The Effect of Temperature and Pressure on the Interfacial Tension of Water Against Methane-Normal Decane Mixtures

Abstract

Abstract The interfacial tension of water against mixtures of methane and normal decane bas been measured in the interval 74 to 350 degrees F and 14.7 to 12,000 psia. These measurements show the range of interfacial-tension values obtained with water against an ideal "live-oil" system under reservoir conditions of temperature and pressure. The interfacial-tension data were obtained by the pendent drop method. The density data used for pendent drop method. The density data used for the pendent drop calculations were based on visual cell pressure volume measurements of the mutually saturated phases. Seven systems covering the methane-decane composition range from 100 percent decane to 100 percent methane were studied at three temperatures and 11 pressure intervals in the single-phase, hydrocarbon region. A minimum in the interfacial-tension vs methane-decane composition curve was observed. The minimum occurred at about the same composition in each isotherm, namely, with a mixture containing nearly equal weights of methane and decane. Both temperature and pressure affected the interfacial tension. For some compositions at constant pressure the interfacial tension increased with increased temperature. Introduction Although crude oil usually occurs in the formation saturated to some degree with methane, interfacial-tension data for methane-oil mixtures against water have not been published. These data are fundamental to an understanding of the role of interfacial forces in oil recovery and provide a basis for interpreting the interfacial tensions against water obtained with "live" crude-oil systems. We obtained interfacial tensions against water for an ideal "live-oil" composed of mixtures of methane and normal decane. Portions of this three-component (water, methane, normal decane) system have been studied and reported and these data serve as limits for our results. Hough et al. presented data for the methane-water system at presented data for the methane-water system at temperatures to 280 degrees F and pressures to 15,000 psia. Stegemeier studied the two-phase methane-decane system to 183 degrees F and 5,100 psia, and Jennings published results for the normal psia, and Jennings published results for the normal decane-water system to 350 degrees F and 12,000 psia. In this study we have obtained data for water-oil interfacial tension as a function of temperature to 350 degrees F. and pressure to 12,000 psia, using a series of live oils of known composition. The interfacial-tension data were obtained by the pendent drop method.