Density of Natural Gases

Density data are reported on 16 saturated hydrocarbon vapors at pressuresranging from 1000 to 8220 lb. per sq. in. and at temperatures ranging from 35?to 250?F. These data have been used to extend the compressibility-factor chartfor natural gases up to 10,000 lb. per sq. in. The relatively large quantity ofhigh-boiling constituents present in high-pressure vapors in equilibrium withcrude oils makes it necessary to include in the analysis of the gas themolecular weight, density, and possibly boiling range of the heptanes andheavier fraction. Relationships have been presented by which the density ofgases may be obtained directly from the temperature, pressure, and gas gravityprovided the gases have a common source or are similar in composition. Introduction The densities of natural gases are necessary in many engineeringcomputations in petroleum production and utilization. Gas reserves, changes inreservoir pressure, gradients in gas wells, metering of gases, pipeline flow, and compression of gases are typical problems requiring the density of the gas.A decade ago, engineering computations used ideal gas laws with deviations upto 500 lb. per sq. in. Recent discoveries of pools having pressures up to 7500lb. per sq. in., and installation of pressure-maintenance and recycling plants, have increased the need for data on gas density at high pressures. Methods Of Computation The accepted method of computing the density or specific volume of naturalgases is the use of the ideal gas law corrected by a compressibility factor.The method proposed by Kay of correlating compressibility factors for gaseousmixtures on pseudo critical properties appears to be satisfactory for naturalgases. The methane-compressibility factor has been shown to deviatesystematically from the behavior of natural gases and a chart giving thesecorrected factors is available. A method of computing specific volume of gaseous mixtures from partial molalvolumes has been reported by Sage and Lacey. Complete data for the computationare not yet available for all hydrocarbon gases. Most of the reported data on gas densities have been in the single-phaseregion removed from the dew point or saturation condition. Since most gases inthe reservoir or while on contact with liquid during flow are saturated, thedetermination of densities under conditions of saturation is particularlyimportant. T.P. 1323