A Novel Detector for Estimation of Induced Loss in the Measuring Volume of Multiphase Flows

W. Olsen, A. Vasdal and E. A. Hammer

Department of Physics and Technology, University of Bergen, Norway, Email: erling.hammer@ift.uib.no

ABSTRACT

High frequency magnetic fields have shown to be suitable for the detection of water fraction in three phase flows in the petroleum industry. Since the water component is conductive and crude oil and gas are non conductive components, the electrical loss in the flow, induced by a high frequency magnetic field, will indicate the amount of water in the three phase flow. The detection of this loss can be done in different ways. The presented work deals with three methods, which seem to be simple, reliable and accurate. The sensor is based on an electromagnetic coil wounded around an insulated liner in a spool pipe through which the mixture flows. The coil is interrogated by electrical pulses and each pulse response, which is a damped oscillating signal (the ringing), is recorded. The time constant of each exponential envelope function will be inversely proportional to the electrical loss induced in the measurement volume. The basic principle of the three methods investigated is based on measuring the period time T and the time constant τ of the ringing signal.

Keywords Magnetic field, eddy currents, damped oscillation, multi phase flow, water fraction