Methods and devices for measuring interface levels between fluids, and uses thereof

An apparatus for measuring concentrations of water in a flow of an oil, gas and water mixture, said apparatus comprising

• a pipe for conveying a flow of a mixture of oil, gas and water;
• an excitation coil around said pipe;
• a detector coil around said pipe in axially spaced relation to said excitation coil, said detector coil having a different resonant frequency from said excitation coil;
• an oscillator for applying an alternating voltage to said excitation coil at a frequency of up to 20 MHz to induce a variable magnetic field in the mixture;
• a voltage detector for registering a resultant detector voltage in said detector coil as a measure of the electrical conductivity of the water in the mixture independently of the fractions of oil and gas in the mixture;
• means for comparing the resultant detector voltage registered in said voltage detector against a calibration value to determine the concentration of water in the mixture.

An apparatus for measuring concentrations of water in a multiphase flow containing water, said apparatus comprising

• a pipe of electrically insulating material for conveying a flow of a multiphase mixture containing water as the only electrically conductive phase;
• an excitation coil around said pipe;
• a detector coil around said pipe in axially spaced relation to said excitation coil, said detector coil having a different resonant frequency from said excitation coil;
• an oscillator for applying an alternating voltage to said excitation coil at a frequency sufficient to induce a variable magnetic field in the mixture;
• a voltage detector for registering a resultant detector voltage in said detector coil as a measure of the electrical conductivity of the water in the multiphase mixture independently of the remaining phases in the multiphase mixture;
• means for comparing the resultant detector voltage registered in said voltage detector against a calibration value to determine the concentration of water in the multiphase mixture.