An Experimental Investigation of Three-Phase Flow of Water-Oil-Gas Mixtures Through Water-Wet Sandstones

ABSTRACT Three-phase relative permeabilities to water-oil-gas mixtures have been measured both under unsteady-and steady-state conditions through fired Berea sandstone. A computer-based photometric device was used for monitoring fractional flow of displacement fluids. An extension of the Welge-JPN method to three-phase flow was used for the calculation of relative permeabilities from displacement data. Several saturation histories relevant to petroleum reservoir exploitation were examined. Steady-state measurements with saturation histories similar to those in the unsteady-state experiments were made on the same core to enable comparison of the results. Water relative permeabilities were found to depend only on water saturation and were practically independent of the saturation histories considered. Gas relative permeabilities depended on the total liquid saturation; the components of the liquid being of no concern. They depended strongly, however, on the direction of saturation change of the gas phase. Oil relative permeabilities seemed to depend on saturations of all the phases present. Although the direction of oil and water saturation change did not influence oil relative permeabilities significantly, the decreasing gas saturation resulted in higher values as compared to those when the gas saturation was increasing. This seems to suggest that trapping of gas facilitates more free movement of oil. Predictions made by the use of Stone's two models yielded lower values of relative permeability to oil when compared to the experimental results, suggesting the inadequacy of these models even for the strongly water-wet rocks used in the present study. Steady-state measurements of three-phase relative permeability yielded results similar to those obtained by the displacement method for both oil and water. However, owing to a different trapping mechanism, the gas phase relative permeability showed a much weaker dependence on the direction of gas saturation change under steady-state conditions when compared to the displacement process.