ACCUFLOW MULTIPHASE METERING SYSTEM (AMMS)
Functional description of Accuflow Multiphase Metering System
The figure below shows the process flow scheme and major components of the Accuflow Multiphase Metering System (AMMS). This metering system consists of a vertical pipe section and a horizontal pipe section connected together as shown. Multiphase fluid (oil, water and gas) from the production flow line enters the vertical pipe tangentially, creating a cyclonic action in the vertical pipe where a majority of gas is separated and flows upward. The slightly downward inclination of the inlet pipe promotes liquid/gas stratification in the inlet pipe that enhances gas/liquid separation in the vertical separator pipe. The remaining gas, mostly in the form of small bubbles, is carried downward with the liquid stream and enters the horizontal pipe section.
Liquid level in the horizontal separator pipe section is controlled in the middle of the pipe using a control valve located in the gas flow line. As the liquid level in the horizontal pipe rises, a liquid level signal is transmitted to the gas control valve. This causes the control valve to “pinch” or close slightly and creates a slightly higher back pressure in the gas phase. The back pressure then “pushes” the liquid to flow at a higher-than-average flow rate that in turns causes the liquid level in the horizontal pipe to fall and stabilize to the set point. Conversely, when the liquid level falls, the control valve opens slightly to reduce the back pressure in the gas phase. This reduction of back pressure causes the liquid to flow out of the system at a lower-than-average flow rate. Consequently, liquid level rises and stabilizes to the set point.
As the liquid stream flows through the horizontal pipe, gas bubbles rise to the gas/liquid interface and are completely separated as the liquid stream flows toward the outlet end of the horizontal pipe. Large gas/liquid interface area, thin gas-bearing liquid layer, and quiescent flow in the horizontal pipe, all contribute to efficient removal of entrained gas bubbles from the liquid stream.
A Coriolis-type flow meter is typically used to measure liquid flow rate. Water cut in the liquid stream is measured with a conventional water cut meter. The Phase Dynamics water cut meter based on microwave frequency shift principle is selected in this application. The Phase Dynamics net oil transmitter has a capability of receiving liquid flow rate signal from the Coriolis flow meter to perform net oil calculations and display net oil and water rates and volumes.
For gas measurement, a conventional vortex meter is typically employed. In this particular application, a vortex meter supplied by Sierra Instrument is used. The Sierra vortex meter has built-in temperature and pressure sensors incorporated in the meter assembly. Its flow transmitter also performs temperature and pressure compensation calculations and displays gas flow rate and volume at standard condition.
After measurement, gas and liquid streams are typically recombined and returned to the multiphase flow line.
Advantages of this system:
• Low cost, compared with Multiphase meters and Conventional Separators.
• Compact and very portable.
• Low maintenance.
• High Efficiency > 90% | 
