ELECTRICAL IMPEDANCE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and incorporates by reference the entire disclosure of U.S. Provisional Patent Application No. 61/838,954, filed June 25, 2013. U.S. Patent No. 5,295,397, issued March 22, 1994, U.S. Patent No. 5,461,932, issued October 31, 1995, and U.S. Patent No. 6,681,189, issued January 20, 2004, are incorporated herein by reference.

BACKGROUND

Field of the Invention

[0002] The present application relates generally to flow meters for fluid measurement and more specifically, but not by way of limitation, to multi-phase flow meters utilizing a perforated orifice plate in combination with an impedance measuring device.

History of the Related Art

[0003] There are many applications that require the measurement of multi-phase fluid flow. Measurement of multi-phase flow determines an amount of liquid and gas passing through a flow meter. Such measurement of multi-phase fluid flow is common in many applications including, but not limited to, food processing, paper manufacture, petrochemical production and refining, HVAC, and power production. Petrochemical production, in particular, presents many areas were measurement of multi-phase fluid flow is desired. Gas wells, for example, contain oil, liquid water, and various gases in the produced fluid. It is necessary to have accurate measurement of the mass flow rate of all components.

[0004] Previous devices utilized radioactive materials to measure multi-phase fluid flow. Such previous devices are expensive, difficult to use, and present numerous safety and regulatory concerns in connection with the use of radioactive materials. SUMMARY

[0005] The present invention relates generally to flow meters for fluid measurement and more specifically, but not by way of limitation, to multi-phase flow meters utilizing a perforated orifice plate in combination with an impedance measuring device. In one aspect, the present invention relates to a multi-phase flow meter. The multi-phase flow meter includes a perforated orifice plate disposed between an upstream pipe section and a downstream pipe section. A first electrode and a second electrode are disposed in the downstream pipe section. An impedance-measuring device is electrically coupled to the first electrode and the second electrode. The perforated orifice plate, in combination with the impedance-measuring device, measures a flow rate of at least one of a first component and a second component of a mixture flowing through the upstream pipe section and the downstream pipe section.

[0006] In another aspect, the present invention relates to a method for measuring multi-phase flow. The method includes flowing a mixture through a perforated orifice plate and determining a pressure drop across the perforated orifice plate. An impedance of the mixture downstream of the perforated orifice plate is measured utilizing an impedance-measuring device. The impedance is utilized to calculate a void fraction of a first component and a second component of the mixture. The pressure drop and the impedance are utilized to determine a flow rate of the first component of the mixture and the second component of the mixture.

[0007] In another aspect, the present invention relates to a method for determining properties of a liquid-liquid dispersion. The method includes applying an electrical signal to the liquid-liquid dispersion and measuring at least one of a gain and a phase shift of the electrical signal. A determination of a dispersion type is made responsive to the measuring of the gain or the phase shift. A volume fraction of at least one component of the liquid-liquid dispersion is calculated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings in which: [0009] FIGURE 1 A is an exploded view of a multi-phase flow meter according to an exemplary embodiment;

[00010] FIGURES IB- ID are front plan views of a perforated orifice plate according to exemplary embodiments;

[00011] FIGURE 2 is a circuit diagram of an impedance-measuring device according to an exemplary embodiment;

[00012] FIGURE 3 is a side view of the multi-phase flow meter according to an exemplary embodiment;

[00013] FIGURE 4 is a perspective view of the multi-phase flow meter according to an exemplary embodiment;

[00014] FIGURE 5 is a flow diagram illustrating a process for using the multi-phase flow meter according to an exemplary embodiment;

[00015] FIGURE 6 a circuit diagram of an amplifier circuit according to an exemplary embodiment; and

[00016] FIGURE 7 is a flow diagram of a process for measuring component fractions and flow rates of a liquid-liquid dispersion.

DETAILED DESCRIPTION

[00017] Various embodiments of the present invention will now be described more fully with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[00018] FIGURE 1 is an exploded view of a multi-phase flow meter 100. The multiphase flow meter 100 includes an upstream pipe section 102 coupled to a downstream pipe section 104. A perforated orifice plate 106 is disposed between a downstream flange 108 of the upstream pipe section 102 and an upstream flange 110 of the downstream pipe section 104. As shown in FIGURES IB- ID, multi-phase flow meters utilizing principles of the invention may include perforated orifice plates having openings arranged in a variety of patterns. In other embodiments, the perforated orifice plate 106 could include any configuration of perforations. In a typical embodiment, the perforated orifice plate 106 is slotted; however, in other embodiments, any type of perforated plate could be utilized. An upstream pressure tap 112 is disposed in the downstream flange 108 of the upstream pipe section 102 and a downstream pressure tap 114 is formed in the upstream flange 110 of the downstream pipe section 104. In a typical embodiment, the upstream pressure tap 112 is located approximately 1 inch upstream from the perforated orifice plate 106 and the downstream pressure tap 114 is located

approximately 1 inch downstream from the perforated orifice plate 106. However, in other embodiments, the upstream pressure tap 112 and the downstream pressure tap 114 may be located any appropriate distance from the perforated orifice plate 106. The upstream pressure tap 112 and the downstream pressure tap 114 are pneumatically coupled to a differential pressure transducer (not shown).

[00019] A first sensor assembly 116 is formed in the downstream pipe section 104 and a second sensor assembly 118 is formed in the downstream pipe section 104 opposite the first sensor assembly 116. The first sensor assembly 116 includes a first electrode 120. The first electrode 120 is exposed to an interior of the downstream pipe section 104; however, the first electrode 120 does not impede flow of the mixture flowing within the downstream pipe section 104. The first electrode 120 is disposed within an insulting tube 122 and the first electrode 120 is secured to a first hood 124 by a first nut 126. A first flange 127 is placed over the first hood 124. A first connector 128 is disposed over the first flange 127 and facilitates electrical connection to the first electrode 120. During use, a first wire (not shown) is coupled to the first connector 128 and is electrically coupled to the first electrode 120. In a typical embodiment, the first sensor assembly 116 is located a distance in the range of less than 1 to approximately 15 pipe diameters downstream of the perforated orifice plate 106.

[00020] The second sensor assembly 118 includes a second electrode 130. The second electrode 130 is exposed to an interior of the downstream pipe section 104; however, the second electrode 130 does not impede flow of the mixture flowing within the downstream pipe section 104. The second electrode 130 is disposed within an insulting tube 132 and the second electrode 130 is secured to a second hood 134 by a second nut 136. A second flange 137 is placed over the second hood 134. A second connector 138 is disposed over the first flange 137 and facilitates electrical connection to the second electrode 130. During use, a first wire (not shown) is coupled to the second connector 138 and is electrically coupled to the second electrode 130. In a typical embodiment, the second sensor assembly 118 is located a distance in the range of less than 1 to approximately 15 pipe diameters downstream of the perforated orifice plate 106.

[00021] During use, the first electrode 120 and the second electrode 130 are placed in contact with the mixture moving within the downstream pipe section 104. In a typical embodiment, the first electrode 120 and the second electrode 130 are electrically coupled to an impedance-measuring device 200 (shown in FIGURE 2). In a typical embodiment, an interior surface of the downstream pipe section 104 is lined with an insulating material such as, for example, epoxy.

[00022] FIGURE 2 is a circuit diagram of an impedance-measuring device 200. The impedance-measuring device 200 includes a multi-frequency signal generator 202 that is electrically coupled to a mixture-impedance-equivalent circuit 204 and a buffer 206. The buffer 206 is electrically coupled, in series, to a low-pass filter 210 and a high-pass filter 212. In a typical embodiment, the high-pass filter 212 is electrically coupled to a data- acquisition device (not shown). In a typical embodiment, when measuring gas-volume fraction the multi-frequency signal generator 202 produces electrical signals at frequencies in the range of approximately 50 kHz to approximately 400 kHz. As will be discussed in more detail hereinbelow, when measuring watercut, the signal generator 202 produces electrical signals at frequencies in the rage of approximately 0.2 MHz to approximately 10 MHz. In a typical embodiment, the multi- frequency signal generator enables the impedance-measuring device 200 to work with both conducting and non-conducting fluids.

[00023] The mixture-impedance-equivalent circuit 204 is represented by a mixture capacitance 214 and a mixture resistance 216. The mixture-impedance-equivalent circuit 204 is connected in series with a first resistor 215. The buffer 206 includes a first amplifier 222. In a typical embodiment, the buffer 206 prevents the low-pass filter 210 and the high-pass filter 212 from loading to the mixture-impedance-equivalent circuit 204.

[00024] The low-pass filter 210 includes a second amplifier 224 electrically coupled to a second resistor 226 and a first capacitor 228. The second resistor 226 and the first capacitor 228 are connected to in parallel. In a typical embodiment, the low-pass filter 210 transmits frequencies below a cutoff frequency and attenuates frequencies above the cutoff frequency. The high-pass filter 212 includes a second capacitor 230 connected in series to a third resistor 232 and a third amplifier 234. A fourth resistor 236 is electrically couple to the third amplifier 234. In a typical embodiment, the high-pass filter 212 transmits frequencies above a high-pass cutoff frequency and attenuates frequencies below the high-pass cutoff frequency. In a typical embodiment, the impedance-measuring device 200 determines a fraction of a flow-channel volume that is occupied by each phase of the mixture (commonly referred to as a "volumetric void fraction").

[00025] FIGURE 3 is a side view of the multi-phase flow meter 100 and FIGURE 4 is a perspective view of the multi-phase flow meter 100. A length of the upstream pipe section 102 is in the range of approximately five pipe diameters. In similar fashion, a length of the downstream pipe section 104 is at least approximately 5 pipe diameters. The first sensor assembly 116 and the second sensor assembly 118 are positioned on the downstream pipe section 104 in the range of less than 1 to approximately 15 pipe diameters from the perforated orifice plate 106.

[00026] In a first embodiment, the multi-phase flow meter measures component flow rates of, for example, a liquid-gas mixture. During operation, the perforated orifice plate 106 homogenizes flow of a mixture flowing through the multi-phase flow meter 100. In a typical embodiment, the perforated orifice plate 106 transforms, for example, slug flow, annular flow, and stratified flow into a uniform homogenous flow such as, for example, a uniform mist or a bubbly flow. In a typical embodiment, a response of the perforated orifice plate 106 is dependent only on a density of the mixture. The perforated orifice plate 106, thus, is substantially insensitive to upstream flow disturbances. As a result, the perforated orifice plate 106 requires shorter lengths of pipe both upstream and downstream of the perforated orifice plate 106. Calibration measurements for the perforated orifice plate 106 to total mixture mass flow rate and the impedance measuring device. In a typical embodiment, a calibration equation of the perforated orifice plate 106 is illustrated in Equation 1

Equation 1 : KY

β ² 2Pmixture^P where .RT is a calibration coefficient of the perforated orifice plate 106, ΔΡ is the pressure differential across the perforated orifice plate 106, rh is the total mass flow rate of the mixture, and Pmixture is the density of the mixture. The variable, /?, is defined according to Equation 2

Equation 2: β = ^ ^{per o ations} where A is a cross- sectional area of the pipe and A _per f _oratiom is an open area of the perforations in the perforated orifice plate 106.

[00027] In a typical embodiment, the mixture includes, for example, at least a liquid and a gas; however, in other embodiments, the mixture may include, for example, more than one liquid such as, for example, an oil and water mixture in combination with one or more gases. The differential pressure transducer measures an upstream pressure pi and a downstream pressure /¾ _. The differential pressure transducer then computes a pressure differential (Ap) across the perforated orifice plate 106.

[00028] During operation, the impedance-measuring device passes an electrical current from the first electrode 120, through the mixture in the downstream pipe section 104, to the second electrode 130. The multi-frequency signal generator 202 measures the mixture capacitance 214 and the mixture resistance 216. Variation of a composition of the mixture induces changes in the mixture capacitance 214 and the mixture resistance 216. Such changes result in a voltage variation on a node between the first resistor 215 and the fluid-impedance- equivalent circuit 204. The data-acquisition system measures a phase shift between a measured signal and a generated signal. The phase shift of low-frequency signals is indicative of a volumetric void fraction of conductive components and the phase shift of high-frequency signals is indicative of a volumetric void fraction of non-conductive components. In addition, static pressure and temperature measurements are conducted downstream of the perforated orifice plate 106 approximately at the location of the first electrode 120 and the second electrode 130. The static pressure and temperature are utilized to calculate a density of the gas phase. The static pressure and temperature are also utilized to obtain a calibration equation since the impedance of the mixture is a function of pressure and temperature.

[00029] Based on the measured electrical impedance, the impedance-measuring device is able to determine a volumetric void fraction of mixture components within the downstream pipe section 104. Volumetric void fraction is determined according to the Equation 3

Equation 3: _t = ^Ql

Qtotal where _t is the volumetric void fraction of a component, (¾ is a volumetric flow rate of the component and Q _to tai is the volumetric flow rate of the mixture. Thus, determination of the volumetric void fraction of mixture components facilitates calculation of the mass flow rate and the volumetric flow rate of the mixture components such as, for example, gas, water, and oil.

[00030] The calculation of volumetric void fraction is independent of a mass flow rate of the mixture and is dependent upon physical properties of components of the mixture such as, for example, liquid and gas. The volumetric void fraction, together with the physical properties, are utilized to calculate a density of the mixture according to Equation 4 Equation 4: Pmixture =∑Pi ^i where p _m i _X is, the density of the mixture, ^is the density of a mixture component, and c^is a volumetric void fraction of the mixture component. Thus, in situations where the mixture includes air, water, and oil, the density of the mixture is expressed as

Pmixture ^~ Pwater water ^~ ^ Pair ^ air Poil &oil -

[00031] The density of the mixture is then used to calculate the mass flow rate of the mixture according to Equation 1. In a typical embodiment, the impedance-measuring device 200 utilizes multiple frequencies to determine a volumetric void fraction of each phase contained in the mixture such as, for example, oil, water, and various gases. Given the mixture density and the mixture mass flow rate, the mass flow rate and the volumetric flow rate of the mixture components can be determined. Since the impedance-measuring device responds differently to materials of differing resistivity and permittivity, utilizing multiple frequencies allows characterization of mixture components and volumetric void fractions of each phase. Thus, by utilizing multiple frequencies, the multi-phase flow meter 100 is able to determine a composition and a mass flow rate of the mixture. In a typical embodiment, the multi-phase flow meter 100 is operable over a gas volume fraction in the range of approximately 0% to approximately 100%.

[00032] FIGURE 5 is a flow diagram illustrating a process 500 for using the multiphase flow meter 100. The process 500 starts at step 502. At step 504, the perforated orifice plate 106 is installed between the upstream pipe section 102 and the downstream pipe section 104. At step 506, the upstream pressure tap 112 and the downstream pressure tap 114 are connected to the differential pressure transducer. At step 508, the first electrode 120 and the second electrode 130 are connected to the impedance-measuring device 200. At step 510, a mixture flows through the multi-phase flow meter 100. At step 512, the perforated orifice plate 106 homogenizes a flow of the mixture. At step 514, the differential pressure transducer measures a pressure drop across the perforated orifice plate 106. At step 516, the impedance- measuring device, via the first electrode 120 and the second electrode 130, measures an impedance of the mixture and calculates a density of the mixture and a volumetric void fraction of the mixture. The mixture density is then used to calculate a mass flow rate of the mixture according to Equation 1. The volumetric void fraction is used to calculate a composition of the mixture. The process 500 ends at step 518.

[00033] In an additional embodiment, the multi-phase flow meter 100 measures phase fractions of a liquid-liquid dispersion such as, for example, a water-in-oil dispersion or an oil-in- water dispersion. FIGURE 6 is a circuit diagram of an amplifier circuit 600. Capacitance 602 and resistance 604 represent capacitance and resistance of the dispersion. Capacitance 606 and resistance 608 represent feedback capacitance and feedback resistance. An operational amplifier 610 is disposed as shown. In some embodiments, the impedance-measuring device 200 may be used interchangeably with the circuit 600. In a typical embodiment, a multi-frequency signal is applied, via the signal generator 202, to the circuit. A gain and a phase shift of the signal at each frequency are then measured.

[00034] During operation, the multi-phase flow meter 100 is utilized to determine a water fraction (referred to as "watercut") in various oil-water dispersions. A plurality of signals are provided to the first electrode 120 and the second electrode 130. In a typical embodiment, the plurality of signals comprise, for example, twelve sinusoidal signals having frequencies ranging from approximately 0.2 to approximately 10 MHz. The measured gain and phase shift at each frequency is utilized to characterize the electrical properties of the dispersion in order to determine electrical permittivity and conductivity of the dispersion. With increasing watercut, the gain of the circuit 600 increases. This is due to higher conductivity and permittivity of water relative to oil. To decrease the dependency of the response of the multi-phase flow meter 100 on the degree of dispersion of the oil- water mixture, a parameter termed Gain Subtraction for Different Frequencies ("GSDF") is calculated according to equation 5.

Equation 5: GSDF = ((G _{6 73MHz} — G _3A6MHz — G _237MHZ — G _{0 6MHZ} ))

[00035] After determination of the GSDF, a determination is made of whether the dispersion is an oil-in-water (o/w) dispersion or a water-in-oil (w/o) dispersion. In an oil-in- water dispersion, water is the continuous phase and oil is the dispersed phase. In a water-in-oil dispersion, oil is the continuous phase and water is the dispersed phase. In a first embodiment, the gain of the circuit 600 at, for example, approximately 0.6MHz is compared to a threshold value of, for example, approximately 0.2. If the gain of the circuit 600 at 0.6 MHz is lower than the threshold value, oil is the continuous phase and the dispersion is a water-in-oil dispersion. In this scenario, the watercut is determined via equation 6.

Equation 6 Watercut _w/o = 129.8GSDF ³ - 68A6GSDF ² + 13.63GSDF - 0.449

On the other hand, if the gain of the circuit 600 at 0.6 MHz is greater than the threshold value, water is the continuous phase and the dispersion is an oil-in-water dispersion. In this scenario, the watercut is determined via equation 7.

Equation 7 Watercut _o/w = -11.1GSDF ⁴ + 23.39GSDF ³ - 17.7SGSDF ² + 6.S69GSDF -

0.319

In other embodiments, a phase shift of an electrical signal applied to the mixture is analyzed relative to a threshold value to determine whether the mixture is an oil-in-water (o/w) mixture or a water-in-oil (w/o) mixture. The threshold value of the phase shift is calculated according to equation 8

Equation 8 0 _t/l =—1.53/ + 235.32

Where/is the frequency of the applied electrical signal. If the observed phase shift is greater that the threshold value, the continuous phase is oil and the dispersion is a water-in-oil (w/o) dispersion. If the phase shift is below the threshold value, the continuous phase is water and the dispersion is an oil-in-water (o/w) dispersion.

[00036] After the watercut is calculated a density of the dispersion can be determined according to equation 4. The pressure drop across the perforated orifice plate can be utilized to calculate the mass flow rate in accordance with equation 1 and the component volumetric flow rates can be calculated according to equation 3 as discussed above. Thus, the multi-phase flow meter 100 may be utilized to accurately determine component fractions and flow rates present in liquid-liquid dispersions.

[00037] FIGURE 7 is a flow diagram of a process 700 for measuring component fractions and flow rates present in a liquid-liquid dispersion. The process 700 starts at step 702. At step 704, the perforated orifice plate 106 is installed between the upstream pipe section 102 and the downstream pipe section 104. At step 706, the upstream pressure tap 112 and the downstream pressure tap 114 are connected to the differential pressure transducer. At step 708, the first electrode 120 and the second electrode 130 are connected to the amplifier circuit 600. At step 710, a liquid-liquid dispersion flows through the multi-phase flow meter 100. At step 712, the perforated orifice plate 106 homogenizes a flow of the liquid-liquid dispersion. At step 714, a multi-frequency electrical signal is applied to the liquid-liquid dispersion. At step 716, a gain and a phase shift of the electrical signal are observed for each frequency. At step 718, the dispersion type is determined. At step 720, the watercut is calculated. At step 722, the differential pressure transducer measures a pressure drop across the perforated orifice plate 106. At step 724, a density of the liquid-liquid dispersion is calculated. The density of the liquid- liquid dispersion is then used to calculate a mass flow rate of the liquid-liquid dispersion according to Equation 1. The process 700 ends at step 726.

[00038] Experimental results demonstrate that the multi-phase flow meter 100 is capable of measuring watercut from 0 - 100% with approximately 3% uncertainty. The multiphase flow meter is not affected by dispersion properties or hysteresis effects. In other embodiments, the multi-phase flow meter is utilized to determine the properties of a mixture comprising two or more phases such as, for example, a water phase, and oil phase, and a gas phase.

[00039] Although various embodiments of the method and system of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Specification, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit and scope of the invention as set forth herein. It is intended that the Specification and examples be considered as illustrative only.