API Publ 2566:2004 pdf download
API Publ 2566:2004 pdf download.State of the Art Multiphase Flow Metering.
Where V0. V, and V9 are the phase velocities of the oil, water, and gas phases in the mixture. The task of any multiphase meter is to estimate the volume fractions and the individual phase velocity in the above equations. In order to accomplish this, the developers of the multiphase meters have employed different technologies and modelling of the multiphase flow to simplify the task (II11, 11-13, 11-24). Over the last 10-15 years we have seen the emergence of some
18-20 vendors of multiphase metering systems (11-27, 11-4) who have used these techniques to develop commercial products. However through mergers and acquisitions the number of vendors has significantly changed. The following three sections discuss techniques used for determination of volumetric fraction as well as component velocity.
7.1- VOLUMETRIC FRACTION MEASUREMENTS USING NON-NUCLEAR METHODS
Several Multiphase Metering Systems use electrical properties to estimate fluid fractions. The ratio of oil, water and gas can be inferred from these electrical properties of the fluid mixture bathing the sensor. The relationship between the fluid mixture fractions and these electrical properties is very complex and requires sophisticated models of sensor geometry and fluid flow in order to determine the required fluid fractions. The following provides a very brief discussion of these methods and their relative merits.
Dielectric Permittivity is a property of matter that resists electrical fields and can be measured by determining the Electrical Impedance. The concentration and spatial distribution of the components of the mixture will impact the resistance. capacitance and inductance of the fluid mixture in the sensor. These electrical properties affect the signal loss and transmission speed of electrical signals in the mixture. Measurement of any combination of these properties can allow the fluid component ratios to be estimated. Electrical Impedance is generally defined as the ratio of Voltage to Current for a specific volume ie. the multiphase meter wetted elements and can be mathematically modelled as a combination of resistance, capacitance and inductance at a specific frequency. From these impedance measurements instruments can utilize lookup tables to determine water cut and other fractions. Alternatively some more sophisticated systems extract information on the dielectric constant of the fluid mixture and use this property in models to predict fluid fractions.
Multiphase Metering Systems tend to use combinations of sensors, frequencies and models to measure an electrical property that enables an estimation of the fluid fractions to be made. Frequency methods from kilohertz up gigahertz have been used in phase fraction measurement devices, as the value of the electrical properties is dependent on frequency All methods have advantages and disadvantages however there is no published data to show any marked superiority of one method.
Some units measure capacitance of a plate capacitor while others determine the inductance of a coil with fluid running through the coil. In general all units use some kind of model and some kind of empirical calibration to support the accuracy required by the end user.
Meter systems employing separation can have greater flexibility of choice in sensors as the fluid streams are assumed to be less complex. However care has to be taken not to under estimate the complexity of the fluid streams. For liquid streams coming out of these separators, water cut monitors as well as the coriolis density-based methods (II -13) can be used to obtain phase fraction information.
