GB2354329A

GB2354329A - Flow meter

Info

Publication number: GB2354329A
Application number: GB0015248A
Authority: GB
Inventors: David Sirda Shanks
Original assignee: AXON INSTR Ltd
Current assignee: AXON INSTR Ltd
Priority date: 1999-06-22
Filing date: 2000-06-22
Publication date: 2001-03-21
Anticipated expiration: 2020-06-22
Also published as: GB0015248D0; GB2354329B; GB9914500D0

Abstract

A flow meter 10 can be used to determine the flow rate of fluid passing therethrough using a restriction or choke 18 in the path of the fluid 26. There is also a ratio tool 28 capable of determining the nature and quantities of fluids passing therethrough. The ratio tool 28 can be used with singlephase and multiphase fluids in an oil or gas pipeline. The forces on choke 18 may be measured by strain gauges 20 or a crystal resonator. The tool 28 may have pairs of plates or bars 30,32,34 for measuring resistance and/or capacitance of the fluid. Pressure and temperature may also be measured. Signals may be transmitted to remote electronics.

Description

1, - - 1:, 1 2354329 "Flow Meter" 3 The present invention relates to a

flow meter, and 4 particularly, but not exclusively, to a flow meter 5 for use in the oil and gas industry. The present 6 invention also provides a ratio tool for determining 7 the ratio of two or more different fluids flowing 8 within a pipeline or the like. 9 10 In many downhole operations, and other areas of oil 11 and gas processing and production, it is advantageous 12 to include a flow meter as part of a tubing string, 13 pipeline, conduit or the like. The flow meter allows 14 for measurement of the amount of fluid that passes 15 through the string or the like, and can be used to 16 determine the flow of fluid both into the string (for 17 example when flushing out a borehole or cementing in 18 a liner) or out of the string (for example during the 19 recovery of hydrocarbons from a wel-l.)-. 20 2 1 Conventionally, there are a number of methods of 2 measuring fluid flow rate. For example, there are 3 simple turbine meters that have moving parts. 4 However, the moving parts often reduce the accuracy 5 and sensitivity of the meter to small flow rates, and 6 in addition reduce the expected lifetime of the 7 meter. 8 9 other examples include non- intrusive methods such as 10 electromagnetic meters that only operate in 11 conductive fluids, and ultrasonic meters the use of 12 which is limited in fluids containing part liquid and 13 part gas. A further disadvantage of both 14 electromagnetic and ultrasonic meters is that the 15 electronics required to obtain measurements from 16 these meters tend to be fairly complex. 17 18 According to a first aspect of the present invention 19 there is provided a flow meter comprising a body, a 20 longitudinal bore provided in the body, a choke in 21 fluid communication with the bore, and at least one 22 force sensor for measuring the magnitude of fluid 23 flow. 24 2S The choke is preferably located within the bore. The 26 bore preferably includes an enlarged diameter 27 portion. The choke is typically positioned 28 downstream of the enlarged diameter portion. 29 30 Optionally, the bore may be provided with a 31 separating device to separate fluids entering the 3 1 flow meter. The separating device typically 2 comprises a profiled wall, for example a spiral.

3 4 The choke is typically suspended within the tubular body by the at least one force sensor. The force 6 sensors typically measure the compressive force 7 applied to the choke by the fluid flow, which is 8 typically in an axial direction. Alternatively, or 9 additionally, the force sensors may measure the shear force applied to the choke by the fluid flow, 11 typically at the mounting of the choke. Preferably, 12 three force sensors are provided. In one embodiment, 13 the force sensors are typically equi-spaced around 14 the inner surface of the bore.

16 The force sensors may also measure the compressive 17 and/or shear force applied to the choke by measuring 18 a pressure difference created around the choke by 19 fluid passing from the enlarged diameter portion of the bore to a smaller diameter portion downstream of 21 the enlarged diameter portion. This effect is 22 related to the Venturi effect. Alternatively, the 23 force sensors may measure the compressive and/or 24 shear force by measuring a reaction force applied to the choke by fluid impacting on the choke. The 26 reaction forces are typically measured in the radial 27 and/or axial direction. The force on the choke is 28 typically generated by a combination of the pressure 29 difference created by fluid expansion from the smaller diameter portion to the enlarged diameter 31 portion and the physical impact force of the fluid on 4 1 the choke itself. The total axial force applied to 2 the choke is typically a momentum force that is 3 proportional to the flow of fluid through the choke. 4 Thus, the flow meter measures flow rate through it by 5 measuring the total momentum force applied to the 6 choke using the force sensors and calibrating this 7 f orce to a measure of f luid f low using the f act that 8 the force is proportional to flow rate. 9 10 Typically, the force sensors measure the magnitude of 11 the force of the fluid flow and calibrates this as a 12 measure of flow rate of the fluid. A ratio tool is 13 typically used to determine the nature and/or density 14 of the fluid passing through the flow meter. 15 16 The force sensor preferably comprises a load cell, 17 such as a strain gauge. The strain gauge is 18 typically mounted on a bar or tube. As a further 19 alternative, the force measurement device may 20 comprise a crystal resonator. The crystal resonator 21 is typically used to measure the shear force applied 22 to the choke. 23 24 The measured force is typically an electrical output 25 from the force sensor, such as a voltage. In a 26 simple embodiment, the electrical output is 27 transmitted via a cable, telemetry system or 28 otherwise to a remote electronics module for further 29 processing. 30 1 Alternatively, the voltage is typically converted 2 using an analogue-to-digital convertor and fed into a 3 processor. The processor may be mounted within the 4 body, or remotely. Alternatively, the electrical output may be converted to a frequency and fed to the 6 processor. The processor typically transmits the 7 measurements from the force sensor(s) to a remote 8 electronics package. The remote electronics package 9 is typically remote from the flow meter, or may form part thereof.

11 12 The flow meter is typically located in a pipeline, 13 such as in a downhole hydrocarbon well, a subsea 14 pipeline or wellhead assembly or in any process plant pipework.

16 17 The remote electronics package typically consists of 18 a power supply, a data transmit and receive 19 electronics system, and a processor to collate and read the data transmitted from the downhole or remote 21 system.

22 23 The flow meter typically operates on a two-wire 24 system (ie signal and power composite and a ground return). This makes the flow meter suitable for use 26 in oil and gas downhole environments. In addition, 27 the flow meter may be used with a downhole instrument 28 cable with a single inner mono conductor, the ground 29 return being provided by the cable sheath or the production tubing.

31 6 1 According to a second aspect of the present invention 2 there is provided a ratio tool comprising at least 3 one fluid identifier sensor positioned in a fluid 4 flow, the fluid identifier sensor being used to 5 determine the nature and/or ratio of the fluid(s) in 6 the fluid flow. 7 8 In one embodiment of the present invention, the fluid 9 identifier sensors are located within an inner wall 10 of a pipe through which the fluid flows. Preferably, 11 three circumferentially spaced fluid sensors are 12 used. The fluid identifier sensors typically 13 comprise a pair of plates. Alternatively, the fluid 14 identifier senors may comprise a pair of solid round 15 bars. 16 17 The electrical resistance of the fluid is typically 18 measured using the at least one fluid identifier 19 sensor to determine the nature and/or ratio of the 20 fluid(s). Preferably, the capacitance of the fluid 21 is also used to determine the nature and/or ratio of 22 the fluid (s). The capacitance of the fluid is 23 typically measured using the at least one fluid 24 identifier sensor. 25 26 In another embodiment of a fluid ratio tool, the 27 resistance of the fluid is typically measured using a 28 resistance bridge measure. The voltage produced by 29 the resistance bridge is typically amplified and may 30 either be input to a processor or converted to a 7 1 frequency and transmitted to a remote electronics 2 package. 3 4 Capacitance is typically measured by applying an 5 alternating current (AC) signal to the fluid, for 6 example through any pair of plates, bars or the like. 7 The capacitance across the plates typically forms 8 part of a filter circuit, thus allowing the fluid 9 dielectric properties to be determined. The 10 frequency response of the filter circuit typically 11 changes as the dielectric of the fluid changes, and 12 can be measured by varying the frequency of the AC 13 signal. 14 15 In an alternative embodiment of the ratio tool, the 16 natural electrical oscillation frequency of the fluid 17 is measured. This can be achieved by making the 18 fluid between the plates, bars etc part of an 19 oscillating circuit. The resonant frequency provides 20 a further measurement of the complex impedance of the 21 fluid. The complex impedance and/or the resonant 22 frequency can be calibrated against known fluids or a 23 look-up table used to provide the nature and/or ratio 24 of the fluid(s). The nature and/or ratio of the 25 fluid(s) can be determined from the complex impedance 26 using mathematical analysis. It will be appreciated 27 that the complex impedance gives a measure of the 28 resistance and/or capacitance of the fluid(s) but in 29 a single measurement without having to do two 30 separate tests. Also, the resistance and/or 31 capacitance can be determined individually and 8 1 compared to the complex impedance that can be 2 determined separately. 3 4 The resistance is preferably measured by applying a 5 direct current (DC) signal to one of the fluid 6 identifier sensors, and measuring the signal received 7 at any one (or more) of the fluid identifier sensors. 8 9 In a preferred embodiment of the fluid ratio tool, 10 the tool comprises a tubular body, the fluid 11 sensor(s) being mounted within the body. The fluid 12 sensor(s) are typically equidistantly spaced around 13 an inner circumference of the tubular body to form an 14 array. The sensors typically comprise plates or 15 bars. The sensors are typically supported by annular 16 rings within the inner circumference, and are 17 preferably spaced therefrom wherein fluid can 18 circulate around the sensors. Preferably, the 19 sensors extend substantially the full length of the 20 tubular body. 21 22 In this embodiment, the resistance is preferably 23 measured by applying a direct current (DC) signal to 24 one of the fluid identifier sensors in the array, and 25 measuring the signal received at any one (or more) of 26 the fluid identifier sensors in the array. 27 Preferably, the DC signal is applied to each sensor 28 sequentially, and the signal is measured at each 29 sensor sequentially. Thus, a more reliable 30 measurement of the resistance of the fluid is 31 determined, as the resistance of substantially all of 9 1 the fluid is measured. An average resistance can be 2 determined from the measurements. This provides the 3 advantage that the resistance of the fluid(s) that 4 are flowing in different portions of the pipeline can 5 be determined. 6 7 In this embodiment, the capacitance is preferably 8 measured by applying an alternating current (AC) 9 signal to one of the fluid identifier sensors in the 10 array, and measuring the signal received at any one 11 (or more) of the fluid identifier sensors in the 12 array. Preferably, the AC signal is applied to each 13 sensor sequentially, and the signal is measured at 14 each sensor sequentially. Thus, a more reliable 15 measurement of the capacitance of the fluid is 16 determined, as the capacitance of substantially all 17 of the fluid is measured. An average capacitance can 18 be determined from the measurements. This provides 19 the advantage that the capacitance of the fluid(s) 20 that are flowing in different portions of the 21 pipeline can be determined. In addition, the AC 22 signal frequency can be varied and the complex 23 impedance of the fluid can be determined from this. 24 25 In an alternative embodiment, the complex impedance 26 can be determined by making the f luid part of a f ree 27 oscillating circuit where the frequency of 28 oscillation is measured. Typical oscillating 29 frequencies may be in the range of a few kHz to 50 or 30 60 kHz, but values outside of this range may also 31 apply. The complex impedance and/or the frequency of 1 oscillation can be used to determine the nature 2 and/or ratio of the fluid (s) using mathematical 3 analysis, or can be calibrated against known fluids 4 or a look-up table used to provide the nature and/or 5 ratio of the fluid (s) 6 7 It will be appreciated that the complex impedance 8 gives a measure of the resistance and/or capacitance 9 of the fluid(s) but in a single measurement without 10 having to do two separate tests. Also, the 11 resistance and/or capacitance can be determined 12 individually and compared to the complex impedance 13 that can be determined separately. 14 15 The remote electronics package typically comprises a 1G power supply, a data transmit and receive electronics 17 system, and a processor to collate and read the data 18 transmitted from the downhole or remote system. 19 20 The ratio tool typically operates on a two-wire 21 system (ie signal and power composite and a ground 22 return). This makes the ratio tool suitable for use 23 in oil and gas downhole environments. In addition, 24 the ratio tool may be used with a downhole instrument 25 cable with a single inner mono conductor, the ground 26 return being provided by the cable sheath or the 27 production tubing. 28 29 The ratio tool, when used with the flow meter, 30 typically allows the flow meter to measure the flow 11 1 rate of multi-phase fluids (ie two or more different 2 fluids) 3 4 Embodiments of the present invention shall now be described, by way of example only, with reference to 6 the accompanying drawings, in which:

7 Fig. 1 is a longitudinal cross-section of a 8 first embodiment of a flow meter in accordance 9 with a first aspect of the present invention; Fig. 2 is a schematic plan view of a first 11 embodiment of a ratio tool in accordance with 12 the second aspect of the present invention 13 incorporated into the flow meter of Fig. 1; 14 Fig. 3a is a longitudinal cross-section of an alternative embodiment of a flow meter in 16 accordance with the first aspect of the present 17 invention; 18 Fig. 3b is a horizontal cross-section of the 19 flow meter of Fig. 3a; Fig. 3c is a cross-sectional view of a 21 cantilever load cell sensor for use with the 22 flow meter of Figs 3a and 3b; 23 Fig. 3d is an end elevation of the load cell of 24 Fig. 3c; Fig. 4 illustrates a choke of the f low meter of 26 Figs 3a and 3b suspended using the load cells of 27 Figs 3c and 3d; 28 Fig. 5 is a longitudinal cross-section of a 29 second embodiment of a ratio tool in accordance with a second aspect of the present invention; 12 1 Figs 6a and 6b are horizontal cross-sections of 2 two different fluid identifier sensor arrays for 3 use with the ratio tool of Fig. 5; 4 Fig. 7a is a schematic representation of the f luid ratio tool of Figs 5, Ga and 6b 6 illustrating fluid flowing between sensors; 7 Fig. 7b illustrates the principle of measuring 8 dielectric strength of a fluid using the fluid 9 ratio tool of Figs 5, 6a and 6b; Fig. 7c illustrates the principle of measuring 11 resistance of a fluid using the fluid ratio tool 12 of Figs 5, 6a and 6b; 13 Fig. 7d is a schematic circuit diagram of a 14 circuit that can be used to measure a complex impedance of a fluid using the fluid ratio tool 16 of Figs 5, Ga and 6b; 17 Fig. 8 is a schematic block diagram of an 18 internal electronics module illustrating a basic 19 electronics system for a self-contained flow meter for use with single-phase fluids; 21 Fig. 9 is a schematic block diagram of an 22 electronics module located locally as part of 23 the ratio tool of Figs 5, Ga and 6b; 24 Fig. 10 illustrates an electronics module that can be used where the fluid ratio tool of Figs 26 5, 6a and 6b and flow meter of Figs 3a and 3b 27 are combined in a single unit; 28 Fig. 11 illustrates an electronics module that 29 can be used to control operation of the f low meter of Figs 3a and 3b in remote applications; 13 1 Fig. 12a is a simplified schematic diagram of a 2 multiplexer unit of Fig. 11; 3 Fig. 12b illustrates the transmission of framed 4 frequencies; Fig. 13 is a schematic block diagram of an 6 electronics module for use with a remote fluid 7 ratio tool; 8 Fig. 14 illustrates a combination electronic 9 module for use with the flow meter of Figs 3a and 3b when combined with the fluid ratio tool 11 of Figs 5, 6a and 6b; 12 Fig. 15 is a plot of flow squared against 13 frequency output derived from a prototype flow 14 meter in accordance with the f irst aspect of the present invention; 16 Fig. 16 shows an exemplary oil well installation 17 using the fluid ratio tool of Figs 5, 6a. and 6b 18 combined with the flow meter of Figs 3a and 3b; 19 Fig. 17 shows a portion of subsea pipeline that includes the flow meter of Figs 3a and 3b and 21 the ratio tool of Figs 5, 6a and 6b; and 22 Fig. 18 illustrates a typical surface pipeline 23 with the ratio tool of Figs 5, 6a and 6b and 24 flow meter of Figs 3a and 3b forming a part thereof.

26 27 Referring to the drawings, Fig. 1 shows a flow meter 28 generally designated 10. Flow meter 10 comprises a 29 substantially tubular body 12 that is advantageously provided with attachment means 14u, 141 to facilitate 31 attaching the flow meter 10 in a tubular string, 14 1 pipeline, conduit or the like. It should be noted 2 that fluid direction is upwards in Fig. 1 as denoted 3 by arrow 26. The terms "upper" and "lower" are used 4 in relation to the orientation of the flow meter 10 5 as seen in Fig. 1, but this is arbitrary. The term 6 "downstream" is used in relation to fluid flow 7 through the flow meter 10 in the direction of arrow 8 26 in Fig. 1, but this is arbitrary. 9 10 Tubular body 12 is provided with a longitudinal 11 through bore 16, which in this embodiment includes an 12 enlarged diameter portion 16e. Located downstream of 13 the enlarged diameter portion 16e is a choke 18 that 14 reduces the enlarged diameter portion 16e into the 15 relatively smaller diameter of an upper portion 16u 16 of bore 16. 17 18 Choke 18 is suspended in the enlarged diameter 19 portion 16e by at least one force sensor 20 (two 20 sensors shown in Fig. 1). Preferably, three force 21 sensors 20 are equidistantly spaced around the inner 22 circumference of bore 16. The f orce sensors 20 are 23 typically used to measure the compressive force 24 and/or the shear force applied to the choke 18 by 25 fluid flow through the meter 10, as will be described 26 hereinafter. It should be noted that the shear force 27 applied to the force sensors 20 could be measured 28 when the choke 18 is suspended from force sensors 20 29 displaced radially inwardly, as will be described. 30 1 A tubing pressure sensor 22, located downstream of 2 the choke 18, is in communication with bore 16 so 3 that fluid pressure within the flow meter 10 can be 4 monitored. Optionally, an external pressure sensor 5 24 in communication with pressure outwith the flow 6 meter 10 may be used to monitor the external pressure 7 outwith the flow meter 10. 8 9 Fluid enters the flow meter 10 via a lower portion 161 of the bore 16. The fluid is then expanded into 11 the enlarged portion 16e of the bore 16 that reduces 12 the velocity of the fluid. Enlarged portion 16e may 13 optionally contain a separating device (not shown) 14 for separating the fluids that enter the flow meter 15 10. The separating device may comprise, for example, 16 an inner profiled wall (e.g. a spiral) that separates 17 the fluids. 18 19 Choke 18 directs the fluid back into a relatively 20 smaller diameter portion 16u of the bore 16. The 21 respective diameters of portions 16u, 161 are 22 substantially the same. As the choke 18 is suspended 23 in the enlarged diameter portion 16e by force sensors 24 20, the compressive and/or shear force applied to the choke 18 by fluid acting thereon can be measured.

26 For example, choke 18 may be forced upwards towards 27 the smaller diameter upper portion 16u by the 28 pressure difference created by the reduction in the 29 diameter between the enlarged portion 16e and the upper portion 16u of the bore 16. The force sensors 16 1 20 will measure the compressive and/or shear force 2 applied by the fluid flow to the choke 18. 3 4 Alternatively, the compressive and/or shear force may 5 be measured using the force applied to the choke 18 6 by fluid physically impacting on the surface of the 7 choke 18. The impact of the fluid on the choke 18 8 causes reaction forces to be present on the choke 18 9 in radial and/or axial directions. 10 11 The force sensors 20 measure the magnitude of the 12 force and the direction of the fluid flow and convert 13 this measurement to a measure of the flow rate 14 through the flow meter 10. The flow meter 10 is 15 therefore measuring the flow rate by measuring the 16 forces applied to the choke 18 placed in the flow of 17 the fluid in the pipeline or tubing. It should be 18 noted that the flow rate can only be determined using 19 this force if the fluid density of the fluids passing 20 through the flow meter 10 are known. This shall be 21 discussed hereinafter. 22 23 The force sensors 20 can be, for example, a strain 24 gauge suitably mounted to a bar or tube, or could 25 alternatively be a shear force sensing crystal 26 resonator. The force sensors 20 could also comprise 27 any other type of direct force measurement device. 28 29 The f orce applied to the choke 18 is calculated by an 30 electronic system based on an electrical output from 31 the force sensor 20, typically a voltage. This 17 1 output can then be converted into a frequency and 2 transmitted to the remote electronics (which may be 3 some distance very remote from the flow meter 10), or 4 can be read by a processor (not shown) using an 5 analogue - to- digital (A/D) converter, both of which 6 can be mounted within the flow meter 10 itself, or at 7 the remote electronics. 8 9 Referring now to Figs 3a and 3b there is shown an 10 alternative embodiment of a flow meter 100, wherein 11 Fig. 3a is a longitudinal cross-section through the 12 flow meter 100, and Fig. 3b is a horizontal cross13 section through the flow meter 100. Flow meter 100 14 is substantially the same as flow meter 10, but the 15 force sensors 120 suspend the choke 118 by extending 16 radially inward and thus measure the shear force 17 applied to the choke 118 by fluid flow through the 18 meter 100. 19 20 Meter 100 includes an entry port 130 and an exit port 21 132, the diameters of the entry and exit ports 130, 22 132 typically being the same as the nominal diameter 23 of the pipeline (not shown) of which the flow meter 24 100 forms part. Fluid flows into the entry port 130 25 and out of the exit port 132 in the direction of 26 arrow 134 Ue upward in Fig. 3a). 27 28 As with the previous embodiment, the longitudinal 29 bore 116 of the meter 100 is provided with an 30 enlarged diameter portion 116e. Choke 118 is 31 suspended in the meter 100 by three shear load cells 18 1 120 that are advantageously equi-spaced around an 2 inner circumference of the enlarged diameter portion 3 116e. Optionally, an entry choke 136 can be used to 4 gradually increase the diameter of the bore 116. 5 Optionally also, the flow meter 100 can include a 6 separator 138 to separate the fluids entering the 7 meter 100 if the fluid within the meter 100 comprises 8 two or more different fluids (ie a liquid and a gas 9 for example). The separator 138 may comprise an 10 inner profiled wall, such as a spiral. 11 12 Meter 100 includes a local electronics unit 140 that 13 is electrically coupled to the shear load cells 120 14 and can be electrically coupled to a remote display 15 and processing unit 142 using, for example, a cable 16 144 or other suitable telemetry system. Electronics 17 unit 140 shall be described in more detail 18 hereinafter. 19 20 Referring particularly to Fig. 4, operation of the 21 meter 100 shall be described. It should be noted 22 that the orientation of the meter 100 has been 23 reversed in Fig. 4 so that fluid flow is downwards. 24 Fig. 4 illustrates the choke 118 suspended using the 25 load cells 120. Choke 118 is advantageously spaced 26 from the internal circumference of the body 112 27 whereby hydrostatic pressure around the choke 118 is 28 substantially equalised. The meter 100 operates by 29 measuring the force F applied to the choke 118 in the 30 direction of the flow (illustrated in Fig. 4 as arrow 31 146).The radial or ring force that is additionally 19 1 applied to the choke 118 is typically cancelled by 2 the choke 118 itself. This is because the choke 118 3 is typically of solid steel and generally cannot 4 expand in a radial direction. 5 6 The load cells 120 are advantageously designed to 7 provide shear force measurement with minimal pressure 8 effect and minimal temperature effect on the 9 operation of the meter 100. 10 11 The restriction to fluid flow that any orifice 12 presents may be analysed using a number of different 13 techniques. In this particular embodiment, the 14 orif ice (ie the choke 118) is given a fluid is resistance property defined as a "Lohm"; 1 Lohm will 16 permit a f low of 100 gallons of water per minute 17 (gal/min) with a pressure drop of 2S pounds per 18 square inch (psi) at a temperature of 80' Fahrenheit. 19 20 The f orce F on the choke 118 may be calculated by the 21 momentum Lohm law using the equation 22 23 F = (S12 L)/400 Equation 1 24 where 26 1 is the flow in gallons per minute through the 27 meter 100; 28 S is the specific gravity of the fluid flowing 29 through the meter 100; 1 L is the choke property in Lohms, defined as the 2 resistance of the reduction of the pipe 3 diameter; and 4 F is the force generated on the choke 118 in pounds (lbs).

6 7 It should be noted from Equation 1 above that the 8 force F generated on the choke 118 is proportional to 9 the square of the flow rate (ie 12) 11 The choke property L can be calculated using 12 2 13 L= 0.76/d 14 where 16 17 d is the diameter of the orifice.

18 19 The meter 100 measures the force F using the load cells 120 by which the choke 118 is suspended. Thus, 21 if the specific gravity of the fluid S is known (or 22 can be determined) then the flow rate I in gallons 23 per minute can be calculated by rearranging equation 24 1 above to make I the subject of the equation, which gives 26 27 1 = WOOF/SL) - Equation 2 28 29 Referring to Figs 3c and 3d, there is shown a schematic representation of a load cell 120.Load 31 cell120 includes an outer housing 122, which 21 1 typically comprises a mounting portion 122m. and shear 2 housing 122s. The mounting portion 122m and shear 3 housing 122s are separated by a reduced diameter 4 portion 122r, which typically comprises an annular 5 slot or notch for example. When pressure is applied 6 to the shear portion 122s, the load cell 120 flexes 7 at the reduced diameter portion 122r. 8 9 The mounting portion 122m. is typically provided with 10 an external screw thread, wherein the mounting 11 portion 122m is threadedly engaged with the outer 12 housing 112 of the flow meter 100, and the shear 13 portion 122s engages the choke 118 (as shown in more 14 detail in Fig. 4) is 16 A cantilever load cell 124 is attached to the 17 mounting portion 122m using any conventional means, 18 and is advantageously attached using means that 19 facilitates rotational adjustment of the cantilever 20 load cell 124, as this requires to be correctly 21 aligned in the direction of movement of the choke 118 22 (as shown in more detail in Fig.4). The cantilever 23 load cell 124 can be provided with adjustment means 24 126 that can be used to finely adjust the position of 25 the load cell 124 in relation to the choke 118 as is 26 known in the art. 27 28 The cantilever load cell 124 is typically provided 29 with a plurality of linear movement strain gauges 30 (not shown) that are used to measure the deflection 31 of the shear portion 122s due to the impact of fluid 22 1 on the choke 118. The readings from the strain 2 gauges are typically summed to give an over-all or 3 average value of the deflection. With the cantilever 4 arrangement of the load cell 124, only deflection of 5 the shear portion 122s is measured; there is no hoop 6 stress, as stresses caused by hydrostatic pressure or 7 expansion are distributed evenly. 8 9 Where the fluid flowing through the meter 10, 100 is 10 a single-phase fluid Ue a fluid that consists of 11 only one f luid as opposed to a mixture of two or more 12 f luids) then pressure and temperature sensors, which 13 form part of an internal electronics module146 (Fig. 14 3a) can be used to determine the density of a known 15 fluid. 16 17 However, if the fluid within the pipeline in which 18 the meter 10, 100 is attached comprises a mixture of 19 more than one fluid, then both the relative 20 quantities of each fluid, and the pressure and 21 temperature of the or each fluid must be determined 22 to determine the average density (or specific gravity 23 S) of the fluid passing through the flow meter 10, 24 100. 25 26 Referring to Figs 1 and 2, there is shown a f irst 27 embodiment of a ratio tool 28 that enables the fluid 28 density of a fluid to be determined, the ratio tool 29 28 preferably being incorporated into and thus 30 forming part of the flow meter 10. The ratio tool 28 31 typically comprises an array of fluid identifier I 23 1 sensors. Ratio tool 28 comprises at least one, and 2 preferably three, pairs of diametrically opposed 3 plates 30 or alternatively bars. The array shown in 4 Fig. 2 comprises three pairs of plates 30, 32, 34 5 that ar-e equidistantly spaced around the inner 6 circumference of the upper portion 16u of the 7 internal bore 16 of the flow meter 10 (Fig. 1) 8 9 The nature of the fluid flowing through the flow 10 meter 10 can be determined by measuring the 11 resistance of the fluid between any pair of plates 12 30, 32, 34. In addition, each pair of plates 30, 32, 13 34 may be used to measure the capacitance of the 14 fluid. The resistance and capacitance measurements 15 that are obtained using the pairs of plates 30, 32, 16 34 give a series of measurements that can be 17 individually used to determine the nature of single18 phase fluids. Collectively, the resistance and 19 capacitance measurements obtained using an array of 20 sensors can be used to determine the nature of multi21 phase fluids across the area of the flowing pipeline, 22 as will be described. 23 24 The resistance of the fluid flow can be determined 25 using a direct resistance bridge measurement means 26 (not shown), the output of which is typically 27 amplified to produce a voltage. This voltage can 28 either be read by a processor (not shown) located 29 within the flow meter 10 (using an analogue-to30 digital (A/D) convertor) or can be converted to a 31 frequency and transmitted to a remote electronics, 24 1 package (not shown) The remote electronics package 2 typically comprises a power supply, data transmit and 3 receive electronics, and a processor to collate and 4 read the data transmitted from the downhole or remote 5 system. 6 7 The capacitance of the fluid can be determined by 8 applying an alternating current (AC) electrical 9 signal between any pair of plates 30, 32, 34 and 10 using the capacitance between the plates 30, 32, 34 11 as part of a filter circuit (not shown). The filter 12 circuit can then be fine-tuned to determine the fluid 13 dielectric properties. In particular, the filter 14 circuit will change its frequency behaviour as the 15 dielectric of the fluid passing between the pairs of 16 plates 30, 32, 34 changes. It should be noted that 17 the ratio tool 28 does not give the dielectric 18 properties directly but can be calibrated using 19 reference fluids, for example using a look-up table 20 or the like. 21 22 In addition, if the frequency of the AC electrical 23 signal is varied (e.g. by scanning the frequency), a 24 measure of the complex impedance of the fluid(s) can 25 be obtained from the frequency response of the filter 26 circuit. The complex impedance and/or the frequency 27 of oscillation can be used to determine the nature 28 and/or ratio of the fluid(s) using mathematical 29 analysis, or can be calibrated against known fluids 30 or a look-up table used to provide the nature and/or 31 ratio of the fluid (s).

1 2 Additionally, or alternatively, the complex impedance 3 of the fluid can be determined by measuring the free 4 oscillating frequency of an oscillating circuit in which the fluid forms a part. Referring to Fig. 7d, 6 there is shown a schematic circuit diagram of an 7 oscillating circuit, generally designated 260. PROBE 8 1 and PROBE 2 in circuit 260 may be any one or more 9 of the pairs of plates 30, 32, 34. The fluid acts as 10 a resistor and/or capacitor element in the 11 oscillating circuit 260. In use, the fluid thus 12 forms part of the oscillating circuit and has a 13 complex impedance between the PROBE 1 and PROBE 2 14 contacts that effectively forms part of the 15 oscillating circuit 260. The fluid creates an 16 oscillating or resonant frequency that is related to 17 the complex impedance of the fluid. The output of 18 the circuit is a resonant frequency of the 19 oscillating circuit 260 that changes as the complex 20 impedance of the fluid changes. Typical oscillating 21 frequencies may be in the range of a few kHz to 50 or 22 60 kHz. 23 24 Since the values of the other components in the 25 circuit 260 are known, the complex impedance of the 26 fluid can be determined using circuit analysis.

27 Additionally, the values of the components can be 28 varied (e.g. under computer control) to allow the 29 oscillating circuit to be more sensitive in different 30 types of fluids. 31 26 1 The nature and/or ratio of the fluids can be 2 determined using the resonant frequency and/or the 3 complex impedance of the fluid. The resonant 4 frequency and/or the complex impedance can be used by 5 calibrating either or both of these against a known 6 fluid, or by using a look-up table, to give an 7 indication of the nature and/or ratio of the f luids. 8 Alternatively, the nature and/or ratio can be 9 determined by mathematically analysing the complex 10 impedance. 11 12 It will be appreciated that the complex impedance 13 gives a measure of the resistance and/or capacitance 14 of the f luid (s) but in a single measurement without 15 having to do two separate tests. Also, the 16 resistance and/or capacitance can be determined 17 individually and compared to the complex impedance 18 that can be determined separately. 19 20 The ratio tool 28 may operate on a two-wire system, 21 wherein the two wires comprise a composite signal and 22 power wire, and a ground return. This makes the 23 ratio tool 28 suitable for use in an oilfield 24 downhole environment and allows use with a downhole 25 instrument cable that has a single inner mono 26 conductor wire, the ground return system being 27 provided by the cable sheath or the production tubing 28 itself, for example. 29 30 Fig. 5 shows a second embodiment of a ratio tool 200, 31 and Figs 6a and 6b are cross-sectional views of two

27 1 different fluid identifier sensor arrays for use with 2 the ratio tool of Fig. 5. 3 4 Referring to Figs 5, 6a and 6b, ratio tool 200 5 includes a body 202 that is provided with an internal 6 through-bore 204. Bore 204 includes an enlarged 7 diameter portion 204e that extends substantially the 8 full longitudinal length of the ratio tool 200. it 9 should be noted that the length of the enlarged 10 diameter portion 204e could be varied within the 11 scope of the invention. 12 13 The ratio tool 200 includes an entry port 206 and an 14 exit port 208, wherein fluid flows from the entry 15 port 206 to the exit port 208 in the direction of 16 arrow 210 (ie downwards in Fig.5). The diameter of 17 the internal bore 204 at or near the entry and exit 18 ports 206, 208 is substantially the same as the 19 diameter of the pipeline in which the ratio tool 200 20 is mounted. The ratio tool 200 is typically provided 21 with means (not shown but can be any conventional 22 means such as screw threads, a pin and/or box 23 connection or the like) to attach it to a pipeline 24 string (not shown,). 25 26 An array of sensors 212 from two to N in number are 27 retained in the enlarged diameter portion 204e by a 28 plurality of ring retainers 214 spaced along the 29 longitudinal length of the sensors 212. Referring to 30 Figs 6a and 6b, the sensors 212 may comprise a 31 plurality of bars 212b (Fig. 6a) or plates 212p(Fig.

28 1 Gb) Each sensor 212 is electrically coupled to an 2 electronics module 216 using a pressure tight 3 electrical feed through 218 (Fig. 5). It should be 4 noted that each sensor 212 is provided with a separate electrical feed through 218, although this 6 is not essential.

7 8 The electronics module 216 can preferably 9 read any combination of the sensors 212 in the array as pairs or groups of pairs.

11 12 As shown in Fig. 7a, in a simple embodiment of the 13 ratio tool 200, only one pair of sensors 212 (ie two) 14 would be used. Fig. 7a. illustrates a horizontal cross-section and a vertical cross-section through a 16 ratio tool illustrating two sensors 212. The shaded 17 area 230 indicates the area of influence on the 18 measurement that the fluid presents to the sensors 19 212. However, the accuracy and reliability of the identifier 200 increases as the number of sensors 212 21 increases, particularly when the sensors 212 are 22 being sequentially scanned as will be described. The 23 total number of sensors 212 in the ratio tool 200 can 24 be any number N, depending upon the physical restriction of the diameter of the pipelines and/or 26 the tool 200. A large number of sensors 212 provide 27 a scanning array with greater versatility and 28 improved accuracy. 29 30 The ratio tool 200 can operate in one of three 31 distinct modes, and typically performs two separate 29 1 measurements on the fluid passing the sensors 212.

2 Referring to Fig. 7b, the ratio tool 200 can be used 3 to measure the dielectric strength of the fluid by 4 applying an AC electrical signal generated by an AC source 240 (and optionally through an amplifier 242) 6 to one of the sensors 212f (which can be either bar 7 212b or plate 212p or any other suitable sensor 8 configuration) The electrical signal detected at 9 any one of the other sensors 212s in the array is amplified by a first stage amplifier 244, passed 11 through a full bridge instrument peak detector 246, 12 and amplified again in a second stage amplifier 248.

13 Note that any two opposed sensors 212f, 212s in the 14 array form a fluid capacitor Cf. The amplitude of the received signal (ie a voltage) is proportional to 16 the dielectric strength of the fluid capacitor Cf and 17 thus in insulating fluids is a measure of the 18 dielectric strength of the fluid. In conductive 19 fluids, this measurement is less accurate but generally gives high amplitude, and in general higher 21 than that obtained with a good insulating fluid.

22 23 It will be appreciated that applying an AC signal to 24 a first sensor 212f and measuring the signal received at a second sensor 212 is limited in that the signal 26 will only be affected by fluid that substantially 27 surrounds the two sensors 212 (illustrated by shaded 28 areas 230 in Fig. 7a). However, to provide a 29 collection of measurements that collectively give better statistical results, and are capable of 31 measuring separated flow regimes, the array of 1 sensors 212 can be scanned by using each sensor 212 2 sequentially as a signal source and measuring the 3 amplitude from all the other sensors 212 4 sequentially. Scanning of the sensors 212 in the 5 array is typically controlled by a local processor 6 as will be described. In addition to this sequential 7 scanning of the sensors 212 using an AC waveform of 8 fixed amplitude and/or frequency, the frequency 9 and/or amplitude of the source AC signal fed into the 10 fluid can be varied. This allows for a more accurate 11 reading where the amplitude and/or frequency of the 12 measured signal is too low to give accurate 13 measurements. In addition, when performing the 14 capacitance tests, the frequency can be varied over a 15 large range, and the measured capacitance plotted 16 against frequency. This allows the Q point of the 17 tuned filter (which may optionally include an 18 inductor to form a filter circuit) to be identified, 19 giving the average and most accurate capacitance of 20 the fluid flowing within the pipeline, conduit or the 21 like. 22 23 The sequential scanning of the sensors 212 is 24 typically used to establish fluid properties in 25 fluids where there is more than one fluid present (eg 26 a multiphase fluid having a liquid and a gas), and 27 they are flowing in separated zones within the 28 pipeline. 29 30 A second measurement that can be performed by the 31 ratio tool 200 is a fluid resistance measurement.

31 1 Referring to Fig. 7c, there is shown a schematic 2 representation of an electrical circuit that is 3 formed when measuring the resistance of the fluid.

4 In a similar manner to the capacitance measurement described above, a DC voltage is applied to a first 6 sensor 212f in the array, and the signal at a second 7 sensor 212s or to the body 202 of the ratio tool 200 8 is measured. In Fig. 7c, the resistance of the fluid 9 is represented as resistance Rf, which is the resistance of the fluid between the two sensors 212f, 11 212s. Two discrete resistors 250 and 252 are used 12 outwith the sensors 212f, 212s to provide a gain 13 setting in a known manner. The DC voltage is applied 14 to resistor 250 through the first sensor 212f. The signal passes through the fluid (ie resistance Rf) 16 and resistor 252 to ground (through sensor 212s).

17 Resistors 250, 252 may be the electrial resistances 18 of the sensors 212f, 212s. Alternatively, resistor 19 252 may comprise the resistance of the casing 202 of 20 the tool 200 if the casing 202 is used as an 21 electrical ground. 22 23 The DC voltage across the fluid resistance Rf is 24 measured, typically via an amplifier and filter 25 circuit 254, and a final gain and offset amplifier 26 256. The output voltage measured is proportional to 27 the resistance of the fluid Rf. 28 29 Thus, the electrical resistance Rf of the fluid 30 within the ratio tool 200 (and thus the pipeline) can 31 be measured.The local processor (not shown) within 32 1 the ratio tool 200 is used to scan the sensors 212 in 2 a manner similar to the capacitance measurements, to 3 provide a collection of measurements to give better 4 statistical results, and measure separated flow 5 regimes. 6 7 The electronics module 216 typically has the 8 capability to alter the resistance range of the 9 measurement from, for example, several megohms to a 10 few hundred ohms to facilitate measurement of a wide 11 range of fluid conditions. Altering of the 12 resistance range is typically automatic under the 13 control of the local processor to suit the measured 14 resistance. 15 16 The auto scaling or ranging is typically performed by 17 applying the highest resistance range to the 18 measuring channel. If a low resistance or off-scale 19 Ue 1000-.) reading is obtained then the range is 20 reduced until the reading becomes zero Ue lowest 21 scale reading or 0'1). The midpoint between the 100% 22 and 0% reading is then selected as a basis for the 23 range for the measurement setting. As the ratio tool 24 200, is processor based it is possible to have two way communication between a display and processing 26 unit positioned remotely from the ratio tool 200, and 27 possibly could use the display and processing unit 28 142 of the flow meter 100 (Fig. 3a) and the local 29 processor within the ratio tool 200. The local processor can thus receive instructions from the 31 display and processing unit and may be instructed, 33 1 for example, to carry out a calibration scan where 2 the setting of gain on all active sensor combinations 3 are scanned for correct gain settings. 4 5 A third measurement that can be performed using the 6 ratio tool 200 is to measure the complex impedance of 7 the fluid. As described above with reference to Fig. 8 7d, the fluid forms part of an oscillating circuit 9 260 that is used to provide a measure of the complex 10 impedance of the fluid. The nature and/or ratio of 11 the fluid(s) can be determined from the complex 12 impedance using mathematical analysis. 13 Alternatively, or additionally, the complex impedance 14 can then be calibrated against a known fluid, or 15 compared to a look-up table to identify the nature 16 and/or ratio of the fluids. 17 18 It will be appreciated that the complex impedance 19 gives a measure of the resistance and/or capacitance 20 of the fluid(s) but in a single measurement without 21 having to do two separate tests. Also, the 22 resistance and/or capacitance can be determined 23 individually and compared to the complex impedance 24 that can be determined separately. 25 26 Fig. 8 is a schematic block diagram of the internal 27 electronics module 140 of the flow meter 100 (Figs. 28 3a and 3b) that illustrates an example of an 29 electronics system for a self-contained flow meter 30 100 in single-phase fluids. 31 34 The electronics module 140 comprises a power supply 300 that provides local power to the electronics system, typically 12v DC and 5V DC for logic. A 4 local processor 302 provides control over the operation of the flow meter 100, and can be used to 6 perform the calculations as detailed above.

7 Processor 302 optionally drives a display unit 304 8 for visual display of flow readings and any other 9 relevant data, the display unit 304 typically being remote from the flow meter 100 and electrically 11 coupled thereto using a wire, cable or other 12 telemetry system. The processor 302 includes a 13 serial interface 308 for two-way communication 14 between the local processor 302 and a remote station.

is This facilitates remote operation and monitoring of 16 the flow meter 100.

17 18 Data readings from the shear load cells 120 of flow 19 meter 100 are acquired by an analogue-to-digital (A/D) convertor 310, the output of which is fed into 21 the processor 302. The three shear load cells 120 22 are schematically shown as one unit 312 as the 23 outputs of these can be connected together in 24 parallel or can be fed into three separate amplifier units (not shown). The output from the load cell 26 unit 312 is fed into a filter and amplifier stage 314 27 that has a voltage output. The voltage output from 28 the amplifier stage 314 can optionally be converted 29 into a frequency by a voltage - to- frequency convertor 316 and fed into the A/D convertor 310, or can be 31 directly fed into the convertor 310.

2 In addition, a pressure sensor 318 and a fluid 3 temperature sensor 320 are used to measure the 4 pressure and temperature within the flow meter 100. 5 The pressure and temperature sensors 318, 320 may be 6 combined into a single sensor body, but the signals 7 are typically measured through two separate data 8 channels. Each data channel includes a filter and 9 amplifier unit 322, 324 and optionally, a voltage-to10 frequency convertor 326, 328, similar to the channel 11 for the load cell unit 312. 12 13 The load cell sensors 120 and the pressure and 14 temperature sensors 318, 320 preferably have their 15 output signals amplified and filtered to remove 16 substantially all background noise and interference 17 in units 314, 322 and 324, respectively. A DC 18 voltage that is generated by the sensors 312, 318, 19 320 can be fed directly into the A/D convertor 310, 20 and can thus be read by the processor 302. 21 22 If higher resolution is required then either a high 23 resolution A/D convertor can be used, or the voltage 24 signals can be converted to a frequency in a voltage25 to-frequency converter 316, 326, 328, and fed into a 26 high frequency reciprocal counter, which may be 27 included as part of the A/D convertor 310 or as a 28 separate unit in place of, or in addition to, the 29 convertor 310. 30

36 1 It will be appreciated that the fluid ratio tool 200 may be included as part of the flow meter 10, 100 as shown in Figs 1 and 2, or can form a separate tool 200 that is used in conjunction with flow meter 10, 5 or can be used independently thereof. Fig. 9 is a 6 schematic block diagram of the electronics 216 7 located locally as part of the ratio tool 200 (Fig. 8 5), the diagram showing the electronics required for 9 the fluid ratio tool 200 independent of a flow meter 10, 100.

11 12 Referring to Fig. 9, the electronics module 216 13 (forming part of the ratio tool 200 of Fig. 5) 14 includes a multiplexer array 350. The inputs to the multiplexer array 350 are each electrically coupled 16 to one of a plurality of sensors 212, which allows a 17 local processor 352 to direct signals to or receive 18 signals from any of the plurality of sensors 212.

19 Module 216 further includes a frequency driver 354 21 that is used to generate the AC signal required to 22 perform the capacitance test described above. The 23 output from the frequency driver 354 may be 24 multiplexed (using array 350) to any of the sensors 212. The frequency driver 354 can also be used to 26 provide the DC voltage required to perform the 27 resistance test described above. Alternatively, the 28 DC voltage may be derived from a local power supply 29 366, optionally through a suitably rated voltage regulator.

31 37 1 Two amplifier and filter units 356, 358 are provided.

2 Unit 356 is electrically coupled to the multiplexer 3 array 350 and can be used to provide either a direct 4 voltage signal to an A/D convertor 360, or to transform the voltage signal to a frequency that is 6 then fed to a counter (in place of or in addition to 7 the A/D convertor 360) for the dielectric 8 measurement. Similarly, unit 358 is coupled to the 9 multiplexer array 350 and can be used to provide either a direct voltage signal to the A/D convertor 11 360, or to transform the voltage signal to a 12 frequency that is then fed to the counter (in place 13 of or in addition to the A/D convertor 360) for the 14 resistance measurements.

is 16 The frequency driver 354 that injects an AC signal 17 into any of the sensors 212 generates an AC drive 18 waveform whose frequency is determined by a drive 19 signal generated by the local processor 352.

21 The electronics module 216 can also be used to 22 determine the complex impedance of the fluid to 23 provide an indication of the nature and/or ratio of 24 the fluid. An oscillating circuit 368 can be used, similar to circuit 260 in Fig. 7d. In this 26 embodiment, any of the sensors 212 can be used as 27 PROBE I and PROBE 2 of Fig. 7d. The multiplexer 3SO 28 can be used to sequentially scan each of the sensors 29 212 so that each sensor 212 can be used as PROBE 1 and PROBE 2. The complex impedance of the fluid 31 between each sensor pair forms part of the 38 1 oscillating circuit 368. The fluid between the 2 sensors 212 creates an oscillating or resonant 3 frequency that is related to the complex impedance of 4 the fluid. The output of circuit 368 is a resonant 5 frequency that changes as the complex impedance of 6 the fluid changes. The resonant frequency is output 7 to the A/D convertor 360, the output of which can 8 subsequently be read by the processor 352. 9 10 The processor 352 can then analyse the resonant 11 frequency and/or the complex impedance by calibrating 12 the value of these against those of known fluid, or 13 by the use of a look-up table to determine the nature 14 and/or ratio of the fluids. The nature and/or ratio 15 of the fluid(s) can be determined from the complex 16 impedance using mathematical analysis. 17 18 The values of the components in the oscillating 19 circuit 368 can be varied by the processor 352 under 20 computer control, thus allowing the circuit 368 to be 21 changed to be more or less sensitive. Also, as the 22 values are known, the complex impedance of the fluid 23 can be determined by circuit analysis, typically 24 performed by the processor 352. 25 26 The electronics module 216 allows the local processor 27 352 to read the sensor array 212 and measure any or 28 all the sensor combinations. 29 30 Data output from the ratio tool 200 is typically an 31 array of bar graph modules or data that can be 39 1 transmitted to a remote computer, typically via a serial interface 364, where software can generate a variety of graphical representations of the data output, or can display the numerical values or a 5 combination thereof 6 7 The processor 3S2 may optionally be coupled to a 8 display unit 362 for displaying the resistance and 9 capacitance measurements described above, in addition 10 to the calculated fluid ratio. The results may be in 11 the form of graphical representations as described 12 above. It should be noted that the processor 3S2 may 13 be directly coupled to the display unit 362, or may 14 be coupled via a telemetry system or the like. 15 16 The local processor 352 may also be programmed to 17 produce a numerical display of fluid ratio in simple 18 fluid regimes, or where graphical data is not 19 required. For remote operation of the tool 200, the 20 processor 352 is provided with the serial interface 21 364 that allows the processor to communicate with a 22 remote host station (not shown) 23 24 The electronics module 216 also includes the local 25 power supply 366 that provides local power to the 26 electronics systems within module 216, typically 12v 27 DC and 5V DC for logic. 28 29 Fig. 10 illustrates an electronics module 400 that 30 can be used where the fluid ratio tool 200 and flow 31 meter 10, 100 are combined either in a single unit or 1 two units operating together. Electronics module 400 2 is a combination of module 140 (Fig. 8) and module 3 216 (Fig. 9). The components and operation of module 4 400 are substantially the same as that of modules 5 140, 216. It should be noted that the A/D 6 convertors/counters 310, 369, local processors 302, 7 352, display units 304, 362, serial interfaces 308, 8 364 and local power supplies 300, 366 do not require 9 to be duplicated, and only one set of these 10 components is shown in Fig. 10. 11 12 Fig. 11 illustrates an electronics module 500 that 13 can be used to control operation of the flow meter 14 10, 100, wherein the meter 10, 100 is located 15 remotely at some distance from the main display and 16 power supply electronics, such as in a subsea or 17 downhole oil well installation. Electronics module 18 500 includes surface electronics 500s that may be 19 positioned, for example, at the surface, and remote 20 electronics 500r that may be located, for example, 21 downhole. The surface and remote electronics 500s, 22 SOOr typically communicate via a cable 510 or a 23 suitable telemetry system. 24 25 Surface electronics 500s includes a power supply 502 26 that provides local power to the surface electronics 27 500s (located, for example, at the surface), and the 28 remote electronics 500r includes a power supply 504 29 to power the remote electronics 500r which may be 30 located, for example, downhole as part of the flow 31 meter 10, 100 or ratio tool 200.Power supplies 502, 41 1 504 are typically 12v DC and 5V for logic, and 24 2 volts for the remote system. Power supply 502 3 generates a DC power supply that is transmitted 4 (through a current limiter 503) to the main power 5 supply 504 for the remote electronics 500r where it 6 can be filtered and regulated to provide local power 7 supplies for the remote electronics 500r. A local 8 processor 506 is used to perform the resistance and 9 capacitance calculations as detailed above and can be 10 used to drive a display unit (not shown) for visual 11 representation of flow readings as well as a serial 12 data interface 508. The display unit is typically 13 located at the surface where an operator of the 14 system can monitor the values of fluid flow rate. 15 16 The processor 506 in the surface electronics 500s 17 acquires readings from the remote electronics 5OOr by 18 reading framed frequencies generated by the remote 19 electronics 500r superimposed on the power supply 20 waveform generated by the surface electronics 500s, 21 which is used as a power supply to the remote 22 electronics 500r. The frequencies are current 23 modulated onto the power waveform and this modulation 24 is received via the power line 510 by an amplifier 25 and filter unit 512 in the surface electronics 500s. 26 The frequency signal generated by the remote 27 electronics 500r is amplified and filtered to remove 28 substantially all of the background interference and 29 noise that has been added to the signal. 30

42 1 It should be noted that the remote electronics SOOr 2 in this embodiment does not include a local 3 processor. This avoids the common problems 4 associated with operating processors in hazardous 5 conditionswherein pressure and temperature can 6 adversely affect their operation. 7 8 The electronics module 500 typically operates on a 9 two-wire system that can be, for example, a 10 mono-conductor cable. 11 12 The three shear load cells 120 are shown as one unit 13 514 in Fig. 11 as the outputs of the cells 120 can be 14 connected together in parallel or fed into three 15 separate amplifier units. A pressure sensor 516 and 16 a fluid temperature sensor 518 are also provided. 17 The pressure and temperature sensors 516, 518 may be 18 combined into a single sensor body, but typically 19 require to be measured through two separate data 20 channels. 21 22 Each of the data channels from unit 514, pressure 23 sensor 516 and temperature sensor 518 include an 24 amplifier and filtering unit 520, 522 and 524 25 respectively. 26 27 In one embodiment, the voltage signals from the 28 amplifier and filtering units 520, 522, 524 are fed 29 into respective voltage- to- frequency converters 526, 30 528, 530 and then into a multiplexer unit 532 which 31 transmits the three frequencies in a repeating 43 1 sequence with a synchronising pulse between each 2 complete three channel transmission as illustrated in 3 Figs 12a and 12b.

4 Referring to Figs 12a and 12b, Fig. 12a is a 6 simplified diagram of the multiplexer unit 532. Unit 7 532 includes a free running four-way logic switch 550 8 that is used to, direct one of three frequencies F]., 9 F2 and F3 or a 0 volt signal to an output 0. The outputs from the load cell unit 514, the pressure 11 sensor 516 and the temperature sensor 518 are 12 assigned a particular frequency F1, F2 or F3. As 13 shown in Fig. 12b, these frequencies F1, F2, F3 are 14 multiplexed using switch 550 into a continuous stream. The stream comprises N cycles of F1, 16 followed by N cycles of F2, followed by N cycles of 17 F3, after which there is a synchronisation pulse that 18 comprises a O-volt (or no frequency signal) for N 19 cycles of Fl. The number of cycles N is chosen to suit the particular application.

21 22 The number of cycles N is typically chosen by taking 23 one of the frequencies, say F1, and selecting a 24 number of cycles of frequency F, that gives a reliable transmission.

26 27 Referring back to Fig. 11, the multiplexed signal (ie 28 the continuous stream in Fig. 12b) is fed into a line 29 driver 534 that modulates the current on the power supply line 510 with the frequencies F1, F2, F3- This 31 modulation is then detected across a sense resistor 44 1 536 in the surface electronics 500s and is fed into 2 the amplifier and filter unit 512 where it is 3 conditioned and amplified. The conditioned signal is 4 then passed to a counter 538 that is used to 5 ascertain which of the three frequencies F1, F2, F3 6 was sent. The frequencies F1, F2, F3 typically relate 7 to a particular reading from the load cell unit 514 8 and the pressure and temperate sensors 516, 518, 9 wherein the fluid flow through the meter 10, 100 can 10 be calculated using Equation 2 above. 11 12 Fig. 13 is a schematic block diagram of an 13 electronics module 600 for use with a remote fluid 14 ratio tool 200, which in this example is used 15 independently of a flow meter 10, 100. Electronics 16 module 600 includes surface electronics 600s that may 17 be positioned, for example, at the surface, and 18 remote electronics 600r that may be located, for 19 example, downhole. The surface and remote 20 electronics 600s, 600r typically communicate via a 21 cable 614 or a suitable telemetry system. 22 23 The remote electronics 600r comprises a multiplexer 24 array 602, the inputs to the multiplexer array 602 25 being electrically coupled to one of the plurality of 26 sensors 212, that allows a local processor 604 to 27 direct signals to or receive signals from any of the 28 sensors 212. 29 30 A frequency driver 606 that applies an AC signal to 31 any of the sensors 212 (depending upon the setting of 1 the multiplexer 602) generates an AC drive waveform 2 whose frequency and amplitude is determined by drive 3 signals generated by the local processor 604. The 4 frequency driver 606 is also used to provide the DC 5 voltage used to perform the resistance test described 6 above. 7 8 Two amplifier and filter units 608, 610 are provided. 9 Unit 608 is coupled to the multiplexer array 602 and 10 can be used to provide either a direct voltage signal 11 to an A/D convertor 612, or to transform the voltage 12 signal to a frequency that is then fed to a counter 13 612 (in place of, or in addition to, the A/D 14 convertor 612) f or the dielectric measurement. 15 Similarly, unit 610 is coupled to the multiplexer 16 array 602 and can be used to provide either a direct 17 voltage signal to the A/D convertor 612, or to 18 transform the voltage signal to a frequency which is 19 then fed to the counter (in place of, or in addition 20 to, the A/D convertor 612) for the resistance 21 measurements. 22 23 The electronics module 600 includes an oscillator 24 circuit 640 that is similar to circuits 260 and 368. 25 Circuit 640 can be used to determine the complex 26 impedance and/or resonant frequency of the fluid that 27 can be used to determine the nature and/or ratio of 28 the fluids, as previously described. 29 46 1 The electronics module 600 allows the local processor 2 G04 to read the sensor array 212 and measure any or 3 all the sensor combinations. 4 5 The local processor 604 transmits data to the surface G electronics GOOs by modulating the current on a power 7 supply line 614 using a line driver G16. The 8 transmission from the remote electronics 6OOr is 9 detected across a sense resistor 630, and the signal 10 is filtered and amplified in a filter and gain unit 11 632, the signal being fed into a counter G33 wherein 12 the transmission can be reconstructed using the 13 processor 618. The processor 618 is provided with a 14 serial data link 634 for transmission of the results 15 to other remote stations, for example. 16 17 Voltage modulation is used to transmit bits of data 18 to the remote electronics 600r from the surface 19 electronics 600s so that operation of the remote 20 electronics 600r can be controlled remotely. 21 22 The remote processor 604 receives commands from the 23 surface electronics 600s by using a surface processor 24 unit 618 to apply voltage modulation to a power 2S supply 620. Power supply 620 generates a voltage 26 modulated power waveform that is transmitted via a 27 current limiter 622 and the power line 614 to the 28 remote electronics 600r. A local power supply 625 in 29 the remote electronics receives the power waveform 30 and filters and rectifies the waveform to provide 31 local power supplies for the remote electronics 600r.

1 2 The modulated signal generated by the surf ace power 3 supply 620 is decoupled from the power line 614 at 4 decoupling capacitor 624 and is then filtered and amplified in an amplifier and filter unit 626. A 6 comparator 628 allows the power waveform 7 communication to be reconstructed and fed in to the 8 processor 604 at the remote location for subsequent 9 execution.

11 Serial communication is typically in ASCII and can 12 be, for example, in a MODBUS format. It will be 13 appreciated that any serial communication protocol 14 could be used.

is 16 The data output from the tool 200 is typically an 17 array of bar graph modules that can be displayed on a is local or remote display (not shown). Data can also 19 be transmitted to a computer where software generates a variety of graphical and representations of the 21 data output.

22 23 The surface processor 618 can also be programmed to 24 produce a numerical display of the fluid ratio in simple fluid regimes or where graphical data is not 26 required.

27 28 Fig. 14 illustrates a combination electronic module 29 680 that includes the electronic module 500 of the flow meter 10, 100 and the electronic module 600 of 31 the fluid ratio tool 200, wherein the fluid ratio 48 1 tool 200 and the flow meter 10, 100 are used 2 together. 3 4 In Fig. 14, it should be noted that only one surface 5 electronics module 500s (600s) is required. 6 7 In order to determine that the mathematical analysis 8 above (Equations 1 and 2) was applicable to a large 9 orifice with an increase and then sudden decrease in 10 diameter, a prototype flow meter (not shown) was 11 constructed, substantially as shown in Figs 3a and 12 3b, but using linear strain gauges in place of the 13 load cells 120. The meter was then tested using 14 water as the f luid, with the average of a number of is test results being used. A voltage-to- frequency 16 convertor was used to convert the output voltage f rom 17 the strain gauges to frequencies to allow the results 18 to be processed by the processor. 19 20 Fig. 15 shows a plot of the f low squared against the 21 frequency output from the strain gauges using the 22 prototype flow meter. The results of the test were 23 plotted, giving a substantially straight line. A 24 best-fit line was drawn through the points, the line 25 having the equation y = 139.97x - 7E+6. From Fig. 15 26 it is clear that the force of the fluid is 27 proportional to the square of the flow, which 28 confirms that Equation 1 above is applicable. 29 30 A number of applications of the flow meter 10, 100 31 and fluid ratio tool 200 will now be described. For 49 1 the purpose of illustrating applications, the 2 illustrations show a combination of the flow meter 3 10, 100 and the fluid ratio tool 200 in use. It 4 should be noted that the flow meter 10, 100 may be 5 used independently of the fluid ratio tool 200, or 6 vice versa. 7 8 Fig. 16 shows an exemplary oil well installation 700. 9 The oil well 700 includes a wellhead 702 located at 10 the surface, and a production tubing string 704 11 suspended therefrom. The tubing string 704 extends 12 downwardly in a wellbore 706 that is typically cased, 13 and includes a flow meter 100 and a ratio tool 200 14 suspended below the flow meter 100. 15 16 The combination electronics module 680 (Fig. 14) is 17 located between the flow meter 100 and the ratio tool 18 200 and controls the operation of both as previously 19 described. Module 680 is electrically coupled via a 20 permanent instrument cable 708 (or otherwise) to the 21 surface electronics module 500s. A wellhead 22 penetrator 710 is used to facilitate passing of the 23 instrument cable 708 through the wellhead 702 whilst 24 maintaining pressure within the wellbore 706. 25 26 Both the flow meter 100 and ratio tool 200 are 27 mounted in the pipeline or tubing string 704 with all 28 fluid within the tubing string 704 preferably passing 29 through them. The choke 118 of the flow meter 100 30 has a positive direction and thus requires the flow 1 meter 100 to be orientated within the pipeline 704 2 correctly. 3 4 The combined electronics module 680 reads the signals 5 from the array of sensors 212 in the fluid ratio tool 6 200, and also the output form the load cells 120 in 7 the flow meter 100. The connections of the flow 8 meter 100 and fluid ratio tool 200 are configured to 9 suit the pipeline 704. 10 11 A display and processing unit in the surface 12 electronics 500s provides a display of flow rate and 13 the fluid ratio values to an operator of the system. 14 These can be monitored continuously to ascertain the 15 type of fluid being extracted from the wellbore 706 16 and in what quantities. By monitoring the flow rate, 17 the operator may also receive indications of any 18 blockages or other problems within the tubing string 19 704 that may adversely affect the flow rate. 20 21 Fig. 17 shows a portion of subsea pipeline 750 that 22 includes the flow meter 100 and ratio tool 200. The 23 combined electronics unit 680 is encased in a 24 pressure tight housing suitable for the water depth 25 of the installation. A submarine cable 752 could be 26 run from the combined electronics unit 680 to the 27 surface, where the surface electronics 500s would be 28 located, which would be able to display the flow rate 29 and ratio information, and may also have a data 30 output to other computer systems, that is typically a 31 serial interface 754. Alternatively, or 51 additionally, a suitable telemetry system may be used.

4 The electrical cable 752 from the subsea combined 5 electronics module 680 to the surface is typically a 6 two-wire system as described above. 7 8 The outer housings 112, 202 of the flow meter 100 and 9 ratio tool 200 are typically manufactured from 10 suitable material for prevention of corrosion and/or 11 may be coated for additional protection. 12 13 Fig. 18 illustrates a typical surface pipeline 800 14 with the flow meter 100 and fluid ratio tool 200 15 forming part thereof. Both the flow meter 100 and 16 ratio tool 200 are mounted in the pipeline 800 with 17 all fluid within the pipeline 800 preferably passing 18 therethrough. The choke 118 of the flow meter 100 19 has a positive direction and is required to be 20 orientated within the pipeline correctly. 21 22 The combined electronics module 680 reads the signals 23 from the array of sensors 212 in the f luid ratio tool 24 200 and also the output form the load cells 120 in 25 the flow meter 100. The pipe connections would be 26 configured to suit the pipeline 800. 27 28 The surface electronics 500s, would provide a display 29 of the flow rate and fluid ratio values, and it 30 typically coupled to the electronics module 680 using 31 a two-wire cable 802. Optionally, the surface 52 1 electronics 500s can display the f low rate and ratio 2 information, and may also have a data output to other 3 computer systems, that is typically a serial 4 interface 804. 5 6 Thus, there is provided a flow meter for use in a 7 pipeline that can be used to measure the flow rate of 8 fluids through the pipeline using in certain 9 embodiments, pressure applied by the fluid flow on a 10 choke or reducing piece. Additionally, there is 11 provided a ratio tool which, in certain embodiments, 12 uses resistance and capacitance measurements of the 13 fluid to determine properties of the fluid to aid in 14 determining the fluid flow. 15 16 Modifications and improvements may be made to the 17 foregoing without departing from the scope of the 18 present invention.

53

Claims

1 CLAIMS

2 1. A flow meter comprising a body, a longitudinal 3 bore provided in the body, a choke in fluid 4 communication with the bore, and at least one force sensor for measuring the magnitude of fluid flow.

6 7

2. A flow meter according to claim 1, wherein the 8 choke is suspended within the body by the at least 9 one force sensor.

11

3. A flow meter according to either preceding 12 claim, wherein the or each force sensor measures a 13 compressive force applied to the choke by the fluid 14 flow.

16

4. A flow meter according to any preceding claim, 17 wherein the or each force sensor measures a shear 18 force applied to the choke by the fluid flow.

19

5. A flow meter according to any preceding claim, 21 wherein the or each force sensor measures a 22 compressive and/or shear force by measuring a 23 reaction force applied to the choke by fluid 24 impacting on the choke.

26

6. A flow meter according to claim S, wherein the 27 reaction force is measured in the radial and/or axial 28 direction.

29 54 1

7. A f low meter according to any one of claims 4 to 2 6, wherein the shear force is measured at a mounting 3 of the choke. 4 5

8. A flow meter according to any preceding claim, 6 wherein three force sensors are provided. 7 8

9. A flow meter according to any preceding claim, 9 further comprising a plurality of force sensors that 10 are equi-spaced around an inner surface of the bore. 11 12

10. A flow meter according to any preceding claim, 13 wherein the bore includes an enlarged diameter 14 portion. 15 16

11. A flow meter according to claim 10, wherein the 17 choke is positioned downstream of the enlarged 18 diameter portion. 19 20

12. A f low meter according to claim 10 or claim 11, 21 wherein the or each force sensor measures a 22 compressive and/or a shear force applied to the choke 23 by measuring a pressure difference created around the 24 choke by fluid passing from the enlarged diameter 25 portion of the bore to a smaller diameter portion 26 downstream of the enlarged diameter portion. 27 28

13. A flow meter according to claim 10, wherein the 29 force on the choke is generated by a combination of 30 the pressure difference created by fluid expansion 31 from the smaller diameter portion to the enlarged 1 diameter portion, and the physical impact force of 2 the fluid on the choke. 3 4

14. A flow meter according to any preceding claim, 5 wherein the total axial force applied to the choke is 6 a momentum force that is proportional to the flow of 7 f luid through the choke. 8 9

15. A f low meter according to any preceding claim, 10 wherein the or each force sensor measures the 11 magnitude of the force of the fluid flow. 12 13

16. A f low meter according to claim 15, wherein the 14 magnitude of the fluid flow is calibrated as a 15 measure of f low rate of the f luid. 16 17

17. A f low meter according to claim 15 or claim 16, 18 wherein a ratio tool is used to determine the nature 19 and/or density of the fluid passing through the flow 20 meter. 21 22

18. A f low meter according to any preceding claim, 23 wherein the or each force sensor comprises a load 24 cell. 25 26

19. A f low meter according to any one of claims 1 to 27 18, wherein the or each f orce sensor comprises a 28 crystal resonator. 29 56 1

20. A f low meter according to claim 19, wherein the 2 crystal resonator is used to measure the shear force 3 applied to the choke.

4

21. A flow meter according to any preceding claim, 6 wherein the bore is provided with a separating device 7 to separate fluids entering the flow meter.

8 9

22. A flow meter according to claim 21, wherein the separating device comprises a profiled wall.

11 12

23. A ratio tool comprising at least one fluid 13 identifier sensor positioned in a fluid flow, the 14 fluid identifier sensor being used to determine the nature and/or ratio of the fluid(s) in the fluid 16 flow.

17 18

24. A ratio tool according to claim 23, wherein the 19 fluid identifier sensors are located within an inner wall of a pipe through which the fluid flows.

21 22

25. A ratio tool according to claim 23 or claim 24, 23 wherein three circumferentially spaced fluid sensors 24 are used.

26

26. A ratio tool according to any one of claims 23 27 to 25, wherein an electrical resistance of the fluid 28 is measured using the at least one fluid identifier 29 sensor to determine the nature and/or ratio of the fluid(s).

31 57 1

27. A ratio tool according to claim 26, wherein the 2 resistance of the fluid is measured using a 3 resistance bridge measure. 4

28. A ratio tool according to claim 26 or claim 27, 6 wherein the resistance is measured by applying a 7 direct current (DC) signal to one of the fluid 8 identifier sensors, and measuring the signal received 9 at any one (or more) of the other fluid identifier 10 sensors. 11 12

29. A ratio tool according to any one of claims 26 13 to 28, wherein a capacitance of the fluid is also 14 used to determine the nature and/or ratio of the 15 fluid(s). 16 17

30. A ratio tool according to claim 29, wherein the 18 capacitance of the fluid is measured using the at 19 least one fluid identifier sensor. 20 21

31. A ratio tool according to claim 29 or claim 30, 22 wherein the capacitance is measured by applying an 23 alternating current (AC) signal to the fluid. 24 25

32. A ratio tool according to any one of claims 23 26 to 31, wherein the or each fluid identifier sensor 27 comprises a pair of plates or a pair of bars. 28 29

33. A ratio tool according to claim 32, wherein the 30 capacitance across the plates or bars forms part of a 31 filter circuit.

58 2

34. A ratio tool according to claim 33, wherein the 3 frequency response of the filter circuit changes as 4 the dielectric of the fluid changes.

6

35. A ratio tool according to any one of claims 23 7 to 25, wherein a complex impedance of the fluid is 8 measured to determine the nature and/or ratio of the 9 fluid(s) in the fluid flow.

11

36. A ratio tool according to claim 35, wherein an 12 oscillating circuit is used to determine the complex 13 impedance of the fluid.

14

37. A ratio tool according to claim 36, wherein the 16 fluid between any of the fluid identifier sensors 17 forms a part of the oscillating circuit.

18 19

38. A ratio tool according to claim 37, wherein the complex impedance of the fluid is determined by 21 performing circuit analysis on the oscillating 22 circuit.

23 24

39. A ratio tool according to any one of claims 36 to 38, wherein the output of the oscillating circuit 26 comprises a resonant frequency that is used to 27 determine the complex impedance of the circuit.

28 29

40. A ratio tool according to claim 23, wherein the body comprises a tubular body, the fluid identifier 31 sensor(s) being mounted within the body.

59 2

41. A ratio tool according to claim 40, wherein the 3 fluid identifier sensor(s) are equidistantly spaced 4 around an inner circumference of the tubular body to 5 form an array. 6 7

42. A ratio tool according to claim 40 or claim 41, 8 wherein the sensors comprise plates or bars. 9 10

43. A ratio tool according to claim 41 or claim 42, 11 wherein the sensors are supported by annular rings 12 within the inner circumference, and are spaced 13 therefrom wherein fluid can circulate around the 14 sensors. 15 16

44. A ratio tool according to any one of claims 40 17 to 43, wherein the sensors extend substantially the 18 full length of the tubular body. 19 20

45. A ratio tool according to any one of claims 40 21 to 44, wherein a resistance of the fluid is measured 22 by applying a direct current (DC) signal to one of 23 the fluid identifier sensors in the array, and 24 measuring the signal received at any one (or more) of 25 the fluid identifier sensors in the array. 26 27

46. A ratio tool according to claim 45, wherein the 28 DC signal is applied to each sensor sequentially, and 29 the signal is measured at each sensor sequentially. 30 1

47. A ratio tool according to claim 45 or claim 46, 2 wherein an average resistance can be determined from 3 the measurements. 4 5

48. A ratio tool according to any one of claims 40 6 to 47, wherein a capacitance of the fluid is measured 7 by applying an alternating current (AC) signal to one 8 of the fluid identifier sensors in the array, and 9 measuring the signal received at any one (or more) of 10 the other fluid identifier sensors in the array. 11 12

49. A ratio tool according to claim 48, wherein the 13 AC signal is applied to each sensor sequentially, and 14 the signal is measured at each sensor sequentially. 15 16

50. A ratio tool according to claim 48 or claim 49, 17 wherein an average capacitance can be determined from 18 the measurements. 19 20

51. A ratio tool according to any one of claims 40 21 to 50, wherein a complex impedance of the fluid is 22 measured. 23 24

52. A ratio tool according to claim 51, wherein the 25 complex impedance is measured by making the fluid 26 form part of an oscillating circuit. 27 28

53. A ratio tool according to claim 52, wherein an 29 output of the oscillating circuit is indicative of 30 the complex impedance of the fluid. 31 61 1

54. A ratio tool according to claim 53, wherein the 2 output of the oscillating circuit comprises a 3 resonant frequency. 4 5

55. A flow meter substantially as hereinbefore 6 described with reference to Figs 1 and 2 of the 7 drawings. 8 9

56. A flow meter substantially as hereinbefore 10 described with reference to Figs 3a to 3d and 4. 11 12

57. A ratio tool substantially as hereinbefore 13 described with reference to Figs 1 and 2 of the 14 drawings. 15 16

58. A ratio tool substantially as hereinbefore 17 described with reference to Figs 5, 6a, 6b and 7a to 18 7c.