Online Validation of Multiphase Flowmeters Using Simple Capacitance Sensors

The calibration of a multiphase flowmeter is usually highly dependent on the flow regime of the mixture being monitored. Since the flow regime present in a pipeline cannot always reliably be predicted, then online calibration of such instruments is usually required. As the range and capabilities of multiphase flowmeters increase, the problems of how to validate the performance of such instruments online also increases. This study considers the extent to which simple capacitance-sensing techniques can be used to validate the multiphase flowmeters´ performance by identifying the carrier, dispersed phase(s), and flow regime in the flow stream. Finite-element analysis, using the ANSYS software, was used to predict the ability of a simple capacitance sensor to identify carrier and phase composition in a range of oil, water, and gas mixtures. The sensor parameters investigated included electrode length, electrode separation, pipe material, and the effect of guards. The results obtained were used to optimize the sensor geometry for reliable identification of carrier and phase(s). The results obtained from the simulation were experimentally verified. It was shown that a capacitance measurement technique combined with statistical and fuzzy-logic-type methods can form the basis of a simple and robust validation unit that could be retrofitted to multiphase flowmeters for online validation. Such a system could be used as an early warning system for instrument malfunctions.