GE MULTIPHASE FLOW METER
GE is working on developing technology architecture for a multiphase flow meter to meet the required performance set by industry. When a mixture of fluids such as oil, water and gas are transported through the pipe, it is extremely challenging to make accurate volumetric flow rate measurement of individual phases without separating them. The basic requirement is to measure the phase fraction at any instant of time in the pipe cross section and the velocity of liquid and gas phases. When the pipe is oriented vertically it is known that the liquid and gas travel at different velocities as there is slip between the phases predominantly due to density differences. Phase fraction is a measure of the fraction of area occupied by the gas against the total area of the pipe cross section. The liquid phase is usually a mixture of oil and water. Hence an additional measurement needs to be made to ascertain the amount of water and oil in the liquid. With the measured phase fraction and the phase velocities, the volume flow rates for each of the phases can be quantified. Where necessary, the mass flow rates of the phases can be computed by measuring component densities. The measurements made through individual technologies/ sensors such as impedance or microwave needs to be related to the parameters of interests such as gas velocity or liquid velocity. In order to find such a relationship and establish a reliable model for this conversion, in depth domain knowledge is a critical requirement along with extensive experimentation. Depending on which phase (oil, water or gas) dominates the flow, the performance of individual technologies can vary significantly. Thus, it is critical to identify the flow state in order to choose sensors that perform the best and are reliable under a given condition. Additionally over a period of time, the salt levels in the water and the composition of oil can change. It is critical for the sensors to estimate these fluid properties real time. GE multiphase meter addresses these challenges in operating environments/conditions, through multiple differentiators compared to other meters in the market. Some of the differentiating elements are the following:
Phase fraction estimate immune to property variation: The impedance sensor system which has 8 electrodes distributed circumferentially can estimate liquid property real time using novel excitation methodologies. Furthermore, models used for estimating liquid to gas ratio are constantly updated whenever there is change in liquid properties. This eliminates the need for frequent sampling of liquid/ fluid as is currently being done in the multiphase meters available in the market.
Impedance hardware that can seamlessly operate across the oil and water continuous flows: In multiphase flow, the liquid either exists in what are called “oil continuous” or “water continuous” regimes. When in an oil continuous regime, the dielectric properties dominate whereas in a water continuous regime, the conductive properties dominate. The conventional approach to solving this problem is to use two different instruments for making measurements in the two types of flows. GE, on the other hand has built custom hardware which has been proven to have a bandwidth that is wide enough for it to operate seamlessly between changes in flow conditions. This ensures that for a given application, a wide operating range can be covered using only one instrument.
Microwave sensors that operate at varying salinity while estimating water-cut reliably: Microwave sensors used in multiphase meters currently available in the market cannot operate in liquids with high salinity. A novel antenna system designed by GE offers high reliability through a protective radome flushed with the inner diameter of the pipe. While this sensor can be used for estimating water-cut and gas fraction, another microwave sensor can track and estimate the varying salinity in absolute terms.
Ultrasound Doppler to profile liquid velocity: A direct measure of the liquid velocity is one of the hardest measurements for a multiphase meter to make. Using Ultrasound Doppler technique on multiphase flow, we can provide information that is not obtained from other technologies. One of the complications in a vertical multiphase flow is that when a large enough gas slug moves upward, it can push the liquid along the wall to move backwards momentarily. It has been shown with the Doppler technique that these directional changes in the liquid can be detected and quantified. With the richness of information that GE’s Doppler method can provide, the measurement accuracy and reliability can be considerably improved.
Dual venturi & differential pressure sensor design for reliable viscosity independent measurements: With water-cut variation over life of the well, viscosity of the liquid emulsion is an unknown. The discharge coefficient of the venturi which is a critical parameter for estimating the total mass flow rate is strongly related to the viscosity of the liquid. Using a dual venturi design with multiple differential pressure measurements and using smart estimation methods, the viscosity dependency can be eliminated from the total mass flow rate estimation.
Novel data analytics for reliable flow rate estimation: Data handling is critical in a