Method for measuring the flow rate of a multi-phase liquid
View Patent ↗The method for measuring the flow rate of a multi-phase liquid determines the speed of sound and the density of each phase, and determining the speed of sound in each of the phases of the liquid within a working temperature range. The amplitudes of the vibrations of the pipe along which the multi-phase liquid flows and the frequencies corresponding thereto are determined A range of frequencies with maximum amplitude values is selected. The measured range of frequencies is divided into three parts—the low frequencies corresponding to the gas phase, the mid-frequencies corresponding to the oil phase, the high frequencies corresponding to the water phase. In each of the parts of said frequencies the maximum values of the amplitude are isolated after the use of fast Fourier transforms. Then the volumetric flow rate of each phase of the liquid is calculated on the basis of a given formula.
1. A method for measuring a flow rate of a multiphase liquid, the method comprising:
measuring a temperature and pressure of a flow of the multiphase liquid, and measuring a density of each phase of the multiphase liquid;
determining a speed of sound in each phase of the multiphase liquid in a working range of temperatures;
measuring and recording amplitudes and frequencies of fluctuations of a pipe in which the multiphase liquid flows;
dividing a range of the frequencies into portions, each portion corresponding to each phase of the multiphase liquid;
applying fast Fourier transformation to each portion and obtaining for each portion maximal amplitudes and corresponding frequencies;
measuring acoustic noise generated by the movement of liquid at its course through a known cross-section;
determining a speed of flow of the liquid by the frequency of the acoustic noise caused by unevenness of the movement of liquid; and
and calculating a volume flow rate of each phase of the multiphase liquid according to a formula:
Q
=
π
·
R
4
·
F
3
·
A
·
K
4
·
C
2
wherein:
Q—is a volumetric flow rate of a phase of the multiphase fluid in m 3 /s;
R—is a radius of the pipe, m;
F—is a maximal frequency of vibration in a selected range for a phase, 1/s;
A—is a maximal amplitude of oscillation at a frequency F, m;
K—is a dimensionless coefficient of proportionality;
C—is a measured speed of sound in a phase of the multiphase liquid, which is experimentally determined for oil and gas, and which is tabular for water.