Method of measuring multi-phase fluid flow downhole
Multi-phase flow is estimated in a flow meter by measuring fluid pressure within the flow meter and using the measured pressure to calculate a density of the flow. A total flow rate through the flow meter is estimated based on the calculated density and a PVT analysis of the fluid. A corrected total mass flow rate is calculated using a liquid/gas slip correction technique. Fluid flow rates are further corrected with a discharge coefficient that varies with changes in the Reynolds number of the fluid. The gas and oil fractions can be determined from the corrected total mass flow rate and gas fraction.
1. A method of estimating a rate of fluid flow with a flow meter comprising:
(a) directing a flow stream through the flow meter and estimating a bulk density of the flow stream;
(b) estimating respective amounts of gas and liquid flow in the flow stream based on the estimate of bulk density and properties of fluid making up the flow stream;
(c) estimate an overreading error in the flow meter based on the amounts of gas and liquid flow of step (b) and properties of fluid making up the flow stream;
(d) reestimating amounts of the gas and liquid flow of step (b) using the estimated overreading error; and
(e) reestimating amounts of the gas and liquid flow of step (d) using a discharge coefficient of the flow meter based on a gas volume fraction of the reestimated amounts of the gas and liquid flow of step (d);
further comprising estimating a Reynolds number for a combination of the gas and liquid flow of step (d), wherein the discharge coefficient of step (e) is based on the Reynolds number; and
wherein when the gas volume fraction is greater than 50%, the reestimated gas flow of step (e) is obtained by multiplying the discharge coefficient with the gas flow of step (d), and wherein when the gas volume fraction is less than or equal to 50%, the reestimated gas flow of step (e) is obtained by multiplying the discharge coefficient with the gas flow of step (b).
2. The method of claim 1 , further comprising sampling fluid from the flow stream, analyzing the sampled fluid, and deriving the properties of fluid making up the flow stream for a range of pressure and temperature based on the analysis.
3. The method of claim 1 , further comprising estimating a bulk flow rate of the flow stream based on the estimate of bulk density and properties a fluid making up the flow stream.
4. The method of claim 3 , further comprising reestimating a bulk flow rate of the flow stream based on the reestimate of the gas and liquid flow of step (d).
5. The method of claim 1 , wherein the flow meter is disposed in a wellbore tubular and the flow stream exits the flow meter into the tubular and is conveyed to a wellhead at to surface.
6. The method of claim 1 , further comprising estimating an amount of liquid to gas phase change in the flow stream between the flow meter and the wellhead based on a property of the fluid making up the flow stream.
7. The method of claim 5 , further comprising estimating respective rates of gas flow and liquid flow in the flow stream at the wellhead based on the amount of liquid to gas phase change.
8. The method of claim 1 , wherein the bulk density of step (a) is based on static head of the fluid along a vertical distance and dynamic fluid flow losses in the flow meter.
9. The method of claim 1 , further comprising sensing pressure at locations selected from the list consisting of along the flow meter, downstream of the flow meter, upstream of the flow meter, and combinations thereof.
10. The method of claim 1 , wherein the flow meter is Venturi type flow meter.