Determining fluid properties

1. A fluid measurement system, comprising:

a fluid flow circuit that comprises at least two liquid sources, a gas source, and a fluid mixer that mixes at least two liquids from the at least two liquid sources to form a liquid phase of a mixed-phase fluid that also includes a gas phase from the gas source;

a pre-polarizing magnet positioned to receive the mixed-phase fluid flow from the fluid mixer;

an Earth's field nuclear magnetic resonance (EFNMR) detector that comprises a radio-frequency (RF) coil, a first electromagnet aligned with the RF coil, and a second electromagnet downstream of and separate from the first electromagnet, the EFNMR detector positioned to receive the mixed-phase fluid from the pre-polarizing magnet; and

a control system communicably coupled to the pre-polarizing magnet and the EFNMR detector and configured to perform operations comprising:

controlling the pre-polarizing magnet to polarize at least the gas phase of the mixed-phase fluid flow to an initial polarization while the first and second electromagnets are unenergized;

controlling the EFNMR detector to measure a plurality of fluid induction decay (FID) values of the polarized gas phase;

determining a velocity of the gas phase based on the plurality of FID values of the polarized gas phase while the first and second electromagnets are unenergized;

energizing the first electromagnet to produce a pulsed magnetic field gradient to suppress one or more signals acquired by the EFNMR detector;

controlling the EFNMR detector simultaneously with the production of the pulsed magnetic field gradient to measure a plurality of FID values of the liquid phase of the mixed-phase fluid;

energizing the second electromagnet to generate a homogeneous polarizing field to polarize the liquid phase of the mixed-phase fluid;

determining a velocity of the liquid phase based on the plurality of FID values of the polarized liquid phase; and

determining a content of the liquid phase based on the plurality of FID values of the mixed-phase fluid.

2. The fluid measurement system of claim 1 , wherein the operation of determining a velocity of the gas phase based on the plurality of FID values of the polarized gas phase comprises applying a pseudo-1D inversion to the plurality of FID values of the gas phase.

3. The fluid measurement system of claim 2 , wherein the operation of determining a velocity of the liquid phase based on the plurality of FID values of the polarized liquid phase comprises applying another pseudo-1D inversion to the plurality of FID values of the liquid phase.

4. The fluid measurement system of claim 3 , wherein the operation of determining a content of the liquid phase based on the plurality of FID values of the mixed-phase fluid comprises determining an oil-water content of the liquid phase with a 2D probability distribution of the velocity of the liquid phase in the mixed-phase fluid flow based on the applied another 1D inversion of the plurality of FID values of the liquid phase and a model kernel matrix.

5. The fluid measurement system of claim 3 , wherein at least one of the pseudo-1D inversion or the another psuedo-1D inversion comprises a Tikhonov inversion.

6. The fluid measurement system of claim 1 , wherein the gas source comprises a pressurized gas source fluidly coupled to the fluid flow circuit between the fluid mixer and the pre-polarizing permanent magnet.

7. The fluid measurement system of claim 1 , wherein the at least two liquids comprise oil and water.

8. The fluid measurement system of claim 1 , wherein the pre-polarizing magnet is positionable at a plurality of distances apart from the EFNMR detector.

9. The fluid measurement system of claim 8 , wherein the operation of controlling the EFNMR detector to measure the plurality of FID values of the polarized gas phase comprises:

controlling the EFNMR detector to measure a first plurality of FID values of the polarized gas phase at a first distance of the plurality of distances; and

controlling the EFNMR detector to measure a second plurality of FID values of the polarized gas phase at a second distance of the plurality of distances.

10. The fluid measurement system of claim 1 , wherein the operation of controlling the EFNMR detector to measure the plurality of FID values of the polarized liquid phase comprises:

controlling the EFNMR detector to measure a first plurality of FID values of the polarized liquid phase at a first pulse time duration of a plurality of electromagnet pulse time durations; and

controlling the EFNMR detector to measure a second plurality of FID values of the polarized liquid phase at a second pulse time duration of the plurality of electromagnet pulse time durations.

11. The fluid measurement system of claim 1 , wherein the plurality of FID values of the polarized gas phase comprise velocity values, and the plurality of FID values of the polarized liquid phase comprise velocity values and T 1 values of the liquid phase.

12. A method for measuring fluid properties, comprising:

circulating a mixed-phase fluid flow through a fluid flow circuit that comprises a gas source, at least two liquid sources, and a fluid mixer that mixes a liquid from each of the at least two liquid sources to form a liquid phase of the mixed-phase fluid flow that includes a gas phase;

circulating the mixed-phase fluid flow through a pre-polarizing magnet;

polarizing at least the gas phase of the mixed-phase fluid flow to an initial polarization with the pre-polarizing magnet;

measuring a plurality of fluid induction decay (FID) values of the polarized gas phase with an Earth's field nuclear magnetic resonance (EFNMR) detector that comprises a radio-frequency (RF) coil, a first electromagnet aligned with the RF coil, and a second electromagnet positioned downstream of and separate from the first electromagnet;

determining a velocity of the gas phase based on the plurality of FID values of the polarized gas phase while the first and second electromagnets are unenergized;

producing a pulsed magnetic field gradient to suppress one or more signals acquired by the EFNMR detector with the first electromagnet;

measuring a plurality of FID values of the liquid phase of the mixed-phase fluid with the EFNMR detector simultaneously with the production of the pulsed magnetic field gradient;

producing a homogeneous polarizing field to polarize the liquid phase of the mixed-phase fluid with the second electromagnet;

determining a velocity of the liquid phase based on the plurality of FID values of the polarized liquid phase; and

determining a content of the liquid phase based on the plurality of FID values of the liquid phase of the mixed-phase fluid.

13. The method of claim 12 , wherein determining a velocity of the gas phase based on the plurality of FID values of the polarized gas phase comprises applying a pseudo-1D inversion to the plurality of FID values of the gas phase.

14. The method of claim 13 , wherein determining a velocity of the liquid phase based on the plurality of FID values of the liquid phase comprises applying another pseudo-1D inversion to the plurality of FID values of the liquid phase.

15. The method of claim 14 , wherein determining a content of the liquid phase based on the plurality of FID values of the mixed-phase fluid comprises determining an oil-water content of the liquid phase with a 2D probability distribution of the velocity of the liquid phase in the mixed-phase fluid flow based on the applied another 1D inversion of the plurality of FID values of the liquid phase and a model kernel matrix.

16. The method of claim 14 , wherein at least one of the pseudo-1D inversion or the another psuedo-1D inversion comprises a Tikhonov inversion.

17. The method of claim 12 , further comprising:

separating the liquid phase into a first liquid flow and a second liquid flow with a liquid separator fluidly coupled to a first liquid source and a second liquid source; and

injecting the gas phase into the liquid phase from a pressurized gas source that is fluidly coupled in the fluid flow circuit between the fluid mixer and the pre-polarizing permanent magnet.

18. The method of claim 17 , wherein the first liquid comprises oil and the second liquid comprises water.

19. The method of claim 12 , further comprising:

positioning the pre-polarizing magnet at a plurality of distances apart from the EFNMR detector.

20. The method of claim 19 , wherein measuring the plurality of FID values of the polarized gas phase with the EFNMR detector comprises:

measuring a first plurality of FID values of the polarized gas phase with the EFNMR detector at a first distance of the plurality of distances; and

measuring a second plurality of FID values of the polarized gas phase with the EFNMR detector at a second distance of the plurality of distances.

21. The method of claim 12 , wherein measuring the plurality of FID values of the polarized liquid phase with the EFNMR detector comprises:

measuring a first plurality of FID values of the liquid phase with the EFNMR detector at a first pulse time duration of a plurality of pulse time durations of the second electromagnet; and

measuring a second plurality of FID values of the liquid phase with the EFNMR detector at a second pulse time duration of a plurality of pulse time durations of the second electromagnet.

22. The method of claim 12 , wherein the plurality of FID values of the polarized gas phase comprise velocity values, and the plurality of FID values of the liquid phase comprise velocity values and T 1 values of the liquid phase.