METHOD FOR OPERATING A NUCLEAR MAGNETIC FLOWMETER AND NUCLEAR MAGNETIC FLOWMETER

Abstract

A method for measuring the flow rate of a multi-phase medium flowing through a measuring tube using a nuclear magnetic resonance flow meter can be used to measure the flow rate of a multi-phase medium in a simplified manner. For this purpose, a measuring device is used which implements, at the end of each pre-magnetization path, 2D tomography in the measurement tube cross-sectional plane with stratification in the z direction; the measurement tube cross-sectional plane is subdivided into layers that are thin compared to the measurement tube diameter; nuclear magnetic resonance measurements are carried out in every layer to determine measurement signals, using pre-magnetization paths of different lengths; the flow rates are measured in every layer based on the measurement signals; and the time is determined from the signal ratios of the amplitudes of the measurement signals in every layer.

Claims

1-17. (canceled)

18. A method for determining the flow of a multi-phase medium flowing through a measuring tube with a nuclear magnetic flowmeter having a pre-magnetization device and a measuring device, the pre-magnetization device having at least two pre-magnetization sections with different known lengths L.sub.1, L.sub.2, . . . , L.sub.n, the method comprising: using a measuring device that implements 2D tomography at the end of each pre-magnetization section in measuring planes perpendicular to a longitudinal axis of the measuring tube, identically dividing the measuring planes into voxels, the dimensions of the voxels being chosen such that only one phase of the medium flows in each voxel, carrying out nuclear magnetic measurement for determining measuring signals, determining the flow velocity of the medium in each voxel in each measuring plane, determining an average flow velocity of the medium for each voxel over all measuring planes from determined values of the flow velocity of each corresponding voxel of the individual measuring planes, determining a signal ratio of measuring signals of each corresponding voxel of the different measuring planes relative to one another, and with the known values for the lengths L.sub.1, L.sub.2 . . . L.sub.n of the pre-magnetization sections, determining spin-lattice relaxation time T.sub.1 in each voxel using the signal ratios.

19. The method according to claim 18, wherein a respective hydrogen index HI in each voxel is determined with the respective spin-lattice relaxation time T.sub.1 and wherein using the spin-lattice relaxation time T.sub.1 and the hydrogen index HI, different phases of the medium and sections of the different phases are determined.

20. The method according to claim 19, wherein the flow rates are determined by integration over the different sections of the medium and multiplication with the respective flow velocities.

21. The method according to claim 18, wherein the nuclear magnetic measurement is implemented with a Carr Purcell Meiboom Gill (CPMG) sequence.

22. The method according to claim 18, wherein the velocity of the medium in every voxel in each plane is determined using the “convective decay” method.

23. The method according to claim 18, wherein amplitudes of the measuring signals at a time t=0 are used for determining the signal ratios.

24. The method according to claim 18, wherein a temporal course of the measuring signals is used for determining the signal ratio.

25. The method according to claim 18, wherein the at least two pre-magnetization sections are implemented by variable RF coils and wherein the measuring planes at the end of each pre-magnetization section are realized by different planes.

26. The method according to claim 18, wherein the at least two pre-magnetization sections are implemented by rotating magnetic arrangements and wherein the measuring planes at the end of each pre-magnetization section are realized in a single spatial plane.

27. The method according to claim 18, wherein the at least two pre-magnetization sections are implemented by RF coils transmitting spoil pulses and wherein the measuring planes at the end of each pre-magnetization section are realized in a single spatial plane.

28. A method for determining the flow of a multi-phase medium flowing through a measuring tube with a nuclear magnetic flowmeter having a pre-magnetization device and a measuring device, the pre-magnetization device having at least two pre-magnetization sections with different known lengths L.sub.1, L.sub.2, . . . L.sub.n, the method comprising: using a measuring device that implements 2D tomography at the end of each pre-magnetization section in a measuring tube cross sectional plane in a z direction, dividing the measuring tube cross sectional plane into thin layers in relation to the measuring tube diameter, carrying out nuclear magnetic measurements in every layer for determining measuring signals with at least two pre-magnetization sections of different lengths, determining the flow velocity in each individual layer using the measuring signals, and determining the spin-lattice relaxation time T.sub.1 time using the signal ratios of the amplitudes of the measuring signals in each layer.

29. The method according to claim 28, wherein the portions of the individual phases in the medium are determined using the absolute amplitudes of the measuring signals.

30. The method according to claim 28, wherein a water to liquid ratio for lower layers in the measuring tubes is determined layer for layer from bottom to top in the measuring tube, wherein a water to liquid curve depending on the position of the layer in the measuring tube is generated using the determined values, wherein a curve is extrapolated based on a last determined value over the entire measuring tube cross section, wherein expected measuring signal amplitudes for the upper layers in the measuring tube are calculated from the extrapolated curve, and wherein a gas volume portion in the upper layers is determined using a difference between the expected measuring signal amplitude and the actual measuring signal amplitude.

31. Nuclear magnetic flowmeter for determining the flow of a medium flowing through a measuring tube, comprising: a pre-magnetization device and a measuring device, wherein the pre-magnetization device implements at least two pre-magnetization sections of differing lengths with the lengths L.sub.1, L.sub.2, . . . L.sub.n, and wherein the measuring device is adapted to implement 2D tomography at the end of each pre-magnetization section either in a measuring plane perpendicular to a longitudinal axis of the measuring tube or in a measuring tube cross sectional plane in a z-direction.

32. Nuclear magnetic flowmeter according to claim 31, further comprising variable RF coils by which the different lengths L.sub.1, L.sub.2, . . . L.sub.n, of the pre-magnetization section are implemented and wherein the measuring planes at the end of every pre-magnetization section fall in the area of the respective RF coil.

33. Nuclear magnetic flowmeter according to claim 31, further comprising rotating magnetic arrangements by which the different lengths L.sub.1, L.sub.2, . . . L.sub.n of the pre-magnetization section are implemented and wherein the measuring planes at the end of each pre magnetization section are realized in a single spatial plane.

34. Nuclear magnetic flowmeter according to claim 31, further comprising variable RF coils which transmit spoil pulses by which the different lengths L.sub.1, L.sub.2, . . . L.sub.n of the pre magnetization section are implemented, and wherein the measuring planes at the end of each pre-magnetization section are realized in a single spatial plane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a schematic illustration of a first preferred embodiment of the nuclear magnetic flowmeter according to the invention,

[0033] FIG. 2 is a schematic illustration of a second preferred embodiment of the nuclear magnetic flowmeter according to the invention,

[0034] FIG. 3 is a schematic illustration of a third preferred embodiment of the nuclear magnetic flowmeter according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] A first embodiment of the nuclear magnetic flowmeter 1 according to the invention is illustrated in FIG. 1. The medium, of which the flow is to be measured, flows through the measuring tube 2. The flowmeter 1 includes a pre-magnetization device 3, wherein the pre-magnetization device 3 includes one or more permanent magnets 10 for generation of a magnetic field interfusing the measuring tube 2, as well as a measuring device 4. Two variable RF coils 11 are arranged in the area of the measuring device 4. The variable RF coils 11 are used for exciting the medium with excitation signals and for receiving measuring signals transmitted from the medium due to excitation signals. A first measuring plane 8, perpendicular to the longitudinal axis of the measuring tube, is located in the first variable RF coil 11. The first pre-magnetization section 6 is thus defined as the section from the beginning of the pre-magnetization device 3 to the first measuring plane 8. A second measuring plane 9, which is also perpendicular to the longitudinal axis of the measuring tube, is located in the second variable RF coil 11. Hence, the second pre-magnetization section 7 is defined as the section from the beginning of the pre-magnetization device 3 to the second measuring plane 9. Since the first measuring plane 8 and the second measuring plane 9 do not spatially coincide with one another, the lengths of the first pre-magnetization section 6 and the second pre-magnetization section 7 are different. 2D tomography is implemented in the measuring planes 8 and 9. It is also possible to implement tomography with slicing in the z direction.

[0036] A second embodiment of the nuclear magnetic flowmeter 1 according to the invention is schematically illustrated in FIG. 2. As opposed to the embodiment illustrated in FIG. 1, the pre-magnetization device 3 has a several rotating magnetic arrangements 5. Six such magnetic arrangements 5 are illustrated, however, the invention is not limited to a certain number of magnetic arrangements 5. Each of the magnetic arrangements 5 generates a magnetic field in a certain strength and direction. The magnetic fields of adjacent rotating magnetic arrangements 5 can be parallel or anti-parallel to one another and it is also possible that a magnetic unit 5 does not generate a magnetic field. The effective pre-magnetization section is defined by the choice of orientation of adjacent magnetic arrangements 5. Both a first pre-magnetization section 6 and a second pre-magnetization section 7 are illustrated. As opposed to the pre-magnetization section 6, 7 according to the first embodiment, both pre-magnetization sections 6, 7 have a different starting point and a common ending point. Hence, the first measuring plane 8 and the second measuring plane 9 coincide in one spatial plane in the measuring device 4. 2D tomography is used in the measuring planes 8 and 9. It is also possible to implement tomography with layering the z direction.

[0037] A third embodiment of the flowmeter 1 according to the invention is illustrated in FIG. 3. The medium, of which the flow is to be measured, flows through the measuring tube 2. Analog to both embodiments described above, the flowmeter contains a pre-magnetization device 3 and a measuring device 4. In the embodiment illustrated in FIG. 3, the pre-magnetization device 3 contains one permanent magnet 10 or several permanent magnets 10 for generating a magnetic field interfusing the medium. Furthermore, the pre-magnetization device 3 contains a RF coil 12 generating a pulse destroying the magnetization of the medium or a pulse sequence destroying the magnetization of the medium. The magnetization generated in the area between the setting in of the pre-magnetization device 3 and the spoil coil 12 is destroyed again by the spoil pulse, so that the beginning of a “new” pre-magnetization section is located at the position of the spoil coil 12.

[0038] The two pre-magnetization sections 6, 7 of different lengths have—as shown—a different beginning, which allows them—as shown in FIG. 3—to have the same ending. The measuring plane 8 and the measuring plane 9 coincide in one single spatial plane in the measuring device 4. 2D tomography is implemented in the measuring planes 8 and 9. It is also possible to implement tomography with layering in the z direction.