Application of Vaporization Equilibrium Constants to Production Engineering Problems

Abstract

The equilibrium constants developed by Souders, Selheimer and Brown havebeen very useful tools in predicting vapor-liquid equilibria during the pastfive years. Their equilibrium constants were computed by assuming idealsolutions and recognizing the deviations of vapors from ideal gas laws. Thesame fundamental concepts were used by Lewis and co-workers for predictingvaporization phenomena by means of fugacities. The equilibrium constants are a function of temperature and pressure andmight be considered as replacing the ratio of the vapor pressure to the totalpressure of Raoult's law. They may be used to compute the vapor or saturationpressure of a liquid or the dew point of a vapor for any pressure ortemperature from the analysis of the mixture much as Raoult's law is used.Likewise, the quantity of a mixture that will vaporize at any equilibrium.temperature and pressure and the composition of the vapor and liquid may becalculated. The purpose of this paper is to review the available equilibrium data ofinterest in petroleum production, to discuss the auxiliary physical propertiesof the hydrocarbons, and to present typical uses of the equilibrium constants.The particular applications chosen are the computation of the results of stageseparation of crude oil and natural gas, the calculation of a pressure-volumecurve of a crude oil-natural gas mixture, and information gleaned from aconsideration of reservoir equilibria.