Two-Phase Isentropic Compressibility and Two-Phase Sonic Velocity for Multicomponent-Hydrocarbon Mixtures

Two-phase compressibility and two-phase sonic velocity of hydrocarbon mixtures are needed for a variety of applications in well testing, metering, and seismic exploration. In this work, a thermodynamic model is presented to estimate the two-phase isentropic compressibility and two-phase sonic velocity. The model accounts for the mass transfer between the equilibrium phases and the effect of capillary pressure. The results reveal that isothermal and isentropic compressibilities can be different by a factor of 20 in the two-phase near the retrograde dewpoint. With the exception of the retrograde dewpoint, the difference between the isentropic compressibility in the single phase and two phase is less than the corresponding difference for the isothermal compressibility. The sonic velocity in the two phase can be either less or more than the single phase. For the hydrocarbon mixtures that the sonic velocity decreases in the two phase, the decrease is much less pronounced than in nonhydrocarbon systems such as water-steam and water-air.