Flowmeter with a measuring device implementing a tomographic measuring principle

Abstract

A flowmeter for determining the flow of a multi-phase medium through a measuring tube has a first and a second measuring device, one of which operates on a tomographic measuring principle and one of uses a measuring principle based on nuclear magnetic resonance. The first measuring device operates in a different manner from the second measuring device, e.g., using a measuring device operating on the measuring principle of pre-magnetization contrast measurement and having a pre-magnetization section with a constant magnetic field. The magnetic field has at least one component perpendicular to the direction of flow of the multi-phase medium and is generated by using magnetic field generating elements, which are arranged around the measuring tube. Additionally, an assembly for exciting nuclear spin by a RF excitation pulse or a RF excitation pulse sequence is part of the measuring device.

Claims

1. A method for operating a flowmeter for determining the flow of a multiphase medium flowing through a measuring tube, comprising: directing a flow of a multiphase medium through a measuring tube having two different types of measuring devices, performing measurements on the flow with the measuring devices, one of measurements being a nuclear magnetic resonance measurement and another of said measurements being an electrical capacitance measurement, and using said measurements to determine an amount of each of respective fractions of which the multiphase medium is comprised, wherein the nuclear magnetic resonance measurement is used to determine a gaseous fraction and a liquid fraction of the medium by applying a gradient magnetic field along y and z axes relative to the measuring tube, an x axis being in a direction of flow through the measuring tube, and wherein said electrical capacitance measurement is used to determine a water fraction and a hydrocarbon fraction using a distribution of one of permittivities and conductivity of the medium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a first embodiment of a flowmeter according to the invention implementing the measuring principle of magnetic resonance tomography and the measuring principle of electrical capacitance tomography,

(2) FIG. 2 shows a second embodiment of a flowmeter according to the invention implementing the measuring principle of electrical capacitance tomography and the measuring principle of pre-magnetization measurement,

(3) FIG. 3 shows a third embodiment of a flowmeter according to the invention implementing the measuring principle of magnetic resonance tomography and the measuring principle of pre-magnetization contrast measurement.

(4) FIG. 4 shows a method for operating a flowmeter for determining the flow of a multiphase medium flowing through a measuring tube having two different types of measuring devices,

(5) FIG. 5 depicts a second method for operating a flowmeter for determining the flow of a multiphase medium flowing through a measuring tube, and

(6) FIG. 6 depicts a third method for operating a flowmeter for determining the flow of a multiphase medium flowing through a measuring tube.

DETAILED DESCRIPTION OF THE INVENTION

(7) All figures show a flowmeter 1 for determining the flow of a multiphase medium flowing through a measuring tube 2. All flowmeters 1 shown in the figures have in common, first of all, a first measuring device 3 and a second measuring device 4. At least one of the first and second measuring devices 3, 4 implements a tomographic measuring principle.

(8) In the embodiment of the flowmeter 1 according to the invention shown in FIG. 1, the first measuring device 1 is realized by an electrical capacitance tomograph. This electrical capacitance tomograph 5 has a number of electrodes 6 symmetrically arranged around the measuring tube 2. The electrical capacitance tomograph 5 is designed such that the electrodes are attachable to the outside to the measuring tube 2. This guarantees that the flow of the multiphase medium through the measuring tube 2 is not influenced or disturbed by the electrodes 6. The measuring signals arising at the electrodes 6 are evaluated by an evaluation unit (not shown here) and are constructed to a two dimensional permittivity distribution map of the cross-section area of the measuring tube 2 by a suitable algorithm.

(9) The second measuring device 4 of the flowmeter 1 shown in FIG. 1 is realized by a magnetic resonance tomograph 7, which is also arranged around the measuring tube 2. The magnetic resonance tomograph 7 includes a unit for generating a constant magnetic field, (not shown), and also a unit for generating a gradient magnetic field G (not shown), that can be superimposed on the constant magnetic field, a exciting coil for generating a RF exciting pulse or a RF exciting pulse sequence (not shown) and also a detection coil (not shown), with which the measuring signal generated by the nuclear spins can be detected. The exciting coil and the detecting coil can be realized a single coil. It is possible to generate a gradient field g along the z-direction, G=G.sub.z.Math.e.sub.z and/or a gradient field along the y-direction G=G.sub.y.Math.e.sub.y. This can be done simultaneously, G=G.sub.y.Math.e.sub.y+G.sub.z.Math.e.sub.z, as well as one after the other. The definition of the x-, y- and z-directions is indicated in the drawings below the FIG. 3 legend.

(10) For the embodiment according to FIG. 2, the first measuring device 3 is realized by a measuring device implementing the measuring principle of pre-magnetization contrast measurement, which shows a pre-magnetization section 8 with a constant magnetic field. The magnetic field has at least one component perpendicular to the direction of flow of the multiphase medium and is generated by magnetic field generating elements 9, which are arranged around the measuring tube 2. The section permeated by the magnetic field depends on the number of magnetic field generating elements 9 and the direction of the generated magnetic fields with respect to each other.

(11) Also an assembly 10 for exciting the nuclear spins by a RF exciting pulse or a RF exciting pulse sequence and for measuring the measuring signals generated by the nuclear spins is part of the first measuring device 3.

(12) According to the embodiment of a flowmeter according to the invention shown in FIG. 4, the second measuring device 4 is realized by an electrical capacitance tomograph 5. This electrical capacitance tomograph 5 can be realized in the same manner and the same things can be achieved as was already mentioned in conjunction with the embodiment according to FIG. 1.

(13) For the embodiment according to the invention shown in FIG. 3, what was already explained above is valid in that it contains a first measuring device 3 and a second measuring device 4. Here, the first measuring device 3 implements the measuring principle of pre-magnetization measurement and contains a pre-magnetization section 8, which is permeated by a constant magnetic field. Also here, the magnetic field is generated by a number of magnetic field generating elements 9, which are arranged around the measuring tube 2, and has at least one component perpendicular to the direction of flow of the multiphase medium. Also here, the measuring device 3 contains an assembly 10 for exciting the nuclear spins by a RF exciting pulse or a RF exciting pulse sequence and for measuring the measuring signals generated by the nuclear spins. The pre-magnetization 8 interfused by the effective magnetic field is defined and varied by the number of the magnetic field generating elements 9 and/or the direction of the magnetic fields generated by the magnetic field generating elements 9 with respect to each other.

(14) For the schematically shown embodiment shown in FIG. 3, it is further valid that the tomographic measuring principle is realized by magnetic resonance tomography. Therefore, the embodiment contains a magnetic resonance tomograph 7. This magnetic resonance tomograph 7 can be realized in the same manner and the same results can be reached as was already mentioned in conjunction with the magnetic resonance tomograph 7 belonging to the embodiment according to FIG. 1.

(15) FIG. 4 depicts a first method for operating a flowmeter for determining the flow of a multiphase medium flowing through a measuring tube. The method comprises the following steps:

(16) In a first step 101, a flow of a multiphase medium is directed through a measuring tube having two different types of measuring devices.

(17) In a second step 102, measurements on the flow are performed with the measuring devices, one of measurements being a nuclear magnetic resonance measurement and another of said measurements being an electrical capacitance measurement.

(18) In a third step 103, said measurements are used to determine an amount of each of respective fractions of which the multiphase medium is comprised.

(19) The third step 103 comprises two sub steps.

(20) In a first sub-step 103a, the nuclear magnetic resonance measurement is used to determine a gaseous fraction and a liquid fraction of the medium by applying a gradient magnetic field along y and z axes relative to the measuring tube, an x axis being in a direction of flow through the measuring tube.

(21) In a second sub-step 103b, the electrical capacitance measurement is used to determine a water fraction and a hydrocarbon fraction using a distribution of one of permittivities and conductivity of the medium.

(22) FIG. 5 depicts a second method for operating a flowmeter for determining the flow of a multiphase medium flowing through a measuring tube. The method comprises the following steps:

(23) In a first step 201, a flow of a multiphase medium is directed through a measuring tube having two different types of measuring devices.

(24) In a second step 202, measurements of the flow are performed with the measuring devices, one of measurements being a nuclear magnetic resonance measurement and another of said measurements being a pre-magnetization contrast measurement.

(25) In a third step 203, the pre-magnetization contrast measurement is used to determine an oil fraction and a water fraction of the multiphase medium by one of changing a length of a pre-magnetization section or by varying measuring positions.

(26) In a fourth step 204, the magnetic resonance measurement is used to determine a gaseous fraction by applying a gradient magnetic field along a z-axis and a y-axis, an x axis being in a direction of flow through the measuring tube.

(27) FIG. 6 depicts a third method for operating a flowmeter for determining the flow of a multiphase medium flowing through a measuring tube. The method comprises the following steps:

(28) In a first step 301, a flow of a multiphase medium is directed through a measuring tube having two different types of measuring devices,

(29) In a second step 302, measurements of the flow are performed with the measuring devices, one of measurements being a nuclear magnetic resonance measurement and other of said measurements being a pre-magnetization contrast measurement and an electrical capacitance measurement.

(30) In a third step 303, the pre-magnetization contrast measurement is used to determine an oil fraction of the multiphase medium by one of changing a length of a pre-magnetization section or by varying measuring positions.

(31) In a fourth step 304, the electrical capacitance is used to determine a hydrocarbon fraction and a water fraction of the multiphase medium from a distribution of one of permittivities and conductivity of the medium.

(32) In a fifth step 305, the magnetic resonance measurement is used to determine a gaseous fraction by applying a gradient magnetic field along a z-axis and a y-axis, an x axis being in a direction of flow through the measuring tube.