Numerical Simulation of Eddy Current Losses in High Frequency Magnetic Field Water Fraction Meters

Erling A Hammer, Fredrik Pettersen and Anders Nødseth

Department of Physics, University of Bergen, Allegt 55, N-5007 Bergen, Erling.Hammer@fi.uib.no

ABSTRACT

Detection of eddy current losses in conducting liquids is a promising principle for detection of water fractions in crude oils. A high frequency magnetic field is generated in a coil around an insulating liner, made as a spool pipe in the production pipe, and the total induced loss in the measurement volume will be dependent on the amount of water in the oil. The electrical loss will occur as a parallel resistance in the coil impedance and since the coil is kept at resonance this loss can be determined by measuring the total coil impedance. This method can be used both in water continuous- and oil/gas- continuous mixtures independent of the gas/oil ratio. The detector can also simultaneously determine the conductivity of the water component in the mixture and is simple, robust and inexpensive. However, it is very difficult to find experimentally, the influence of the size of the droplets at constant water fractions on the measurement results. Numerical simulation based on mathematical modelling of this sensor has solved the problem and has given us much more useful information for optimising the sensor design than we expected.

The results will be given and discussed and compared with experimental data. If the mixture is homogeneous one coil around the pipe is sufficient. In inhomogeneous flows, as in down hole situations at inclined or horizontal pipes a number of coils around the pipe can be used making a tomographic system.

Keywords Water cut, electrical loss, eddy current, magnetic induction.