Acoustic velocities in petroleum fluids: Measurement and prediction

Acoustic velocity or speed of sound is a thermodynamic property which may be used to estimate thermophysical properties needed for hydrocarbon production and processing. In this paper, experimental data is reported on the speed of sound in n-octane, a binary mixture of (n-octane+n-hexadecane), a binary mixture of (n-decane+n-hexadecane) and a ternary mixture of (n-octane+n-decane+n-hexadecane) at temperature of (293 to 393) K and at pressures up to 100 MPa. In addition a predictive method for the speed of sound in liquid hydrocarbons is presented and validated by comparison with both the present data and the literature data. The model is based on the extended principle of corresponding states with two reference fluids, chosen as n-C18 and n-C28 in which the parameters may be estimated from the knowledge of molecular weight. The method can be used for both pure liquid n-alkanes and their mixtures from propane to very heavy hydrocarbons (~C50) at pressures of (0.1 to 150) MPa and at temperatures from (200 to 400) K. The method has been evaluated by comparison with over 2000 data points for pure normal alkanes (from C3 to C36), as well as for binary and ternary mixtures, petroleum fractions and crude oils, and is found to predict speed of sound in these fluids within ±2%.