Vapor-liquid Equilibria of Natural Gas-Crude Oil Systems

Abstract

Abstract Equilibrium data are reported on the composition and densities of coexistingvapor and liquid phases as a function of pressure and temperature for fourhydrocarbon systems prepared from crude oil and natural gas. The data wereobserved over a range of pressures from 1000 to 8220 lb. per sq. in. and attemperatures ranging from 35? to 250?F. The compositions of the hydrocarbon systems were such that the criticaltemperatures of the mixtures were lower than the range of the investigation.Under these conditions, it is shown that the composition of the systems has amarked effect upon both the absolute value of the equilibrium constants and thechange of the constants with pressure for the several components comprising thesystem. From weight-balance considerations, it has been possible to constructthe partial phase diagram of a mixture of a 49.9? A.P.I. crude oil and naturalgas having a gas-oil ratio of 3660 cu. ft. per barrel. Descriptions of theapparatus used, the analytical procedure, the material used, and theequilibrium measurements are included. A knowledge of the physical behavior of naturally occurring hydrocarbonmixtures is fundamental to the treatment of many problems in the production, transportation and refining of petroleum. The recent discoveries of poolshaving formation pressures up to 7500 lb. per sq. in. and higher, and the development of full-scaleequipment to operate at pressures of 5000 lb. per sq. in. or more have greatlyincreased the need for knowledge of the composition, temperature, pressure anddensity relationships of coexisting vapor and liquid hydrocarbon phases. The following paper presents the results of investigations upon 22 mixtures ofnatural gas and crude oil of known composition that had been brought toequilibrium under controlled conditions of temperature and pressure. Data arepresented upon the densities and compositions of the coexisting vapor andliquid phases for four different systems containing hydrocarbon material havingboiling points from minus 258?F. to well over 1000?F. The data were observedover a pressure range from 1000 lb. per sq. in. to 8220 lb. per sq. in. and atemperature range from 35? to 250?F. The accepted method of computing the physical relationship between twocoexisting phases of a hydrocarbon mixture is by use of the "equilibriumconstant" K as proposed by Souders, Selheimer, and Brown. T.P. 1651