Calculation of Equilibria in Hydrocarbon Mixtures

The application of hydrocarbon equilibrium data to various problemsencountered in refining and in natural gasoline recovery is an old and wellestablished practice. Both generalized data and data on? specific hydrocarbonsystems have been made available by a number of investigators. More recentlysuch data have been applied to the relations governing the separation of oiland gas both in the reservoir and at the surface. Most of the applications toproduction problems, however,. have been based upon examinations of surfacesamples of oil and gas. This paper describes a technique that has been usedsatisfactorily in a number of cases to calculate directly from the hydrocarbonanalysis of and auxiliary laboratory data on a subsurface sample of thereservoir fluid the behavior of the oil and gas during the various stages ofseparation at the surface incident to production. Types of Information Calculated The system of calculations is not designed to supplant field data, but ratherto correlate with them laboratory data obtained under controlled conditions inorder to obtain a more complete and exact picture than usually is possiblethrough the use of field data alone. The chief advantage of the calculations isthe possibility of their use at a minimum of both time and expense to determinecompletely the effect of any possible operating technique upon each of thefollowing:The gas-oil ratio resulting from liberation of the dissolvedgas;the composition and gasoline content of the liberated gas;thecomposition and gravity of the residual oil;the amount and composition of the gas liberated upon flashing the oil from the separator to the stock tank;the shrinkage of the oil in passing from the reservoir to the stocktank. This information is frequently essential to the correct determination of theadvisability of installing a natural gasoline plant, to design such a plant totake care of seasonal production, and to determine the optimum separatorpressures to carry in various parts of a field. T.P. 872