Methods for measuring properties of multiphase oil-water-gas mixtures
Methods for real-time, continuous measurements of the composition and other properties of individual phases of petroleum, water and gas mixtures during the oil production process, without requiring test separators, test lines, with associated valving and instrumentation, are described. Embodiments of the present invention direct ultrasonic sound transmission through a flowing multiphase fluid in three frequency ranges: low frequencies, gas bubble resonance frequencies, and high frequencies, wherein certain sound propagation measurements, including sound speed, sound attenuation and sound scattering, are made in one or more of the three separate frequency regions, from which the multiphase composition and other properties are extracted without having to separate the multiphase fluid or the gas from the flowing stream.
1. A method for determining the composition of an oil-water mixture in a gas bubble-water-oil mixture in a pipe or other container having a wall with an inner surface defining a cavity, comprising the steps of:
applying pulsed oscillatory acoustic energy to the wall of the pipe or container such that an acoustic pulse is transmitted along a path through the mixture, and wherein the lowest frequency of the oscillatory acoustic energy in the gas-water-oil mixture is greater than 500 kHz;
moving the gas bubbles out of the path of transmission of the acoustic pulse transmitted through the mixture;
receiving pulsed acoustic energy arriving at the wall of the pipe or container; and
measuring the time of flight of the pulsed acoustic energy through the mixture from which sound speed of the pulsed acoustic energy is determined;
whereby the composition of the oil-water mixture is calculated.
2. The method of claim 1 , wherein said step of measuring the time of flight of the pulsed acoustic energy comprises a cross-correlation measurement.
3. The method of claim 1 , further comprising the step of obtaining the density of the oil as a function of temperature.
4. The method of claim 1 , further comprising the step of obtaining the density of the water as a function of temperature.
5. The method of claim 1 , wherein said step of moving bubbles out of the path of transmission of the acoustic pulse is achieved by generating annular acoustic standing waves in the pipe or container, whereby an accompanying acoustic force moves the bubbles out of the transmission path of the acoustic pulse.
6. The method of claim 1 , wherein the gas-water-oil mixture is moving through the cavity of the pipe or container.
7. The method of claim 1 , wherein the pulsed oscillatory acoustic energy is chosen from a frequency chirp and a tone burst, having a chosen frequency range.
8. The method of claim 7 , wherein the chosen frequency range is between 500 kHz and 5 MHz.