Ultrasonic flow meters, in addition to calculating flow rate, measure the speed of sound in the fluid at the local fluid pressure and temperature. It is desirable to be able to compute the crude oil specific gravity at base (i.e. standard temperature and pressure) conditions from this measurement. However, there is no straightforward way to do this, in large part because there is no accepted standard for computing crude oil sonic velocity as a function of pressure, temperature, and base density. The authors develop an approach for computing sonic velocity for crude oil. Using this as a foundation, they propose a calculation approach to compute crude oil specific gravity as a function of observed speed of sound, pressure, and temperature.
The motivation for this work was to be able to compute crude oil density from sonic velocity, pressure, and temperature. Pipeline companies often have ultrasonic flow meters at pump stations that, as part of measuring flow, compute sonic velocity. Because of cost, densitometers are usually much more sparsely spaced. Since elevation head depends directly on density, a measurement of fluid density can improve hydraulic modeling calculations.