Acoustically relevant properties of four crude oils at oceanographic temperatures and pressures

Inversions of models of broadband acoustic scattering to detect and quantify weakly scattering targets, such as oil droplets in seawater, require precise knowledge of the physical properties that determine scattering. When the characteristic impedance contrast between a target and the surrounding medium is weak, small differences between the true and modeled impedance can cause significant errors in modeled scattering. For crude oil, currently available empirical models of density and sound speed are derived from measurements made at reservoir conditions (high temperature and pressure), which may not be relevant to oceanographic conditions due to phase changes in the oil. Measurements of the density and sound speed, as well as thermal characterization of phase changes via differential scanning calorimetry, of four crude oils at oceanographically relevant temperatures and pressures were made and compared to a commonly used empirical model for sound speed and density. Significant deviations between the measured and modeled values were found and different empirically fit models were developed. A literature review of sound speed data was also performed, and the innovative empirical model shows improvement over the commonly used empirical model for both the data measured here and the measurements in the literature.