Online Multiphase Flow Measurement using Earth’s Field Nuclear Magnetic Resonance

Multiphase flow metering has significant potential in a number of industries; particularly in the oil and gas industry with regards to assisting the development of marginal fields and monitoring subsea processing. We demonstrate the novel use of a nuclear magnetic resonance (NMR) multiphase flow meter consisting of a pre-polarising permanent magnet upstream of an Earth’s field NMR detection coil. The application of suitable signal analysis in interpreting the 1H NMR signal acquired from a flowing stream allows determination of the relevant velocity probability distribution. The accuracy of such velocity distributions is verified using superficial velocity measurements obtained from an in-line rotameter as well as comparison to theoretical turbulent velocity distributions. The flow metering system has been successfully applied to two phase air/water flows in order to simultaneously track both liquid holdup and liquid velocity with time in both the stratified and slug flow regimes.