The Effect of Temperature and Interfacial Tension on Water/Oil Relative Permeabilities of Consolidated Sands

Abstract

ABSTRACT Relative permeability data for high- and low-tension systems were obtained experimentally at temperatures ranging from 22°C to 175°C. No other data have been reported for high temperatures and low interfacial tensions. Results for high-tension systems at elevated temperatures and for low-tension systems at room temperature are compared with other published data. The results of this study can be used to predict the performance and efficiency of enhanced oil recovery methods in which chemicals are considered for use with hot waterfloods or as steamflood additives. They are of particular interest with respect to steamfloods in viscous oil reservoirs. Equipment was designed and constructed to measure water-oil relative permeabilities at elevated temperatures and pressures. It can be used for both steady-state and unsteady-state dynamic displacement measurements. The apparatus permits very accurate measurement of fluid saturations volumetrically by monitoring the oil content of the total system using a high pressure, high temperature water-oil separator. Experiments were conducted on fired Berea sandstone cores using n-dodecane and 1% NaCl brine. Aqueous low-concentration surfactant solutions were used to change interfacial tension levels. For the experiments reported here, the fluid pressure was kept constant at 300 psig and the overburden pressure at 650 psig. The experimental results indicate that relative permeability curves are affected by temperature, especially at low IFT's. For the high-tension system, relative permeability to oil increased and relative permeability to water decreased at a given saturation while residual oil saturation decreased and irreducible water saturation increased with increasing temperature. Water/oil relative permeability ratio decreased with temperature at a given water saturation. These results suggest an increase in the preferential water wettability of sandstone with temperature. Temperature effects were found to be more pronounced for low-tension than for high-tension systems. Residual oil saturation decreased significantly at higher temperatures, but only a small change in irreducible water saturation was observed. At any given temperature, irreducible water saturation for the low-tension system was lower than that observed for the high-tension system. Relative permeability to oil and water both increased with increasing temperature up to 100°C for the low-tension system. At higher temperatures, a decrease in relative permeability to water was observed, probably due to wettability alteration. The steady-state technique showed a hysteresis effect in relative permeability curves which tended to diminish at high temperatures and low IFT's. Rate effect was not significant for the rates used in this study. The change in wettability of the rock and reduction of IFT with increasing temperature were important factors affecting the observed relative permeability curves.