Apparatus and method for measuring liquid and gas flow rates in a stratified multi-phase flow

1. A method for determining a flow rate for a component of a gravitationally stratified two-phase fluid flow within a substantially horizontally extending pipe section, comprising the steps of:

providing a first flow meter located at a gravitational top portion of the pipe section;

providing a second flow meter located at a gravitational bottom portion of the pipe section;

determining a gas component velocity value by sensing fluid flow traveling in the gravitational top portion of the pipe section using the first flow meter, and determining a liquid component velocity value by sensing fluid traveling in the gravitational bottom portion of the pipe section using the second flow meter, wherein the gravitational top and gravitational bottom portions of the pipe are substantially axially aligned with one another;

determining a density of the two-phase fluid flow within the pipe section using a density meter, and creating a measured fluid density value representative of the two-phase fluid flow; and

determining a flow rate value for at least one of the liquid component of the fluid flow and the gas component of the fluid flow within the pipe section, using the measured fluid density and the respective determined liquid component velocity and gas component velocity.

2. The method of claim 1 , wherein the gravitational top portion of the pipe section is defined by a radial angle θ, which angle is equal to or less than 90 degrees.

3. The method of claim 2 , wherein the gravitational bottom portion of the pipe section is defined by the radial angle θ.

4. The method of claim 1 , wherein the step of determining the flow rate value includes provision of a density value of the liquid component of the fluid flow and a density value of the gas component of the fluid flow within the pipe section, and uses the measured fluid density value, the liquid component density value, and the gas component density value to determine the flow rate value of at least one of the liquid component and the gas component of the fluid flow within the pipe section.

5. The method of claim 4 , wherein the step of determining the flow rate value further comprises the provision of a cross-sectional geometry of the pipe section, which cross-sectional geometry has a cross-sectional area.

6. The method of claim 1 , wherein the step of determining a density of the fluid flow includes determining if the measured fluid density value is substantially equal to or less than a density value of the liquid component of the fluid flow within the pipe section.

7. The method of claim 1 , wherein the first and second flow meters are each operable to sense local unsteady pressures caused by coherent structures convecting locally within the fluid flow relative to the respective flow meter.

8. The method of claim 1 , wherein the first and second flow meters are axially aligned, and opposite one another on the pipe section, and each extends a distance along an outer surface of the pipe section defined by a radial angle θ, which angle is less than 90 degrees.

9. The method of claim 1 , further comprising the step of determining a degree of fluid phase stratification of the fluid flow utilizing information provided in a database that includes flow velocity values and gas volume fraction values.

10. The method of claim 1 , further comprising the step of determining a bulk flow velocity of the fluid flow, and using the bulk flow velocity to evaluate the gas component velocity value and the liquid component velocity value.

11. An apparatus for determining a flow rate for a component of a gravitationally stratified two-phase fluid flow within a substantially horizontally extending pipe section, the apparatus comprising:

a top flow meter disposed at a gravitational top portion of the pipe, wherein the top flow meter is operable to measure a velocity of the fluid flow local to the top flow meter and produce a gravitational top fluid velocity value;

a bottom flow meter disposed at a gravitational bottom portion of the pipe, wherein the bottom flow meter is operable to measure a velocity of the fluid flow local to the bottom flow meter and produce a gravitational bottom fluid velocity value;

a density meter operable to measure a density of the two-phase fluid flow within the pipe section and create a measured fluid density value representative of the two-phase fluid flow; and

a processor operable to determine a flow rate value for at least one of a liquid component of the fluid flow and a gas component of the fluid flow within the pipe section using one of the gravitational top fluid velocity value and the gravitational bottom fluid velocity, and the measured fluid density value.

12. The apparatus of claim 11 , wherein each of the top and bottom flow meters are operable to sense local unsteady pressures caused by coherent structures convecting locally within the fluid flow relative to the respective flow meter.

13. The apparatus of claim 11 , wherein the top flow meter extends for a distance along an outer surface of the pipe section defined by a radial angle θ, which angle is equal to or less than 90 degrees.

14. The apparatus of claim 13 , wherein the bottom flow meter extends for a distance along the outer surface of the pipe defined by the radial angle θ.

15. The apparatus of claim 14 , wherein the top and bottom flow meters are axially aligned, and opposite one another on the pipe section.