HIGH-SIDE CURRENT MEASUREMENT TECHNIQUE FOR MULTI-PHASE FLUID

BACKGROUND

[1] A flow process may include a process in which a fluid flows through a conduit. Flow processes are involved in several different industries, such as the oil and gas, refining, food and beverage, chemical and petrochemical, power generation, pharmaceutical, and water and wastewater treatment industries. The fluid(s) involved in various flow processes may be a single-phase fluid (e.g., gas, water, or a liquid/liquid mixture, etc.) and/or a multi-phase mixture (e.g., oil and sand, or a liquid/solid mixture, etc.). The multi-phase mixture may include a flow of materials having more than one phase, such as a two-phase liquid/gas mixture,a solid/gas mixture, a solid/liquid mixture, a liquid/liquid mixture, a gas entrained liquid or a three-phase mixture.

[2] In certain industries, such as the oil and gas industiy, a flow process may be monitored or measured to determine the amounts of different components in the flowing fluids and/or the flow rates of the fluid components. For example, when drawing oil and gas from the ocean, oil, water, gas, and sand may be drawn through a pipe in varying amounts and at varying rates. Measuring the amounts and/or flow rates of such a multi-phase mixture may improve oil and gas production processes. For instance, a process of drawing oil and gas may be adjusted in response to high amounts of water or sand in the drawn mixture.

[3] Some techniques for monitoring or measuring different fluid components in oil and gas flow processes include using multi-phase metering systems to measure the impedance of the different fluids flowing through the pipe. However, flow processes may sometimes involve high-impedance fluids that may be difficult to monitor. Furthermore, depending on the nature of the fluids to be measured, the flow patterns of the fluids flowing through the conduit, and/or the configuration of the multi-phase metering system, parasitic impedances may interfere with accurate monitoring and measuring of the flow process. Conventional multi-phase metering techniques may not be sufficiently accurate in measuring flow processes involving relatively high- impedance fluids and/or high parasitic impedances.

BRIEF DESCRIPTION

[4] One embodiment includes a system configured to measure one or more parameters related to a measured load. The system includes a differential amplifier having a first input and a second input. The system also includes an electrode connected to the first input of the differential amplifier. The electrode is configured to deliver a current through the measured load. A first sensing impedance connected to the first input of the differential amplifier is configured to cany current through one or more of the measured load or a parasitic load in parallel to the measured load. The system also includes a balance load connected to the second input of the differential amplifier and connected to a ground of the system. The balance load is configured to balance the parasitic load. The system further includes a second sensing impedance connected to the second input. The second sensing impedance has an impedance substantially equal to that of the first sensing impedance and is configured to carry current through the balance load.

[5] In another embodiment, a multi-phase metering system is provided. The multi-phase metering system includes a transport pipe configured to transport one or more flow components of a flow process. The multi-phase metering system also includes one or more electrodes configured to measure one or more parameters of the one or more flow components flowing through the transport pipe. Furthermore, the multi-phase metering system includes measurement electronics having measurement circuitry in communication with the one or more electrodes. The measurement circuitry includes a balance load having an impedance that is substantially equal to a parasitic impedance of the multi-phase metering system.

[6] Another embodiment includes a method of monitoring a flow parameter in a multi-phase fluid metering system. The method includes sensing a differential voltage drop across a portion of flowing components in the multi-phase fluid metering system and using a balance load to balance a parasitic impedance of the multi-phase fluid metering system.

BRIEF DESCRIPTION OF THE DRAWINGS

[7] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[8] FIG. 1 is a schematic diagram of a multi-phase metering system for determining a parameter associated with one or more fluids flowing through a pipe, in accordance with techniques of the present disclosure;

FIGS. 2-4 are schematic diagrams of a cross-sectional view of pipe in a multi-phase metering system, in accordance with techniques of the present disclosure;

[10] FIG. 5 is a schematic diagram of a cross-sectional view of a sensor connected to multi-phase metering circuitry, in accordance with techniques of the present disclosure; and

[11] FIG. 6 is a circuit diagram of circuitry suitable for measuring currents through a multi-phase flow process, in accordance with techniques of the present disclosure.

DETAILED DESCRIPTION

[12] Embodiments of the present disclosure involve systems and methods for more accurately determining the electrical impedance through a volume being measured. Determining the electrical impedance may involve measuring electrical conditions of the volume, such as the voltage across the volume and the current flowing through the volume. In some embodiments, measuring the voltage across the volume and sensing the current through the volume may involve measuring the electrical conditions between electrode pairs arranged on the volume. For example, one implementation of an impedance measurement system includes a multi-phase metering system which may include electrodes arranged about a conduit. The electrodes may be configured to transmit and/or receive current through the conduit and/or through the fluids flowing through the conduit. The multi-phase metering system may also include circuitry suitable for calculating and processing various parameters of the fluid(s) flowing through the conduit based on the electrode measurements.

[13] One example of a multi-phase metering system for determining a parameter associated with one or more fluids flowing through a pipe is provided in FIG. 1. The multi-phase metering system 10 includes a conduit, such as a duct or a pipe 12 suitable for transporting fluids. The system 10 may include one or more electrodes 14 arranged about the transport pipe 12, and the electrodes 14 may be electrically connected to measurement electronics 16 having circuitry 18 and one or more processors 17 suitable for receiving and analyzing electrode measurements to determine one or more parameters related to the fluids flowing through the pipe 12.

[14] For example, during oil and gas production, oil, water, gas, and/or sand, referred to generally as flow components, may be drawn through a marine production platform through the pipe 12. Such flow components may flow simultaneously through the pipe 12, and the distribution of the different flow components may also flow in various patterns within the pipe 12. The pipe 12 may have a substantially circular cross section and may be suitable for transporting various types of flow components. The flow components may flow in different axial and/or radial patterns and may be stratified and/or non-stratified within the pipe 12.

[15] In some embodiments, the multi-phase metering system 10 may be used to monitor parameters related to the flow patterns of the various flow components through the transport pipe 12. For example, the system 10 may by used to continuously measure one or more parameters, such as flow velocity, volume flow rate, etc., of the flow components. The system 10 may include one or more electrodes 14 disposed about the pipe 12. For example, in some embodiments, the electrodes 14 may be arranged in an electrode body 15 having a substantially circular cross section. The electrode body 15 may be positioned concentrically in relation to the pipe 12, such that when the flow components travel through the pipe 12, one or more parameters of a portion of the flow components traveling through a cross-section of the pipe 12 may be measured.

[16] The electrodes 14 may be suitable for measuring electrical characteristics of the flow components
traveling through the cross-sectional area of the pipe 12 around which the electrode body 15 is positioned. For example, FIG. 2 is a cross- sectional illustration of the pipe 12 having multiple electrodes 14 arranged concentrically with a cross-section of the pipe 12. In some embodiments, one or more electrodes 14 (e.g., a transmit electrode 14a) may transmit a current through the flow components and a corresponding electrode 14 (e.g., a receive electrode 14b) may measure the corresponding electrical field generated in response to the transmitted current. In some embodiments, the measurement electronics 16 may be suitable for transmitting a current to the flow components. For example, the measurement electronics 16 may include a signal generator which may be used to apply an AC voltage to the pipe 12 and flow components through the transmit electrode 14. The measurement electronics 16 may also include circuitry 18 suitable for measuring and outputting the electrical response of the flow components.

[17] As illustrated in FIG. 2, each electrode pair may be oppositely disposed, such as transmit and receive electrodes 14a and 14b, 14c and 14d, 14e and 14f, and 14g and 14h, respectively. In some embodiments, as illustrated in FIG. 3, electrode pairs may be adjacently paired, such as transmit and receive electrodes 14i and 14j, 14k and 141, 14m and 14n, and 14o and 14p, respectively. Furthermore, in some embodiments, as illustrated in FIG. 4, electrode pairs may be otherwise differently paired such as transmit and receive electrodes 14q and 14r, 14s and 14t, 14u and 14v, and 14w and 14x, respectively. In one or more embodiments, electrode pairs may be arranged and configured to transmit currents and/or measure an electrical condition of the flow components traveling through the pipe 12. It should be noted that while FIGS. 2-4 each include eight electrodes 14 disposed around an axial cross-section of the pipe 12, in other embodiments, different numbers of electrodes 14 may be arranged around an axial cross-section of the pipe 12, and electrodes 14 may also be arranged at multiple axial cross-sections of the pipe 12. Furthermore, in some embodiments, a multi-phase metering system 10 may involve different arrangements of electrodes 14 around the pipe 12. For example, an electrode pair may be arranged across a longitudinal length of the pipe 12.

[18] Furthermore, in some embodiments, the electrodes 14 may be disposed over an inner surface of the pipe 12 (i.e., disposed on a side of the pipe 12 adjacent to the flow components), as illustrated in FIGS. 1-4. In other embodiments, the electrodes 14 may also be disposed on an outer surface of the pipe 12 (i.e., disposed on a side of the pipe 12 opposite of the flow components), as illustrated in FIG. 5. In some embodiments, a shielding of the electrode 14 may be connected to measurement circuitry 18 by a shielding 24 of a coaxial cable 20

The electrical field generated between each electron pair may be measured and analyzed by measurement electronics 16 of the multi-phase metering system 10 to determine various parameters of the flow components based on the measured electrical conditions. The measurement electronics 16 may include a processor 17 which may determine various parameters based on the measured electrical characteristics of the flow components. For example, the processor 17 may determine the differential voltage between an electrode pair (e.g., transmit electrode 14a and receive electrode 14b) to determine the impedance of one or more flow components traveling between the electrode pair. As different fluid components such as oil, water, gas, and sand each have different impedances, the processor 17 may determine various parameters of the flow components, such as quantity, flow velocity, volume flow rate, etc., of different flow components based on the measured impedance. Moreover, as several electrode pairs may be arranged about a cross- sectional area of the pipe 12, substantially all of the flow components traveling through a cross-sectional area may be determined. For example, the processor 17 may decompose a cross-section of the flow stream through a cross-sectional area of the pipe 12 based on the electrode measurements of the electrode body 15 disposed about the cross sectional area.

[20] Depending on the nature of the flow components being measured, the process in which the flow components are transported through the pipe 12, and/or the length of the coaxial cable 20 (FIG. 5), undesirable parasitic impedances may sometimes interfere with accurately measuring differential voltages and/or sensing current through the flow components traveling through the pipe 12. In particular, flow components that move at relatively high velocities through the pipe 12 and have relatively small changes in load impedance may be difficult to accurately measure and analyze. For example, fluids drawn during oil and gas production may flow through a pipe 12 at a relatively high velocity. Such flow components may flow in different axial and/or radial patterns in the pipe 12 at relatively high frequencies. Furthermore, the quantities of the different flow components drawn through the pipe 12 may change during the flow process, but significant changes in the ratio of different flow components may result in relatively small changes , in the load impedance which may be difficult to detect. Moreover, small changes in impedance may be particularly difficult to detect when parasitic impedances interfere with the metering system. In some systems, relatively large parasitic impedances may draw a leakage current that is larger than the load current, or the current measured between an electrode pair.

[21] In some embodiments, the measurement electronics 16 may include circuitry 18 that compensates for parasitic impedances, such that the load current may be more accurately detected. FIG. 6 is a circuit diagram representing measurement circuitry 18 in one or more embodiments of the present disclosure. In some embodiments, the measurement circuitry 18 represents the electronic relationship between a transmit and receive electrode pair (e.g., transmit electrode 14a and receive electrode 14b from FIG. 2). For example, the resistance Rsense 26 may represent the resistance of a receive electrode 14b which may be connected to an input 38 of a differential amplifier 30 and a grounded DC power supply 36. The power supply 36 may represent the current transmitted by a transmit electrode 14a. The circuitry 18 may amplify the differential voltage drop across the high-side Rsense 26 to determine the current flowing through the flow components of the pipe 12. The flow components is represented as the load 28 in the circuitry 18 and connected in series to the Rsense 26.

[22] Parasitic impedances that may draw current from the power source 36 are represented in the circuitry 18 as a parasitic load 32 in parallel to the measured load 28. Depending on the parasitic load 32, the current drawn through the parasitic load 32 may be greater than the current drawn through the measured load 28. In such instances, the differential amplifier 30, which may conventionally have another input 40 connected to ground, may not be able to accurately measure the differential voltage through the measured load 28 due to the large common mode voltage created by the parasitic load 32 in parallel with the measured load 28.

[23] In some embodiments, the measurement circuitry 18 may include a balance load 34 connected between the input 40 of the differential amplifier 30 and the power source ground. The circuitry 18 may also include a second resistance Rsense' 44 connected to the power supply 36 in series with the balance load 34 and in parallel with the sense resistance Rsense 26. The balance load 34 may have an impedance that is substantially equal to the impedance of the parasitic load 32, and the second resistance Rsense' 44 may be substantially equal to the sense resistance Rsense 26. As such, the voltage drop from the current flowing through the balancing load 34 may be substantially equal to the voltage drop from the current flowing through the parasitic load 32. Because the differential amplifier 30 may produce an output 42 that is proportional to the difference in the voltages at its two inputs 38 and 40, the impedance of the parasitic capacitance 32 may not significantly affect the output 42 of the differential amplifier 30 when the balancing impedance 34 is equal to the parasitic impedance 32.

[24] As the output 42 of the differential amplifier 30 may be proportional to the difference in voltage measured across the flow components between a transmit (e.g., electrode 14a) and a receive (e.g., electrode 14b) electrode pair, the output 42 may be used to determine characteristics of the measured flow components. In one embodiment, multiple electrode pairs (e.g., electrode pair 14a and 14b, electrode pair 14c and 14d, and electrode pair 14 e and 14f) may be continuously used to measure the differential voltages between each pair throughout a flow process, and the corresponding output 42 from each electrode pair may be transmitted in parallel to one or more processors 17. In some embodiments, each of multiple processors 17 may be used to process each of the outputs 42 from multiple electrode pair measurements in parallel. In other embodiments, multiple outputs 42 may be multiplexed to one processor 17 for processing. The one or more processors 17 may determine electrical characteristics, such as the impedance, of the flow components measured between each electrode pair. Based on the continuously measured outputs 42, the one or more processors 17 may determine parameters of different flow components substantially in real time. For example, the one or more processors 17 may continuously determine the quantity, flow velocity, volume flow rate, etc., of different flow components during a measurement process.

[25] In some embodiments, the Rsense' 44 may be between 10 Q to 1 kQ. For example, in one embodiment, Rsense' 44 may be approximately 200 Q. In some embodiments, the balance load 34 may have an impedance between 1 pF to 500 pF. For example, in one embodiment, the balance load 34 may have an impedance of approximately 30 pF. Furthermore, in some embodiments, the magnitude of the impedance of the measured load 28 may be between 5 fit and 1 MQ. In different embodiments, each of the Rsense' 44, balance load 34, and measured load 28 may be different depending on the load being measured and/or the system used to measure the load. For example, in multi-phase metering systems, the parasitic load 32 may be affected by parameters such as the length of the coaxial cable 20 and/or the impedance of the measured load 28. Therefore, to balance the voltage drop across an estimated parasitic load 32, the balance load 34 may be based on the length of the coaxial cable 20, the impedance of the measured load 28, and/or a known parasitic load impedance.

[26] It should be noted that while various elements of the measurement circuitry 18 are represented as resistors or loads having a resistance or capacitance, in one or more embodiments, the measurement circuitry may include elements having different electrical responses to the current supplied by the power supply 36. For example, while the resistor Rsense 26 generally represents a resistance of the sensing electronics in an electrode 14, the sensing electronics may include additional elements having a capacitance in addition to the resistance represented by resistor Rsense 26. Furthermore, while an example range of the parasitic and balance loads 32 and 34 are provided in Farads, in some embodiments, the balance load 34 may have a resistive component to substantially match the impedance of the parasitic load 32.

[27] Furthermore, while multi-phase metering systems are described in the disclosure as one example for an impedance measuring system with parasitic impedance balancing circuitry, one or more embodiments may be suitable for different types of measuring systems and may not be limited to multi-phase metering. Moreover, while oil and gas production is used as an example for an industry in which the present multi-phase metering techniques may be utilized, the present disclosure may be applied to other industries and is not limited to oil and gas production.

[28] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

CLAIMS:

1. A system configured to measure one or more parameters related to a measured load, the system comprising:

a differential amplifier having a first input and a second input;

an electrode connected to the first input, wherein the electrode is configured to deliver a current through the measured load;

a first sensing impedance connected to the first input, wherein the first sensing impedance is configured to carry current through one or more of the measured load or a parasitic load in parallel to the measured load;

a balance load connected to the second input and connected to a ground of the system, wherein the balance load is configured to balance the parasitic load; and

a second sensing impedance connected to the second input, wherein the second sensing impedance comprises an impedance substantially equal to that of the first sensing impedance, and wherein the second sensing impedance is configured to carry current through the balance load.

2. The system of claim 1, wherein the first input is connected between the first sensing impedance and the measured load.

3. The system of claim 1, comprising an electrode body configured to measure a flow process through a conduit, wherein the electrode body comprises one or more electrodes.

4. The system of claim 3, wherein the measured load comprises one or more flow components of the flow process, and wherein the one or more electrodes are configured to sense a respective current through the one or more flow components.

5. The system of claim 1, wherein the one or more parameters related to a measured load comprises a flow velocity of one or more flow components of the measured load, wherein the one or more flow components comprises water, oil, gas, sand, and combinations thereof.

6. The system of claim 1, comprising a pipe suitable for transporting the measured load, wherein the electrode is configured couple to the pipe to sense the current through the measured load.

7. A multi-phase metering system comprising:

a transport pipe configured to transport one or more flow components of a flow process;

one or more electrodes configured to measure an electrical condition of the one or more flow components flowing through the transport pipe; and

measurement electronics comprising measurement circuitry in communication with the one or more electrodes and comprising a balance load having an impedance that is substantially equal to a parasitic impedance of the multi-phase metering system.

8. The multi-phase metering system of claim 7, wherein the electrical condition comprises a voltage drop over the one or more flow components, a current through the one or more flow components, an impedance of the one or more flow components, or combinations thereof.

9. The multi-phase metering system of claim 7, wherein the one or more electrodes are arranged in an electrode body arranged substantially concentrically with a cross-section of the transport pipe.

10. The multi-phase metering system of claim 7, wherein the measurement electronics comprises a processor configured to receive the electrical condition measurements from the one or more electrodes and configured to determine one or more parameters related to the one or more flow components based on the electrical condition.

11. The multi-phase metering system of claim 10, wherein the one or more parameters comprises one or more of a flow velocity, a volume flow rate, and a quantity of one or more of the flow components in a cross-sectional area of the transport pipe.

12. The multi-phase metering system of claim 7, comprising a differential amplifier configured to output a voltage proportional to the differential voltage drop across a portion of the one or more flow components.

13. The multi-phase metering system of claim 12, wherein the differential amplifier comprises a first input and a second input, and wherein the first input is connected to one of the one or more electrodes to measure an electrical condition of the portion of the one or more flow components

14. The multi-phase metering system of claim 13, wherein the balance load is arranged between the second input and a ground of the multi-phase measuring system.

15. The multi-phase metering system of claim 13, wherein the measurement circuitry comprises a balance impedance comprising an impedance substantially equal to an impedance of one of the one or more electrodes, wherein the second input is connected between the balance impedance and the balance load.

16. The multi-phase metering system of claim 15, wherein the balance impedance is between 10 Ω to 1 kΩ.

17. The multi-phase metering system of claim 7, wherein the balance load is between 1 pF to 500 pF.

18. The multi-phase metering system of claim 7, wherein a magnitude of an impedance of a Ωmeasured portion of the one or more flow components is between 5 Ω and 1 MΩ.

19. A method of monitoring a flow parameter in a multi-phase fluid metering system, the method comprising:

sensing a differential voltage drop across a portion of flowing components in the multi-phase fluid metering system; and

using a balance load to balance a parasitic impedance of the multi-phase fluid metering system.

20. The method of claim 19, comprising outputting a voltage proportional to a voltage difference between a first voltage input and a second voltage input, wherein the first voltage input comprises a voltage drop over the portion of the flowing components and the voltage drop over the parasitic impedance and the second voltage input comprises a voltage drop over the balance load.

21. The method of claim 20, comprising determining the flow parameter based on the output voltage.