GB2386691A - A ratio tool - Google Patents

Abstract

A ratio tool is described that is capable of determining the nature and quantities of fluids passing therethrough. The ratio tool can be used with single or multiple phase fluids but is particularly suited for use in multiphase fluids. The ratio tool uses sensors which measure electrical properties of the fluid. The electrical properties are either the impedance or both resistance and capacitance.

Description

l 1 "Ratio Tool" 3 The present invention relates to a ratio tool, and 4

particularly, but not exclusively, to a ratio tool 5 for use in the oil and gas industry. Embodiments of 6 the present invention provide a ratio tool for 7 determining the ratio of two or more different 8 fluids flowing within a pipeline or the like.

10 In many downhole operations, and other areas of oil 11 and gas processing and production, it is 12 advantageous to include a flow meter as part of a 13 tubing string, pipeline, conduit or the like. The 14 flow meter allows for measurement of the amount of 15 fluid that passes through the string or the like, 16 and can be used to determine the flow of fluid both 17 into the string (for example when flushing out a.; -.

18 borehole or cementing in a liner) or out of.the.

19 string (for example during the recovery of -:: 20 hydrocarbons from a well).

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, 6 and in addition reduce the expected lifetime of the 7 meter.

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 13 and 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.

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.

25 The choke is preferably located within the bore.

26 The bore preferably includes an enlarged diameter 27 portion. The choke is typically positioned 28 downstream of the enlarged diameter portion.

30 Optionally, the bore may be provided with a 31 separating device to separate fluids entering the

1 flow meter. The separating device typically 2 comprises a profiled wall, for example a spiral.

4 The choke is typically suspended within the tubular 5 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 10 shear force applied to the choke by the fluid flow, 11 typically at the mounting of the choke.

12 Preferably, three force sensors are provided. In 13 one embodiment, the force sensors are typically 14 equi-spaced around 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 20 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 25 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 30 smaller diameter portion to the enlarged diameter 31 portion and the physical impact force of the fluid 32 on the choke itself. The total axial force applied

1 to the choke is typically a momentum force that is 2 proportional to the flow of fluid through the choke.

3 Thus, the flow meter measures flow rate through it 4 by measuring the total momentum force applied to the 5 choke using the force sensors and calibrating this 6 force to a measure of fluid flow using the fact that 7 the force is proportional to flow rate.

9 Typically, the force sensors measure the magnitude 10 of the force of the fluid flow and calibrates this 11 as a measure of flow rate of the fluid. A ratio 12 tool is typically used to determine the nature 13 and/or density of the fluid passing through the flow 14 meter.

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.

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.

31 Alternatively, the voltage is typically converted 32 using an analogueto-digital convertor and fed into

1 a processor. The processor may be mounted within 2 the body, or remotely. Alternatively, the 3 electrical output may be converted to a frequency 4 and fed to the processor. The processor typically 5 transmits the measurements from the force sensor(s) 6 to a remote electronics package. The remote 7 electronics package is typically remote from the 8 flow meter, or may form part thereof.

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

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

21 The flow meter typically operates on a two-wire 22 system (ie signal and power composite and a ground 23 return). This makes the flow meter suitable for use 24 in oil and gas downhole environments. In addition, 25 the flow meter may be used with a downhole 26 instrument cable with a single inner mono conductor, 27 the ground return being provided by the cable sheath 28 or the production tubing.

30 According to a second aspect of the present 31 invention there is provided a ratio tool comprising 32 at least one fluid identifier sensor positioned in a

1 fluid flow, the fluid identifier sensor being used 2 to determine the nature and/or ratio of the fluid(s) 3 in the fluid flow.

5 In one embodiment of the present invention, the 6 fluid identifier sensors are located within an inner 7 wall of a pipe through which the fluid flows 8 Preferably, three circumferentially spaced fluid 9 sensors are used The fluid identifier sensors 10 typically comprise a pair of plates. Alternatively, 11 the fluid identifier senors may comprise a pair of 12 solid round bars.

14 The electrical resistance of the fluid is typically 15 measured using the at least one fluid identifier 16 sensor to determine the nature and/or ratio of the 17 fluid(s). Preferably, the capacitance of the fluid 18 is also used to determine the nature and/or ratio of 19 the fluid(s). The capacitance of the fluid is 20 typically measured using the at least one fluid 21 identifier sensor.

23 In another embodiment of a fluid ratio tool, the 24 resistance of the fluid is typically measured using 25 a resistance bridge measure The voltage produced 26 by the resistance bridge is typically amplified and 27 may either be input to a processor or converted to a 28 frequency and transmitted to a remote electronics 29 package.

31 Capacitance is typically measured by applying an 32 alternating current (AC) signal to the fluid, for

1 example through any pair of plates, bars or the 2 like. The capacitance across the plates typically 3 forms part of a filter circuit, thus allowing the 4 fluid dielectric properties to be determined. The 5 frequency response of the filter circuit typically 6 changes as the dielectric of the fluid changes, and 7 can be measured by varying the frequency of the AC 8 signal.

10 In an alternative embodiment of the ratio tool, the 11 natural electrical oscillation frequency of the 12 fluid is measured. This can be achieved by making 13 the fluid between the plates, bars etc part of an 14 oscillating circuit. The resonant frequency 15 provides a further measurement of the complex 16 impedance of the fluid. The complex impedance 17 and/or the resonant frequency can be calibrated 18 against known fluids or a look-up table used to 19 provide the nature and/or ratio of the fluid(s).

20 The nature and/or ratio of the fluid(s) can be 21 determined from the complex impedance using 22 mathematical analysis. It will be appreciated that 23 the complex impedance gives a measure of the 24 resistance and/or capacitance of the fluid(s) but in 25 a single measurement without having to do two 26 separate tests. Also, the resistance and/or 27 capacitance can be determined individually and 28 compared to the complex impedance that can be 29 determined separately.

31 The resistance is preferably measured by applying a 32 direct current (DC) signal to one of the fluid

1 identifier sensors, and measuring the signal 2 received at any one (or more) of the fluid 3 identifier sensors.

5 In a preferred embodiment of the fluid ratio tool, 6 the tool comprises a tubular body, the fluid 7 sensor(s) being mounted within the body. The fluid 8 sensor(s) are typically equidistantly spaced around 9 an inner circumference of the tubular body to form 10 an array. The sensors typically comprise plates or ll bars. The sensors are typically supported by 12 annular rings within the inner circumference, and 13 are preferably spaced therefrom wherein fluid can 14 circulate around the sensors. Preferably, the 15 sensors extend substantially the full length of the 16 tubular body.

18 In this embodiment, the resistance is preferably 19 measured by applying a direct current (DC) signal to 20 one of the fluid identifier sensors in the array, 21 and measuring the signal received at any one (or 22 more) of the fluid identifier sensors in the array.

23 Preferably, the DC signal is applied to each sensor 24 sequentially, and the signal is measured at each 25 sensor sequentially. Thus, a more reliable 26 measurement of the resistance of the fluid is 27 determined, as the resistance of substantially all 28 of the fluid is measured. An average resistance can 29 be determined from the measurements. This provides 30 the advantage that the resistance of the fluid(s) 31 that are flowing in different portions of the 32 pipeline can be determined.

2 In this embodiment, the capacitance is preferably 3 measured by applying an alternating current (AC) 4 signal to one of the fluid identifier sensors in the 5 array, and measuring the signal received at any one 6 (or more) of the fluid identifier sensors in the 7 array. Preferably, the AC signal is applied to each 8 sensor sequentially, and the signal is measured at 9 each sensor sequentially. Thus, a more reliable 10 measurement of the capacitance of the fluid is 11 determined, as the capacitance of substantially all 12 of the fluid is measured. An average capacitance: 13 can be determined from the measurements. This 14 provides the advantage that the capacitance of the 15 fluid(s) that are flowing in different portions of 16 the pipeline can be determined. In addition, the AC 17 signal frequency can be varied and the complex 18 impedance of the fluid can be determined from this.

20 In an alternative embodiment, the complex impedance 21 can be determined by making the fluid part of a free 22 oscillating circuit where the frequency of 23 oscillation is measured. Typical oscillating 24 frequencies may be in the range of a few kHz to 50 25 or 60 kHz, but values outside of this range may also 26 apply. The complex impedance and/or the frequency of 27 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 It will be appreciated that the complex impedance 2 gives a measure of the resistance and/or capacitance 3 of the fluid(s) but in a single measurement without 4 having to do two separate tests. Also, the 5 resistance and/or capacitance can be determined 6 individually and compared to the complex impedance 7 that can be determined separately.

9 The remote electronics package typically comprises a 10 power supply, a data transmit and receive 11 electronics system, and a processor to collate and 12 read the data transmitted from the downhole or 13 remote system.

15 The ratio tool typically operates on a two-wire 16 system (ie signal and power composite and a ground 17 return). This makes the ratio tool suitable for use 18 in oil and gas downhole environments. In addition, 19 the ratio tool may be used with a downhole 20 instrument cable with a single inner mono conductor, 21 the ground return being provided by the cable sheath 22 or the production tubing.

24 The ratio tool, when used with the flow meter, 25 typically allows the flow meter to measure the flow 26 rate of multi-phase fluids (ie two or more different 27 fluids).

29 Embodiments of the present invention shall now be 30 described, by way of example only, with reference to 31 the accompanying drawings, in which:

1 Fig. 1 is a longitudinal cross-section of a 2 first embodiment of a flow meter in accordance 3 with a first aspect of the present invention; 4 Fig. 2 is a schematic plan view of a first 5 embodiment of a ratio tool in accordance with 6 the second aspect of the present invention 7 incorporated into the flow meter of Fig. 1; 8 Fig. 3a is a longitudinal cross-section of an 9 alternative embodiment of a flow meter in 10 accordance with the first aspect of the present ll invention; 12 Fig. 3b is a horizontal cross-section of the 13 flow meter of Fig. 3a; 14 Fig. 3c is a cross-sectional view of a 15 cantilever load cell sensor for use with the 16 flow meter of Figs 3a and 3b; 17 Fig. 3d is an end elevation of the load cell of 18 Fig. 3c; 19 Fig. 4 illustrates a choke of the flow meter of 20 Figs 3a and 3b suspended using the load cells 21 of Figs 3c and 3d; 22 Fig. 5 is a longitudinal cross-section of a 23 second embodiment of a ratio tool in accordance 24 with a second aspect of the present invention; 25 Figs 6a and 6b are horizontal cross-sections of 26 two different fluid identifier sensor arrays 27 for use with the ratio tool of Fig. 5; 28 Fig. 7a is a schematic representation of the 29 fluid ratio tool of Figs 5, 6a and 6b 30 illustrating fluid flowing between sensors;

1 Fig. 7b illustrates the principle of measuring 2 dielectric strength of a fluid using the fluid 3 ratio tool of Figs 5, 6a and 6b; 4 Fig. 7c illustrates the principle of measuring 5 resistance of a fluid using the fluid ratio 6 tool of Figs 5, 6a and 6b; 7 Fig. 7d is a schematic circuit diagram of a 8 circuit that can be used to measure a complex 9 impedance of a fluid using the fluid ratio tool 10 of Figs 5, 6a and 6b; 11 Fig. 8 is a schematic block diagram of an 12 internal electronics module illustrating a 13 basic electronics system for a self-contained 14 flow meter for use with single-phase fluids; 15 Fig. 9 is a schematic block diagram of an 16 electronics module located locally as part of 17 the ratio tool of Figs 5, 6a and 6b; 18 Fig. 10 illustrates an electronics module that 19 can be used where the fluid ratio tool of Figs 20 5, 6a and 6b and flow meter of Figs 3a and 3b 21 are combined in a single unit; 22 Fig. 11 illustrates an electronics module that 23 can be used to control operation of the flow 24 meter of Figs 3a and 3b in remote applications; 25 Fig. 12a is a simplified schematic diagram of a 26 multiplexer unit of Fig. 11; 27 Fig. 12b illustrates the transmission of framed 28 frequencies; 29 Fig. 13 is a schematic block diagram of an 30 electronics module for use with a remote fluid 31 ratio tool;

1 Fig. 14 illustrates a combination electronic 2 module for use with the flow meter of Figs 3a 3 and 3b when combined with the fluid ratio tool 4 of Figs 5, 6a and 6b; 5 Fig. 15 is a plot of flow squared against 6 frequency output derived from a prototype flow 7 meter in accordance with the first aspect of 8 the present invention; 9 Fig. 16 shows an exemplary oil well 10 installation using the fluid ratio tool of Figs 11 5, 6a and 6b combined with the flow meter of 12 Figs 3a and 3b;:.

13 Fig. 17 shows a portion of subsea pipeline that 14 includes the flow meter of Figs 3a and 3b and 15 the ratio tool of Figs 5, 6a and 6b; and 16 Fig. 18 illustrates a typical surface pipeline 17 with the ratio tool of Figs 5, 6a and 6b and 18 flow meter of Figs 3a and 3b forming a part 19 thereof. 21 Referring to the drawings, Fig. 1 shows a flow meter 22 generally designated lO. Flow meter 10 comprises a 23 substantially tubular body 12 that is advantageously 24 provided with attachment means 14u, 141 to 25 facilitate attaching the flow meter 10 in a tubular 26 string, pipeline, conduit or the like. It should be 27 noted that fluid direction is upwards in Fig. 1 as 28 denoted by arrow 26. The terms "upper" and "lower" 29 are used in relation to the orientation of the flow 30 meter 10 as seen in Fig. 1, but this is arbitrary.

31 The term "downstream" is used in relation to fluid

1 flow through the flow meter 10 in the direction of 2 arrow 26 in Fig. 1, but this is arbitrary.

4 Tubular body 12 is provided with a longitudinal 5 through bore 16, which in this embodiment includes 6 an enlarged diameter portion lee. Located 7 downstream of the enlarged diameter portion 16e is a 8 choke 18 that reduces the enlarged diameter portion 9 16e into the relatively smaller diameter of an upper 10 portion 16u of bore 16.

12 Choke 18 is suspended in the enlarged diameter 13 portion 16e by at least one force sensor 20 (two 14 sensors shown in Fig. 1). Preferably, three force 15 sensors 20 are equidistantly spaced around the inner 16 circumference of bore 16. The force sensors 20 are 17 typically used to measure the compressive force 18 and/or the shear force applied to the choke 18 by 19 fluid flow through the meter 10, as will be 20 described hereinafter. It should be noted that the 21 shear force applied to the force sensors 20 could be 22 measured when the choke 18 is suspended from force 23 sensors 20 displaced radially inwardly, as will be 24 described.

26 A tubing pressure sensor 22, located downstream of 27 the choke 18, is in communication with bore 16 so 28 that fluid pressure within the flow meter 10 can be 29 monitored. Optionally, an external pressure sensor 30 24 in communication with pressure outwith the flow 31 meter 10 may be used to monitor the external 32 pressure outwith the flow meter 10.

2 Fluid enters the flow meter 10 via a lower portion 3 161 of the bore 16. The fluid is then expanded into 4 the enlarged portion 16e of the bore 16 that reduces 5 the velocity of the fluid. Enlarged portion 16e may 6 optionally contain a separating device (not shown) 7 for separating the fluids that enter the flow meter 8 10. The separating device may comprise, for 9 example, an inner profiled wall (e.g. a spiral) that 10 separates the fluids.

12 Choke 18 directs the fluid back into a relatively: 13 smaller diameter portion 16u of the bore 16. The 14 respective diameters of portions 16u, 161 are 15 substantially the same. As the choke 18 is 16 suspended in the enlarged diameter portion 16e by 17 force sensors 20, the compressive and/or shear force 18 applied to the choke 18 by fluid acting thereon can 19 be measured. For example, choke 18 may be forced 20 upwards towards the smaller diameter upper portion 21 16u by the pressure difference created by the 22 reduction in the diameter between the enlarged 23 portion 16e and the upper portion 16u of the bore 24 16. The force sensors 20 will measure the 25 compressive and/or shear force applied by the fluid 26 flow to the choke 18.

28 Alternatively, the compressive and/or shear force 29 may be measured using the force applied to the choke 30 18 by fluid physically impacting on the surface of 31 the choke 18. The impact of the fluid on the choke

l 18 causes reaction forces to be present on the choke 2 18 in radial and/or axial directions.

4 The force sensors 20 measure the magnitude of the 5 force and the direction of the fluid flow and 6 convert this measurement to a measure of the flow 7 rate through the flow meter 10. The flow meter 10 8 is therefore measuring the flow rate by measuring 9 the forces applied to the choke 18 placed in the 10 flow of the fluid in the pipeline or tubing. It ll should be noted that the flow rate can only be 12 determined using this force if the fluid density of 13 the fluids passing through the flow meter 10 are 14 known. This shall be discussed hereinafter.

16 The force sensors 20 can be, for example, a strain 17 gauge suitably mounted to a bar or tube, or could 18 alternatively be a shear force sensing crystal 19 resonator. The force sensors 20 could also comprise 20 any other type of direct force measurement device.

22 The force applied to the choke 18 is calculated by 23 an electronic system based on an electrical output 24 from the force sensor 20, typically a voltage. This 25 output can then be converted into a frequency and 26 transmitted to the remote electronics (which may be 27 some distance very remote from the flow meter 10), 28 or can be read by a processor (not shown) using an 29 analogue-to-digital (A/D) converter, both of which 30 can be mounted within the flow meter 10 itself, or 31 at the remote electronics.

i7 1 Referring now to Figs 3a and 3b there is shown an 2 alternative embodiment of a flow meter 100, wherein 3 Fig. 3a is a longitudinal crosssection through the 4 flow meter 100, and Fig. 3b is a horizontal cross 5 section through the flow meter 100. Flow meter 100 6 is substantially the same as flow meter 10, but the 7 force sensors 120 suspend the choke 118 by extending 8 radially inward and thus measure the shear force 9 applied to the choke 118 by fluid flow through the 10 meter 100.

12 Meter 100 includes an entry port 130 and an exit 13 port 132, the diameters of the entry and exit ports 14 130, 132 typically being the same as the nominal 15 diameter of the pipeline (not shown) of which the 16 flow meter 100 forms part. Fluid flows into the 17 entry port 130 and out of the exit port 132 in the 18 direction of arrow 134 (ie upward in Fig. 3a).

20 As with the previous embodiment, the longitudinal 21 bore 116 of the meter 100 is provided with an 22 enlarged diameter portion 116e. Choke 118 is 23 suspended in the meter 100 by three shear load cells 24 120 that are advantageously equi-spaced around an 25 inner circumference of the enlarged diameter portion 26 116e. Optionally, an entry choke 136 can be used to 27 gradually increase the diameter of the bore 116.

28 optionally also, the flow meter 100 can include a 29 separator 138 to separate the fluids entering the 30 meter 100 if the fluid within the meter 100 31 comprises two or more different fluids (ie a liquid

1 and a gas for example). The separator 138 may 2 comprise an inner profiled wall, such as a spiral.

4 Meter 100 includes a local electronics unit 140 that 5 is electrically coupled to the shear load cells 120 6 and can be electrically coupled to a remote display 7 and processing unit 142 using, for example, a cable 8 144 or other suitable telemetry system. Electronics 9 unit 140 shall be described in more detail lo hereinafter. 12 Referring particularly to Fig. 4, operation of the 13 meter 100 shall be described. It should be noted 14 that the orientation of the meter 100 has been 15 reversed in Fig. 4 so that fluid flow is downwards.

16 Fig. 4 illustrates the choke 118 suspended using the 17 load cells 120. Choke 118 is advantageously spaced 18 from the internal circumference of the body 112 19 whereby hydrostatic pressure around the choke 118 is 20 substantially equalized. The meter 100 operates by 21 measuring the force F applied to the choke 118 in 22 the direction of the flow (illustrated in Fig. 4 as 23 arrow 146). The radial or ring force that is 24 additionally applied to the choke 118 is typically 25 cancelled by the choke 118 itself. This is because 26 the choke 118 is typically of solid steel and 27 generally cannot expand in a radial direction.

29 The load cells 120 are advantageously designed to 30 provide shear force measurement with minimal 31 pressure effect and minimal temperature effect on 32 the operation of the meter 100.

it 2 The restriction to fluid flow that any orifice 3 presents may be analysed using a number of different 4 techniques. In this particular embodiment, the 5 orifice (ie the choke 118) is given a fluid 6 resistance property defined as a "Lohm"; 1 Lohm will 7 permit a flow of 100 gallons of water per minute 8 (gal/min) with a pressure drop of 25 pounds per 9 square inch (psi) at a temperature of 80 10 Fahrenheit. 12 The force F on the choke 118 may be calculated by: 13 the momentum Lohm law using the equation 15 F = (S*I2*L)/400 - Equation 1 17 where 18 I is the flow in gallons per minute through the l9 meter 100; 20 S is the specific gravity of the fluid flowing 21 through the meter 100; 22 L is the choke property in Lohms, defined as 23 the resistance of the reduction of the pipe 24 diameter; and 25 F is the force generated on the choke 118 in 26 pounds (lbs).

28 It should be noted from Equation 1 above that the 29 force F generated on the choke 118 is proportional 30 to the square of the flow rate (ie I2) .

32 The choke property L can be calculated using

l 2 L = 0.76/d2, 4 where 6 d is the diameter of the orifice.

8 The meter 100 measures the force F using the load 9 cells 120 by which the choke 118 is suspended.

10 Thus, if the specific gravity of the fluid S is 11 known (or can be determined) then the flow rate I in 12 gallons per minute can be calculated by rearranging 13 equation 1 above to make I the subject of the 14 equation, which gives 16 I = 4(400F/S*L) - Equation 2 18 Referring to Figs 3c and 3d, there is shown a 19 schematic representation of a load cell 120. Load 20 cell 120 includes an outer housing 122, which 21 typically comprises a mounting portion 122m and 22 shear housing 122s The mounting portion 122m and 23 shear housing 122s are separated by a reduced 24 diameter portion 122r, which typically comprises an 25 annular slot or notch for example. When pressure is 26 applied to the shear portion 122s, the load cell 120 27 flexes at the reduced diameter portion 122r.

29 The mounting portion 122m is typically provided with 30 an external screw thread, wherein the mounting 31 portion 122m is threadedly engaged with the outer 32 housing 112 of the flow meter 100, and the shear

1 portion 122s engages the choke 118 (as shown in more 2 detail in Fig. 4) .

4 A cantilever load cell 124 is attached to the 5 mounting portion 122m using any conventional means, 6 and is advantageously attached using means that 7 facilitates rotational adjustment of the cantilever 8 load cell 124, as this requires to be correctly 9 aligned in the direction of movement of the choke 10 118 (as shown in more detail in Fig.4). The 11 cantilever load cell 124 can be provided with 12 adjustment means 126 that can be used to finely 13 adjust the position of the load cell 124 in relation 14 to the choke 118 as is known in the art.

16 The cantilever load cell 124 is typically provided 17 with a plurality of linear movement strain gauges 18 (not shown) that are used to measure the deflection l9 of the shear portion 122s due to the impact of fluid 20 on the choke 118. The readings from the strain 21 gauges are typically summed to give an over-all or 22 average value of the deflection. With the 23 cantilever arrangement of the load cell 124, only 24 deflection of theshear portion 122s is measured; 25 there is no hoop stress, as stresses caused by 26 hydrostatic pressure or expansion are distributed 27 evenly. 29 Where the fluid flowing through the meter 10, 100 is 30 a single-phase fluid (ie a fluid that consists of 31 only one fluid as opposed to a mixture of two or 32 more fluids) then pressure and temperature sensors,

1 which form part of an internal electronics module 2 146 (Fig. 3a) can be used to determine the density 3 of a known fluid.

5 However, if the fluid within the pipeline in which 6 the meter 10, 100 is attached comprises a mixture of 7 more than one fluid, then both the relative 8 quantities of each fluid, and the pressure and 9 temperature of the or each fluid must be determined 10 to determine the average density (or specific 11 gravity S) of the fluid passing through the flow 12 meter 10, 100 14 Referring to Figs 1 and 2, there is shown a first 15 embodiment of a ratio tool 28 that enables the fluid 16 density of a fluid to be determined, the ratio tool 17 28 preferably being incorporated into and thus 18 forming part of the flow meter 10. The ratio tool 19 28 typically comprises an array of fluid identifier 20 sensors. Ratio tool 28 comprises at least one, and 21 preferably three, pairs of diametrically opposed 22 plates 30 or alternatively bars. The array shown in 23 Fig. 2 comprises three pairs of plates 30, 32, 34 24 that are equidistantly spaced around the inner 25 circumference of the upper portion 16u of the 26 internal bore 16 of the flow meter 10 (Fig. 1) .

28 The nature of the fluid flowing through the flow 29 meter 10 can be determined by measuring the 30 resistance of the fluid between any pair of plates 31 30, 32, 34. In addition, each pair of plates 30, 32 32, 34 may be used to measure the capacitance of the

1 fluid. The resistance and capacitance measurements 2 that are obtained using the pairs of plates 30, 32, 3 34 give a series of measurements that can be 4 individually used to determine the nature of single 5 phase fluids. Collectively, the resistance and 6 capacitance measurements obtained using an array of 7 sensors can be used to determine the nature of 8 multi-phase fluids across the area of the flowing 9 pipeline, as will be described.

ll The resistance of the fluid flow can be determined 12 using a direct resistance bridge measurement means 13 (not shown), the output of which is typically 14 amplified to produce a voltage. This voltage can 15 either be read by a processor (not shown) located 16 within the flow meter 10 (using an analogue-to 17 digital (A/D) convertor) or can be converted to a 18 frequency and transmitted to a remote electronics, 19 package (not shown). The remote electronics package 20 typically comprises a power supply, data transmit 21 and receive electronics, and a processor to collate 22 and read the data transmitted from the downhole or 23 remote system.

25 The capacitance of the fluid can be determined by 26 applying an alternating current (AC) electrical 27 signal between any pair of plates 30, 32, 34 and 28 using the capacitance between the plates 30, 32, 34 29 as part of a filter circuit (not shown). The filter 30 circuit can then be fine-tuned to determine the 31 fluid dielectric properties. In particular, the 32 filter circuit will change its frequency behaviour

1 as the dielectric of the fluid passing between the 2 pairs of plates 30, 32, 34 changes. It should be 3 noted that the ratio tool 28 does not give the 4 dielectric properties directly but can be calibrated 5 using reference fluids, for example using a look-up 6 table or the like.

8 In addition, if the frequency of the AC electrical 9 signal is varied (e.g. by scanning the frequency), a 10 measure of the complex impedance of the fluid(s) can 11 be obtained from the frequency response of the 12 filter circuit. The complex impedance and/or the 13 frequency of oscillation can be used to determine 14 the nature and/or ratio of the fluid(s) using 15 mathematical analysis, or can be calibrated against 16 known fluids or a look-up table used to provide the 17 nature and/or ratio of the fluid(s).

19 Additionally, or alternatively, the complex 20 impedance of the fluid can be determined by 21 measuring the free oscillating frequency of an 22 oscillating circuit in which the fluid forms a part.

23 Referring to Fig. 7d, there is shown a schematic 24 circuit diagram of an oscillating circuit, generally 25 designated 260. PROBE 1 and PROBE 2 in circuit 260 26 may be any one or more of the pairs of plates 30, 27 32, 34. The fluid acts as a resistor and/or 28 capacitor element in the oscillating circuit 260.

29 In use, the fluid thus forms part of the oscillating 30 circuit and has a complex impedance between the 31 PROBE 1 and PROBE 2 contacts that effectively forms 32 part of the oscillating circuit 260. The fluid

1 creates an oscillating or resonant frequency that is 2 related to the complex impedance of the fluid. The 3 output of the circuit is a resonant frequency of the 4 oscillating circuit 260 that changes as the complex 5 impedance of the fluid changes. Typical oscillating 6 frequencies may be in the range of a few kHz to 50 7 or 60 kHz.

9 Since the values of the other components in the 10 circuit 260 are known, the complex impedance of the 11 fluid can be determined using circuit analysis.

12 Additionally, the values of the components can be 13 varied (e.g. under computer control) to allow the 14 oscillating circuit to be more sensitive in 15 different types of fluids.

17 The nature and/or ratio of the fluids can be 18 determined using the resonant frequency and/or the 19 complex impedance of the fluid. The resonant 20 frequency and/or the complex impedance can be used 21 by calibrating either or both of these against a 22 known fluid, or by using a look-up table, to give an 23 indication of the nature and/or ratio of the fluids.

24 Alternatively, the nature and/or ratio can be 25 determined by mathematically analyzing the complex 26 impedance.

28 It will be appreciated that the complex impedance 29 gives a measure of the resistance and/or capacitance 30 of the fluid(s) but in a single measurement without 31 having to do two separate tests. Also, the 32 resistance and/or capacitance can be determined

1 individually and compared to the complex impedance 2 that can be determined separately.

4 The ratio tool 28 may operate on a two-wire system, 5 wherein the two wires comprise a composite signal 6 and power wire, and a ground return. This makes the 7 ratio tool 28 suitable for use in an oilfield

8 downhole environment and allows use with a downhole 9 instrument cable that has a single inner mono 10 conductor wire, the ground return system being 11 provided by the cable sheath or the production 12 tubing itself, for example.

14 Fig. 5 shows a second embodiment of a ratio tool 15 200, and Figs 6a and 6b are cross-sectional views of 16 two different fluid identifier sensor arrays for use 17 with the ratio tool of Fig. 5.

19 Referring to Figs 5, 6a and 6b, ratio tool 200 20 includes a body 202 that is provided with an 21 internal through-bore 204. Bore 204 includes an 22 enlarged diameter portion 204e that extends 23 substantially the full longitudinal length of the 24 ratio tool 200. It should be noted that the length 25 of the enlarged diameter portion 204e could be 26 varied within the scope of the invention.

28 The ratio tool 200 includes an entry port 206 and an 29 exit port 208, wherein fluid flows from the entry 30 port 206 to the exit port 208 in the direction of 31 arrow 210 (ie downwards in Fig.5). The diameter of 32 the internal bore 204 at or near the entry and exit

1 ports 206, 208 is substantially the same as the 2 diameter of the pipeline in which the ratio tool 200 3 is mounted. The ratio tool 200 is typically 4 provided with means (not shown but can be any 5 conventional means such as screw threads, a pin 6 and/or box connection or the like) to attach it to a 7 pipeline string (not shown,).

9 An array of sensors 212 from two to N in number are 10 retained in the enlarged diameter portion 204e by a 11 plurality of ring retainers 214 spaced along the 12 longitudinal length of the sensors 212. Referring: 13 to Figs 6a and 6b, the sensors 212 may comprise a 14 plurality of bars 212b (Fig. 6a) or plates 212p 15 (Fig. 6b). Each sensor 212 is electrically coupled 16 to an electronics module 216 using a pressure tight 17 electrical feed through 218 (Fig. 5). It should be 18 noted that each sensor 212 is provided with a 19 separate electrical feed through 218, although this 20 is not essential.

22 The electronics module 216 can preferably 23 read any combination of the sensors 212 in the array 24 as pairs or groups of pairs.

26 As shown in Fig. 7a, in a simple embodiment of the 27 ratio tool 200, only one pair of sensors 212 (ie 28 two) would be used. Fig. 7a illustrates a 29 horizontal cross-section and a vertical cross 30 section through a ratio tool illustrating two 31 sensors 212. The shaded area 230 indicates the area 32 of influence on the measurement that the fluid

1 presents to the sensors 212. However, the accuracy 2 and reliability of the identifier 200 increases as 3 the number of sensors 212 increases, particularly 4 when the sensors 212 are being sequentially scanned 5 as will be described. The total number of sensors 6 212 in the ratio tool 200 can be any number N. 7 depending upon the physical restriction of the 8 diameter of the pipelines and/or the tool 200. A 9 large number of sensors 212 provide a scanning array 13 with greater versatility and improved accuracy.

12 The ratio tool 200 can operate in one of three 13 distinct modes, and typically performs two separate 14 measurements on the fluid passing the sensors 212.

15 Referring to Fig. 7b, the ratio tool 200 can be used 16 to measure the dielectric strength of the fluid by 17 applying an AC electrical signal generated by an AC 18 source 240 (and optionally through an amplifier 242) lo to one of the sensors 212f (which can be either bar 20 212b or plate 212p or any other suitable sensor 21 configuration). The electrical signal detected at 22 any one of the other sensors 212s in the array is 23 amplified by a first stage amplifier 244, passed 24 through a full bridge instrument peak detector 246, 25 and amplified again in a second stage amplifier 248.

26 Note that any two opposed sensors 212f, 212s in the 27 array form a fluid capacitor Cf. The amplitude of 28 the received signal (ie a voltage) is proportional 29 to the dielectric strength of the fluid capacitor Cf 30 and thus in insulating fluids is a measure of the 31 dielectric strength of the fluid. In conductive 32 fluids, this measurement is less accurate but

l generally gives high amplitude, and in general 2 higher than that obtained with a good insulating 3 fluid 5 It will be appreciated that applying an AC signal to 6 a first sensor 212f and measuring the signal 7 received at a second sensor 212 is limited in that 8 the signal will only be affected by fluid that 9 substantially surrounds the two sensors 212 lo (illustrated by shaded areas 230 in Fig. 7a).

11 However, to provide a collection of measurements 12 that collectively give better statistical results, 13 and are capable of measuring separated flow regimes, 14 the array of sensors 212 can be scanned by using 15 each sensor 212 sequentially as a signal source and 16 measuring the amplitude from all the other sensors 17 212 sequentially. Scanning of the sensors 212 in 18 the array is typically controlled by a local 19 processor, as will be described. In addition to 20 this sequential scanning of the sensors 212 using an 21 AC waveform of fixed amplitude and/or frequency, the 22 frequency and/or amplitude of the source AC signal 23 fed into the fluid can be varied. This allows for a 24 more accurate reading where the amplitude and/or 25 frequency of the measured signal is too low to give 26 accurate measurements. In addition, when performing 27 the capacitance tests, the frequency can be varied 28 over a large range, and the measured capacitance 29 plotted against frequency. This allows the Q point 30 of the tuned filter (which may optionally include an 31 inductor to form a filter circuit) to be identified, 32 giving the average and most accurate capacitance of

1 the fluid flowing within the pipeline, conduit or 2 the like.

4 The sequential scanning of the sensors 212 is 5 typically used to establish fluid properties in 6 fluids where there is more than one fluid present 7 (en a multiphase fluid having a liquid and a gas), 8 and they are flowing in separated zones within the 9 pipeline. 11 A second measurement that can be performed by the 12 ratio tool 200 is a fluid resistance measurement.

13 Referring to Fig. 7c, there is shown a schematic 14 representation of an electrical circuit that is 15 formed when measuring the resistance of the fluid.

16 In a similar manner to the capacitance measurement 17 described above, a DC voltage is applied to a first 18 sensor 212f in the array, and the signal at a second l9 sensor 212s or to the body 202 of the ratio tool 200 20 is measured. In Fig. 7c, the resistance of the 21 fluid is represented as resistance Rf, which is the 22 resistance of the fluid between the two sensors 23 212f, 212s. Two discrete resistors 250 and 252 are 24 used outwith the sensors 212f, 212s to provide a 25 gain setting in a known manner. The DC voltage is 26 applied to resistor 250 through the first sensor 27 212f. The signal passes through the fluid (ie 28 resistance Of) and resistor 252 to ground (through 29 sensor 212s). Resistors 250, 252 may be the 30 electrial resistances of the sensors 212f, 212s.

31 Alternatively, resistor 252 may comprise the

l resistance of the casing 202 of the tool 200 if the 2 casing 202 is used as an electrical ground.

4 The DC voltage across the fluid resistance Rf is 5 measured, typically via an amplifier and filter 6 circuit 254, and a final gain and offset amplifier 7 256. The output voltage measured is proportional to 8 the resistance of the fluid Rf.

10 Thus, the electrical resistance Rf of the fluid 11 within the ratio tool 200 (and thus the pipeline) 12 can be measured. The local processor (not shown) 13 within the ratio tool 200 is used to scan the 14 sensors 212 in a manner similar to the capacitance 15 measurements, to provide a collection of 16 measurements to give better statistical results, and 17 measure separated flow regimes.

19 The electronics module 216 typically has the 20 capability to alter the resistance range of the 21 measurement from, for example, several megohms to a 22 few hundred ohms to facilitate measurement of a wide 23 range of fluid conditions. Altering of the 24 resistance range is typically automatic under the 25 control of the local processor to suit the measured 26 resistance.

28 The auto scaling or ranging is typically performed 29 by applying the highest resistance range to the 30 measuring channel. If a low resistance or off-scale 31 (in 100%) reading is obtained then the range is 32 reduced until the reading becomes zero (ie lowest

1 scale reading or 0%). The midpoint between the 100% 2 and 0\ reading is then selected as a basis for the 3 range for the measurement setting. As the ratio 4 tool 200, is processor based it is possible to have 5 two way communication between a display and 6 processing unit positioned remotely from the ratio 7 tool 200, and possibly could use the display and 8 processing unit 142 of the flow meter 100 (Fig. 3a) 9 and the local processor within the ratio tool 200.

10 The local processor can thus receive instructions ll from the display and processing unit and may be 12 instructed, for example, to carry out a calibration 13 scan where the setting of gain on all active sensor 14 combinations are scanned for correct gain settings.

16 A third measurement that can be performed using the 17 ratio tool 200 is to measure the complex impedance 13 of the fluid. As described above with reference to 19 Fig. 7d, the fluid forms part of an oscillating 20 circuit 260 that is used to provide a measure of the 21 complex impedance of the fluid. The nature and/or 22 ratio of the fluid(s) can be determined from the 23 complex impedance using mathematical analysis.

24 Alternatively, or additionally, the complex 25 impedance can then be calibrated against a known 26 fluid, or compared to a look-up table to identify 27 the nature and/or ratio of the fluids.

29 It will be appreciated that the complex impedance 30 gives a measure of the resistance and/or capacitance 31 of the fluid(s) but in a single measurement without 32 having to do two separate tests. Also, the

1 resistance and/or capacitance can be determined 2 individually and compared to the complex impedance 3 that can be determined separately.

5 Fig. 8 is a schematic block diagram of the internal 6 electronics module 140 of the flow meter 100 (Figs.

7 3a and 3b) that illustrates an example of an 8 electronics system for a self-contained flow meter 9 100 in single-phase fluids.

11 The electronics module 140 comprises a power supply 12 300 that provides local power to the electronics 13 system, typically +12v DC and 5V DC for logic. A 14 local processor 302 provides control over the 15 operation of the flow meter 100, and can be used to 16 perform the calculations as detailed above.

17 Processor 302 optionally drives a display unit 304 18 for visual display of flow readings and any other 19 relevant data, the display unit 304 typically being 20 remote from the flow meter 100 and electrically 21 coupled thereto using a wire, cable or other 22 telemetry system. The processor 302 includes a 23 serial interface 308 for two-way communication 24 between the local processor 302 and a remote 25 station. This facilitates remote operation and 26 monitoring of the flow meter 100.

28 Data readings from the shear load cells 120 of flow 29 meter 100 are acquired by an analogue-to-digital 30 (A/D) convertor 310, the output of which is fed into 31 the processor 302. The three shear load cells 120 32 are schematically shown as one unit 312 as the

1 outputs of these can be connected together in 2 parallel or can be fed into three separate amplifier 3 units (not shown). The output from the load cell 4 unit 312 is fed into a filter and amplifier stage 5 314 that has a voltage output. The voltage output 6 from the amplifier stage 314 can optionally be 7 converted into a frequency by a voltage-to-frequency 8 convertor 316 and fed into the A/D convertor 310, or 9 can be directly fed into the convertor 310.

11 In addition, a pressure sensor 318 and a fluid 12 temperature sensor 320 are used to measure the 13 pressure and temperature within the flow meter 100.

14 The pressure and temperature sensors 318, 320 may be 15 combined into a single sensor body, but the signals 16 are typically measured through two separate data 17 channels. Each data channel includes a filter and 18 amplifier unit 322, 324 and optionally, a voltage 19 to-frequency convertor 326, 328, similar to the 20 channel for the load cell unit 312.

22 The load cell sensors 120 and the pressure and 23 temperature sensors 318, 320 preferably have their 24 output signals amplified and filtered to remove 25 substantially all background noise and interference

26 in units 314, 322 and 324, respectively. A DC 27 voltage that is generated by the sensors 312, 318, 28 320 can be fed directly into the A/D convertor 310, 29 and can thus be read by the processor 302.

31 If higher resolution is required then either a high 32 resolution A/D convertor can be used, or the voltage

1 signals can be converted to a frequency in a 2 voltage-to-frequency converter 316, 326, 328, and 3 fed into a high frequency reciprocal counter, which 4 may be included as part of the A/D convertor 310 or 5 as a separate unit in place of, or in addition to, 6 the convertor 310.

8 It will be appreciated that the fluid ratio tool 200 9 may be included as part of the flow meter 10, 100 as 10 shown in Figs 1 and 2, or can form a separate tool 11 200 that is used in conjunction with flow meter 10, 12 or can be used independently thereof. Fig. 9 is a 13 schematic block diagram of the electronics 216 14 located locally as part of the ratio tool 200 (Fig. 15 5), the diagram showing the electronics required for 16 the fluid ratio tool 200 independent of a flow meter 17 10, 100.

19 Referring to Fig. 9, the electronics module 216 20 (forming part of the ratio tool 200 of Fig. 5) 21 includes a multiplexer array 350. The inputs to the 22 multiplexer array 350 are each electrically coupled 23 to one of a plurality of sensors 212, which allows a 24 local processor 352 to direct signals to or receive 25 signals from any of the plurality of sensors 212.

27 Module 216 further includes a frequency driver 354 28 that is used to generate the AC signal required to 29 perform the capacitance test described above. The 30 output from the frequency driver 354 may be 31 multiplexed (using array 350) to any of the sensors 32 212. The frequency driver 354 can also be used to

1 provide the DC voltage required to perform the 2 resistance test described above. Alternatively, the 3 DC voltage may be derived from a local power supply 4 366, optionally through a suitably rated voltage 5 regulator. 7 Two amplifier and filter units 356, 358 are 8 provided. Unit 356 is electrically coupled to the 9 multiplexer array 350 and can be used to provide 10 either a direct voltage signal to an A/D convertor ll 360, or to transform the voltage signal to a 12 frequency that is then fed to a counter (in place of 13 or in addition to the A/D convertor 360) for the 14 dielectric measurement. Similarly, unit 358 is 15 coupled to the multiplexer array 350 and can be used 16 to provide either a direct voltage signal to the A/D 17 convertor 360, or to transform the voltage signal to 18 a frequency that is then fed to the counter (in 19 place of or in addition to the A/D convertor 360) 20 for the resistance measurements.

22 The frequency driver 354 that injects an AC signal 23 into any of the sensors 212 generates an AC drive 24 waveform whose frequency is determined by a drive 25 signal generated by the local processor 352.

27 The electronics module 216 can also be used to 28 determine the complex impedance of the fluid to 29 provide an indication of the nature and/or ratio of 30 the fluid. An oscillating circuit 368 can be used, 31 similar to circuit 260 in Fig. 7d. In this 32 embodiment, any of the sensors 212 can be used as

1 PROBE 1 and PROBE 2 of Fig. 7d The multiplexer 350 2 can be used to sequentially scan each of the sensors 3 212 so that each sensor 212 can be used as PROBE 1 4 and PROBE 2. The complex impedance of the fluid 5 between each sensor pair forms part of the 6 oscillating circuit 368. The fluid between the 7 sensors 212 creates an oscillating or resonant 8 frequency that is related to the complex impedance 9 of the fluid. The output of circuit 368 is a 10 resonant frequency that changes as the complex 11 impedance of the fluid changes. The resonant 12 frequency is output to the A/D convertor 360, the 13 output of which can subsequently be read by the 14 processor 352.

16 The processor 352 can then analyst the resonant 17 frequency and/or the complex impedance by 18 calibrating the value of these against those of 19 known fluid, or by the use of a look-up table to 20 determine the nature and/or ratio of the fluids.

21 The nature and/or ratio of the fluid(s) can be 22 determined from the complex impedance using 23 mathematical analysis.

25 The values of the components in the oscillating 26 circuit 368 can be varied by the processor 352 under 27 computer control, thus allowing the circuit 368 to 28 be changed to be more or less sensitive. Also, as 29 the values are known, the complex impedance of the 30 fluid can be determined by circuit analysis, 31 typically performed by the processor 352.

1 The electronics module 216 allows the local 2 processor 352 to read the sensor array 212 and 3 measure any or all the sensor combinations.

5 Data output from the ratio tool 200 is typically an 6 array of bar graph modules or data that can be 7 transmitted to a remote computer, typically via a 8 serial interface 364, where software can generate a 9 variety of graphical representations of the data 10 output, or can display the numerical values or a 11 combination thereof.

13 The processor 352 may optionally be coupled to a 14 display unit 362 for displaying the resistance and 15 capacitance measurements described above, in 16 addition to the calculated fluid ratio. The results 17 may be in the form of graphical representations as 18 described above It should be noted that the 19 processor 352 may be directly coupled to the display 20 unit 362, or may be coupled via a telemetry system 21 or the like.

23 The local processor 352 may also be programmed to 24 produce a numerical display of fluid ratio in simple 25 fluid regimes, or where graphical data is not 26 required. For remote operation of the tool 200, the 27 processor 352 is provided with the serial interface 28 364 that allows the processor to communicate with a 29 remote host station (not shown).

31 The electronics module 216 also includes the local 32 power supply 366 that provides local power to the

1 electronics systems within module 216, typically 2 +12v DC and 5V DC for logic.

4 Fig. 10 illustrates an electronics module 400 that 5 can be used where the fluid ratio tool 200 and flow 6 meter 10, 100 are combined either in a single unit 7 or two units operating together. Electronics module 8 400 is a combination of module 140 (Fig. 8) and 9 module 216 (Fig. 9). The components and operation 10 of module 400 are substantially the same as that of 11 modules 140, 216. It should be noted that the A/D 12 convertors/counters 310, 369, local processors 302, 13 352, display units 304, 362, serial interfaces 308, 14 364 and local power supplies 300, 366 do not require 15 to be duplicated, and only one set of these 16 components is shown in Fig. 10.

18 Fig. 11 illustrates an electronics module 500 that 19 can be used to control operation of the flow meter 20 10, 100, wherein the meter 10, 100 is located 21 remotely at some distance from the main display and 22 power supply electronics, such as in a subsea or 23 downhole oil well installation. Electronics module 24 500 includes surface electronics 500s that may be 25 positioned, for example, at the surface, and remote 26 electronics 500r that may be located, for example, 27 downhole. The surface and remote electronics 500s, 28 500r typically communicate via a cable 510 or a 29 suitable telemetry system.

31 Surface electronics 500s includes a power supply 502 32 that provides local power to the surface electronics

1 500s (located, for example, at the surface), and the 2 remote electronics 500r includes a power supply 504 3 to power the remote electronics 500r which may be 4 located, for example, downhole as part of the flow 5 meter 10, 100 or ratio tool 200. Power supplies 6 502, 504 are typically +12v DC and 5V for logic, and 7 24 volts for the remote system. Power supply 502 8 generates a DC power supply that is transmitted 9 (through a current limiter 503) to the main power lo supply 504 for the remote electronics 500r where it 11 can be filtered and regulated to provide local power 12 supplies for the remote electronics 500r A local 13 processor 506 is used to perform the resistance and 14 capacitance calculations as detailed above and can 15 be used to drive a display unit (not shown) for 16 visual representation of flow readings as well as a 17 serial data interface 508. The display unit is 18 typically located at the surface where an operator 19 of the system can monitor the values of fluid flow 20 rate. 22 The processor 506 in the surface electronics 500s 23 acquires readings from the remote electronics 500r 24 by reading framed frequencies generated by the 25 remote electronics 500r superimposed onthe power 26 supply waveform generated by the surface 27 electronics 500s, which is used as a power supply to 28 the remote electronics 500r. The frequencies are 29 current modulated onto the power waveform and this 30 modulation is received via the power line 510 by an 31 amplifier and filter unit 512 in the surface 32 electronics 500s. The frequency signal generated by

l 1 the remote electronics 500r is amplified and 2 filtered to remove substantially all of the 3 background interference and noise that has been

4 added to the signal.

6 It should be noted that the remote electronics 500r 7 in this embodiment does not include a local 8 processor. This avoids the common problems 9 associated with operating processors in hazardous 10 conditions wherein pressure and temperature can 11 adversely affect their operation.

13 The electronics module 500 typically operates on a 14 two-wire system that can be, for example, a 15 mono-conductor cable.

17 The three shear load cells 120 are shown as one unit 18 514 in Fig. 11 as the outputs of the cells 120 can 19 be connected together in parallel or fed into three 20 separate amplifier units. A pressure sensor 516 and 21 a fluid temperature sensor 518 are also provided 22 The pressure and temperature sensors 516, 518 may be 23 combined into a single sensor body, but typically 24 require to be measured through two separate data 25 channels. 27 Each of the data channels from unit 514, pressure 28 sensor 516 and temperature sensor 518 include an 29 amplifier and filtering unit 520, 522 and 524 30 respectively.

1 In one embodiment, the voltage signals from the 2 amplifier and filtering units 520, 522, 524 are fed 3 into respective voltage-tofrequency converters 526, 4 528, 530 and then into a multiplexer unit 532 which 5 transmits the three frequencies in a repeating 6 sequence with a synchronizing pulse between each 7 complete three channel transmission as illustrated 8 in Figs 12a and 12b.

10 Referring to Figs 12a and 12b, Fig. 12a is a 11 simplified diagram of the multiplexer unit 532.

12 Unit 532 includes a free running four-way logic 13 switch 550 that is used to direct one of three 14 frequencies F1, F2 and F3 or a 0 volt signal to an 15 output O. The outputs from the load cell unit 514, 16 the pressure sensor 516 and the temperature sensor 17 518 are assigned a particular frequency F1, F2 or F3.

18 As shown in Fig. 12b, these frequencies F1, F2, F3 19 are multiplexed using switch 550 into a continuous 20 stream. The stream comprises N cycles of F1, 21 followed by N cycles of F2, followed by N cycles of 22 F3, after which there is a synchronization pulse 23 that comprises a Ovolt (or no frequency signal) for 24 N cycles of F1. The number of cycles N is chosen to 25 suit the particular application.

27 The number of cycles N is typically chosen by taking 28 one of the frequencies, say Fl, and selecting a 29 number of cycles of frequency F1 that gives a 30 reliable transmission.

1 Referring back to Fig. 11, the multiplexed signal 2 (ie the continuous stream in Fig. 12b) is fed into a 3 line driver 534 that modulates the current on the 4 power supply line 510 with the frequencies F1, F2, 5 F3. This modulation is then detected across a sense 6 resistor 536 in the surface electronics 500s and is 7 fed into the amplifier and filter unit 512 where it 8 is conditioned and amplified. The conditioned 9 signal is then passed to a counter 538 that is used 10 to ascertain which of the three frequencies F1, F2, 11 F3 was sent. The frequencies F1, F2, F3 typically 12 relate to a particular reading from the load cell 13 unit 514 and the pressure and temperate sensors 516, 14 518, wherein the fluid flow through the meter 10, 15 100 can be calculated using Equation 2 above.

17 Fig. 13 is a schematic block diagram of an 18 electronics module 600 for use with a remote fluid 19 ratio tool 200, which in this example is used 20 independently of a flow meter 10, 100. Electronics 21 module 600 includes surface electronics 600s that 22 may be positioned, for example, at the surface, and 23 remote electronics 600r that may be located, for 24 example, downhole. The surface and remote 25 electronics 600s, 600r typically communicate via a 26 cable 614 or a suitable telemetry system.

28 The remote electronics 600r comprises a multiplexer 29 array 602, the inputs to the multiplexer array 602 30 being electrically coupled to one of the plurality 31 of sensors 212, that allows a local processor 604 to

1 direct signals to or receive signals from any of the 2 sensors 212.

4 A frequency driver 606 that applies an AC signal to 5 any of the sensors 212 (depending upon the setting 6 of the multiplexer 602) generates an AC drive 7 waveform whose frequency and amplitude is determined 8 by drive signals generated by the local processor 9 604. The frequency driver 606 is also used to lo provide the DC voltage used to perform the 11 resistance test described above.

13 Two amplifier and filter units 608, 610 are 14 provided. Unit 608 is coupled to the multiplexer 15 array 602 and can be used to provide either a direct 16 voltage signal to an A/D convertor 612, or to 17 transform the voltage signal to a frequency that is 18 then fed to a counter 612 (in place of, or in 19 addition to, the A/D convertor 612) for the 20 dielectric measurement. Similarly, unit 610 is 21 coupled to the multiplexer array 602 and can be used 22 to provide either a direct voltage signal to the A/D 23 convertor 612, or to transform the voltage signal to 24 a frequency which is then fed to the counter (in 25 place of, or in addition to, the A/D convertor 612) 26 for the resistance measurements.

28 The electronics module 600 includes an oscillator 29 circuit 640 that is similar to circuits 260 and 368.

30 Circuit 640 can be used to determine the complex 31 impedance and/or resonant frequency of the fluid

1 that can be used to determine the nature and/or 2 ratio of the fluids, as previously described.

4 The electronics module 600 allows the local 5 processor 604 to read the sensor array 212 and 6 measure any or all the sensor combinations.

8 The local processor 604 transmits data to the 9 surface electronics 600s by modulating the current lo on a power supply line 614 using a line driver 616.

11 The transmission from the remote electronics 600r is 12 detected across a sense resistor 630, and the signal 13 is filtered and amplified in a filter and gain unit 14 632, the signal being fed into a counter 633 wherein 15 the transmission can be reconstructed using the 16 processor 618. The processor 618 is provided with a 17 serial data link 634 for transmission of the results 18 to other remote stations, for example.

20 Voltage modulation is used to transmit bits of data 21 to the remote electronics 600r from the surface 22 electronics 600s so that operation of the remote 23 electronics 600r can be controlled remotely.

25 The remote processor 604 receives commands from the 26 surface electronics 600s by using a surface 27 processor unit 618 to apply voltage modulation to a 28 power supply 620. Power supply 620 generates a 29 voltage modulated power waveform that is transmitted 30 via a current limiter 622 and the power line 614 to 31 the remote electronics 600r. A local power supply 32 625 in the remote electronics receives the power

1 waveform and filters and rectifies the waveform to 2 provide local power supplies for the remote 3 electronics 600r 5 The modulated signal generated by the surface power 6 supply 620 is decoupled from the power line 614 at 7 decoupling capacitor 624 and is then filtered and 8 amplified in an amplifier and filter unit 626. A 9 comparator 628 allows the power waveform 10 communication to be reconstructed and fed in to the 11 processor 604 at the remote location for subsequent 12 execution. 14 Serial communication is typically in ASCII and can 15 be, for example, in a MODBUS format. It will be 16 appreciated that any serial communication protocol 17 could be used.

19 The data output from the tool 200 is typically an 20 array of bar graph modules that can be displayed on 21 a local or remote display (not shown). Data can 22 also be transmitted to a computer where software 23 generates a variety of graphical and representations 24 of the data output.

26 The surface processor 618 can also be programmed to 27 produce a numerical display of the fluid ratio in 28 simple fluid regimes or where graphical data is not 29 required. 31 Fig. 14 illustrates a combination electronic module 32 680 that includes the electronic module 500 of the

i 1 flow meter 10, 100 and the electronic module 600 of 2 the fluid ratio tool 200, wherein the fluid ratio 3 tool 200 and the flow meter 10, 100 are used 4 together. 6 In Fig. 14, it should be noted that only one surface 7 electronics module 500s (600s) is required.

9 In order to determine that the mathematical analysis 10 above (Equations 1 and 2) was applicable to a large 11 orifice with an increase and then sudden decrease in 12 diameter, a prototype flow meter (not shown) was 13 constructed, substantially as shown in Figs 3a and 14 3b, but using linear strain gauges in place of the 15 load cells 120. The meter was then tested using 16 water as the fluid, with the average of a number of 17 test results being used. A voltage-to-frequency 18 convertor was used to convert the output voltage 19 from the strain gauges to frequencies to allow the 20 results to be processed by the processor.

22 Fig. 15 shows a plot of the flow squared against the 23 frequency output from the strain gauges using the 24 prototype flow meter. The results of the test were 25 plotted, giving a substantially straight line. A 26 best-fit line was drawn through the points, the line 27 having the equation y = 139.97x - 7E+6. From Fig. 28 15 it is clear that the force of the fluid is 29 proportional to the square of the flow, which 30 confirms that Equation 1 above is applicable.

: 1 A number of applications of the flow meter 10, 100 2 and fluid ratio tool 200 will now be described. For 3 the purpose of illustrating applications, the 4 illustrations show a combination of the flow meter 5 10, 100 and the fluid ratio tool 200 in use. It 6 should be noted that the flow meter 10, 100 may be 7 used independently of the fluid ratio tool 200, or 8 vice versa.

10 Fig. 16 shows an exemplary oil well installation 11 700. The oil well 700 includes a wellhead 702 12 located at the surface, and a production tubing 13 string 704 suspended therefrom. The tubing string 14 704 extends downwardly in a wellbore 706 that is 15 typically cased, and includes a flow meter 100 and a 16 ratio tool 200 suspended below the flow meter 100.

18 The combination electronics module 680 (Fig. 14) is 19 located between the flow meter 100 and the ratio 20 tool 200 and controls the operation of both as 21 previously described. Module 680 is electrically 22 coupled via a permanent instrument cable 708 (or 23 otherwise) to the surface electronics module 500s.

24 A wellhead penetrator 710 is used to facilitate 25 passing of the instrument cable 708 through the 26 wellhead 702 whilst maintaining pressure within the 27 wellbore 706.

29 Both the flow meter 100 and ratio tool 200 are 30 mounted in the pipeline or tubing string 704 with 31 all fluid within the tubing string 704 preferably 32 passing through them. The choke 118 of the flow

1 meter 100 has a positive direction and thus requires 2 the flow meter 100 to be orientated within the 3 pipeline 704 correctly.

5 The combined electronics module 680 reads the 6 signals from the array of sensors 212 in the fluid 7 ratio tool 200, and also the output form the load 8 cells 120 in the flow meter 100. The connections of 9 the flow meter 100 and fluid ratio tool 200 are 10 configured to suit the pipeline 704.

12 A display and processing unit in the surface 13 electronics 500s provides a display of flow rate and 14 the fluid ratio values to an operator of the system.

15 These can be monitored continuously to ascertain the 16 type of fluid being extracted from the wellbore 706 17 and in what quantities. By monitoring the flow 18 rate, the operator may also receive indications of 19 any blockages or other problems within the tubing 20 string 704 that may adversely affect the flow rate.

22 Fig. 17 shows a portion of subsea pipeline 750 that 23 includes the flow meter 100 and ratio tool 200. The 24 combined electronics unit 630 is encased in a 25 pressure tight housing suitable for the water depth 26 of the installation. A submarine cable 752 could be 27 run from the combined electronics unit 680 to the 28 surface, where the surface electronics 500s would be 29 located, which would be able to display the flow 30 rate and ratio information, and may also have a data 31 output to other computer systems, that is typically 32 a serial interface 754. Alternatively' or

: 1 additionally, a suitable telemetry system may be 2 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.

8 The outer housings 112, 202 of the flow meter 100 9 and ratio tool 200 are typically manufactured from 10 suitable material for prevention of corrosion and/or 11 may be coated for additional protection.

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 loo 19 has a positive direction and is required to be 20 orientated within the pipeline correctly.

22 The combined electronics module 680 reads the 23 signals from the array of sensors 212 in the fluid 24 ratio tool 200 and also the output form the load 25 cells 120 in the flow meter 100. The pipe 26 connections would be configured to suit the pipeline 27 800.

29 The surface electronics 500s would provide a display 30 of the flow rate and fluid ratio values, and it 31 typically coupled to the electronics module 680 32 using a two-wire cable 802. Optionally, the surface

1 electronics 500s can display the flow rate and ratio 2 information, and may also have a data output to 3 other computer systems, that is typically a serial 4 interface 804.

6 Thus, there is provided a flow meter for use in a 7 pipeline that can be used to measure the flow rate 8 of 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.

16 Modifications and improvements may be made to the 17 foregoing without departing from the scope of the 18 present invention.

Claims (32)

1 CLAIMS

2 1. A ratio tool comprising a body, a longitudinal 3 bore provided in the body, and a plurality of fluid 4 identifier sensors positioned in a fluid flow 5 through the bore, wherein the fluid identifier 6 sensors are capable of measuring the resistance and 7 capacitance of the fluid flow through the ratio tool 8 to determine the nature and/or ratio of the fluid(s) 9 in the fluid flow.

11

2. A ratio tool according to claim 1, wherein the 12 body comprises a tubular body, the fluid identifier 13 sensors being mounted within the body.

15

3. A ratio tool according to either preceding 16 claim, wherein the fluid identifier sensors are 17 equidistantly spaced around an inner circumference 18 of the body to form an array.

20

4. A ratio tool according to any preceding claim, 21 wherein the resistance of the fluid is measured 22 using a resistance bridge measure.

24

5. A ratio tool according to any one of claims 1 25 to 3, wherein the resistance of the fluid is 26 measured by applying a direct current (DC) signal to 27 one of the fluid identifier sensors, and measuring 28 the signal received at any one (or more) of the 29 other fluid identifier sensors.

31

6. A ratio tool according to claim 5, wherein the 32 DC signal is applied to each fluid identifier sensor

-D 1 sequentially, and the signal is measured at each 2 fluid identifier sensor sequentially.

4

7. A ratio tool according to claim 5 or claim 6, 5 wherein an average resistance can be determined from 6 the measurements.

8

8. A ratio tool according to any preceding claim, 9 wherein the capacitance of the fluid is measured by 10 applying an alternating current (AC) signal to one 11 of the fluid identifier sensors, and measuring the 12 signal received at any one (or more) of the other 13 fluid identifier sensors.

15

9. A ratio tool according to claim 8, wherein the 16 AC signal is applied to each fluid identifier sensor 17 sequentially, and the signal is measured at each 18 fluid identifier sensor sequentially.

20

10. A ratio tool according to claim 8 or claim 9, 21 wherein an average capacitance can be determined 22 from the measurements.

24

11. A ratio tool according to any preceding claim, 25 wherein the capacitance across the fluid identifier 26 sensors forms part of a filter circuit.

28

12. A ratio tool according to claim 11, wherein the 29 frequency response of the filter circuit changes as 30 the dielectric of the fluid changes.

1

13. A ratio tool according to any preceding claim, 2 wherein the bore is provided with a separating 3 device to separate fluids entering the ratio tool.

5

14. A ratio tool according to claim 13, wherein the 6 separating device comprises a profiled wall.

8

15. A ratio tool according to any preceding claim, 9 wherein the fluid identifier sensors comprise plates 10 or bars.

12

16. A ratio tool according to any preceding claim, 13 wherein the fluid identifier sensors are supported 14 by annular rings within the body, and are spaced 15 therefrom wherein fluid can circulate around the 16 fluid identifier sensors.

18

17. A ratio tool according to any preceding claim, 19 wherein the fluid identifier sensors extend 20 substantially the full length of the tubular body.

22

18. A ratio tool comprising a body, a longitudinal 23 bore provided in the body, and a plurality of fluid 24 identifier sensors positioned in a fluid flow 25 through the bore, wherein the fluid identifier 26 sensors are capable of measuring the complex 27 impedance of the fluid flow through the ratio tool 28 to determine the nature and/or ratio of the fluid(s) 29 in the fluid flow.

1

19. A ratio tool according to claim 18, wherein 2 the body comprises a tubular body, the fluid 3 identifier sensors being mounted within the body.

5

20. A ratio tool according to claim 18 or claim 19, 6 wherein the fluid identifier sensors are 7 equidistantly spaced around an inner circumference 8 of the body to form an array.

10

21. A ratio tool according to any one of claims 18 11 to 20, wherein an oscillating circuit is used to 12 determine the complex impedance of the fluid.

14

22. A ratio tool according to claim 21, wherein the 15 fluid between any of the fluid identifier sensors 16 forms a part of the oscillating circuit.

18

23. A ratio tool according to claim 21 or claim 22, 19 wherein the complex impedance of the fluid is 20 determined by performing circuit analysis on the 21 oscillating circuit.

23

24. A ratio tool according to any one of claims 21 24 to 23, wherein an output of the oscillating circuit 25 is indicative of the complex impedance of the fluid.

27

25. A ratio tool according to claim 24, wherein the 28 output of the oscillating circuit comprises a 29 resonant frequency that is used to determine the 30 complex impedance of the circuit

! 1

26. A ratio tool according to any one of claims 18 2 to 25, wherein the bore is provided with a 3 separating device to separate fluids entering the 4 ratio tool.

6

27. A ratio tool according to claim 26, wherein the 7 separating device comprises a profiled wall.

9

28. A ratio tool according to any one of claims 18 lO to 27, wherein the fluid identifier sensors comprise 11 plates or bars.

13

29. A ratio tool according to any one of claims 18 14 to 28, wherein the fluid identifier sensors are 15 supported by annular rings within the body, and are 16 spaced therefrom wherein fluid can circulate around 17 the fluid identifier sensors.

19

30. A ratio tool according to any one of claims 18 20 to 29, wherein the fluid identifier sensors extend 21 substantially the full length of the tubular body.

23

31. A ratio tool substantially as hereinbefore 24 described with reference to Figs 1 and 2 of the 25 drawings.

27

32. A ratio tool substantially as hereinbefore 28 described with reference to Figs 5, 6a, 6b and 7a to 29 7d of the drawings.