Determining fluid properties

A fluid measurement system, comprising:

• a fluid flow circuit that comprises an oil source, a water source, and a fluid mixer that mixes oil from the oil source and water from the water source into a mixed oil-water liquid flow;
• a pre-polarizing magnet positioned to receive the mixed oil-water liquid flow from the fluid mixer;
• an Earth's field nuclear magnetic resonance (EFNMR) detector that comprises a radio-frequency (RF) coil and surrounding electromagnet positioned to receive the mixed oil-water liquid flow 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 position to polarize the mixed oil-water liquid flow to an initial polarization;
• controlling the electromagnet to additionally polarize the polarized mixed oil-water liquid flow at the initial polarization to an additional polarization;
• controlling the EFNMR detector to measure a plurality of fluid induction decay (FID) values of the additionally polarized mixed oil-water liquid flow;
• transforming the measured plurality of FID values from a non-adiabatic transition from an Earth's field to a polarizing field to an effective adiabatic transition from the Earth's field to the polarizing field;
• determining a velocity of the oil in the mixed oil-water liquid flow and a velocity of the water in the mixed oil-water liquid flow from the transformed plurality of FID values based on differences in NMR signal relaxation properties of the transformed plurality of FID values;
• and
• determining an oil content and a water content of the mixed oil-water liquid flow from the transformed plurality of FID values based on differences in NMR signal relaxation properties of the transformed plurality of FID values, wherein the operations of determining the velocity and content of the oil in the mixed oil-water liquid flow and the velocity and content of the water in the mixed oil-water liquid flow comprise:
• applying a pseudo-1D inversion to a selected portion of the plurality of FID values, and
• determining a 2D probability distribution of the velocity of the oil in the mixed oil-water liquid flow and the velocity of the water in the mixed oil-water liquid flow based on the applied 1D inversion of the selected portion of the plurality of FID values and a model kernel matrix.