Flowmeter for measuring flow rate in continuous flow of oil

Abstract

A flowmeter and method for measuring the flow rate of a continuous multiphase flow of oil, wherein the flow includes water droplets, the flowmeter including at least one magnetic field generator configured to provide a magnetic field of known strength to the flow, the flowmeter also including at least one sensor for measuring the charge at the sensor relative to the ground, the sensor being located at a certain distance from the magnetic field axis and the center of the flow axis, and having substantially the same axial position as the magnetic field axis, wherein the flowmeter also includes measurement and calculation means for calculating the flow rate based on the measured charge.

Description

Technical Field

[0001] The present invention relates to a flow meter and a method for measuring the flow rate of an oil continuous multiphase flow having water content. Background Art

[0002] Measuring parameters such as multiphase fluid flow velocity is of great importance in the oil and gas (hydrocarbon) industry and other fields with complex flow conditions. Many solutions have been proposed and used, such as differential pressure in Venturi flowmeters or insertion flowmeters, ultrasonic Doppler measurement, and electromagnetic measurement. Flow measurement often uses a number of different sensors, electrodes, and devices, making the measurement setup complex and expensive. Therefore, there is a need to reduce the number of components, especially those in direct contact with the fluid, and to use the same sensor to measure different flow parameters whenever possible.

[0003] In WO2020084132 / NO20181382, flow measurement is performed using electrodes and electric fields, where different types of electrode configurations are used to measure the composition of the flow, but the measured changes can also be used to measure the flow rate. However, the latter does require a certain degree of change in the flow composition.

[0004] Another method for measuring flow velocity is discussed in US9163967 and WO2007 / 009097. This solution is useful in the case of continuous water flowing through a magnetic field by using electrodes arranged along the circumference of the pipe, which provides a voltage difference perpendicular to the magnetic field and the flow direction. However, this solution is not suitable for non-conductive flows and therefore has limited use in oil and gas related measurements. In WO2007 / 009097, this problem is addressed by using electrodes to measure velocity in the direction of flow if the water content of the fluid is too low. Summary of the Invention

[0005] It is therefore an object of the present invention to provide an alternative method for measuring the flow rate of a non-conductive fluid flow, wherein the flow has a stable flow regime and composition, preferably using existing electrode configurations. This object is achieved in the accompanying claims.

[0006] The invention is therefore based on the fact that any conductive or dipolar molecule, even in a non-conductive flow, will be affected by a magnetic field and will develop a charge difference in any direction except parallel to the field, with a maximum value when perpendicular to the field. This can be measured using electrodes placed at a certain distance from the axis of the magnetic field, using a low impedance circuit to measure the charge relative to the ground level. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention will now be described with reference to the accompanying drawings which illustrate the invention by way of example.

[0008] Figure 1a and Figure 1b Measurements according to the prior art are described, as shown in US9163967.

[0009] Figure 2a and Figure 2b The measuring method according to the invention is shown.

[0010] Figure 3a -e illustrates the effect of a magnetic field on water droplets in a flow according to the present invention.

[0011] Figure 4 A practical implementation of the invention is described.

[0012] Figure 5 The relationship between water velocity, WVF and voltage measured according to the present invention is illustrated. DETAILED DESCRIPTION

[0013] Figure 1a The basic relationship of the known technology is shown, which shows a cross section of a pipe 1 and at least one electrode 2 for measuring velocity. Two coils B1 and B2 are used to generate a substantially uniform magnetic field B, which extends through the pipe 1. The pipe material is selected so as not to interfere with the magnetic field B. The measurement principle is based on the fact that when a continuous fluid 4a of water (possibly including oil droplets 4b) flows through the magnetic field B, Faraday's law of electromagnetic induction states that when a moving conductor such as a continuous fluid of water passes through a magnetic field, an induced voltage is generated. This is in Figure 1a In the figure, it is represented by the positive and negative changes + / - at the pipe wall 1. The voltage induced by this can be measured at the electrode 2 at a certain distance from the magnetic field axis and the flow axis, so the voltage corresponds to

[0014] ΔE=kBvD

[0015] ΔE is the potential between two opposing electrodes, k is the calibration constant, B is the magnetic field strength, v is the water velocity, and D is the distance between the two measuring electrodes. The water velocity v can be easily calculated. As described in US9163967, it has been demonstrated that the use of magnetic field and voltage to measure water velocity in multiphase flow can achieve good performance. The measured differential voltage is a function of the local water velocity and the local water volume fraction (WFV). The measured potential difference is therefore expressed as

[0016] ΔE=f(v ij ,wvf ij )

[0017] From the bottom Figure 1b It can be seen that the potential at electrode 2 can be measured using the well-known circuit 2b.

[0018] exist Figure 1a In the embodiment, the velocity electrode 2 is composed of one of several electrodes e1-e6, for example, an electrode for dielectric constant measurement; the velocity electrode 2 can also be used to measure the velocity at other positions relative to the magnetic field axis, and thus can also provide information about the velocity distribution on the pipe cross section.

[0019] The present invention Figure 2a and 2b As shown, a magnetic field B is applied by coils B1 and B2 to provide a uniform magnetic field B with a defined direction through a pipe 1, in which there is a continuous multiphase flow 3b of oil containing water droplets 3a. The amount of water required will depend on the flow conditions and the accuracy of the measurement, but if the water content is stable, the relative difference in the measurement will provide an indication of the fluid flow rate.

[0020] In addition to Faraday's law, the water droplet 3a in the oil continuous flow 3b will also be subjected to the Lorentz force, which combines the electric and magnetic forces acting on the charges in the water droplet 3a in the oil flow 3b. The electromagnetic field and the induced voltage give an electromotive force, which is determined by the circular motion of the charges in the conductor in the closed loop defined by the water droplet in the non-conductive flow. Figure 2a In the example above, this is represented by the positive and negative charges in the water droplet, but in reality, there is a cycle of charge in the water droplet. The principle of this will be explained in detail below.

[0021] When the water droplets 3a pass through the magnetic field B, the magnetic field generates an induced potential inside each water droplet 3a, such as Figure 2a These individual potentials generate an electric field that capacitively couples to the electrodes, and the charge is picked up by the charge measurement electronics (charge amplifier) ​​A. The measured differential charge is a function of the local water velocity and the local water volume fraction (WVF). However, the measured differential charge is linear with the water velocity but nonlinear with the WVF.

[0022] ΔQ=f(v ij ,wvf ij )

[0023] Where △Q is the induced charge relative to the ground.

[0024] In this way, the measured charge change will indicate a corresponding flow rate change. This measurement can be relative, based on the change relative to a measurement under known conditions, or it can be based on a predetermined model that takes into account predetermined WVF measurements or real-time measured WVF in relation to velocity measurements.

[0025] Likewise, in Figure 2bThe circuitry for measuring the charge at each electrode 2a is shown in Figure 2. Flow velocity can be measured with one electrode 2, preferably placed perpendicular to the magnetic field and flow direction to optimize the signal-to-noise ratio, but a number of electrodes e1-e6 can also be used to provide an indication of the flow profile.

[0026] The magnetic field can be constant or vary at a known frequency. The latter means that the measured charge will change in sync with the changing magnetic field, which can be used to eliminate errors and interference in the measurement results.

[0027] The measurement can be calibrated or adjusted based on known water volume fraction, salinity, etc. to reduce the uncertainty in the velocity measurement; this can be based on regular sampling of the flow content, or measurements taken in the vicinity of that measurement to provide an accurate understanding of the flow conditions.

[0028] Figures 3a-3e The principle behind the invention is explained. Figure 3a The figure shows the distribution of a typical magnetic field B in a pipe 1. The actual solution, depending on the coils and the material, may deviate from this, possibly at the expense of reduced measurement accuracy.

[0029] Figure 3b The induced current density 3c is shown in a water droplet 3a moving at a certain speed under an imposed magnetic field B. The water droplet 3a is immersed in a multiphase flow 3b of a non-conductive phase (gas or oil). Note that denser lines indicate greater current density.

[0030] Figure 3c Explained by Figure 3b The induced voltage generated by the current density in the

[0031] Figure 3d Explained by Figure 3c The electric field distribution in the non-conductive fluid phase 3b is generated by the potential in . Again, denser lines represent greater electric field strength.

[0032] Figure 3e The figure illustrates the electric field distribution E formed by multiple water droplets 3a moving at a certain speed in a non-conductive phase 3b. The charge from these droplets is captured by electrodes 2 and transferred to a low-impedance circuit (charge amplifier) ​​2a. As mentioned above, the electrodes 2 in this embodiment are placed perpendicular to the direction of the magnetic field and flow to optimize the measurement. The measured capacitance provides a measure of the flow rate.

[0033] Figure 4A practical solution is described, in which coils B1 and B2 are located on opposite sides of pipe 1. This can be combined with other measurement devices, such as those described above, or as disclosed in US 7,276,916 B2, using additional coils B3 and B4 to measure the water volume fraction. It can also be combined with the solution discussed in WO2020084132 / NO20181382, using the same electrodes but possibly with additional measurement circuitry connected to them.

[0034] exist Figure 5 Shown in Figure 2b The output voltage of the charge measurement electronics 2a is shown at different WVFs. WVF1 is 40%, WVF2 is 20%, WVF3 is 10%, and WVF4 is 5%. This graph shows the relationship between charge and water flow rate and WVF. It can be seen that the measurement accuracy increases with increasing WVF. However, depending on the sensor circuit, the measurement results are reliable at least down to 5% WVF or lower.

[0035] In summary, the present invention relates to a flow meter and a corresponding method for measuring the flow velocity of a continuous multiphase flow of oil, wherein the flow includes water droplets, preferably with a known WVF. The flow meter comprises at least one magnetic field generator configured to provide a magnetic field of known strength to the flow, and at least one sensor for measuring the charge at the sensor relative to a ground level or a reference level, the sensor being a capacitive sensor or a high-impedance sensor. The sensor is positioned at a distance from the center of the magnetic field axis and the flow axis, with its axial position being substantially the same as the magnetic field axis. The flow meter comprises a calculation unit for calculating a measure of the flow velocity based on the measured charge.

[0036] Preferably, the at least one sensor is positioned perpendicular to the axis and the magnetic field axis to maximize measurement sensitivity. To further enhance sensitivity, at least two sensors may be mounted on opposite sides of the pipeline and the magnetic field. Another embodiment may include multiple sensors distributed along the inner pipeline surface, connected to a measuring instrument that analyzes the charge distribution to determine the velocity distribution across the flow cross section.

[0037] The magnetic field strength may be a time varying magnetic field strength and the flow meter may then be configured to measure a response of the at least one sensor to the varying magnetic field.

[0038] The at least one sensor is placed in the pipe wall and can be electrically isolated from the flow or in electrical contact with the flow, depending on the available sensors and the application scenario.

[0039] The flow meter may further comprise a water volume fraction measuring device for measuring the water content of the flow, the calculation unit being adapted to calculate the velocity based on the determined water content, or a storage device for predetermined information about the water content of the fluid flow, the calculation unit being adapted to calculate the velocity based on the determined water content. The calculation unit is calibrated based on known flow conditions, and the flow velocity is measured based on the measured deviation from the known flow conditions.

Claims

1. A flow meter for measuring the flow rate of water in a continuous multiphase flow of oil, the flow meter comprising at least one magnetic field generator configured to provide a magnetic field of known strength to the flow, the flow meter further comprising at least one sensor for measuring an electric charge at the sensor relative to a ground level, the sensor having a low impedance circuit and being positioned away from the center of the axis of the magnetic field and the axis of the flow and at substantially the same axial position as the axis of the magnetic field, wherein the flow meter further comprises a calculation unit for calculating a measure of the flow rate based on the measured electric charge.

2. The flow meter according to claim 1, wherein The at least one sensor is positioned remotely in a direction perpendicular to an axis of the flow and the magnetic field.

3. The flow meter of claim 1, comprising at least two sensors positioned on opposite sides of the pipe and the magnetic field.

4. The flow meter according to claim 1, wherein: The magnetic field has a magnetic field strength that varies with time, and the flow meter is configured to measure a response of the at least one sensor to the varying magnetic field.

5. The flow meter according to claim 1, wherein The at least one sensor is located in the pipe wall and is electrically isolated from the flow.

6. The flow meter according to claim 1, wherein: The at least one sensor is located in the pipe wall and is in electrical contact with the galvanic conductor.

7. The flow meter according to claim 1, comprising a plurality of sensors distributed along the surface of the inner pipe, the sensors being connected to a measuring instrument for determining the water velocity distribution in the flow cross section.

8. The flow meter according to claim 1, comprising a water volume fraction measuring instrument to measure the water content of the flow, the calculation unit being also adapted to calculate the water flow velocity based on the determined water content.

9. The flow meter according to claim 1, comprising storage means comprising predetermined information on the water content of the fluid flow, said calculation unit being also adapted to calculate the speed based on the determined predetermined water content.

10. The flow meter according to claim 1, wherein The computing unit is calibrated based on known flow conditions and the velocity of the water is measured based on the measured deviation from the known flow conditions.

11. A method for measuring the flow rate of water in a continuous flow of a non-conductive oil or gas fluid in a pipeline, the method comprising the following steps: applying a magnetic field across the fluid flow; measuring the charge at the sensor using a sensor located at the pipe wall outside the axis of the magnetic field, the sensor having a low impedance circuit; The water flow velocity is calculated based on the amount of charge measured at the sensor.

12. The method according to claim 11, characterized in that The water flow velocity is calculated based on the measured change and the water volume fraction WVF of the flow.

13. The method of claim 12, further comprising the step of measuring the WVF of the flow prior to calculating.

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