Petroleum Research Petroleum Research 2018 (July-September), Vol. 28, No. 100. 19-22 DOI: 10.22078/pr.2018.2960.2381 Measurement of Multiphase Flow of Oil and Gas Using Soft Sensor Keywords: Measurement System, Multiphase Flow, Oil and Gas, Soft Sensor, Nonlinear Observer. Abolfazle Varvani Farahani* and Mohsen Montazeri Department of Control, Faculty of Electrical Engineering, Shahid Behesht University, Tehran, Iran m_montazeri@sbu.ac.ir DOI: 10.22078/pr.2018.2960.2381 This paper presents sof sensor as a mul tphase fow meter. Nonlinear observer with Ensemble Kalman flter (EnKF) by Navier Stocks equa tons for in line fow is used to es tma te the oil and gas fow. Finite element method and EnKF are used along two scenarios; in addi ton, in the frst scenario, the es tmaton is done wi th the refnery output measurement, and in the second scenario, this es tmaton is done wi th the producton unit output measurement. In this ar tcle, we don’ t use primary element for mul tphase fow measurement, instead of that fow will be estma ted using some secondary variables (like pressure, temperature, output single phase fow, phase fracton and etc that can be measured directly with high accuracy). Results of comparison between two mentoned scenarios show that also the es tmaton wi th output measurement is not accurate, but the accuracy and repeatability of second scenario (es tmaton wi th producton uni t measurement) is in the acceptable standard range. Thus we can conclude that this sof sensor can be used as a backup for primary system and also as a primary system for mul tphase fow measurement. Received: June/27/2017 Accepted: January/09/2018 Abstract