Calculation of Pressure-Temperature Phase Envelopes of Multicomponent Systems

K-factor data for hydrocarbon systems have been correlated as a function of temperature, pressure and convergence pressure. Recently, a very precise technique was developed to predict precise technique was developed to predict accurate convergence pressures, even in the area of the critical state. It is the object of this paper to demonstrate bow this convergence pressure paper to demonstrate bow this convergence pressure calculation can be used to determine the p-T envelopes of multicomponent systems, including the retrograde region. Introduction The petroleum engineer is interested in the p-T envelope that describes the fluid existing in a given reservoir. If the reservoir temperature and pressure are sufficiently high, relative to this pressure are sufficiently high, relative to this phase envelope, it may be economically feasible phase envelope, it may be economically feasible to miscibly displace the reservoir fluid with a drier, less expensive gas (Fig. 1). These phase envelopes are normally established by laboratory measurements involving expensive PVT equipment. By the use of a computer program that utilizes some of the latest correlations of hydrocarbon property data, these envelopes can be generated property data, these envelopes can be generated in seconds from composition analysis data including the molecular weight of the C7+ fraction. It is the purpose of this paper to show how convergence pressures can be used to predict be p-T envelopes of multicomponent systems. p-T envelopes of multicomponent systems. Convergence pressure is shown to be a phase-rule variable for the two-phase, three-component system at equilibrium. Ternary phase diagrams are presented for three-component systems that define the convergence pressure for a given temperature pressure, and system composition. PREDICTION OF THE PREDICTION OF THE PRESSURE-TEMPERATURE ENVELOPE OF A PRESSURE-TEMPERATURE ENVELOPE OF A TWO-COMPONENT SYSTEM The data for the two-component system will be used to demonstrate how convergence pressure calculations can be used to predict p-T envelopes for multicomponent systems. Figs. 2 and 3 show experimental p-T-Z data for a system such as the ethane-heptane system. (p-Z)T = C1 data has been used to establish convergence pressure K-factor correlations such as those published in the 1957 NGSMA Data Book. These K-factors are plotted as functions of T, p, p cv. plotted as functions of T, p, p cv. These data, in turn, can be used to predict the (p-T)Z = C1 envelope. Suppose we wish to calculate the p-T envelope of Mixture Z of Fig. 3. To use the convergence pressure correlations to establish such a p-T envelope, the following three methods (A, B and C) were developed to predict dewpoint and/or bubble-point states. The predict dewpoint and/or bubble-point states. The method depends on whether the temperature was equal to, greater, or less than the critical temperature. SPEJ P. 243