturation is equal to the kerosene relative phase permeability under connate water saturation (within a measurement error of 5%). This effect is attributed to the pseudoplastic behavior of oil. The final results of phase permeability measurements for both oil and kerosene, given the measurement error of 5%, have no effect on further calculations. Decreasing the bottomhole pressure at low GOR (up to 40 m3/t) does not affect oil relative permeability; that is why application of the sets of equipment for gas extraction from wellbore annulus (KOGS) causes no damage to the reservoir fluid inflow to a well's bottomhole.
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