Vaporization Characteristics of Carbon Dioxide in a Natural Gas-Crude Oil System

Abstract

Abstract The vaporization characteristics of carbon dioxide in a League City naturalgas - Billings crude oil system were studied at three temperatures, 38?, 120?, and 202' F and for pressures ranging from 600 to 8,500 psi. Variation of carbondioxide concentration up to 12 mole per cent in the composite showed no effecton the equilibrium vaporization ratios (K values) of the hydrocarbonconstituents or on the K value of carbon dioxide itself. It was shown thatcarbon dioxide is more soluble in crudes than in distillates which is contraryto the behavior of methane. A working chart of carbon dioxide K values is presented. Introduction The study of the equilibrium vaporization ratios of mixtures of paraffinhydrocarbons has been rather thorough. In the past few years considerableattention has been paid to the vaporization characteristics of the so-callednoncondensable gases such as nitrogen, carbon dioxide, and hydrogen sulfide inmixtures of hydrocarbons, since they usually occur to some extent in most crudeoils and natural gases. Knowledge of this behavior is useful to both theproduction and refining phases of the petroleum industry. This paper reports the equilibrium vaporization ratios (K's) of carbondioxide in a mixture of League City natural gas and Billings crude oil, andcompares them to those obtained in a natural gas-distillate system. Theequilibrium vaporization ratios for the hydrocarbon components in this systemhad previously been studied by Roland. In addition to the determination of theK values for carbon dioxide, the K values for methane and ethane were alsodetermined in order to observe what effect, if any, the presence of carbondioxide had on these K values. The concentration of carbon dioxide was alsovaried in order to observe the effect of this variable on the carbon dioxide Kvalues. Experimental Procedure The apparatus used in this study consisted of a stainless steel equilibriumcell of about 2 liters capacity. The cell was mounted on trunions permittingrocking in a thermostatically controlled oil bath. Two high pressure valvesfitted with steel tubing were mounted on the top of the cell, one was used forsampling the equilibrium gas phase and the other for sampling the equilibriumliquid phase by means of an induction tube within the cell. Stainless steeltubing from the bottom of the cell led to a mercury reservoir and manifoldwhich was connected to a free-piston type pressure gauge manufactured by theAmerican Instrument Co. and to a volumetric pump. The temperature of the oilbath was measured by means of a calibrated mercury-in-glass thermometer. T.P. 3058