GB2530601A - Method and apparatus for monitoring of the multiphase flow in a pipe - Google Patents

Abstract

A monitoring apparatus for monitoring a multiphase flow in a pipe using magnetic induction tomography comprises at least two annular arrays 41, 37 of coils disposed around a pipe, each coil being adapted to transmit an electromagnetic field when energized by an input electrical signal and/or to receive an electromagnetic field and generate an output electrical signal, and at least one screening device for screening at least one of the coils of at least one of the annular arrays from an interfering electromagnetic field emitted from at least one other coil, the screening device comprising an annular screen located around the pipe.

Description

for moni toñn'of the multi hase flow ins inc The present invention relates to a method of, and a monitoring apparatus for, monitoring a muhiphase flow in a pipe using magnetic inducdon tomography. The multiphase flow comprises fluids, and may comprise a mixture of liquids, or one or more liquids in a mixture with solids and/or gases. This invention relates to a multiphase flow metering apparatus and method which has a number of applications, in particular within the oil and gas exploration and production industry. The method and apparatus is an arrangement of coils suitable for improving the use on Magnetic Induction Tomography, either used alone or in coiunction with other techniques such as those mentioned in 0B2507348A.

In the current state of the art the opuimisation of production from subsea wells is difficuk because flow horn multiple *el s is often uornu gled in subsea manifolds ard transfcncd to surthce through a single flowline. As a result, the flow from any on.e well, is not measured and so cannot be optimised by means of artificial lift or other techniques. For example, if there is an increase in the production of water at surhice then it is unknown from which welt it is coming. The multiphase flowrneters in the market today are expensive and may not he reliable enough to be plaued on each welD ed Multicomponent flows are often loosely called multiphase. For example, a mixed flow of' oil and water is not muiuphase (it is one phase liquid) but it is multiconiponeni (two components oil and water). A typical oilfield flow of oil, gas and water may often contain solids (for example, sand or hydrates.) and thus have four components but only three phases. Throughout this specification, the same loose convention as in many industries is adopted and the terms nulticomponcnt and multiphase me used irterchangeably to mean the sane thEng a mixture of fluids and solids flowing in a pipe.

In the case of' a nultiphase flow with several components, the operator (for example, an oil company) requirement may he the volume or mass fiowrate of some or all of components. In a typica.t oilfleld flow the operator requires the measurement of the mass flow of gas, oil and often thc ater, oat typically ot speciflcal the solids Although measurement of the flowrate or concentration of solids isa uceflj additwoal neasw.ement and can help determine the health of the dowohole sand screens or gravel packs, Early detection of' the potential failure of these elements of the system will help reduce failure of other components due to, for example, c osion There are many applications of multiphase flowmeters in the oil industry for flows of gas. oil.

water and solids: downhole., welihead, platidna, pipelines, subsea. wet gas, heavy oil, gas liii, tar sands etc. The further upstream in the process the more complex and demanding the condinons, so subsea and dowrihole are the most difficult, An oil well starts life producing mainly oil, but as the oil depressurizes along the flow line gas is liberated, so at the welihead there is almost always some gas present. In addition, most wells produce some i -iter and the smo mt rncicses thiough t e life of the well unu by l e ud u' its life the well may he producing mostly water. Because of the long flow path even small quantities of gas may cause the well to slug oscillating between high liquid and high gas states.

A gas well starts life producing mainly gas, hut frequently (lila is associated with the production of light oil luiown as condensate and again later in life some water is likely to he produced.

Therefhre both oil and gas wells generate muitiphase flows with gas, oil and water almost always present in highly variable quantities, and in addition many reservoir formations produce sand as a natural part of production, and any workover of the reservoir will often leave some solids to be cleaned out over the succeeding days or weeks.

In this specification and claims the temi oil well' will be used to represent any kind of well drilled for oil and gas exploration and/or production, including injection wells that can he used for the purposes of production enhancement.

it is very beneficial fhr both the reservoir and production engineers to have reliable messurerrdnt of the mi Itiple phases in the producuon fiom a ivell l' adthtion to the quantitative measurements of the volume or mass flowrates of the individual components, it is also very beneficial to determine the flow regime, that is, how the different phases are distributed in the flow. For example, the same volume of gas arriving at surface as slugs rather than evenly distributed in the flow represents very different production scenarios and poses thheient probiem to the production engineer Reahtime determ aation of these cifferent anc changing flow regimes would offer reservoir and production engineers a deeper insight into production and so allow improved optimization.

The historical normal method for measuring flowrate of oil, gas and water is to use a separator that sepatates the invut fo%4 ito output flows of I, gas and water wth three uideptndert singlep-iase floikn eterb to mea',uu. cach In produeflon trns m still the prime measurenert technique here the flow needs to he separated anyway for use in the downstream process. For well testing, well rnonitonng and subsea completions however the separator is a large.

expensive and not very accurate unit and is steadily being replaced by multiphase fiowmeters.

However, as already mentioned, multiphase fiowmeters available in the market have many drawbacks tha.t have limited their application and the invention here disclosed addresses these shortcomings. in particular, multiphase flowmeters on the market today widely use a nuclear source (sometimes more than one) and restrict the flow by the use of a \enturi element to the meter.

[he otifleld envuni met is phyia1l. demanding -high pessuic (up to 1000 lan with vigh tempetatures of the fiwds (up to S0 defrees Ce1stu), snaion ot physical properties of the oil and gas (PVT), variation in salinity of the produced water, issues of H2S production (known as sour gas), subsea or downhole access etc. This has led to various meter designs involving multiple technologies in order to address each challenge As a result the cost base is high, independent of the technologies used.

A list of the main multiphase fiowmeters available can he thund in oil industry catalogues (see for example MPFM Handbook Revision 2 2005 iSBN-S29l34i-89-3) along with the technologies used in each. The essence of many of them is that the overaH mass flow is estimated by a Venturi meter. in most the density is estimated using a gamma density meter and then some sort of electncal method is used to esnm:te the oihkater rat o The on mon use of a gamma ray nuclcar source is one particular requirement of devices that the indostry has wanted to remove for some time. Obviously the use of a nuclear source brings issues related to health and safety but also security in some situations. The common use of a Venturi has also lead to reliabiiiy issues, This is due to the thct that the pressure in the meter can he very high (i000s ofFS! hut pressure drop across the Venturi is typically less than 0.1 PSi As a result it & typical to ha\ e a CC[ta pressure (dP) sensoi iather than to ibsolute pressure sensos one each side ot he Venturi It sho.ild also be noted that the Verturi imposes a restrktior in the flow. Unfortunately, dP sensors can he a source of reliability issues, for example, a blockage or restriction of the pressure feed on one side of the sensor causes an oveTpressure resulting in the sensor failing. Large pressure transients cross the Venturi can have a similar result. It is not uncommor fort iese dP gaugcs to fa I vit:iin a ycr ci two of opntion Another issue with solutions in the prior art is the fact that average densities and velocities are generally estimated across the meter, for example. the nuclear absorption provides an average density estimation across the meter. Also, it is well known that in many situations the velocity of the different phases can be quite different, for example. the velocity of' the gas bubbles can he very different to the velocity of the oil or water in which they travel. The difference is often called the slip velocity' of one phase relative to another, Because the various fluids are high'y fluctuating in both space and time, it can be shown that there is an unbounded error if the averagc phsse concentration is multiplied by the n erage phase eluetty o get aerage phase volumetric fiowrate, this error may easily he 50% of the reading, see Hunt 2012. in fact, the phase velocity and concentration must be multiplied together before integration across the flow to get the correct answer, However, generally, cun'ent muitiphase flowmeters do the multiplication incorrectly because they are based on independent devices that average across the flow first, Corrections may be attempted by using slip velocity models. However the fundamental problem of the incorrect integration process means that the correction is often large and uncertain.

The only wv tc reduce the sEp velocity to 7e1o s to comnleteiy hourogcnize he different phases before metering but this would necessitate significant separation problem a downstream, otherwise accurate rnuhiphase fiowrate measurements must start with independent estimates of velocity and concentration of each component across the flow, Another issue with thc solutions prcsenfly available us that phase concentrations a"e averages and it is unknown how these phaceq are dustuhutee in the flow lot exan'plc a mLt3r may indicate that the flow stream contains 70% oil and 30% gas, However, it is not necessarily known if the gas is distributed in small bubbles in the stream or in larger hubbies or even a single bubble.

Finally, some prior art has attempted to address some of these issues, for example, see EP 2379990 Al Muitiphaceflownreter. However, the resulting solution involves splitting the flow such that the meter has an obatniction in the flow stream. In many applications the measurement must he nomintrusive so that access to the pipeline is not impeded. The addition of an obstruction in the meter has signifrcant disadvantages, For example, anything directly in the Jow path Ub a tendem y to erode, leading to arIy fadure Thu increased pressure th'op an also rmpact production perfbrmance. 4.

1Threephase flow has nine variables: the velocity, density and concentration (often call holdup) of each phase. If the pipe contains only the three phases then the sum of concentrations = 100%. Therefore, in principle eight measurements are required. In instruments available today there are generally less than 8 measurements (often using different technologies) and so assumptions are required. For example, phase densities are measured using samples of fluids and are considered constant between samples, slip velocities are calculated using models or all phases are premixed before passing through the meter and it k assumed all 3 velocities are equal. Any of these assumptions can introduce significant errors in the measurements obtained.

it is understood that electromagnetic energy can provide information related to certain physical properties of materials exposed to this type of energy. Well known exampies include the electromagnetic flowneter, electrical capacitance tomography (ECT), dectrical resistance tomography (.ER.T) and magnetic inductance tomography (MIT). In each case a varying electric or magnetic field can be applied across the material and measurements of voltage, current and magnetic fi&d can be used to measure certain physical parameters of the constituent components.

The present invention provides a monitoring appararus tar monitonng a niultiphase flow in a pipe using magnetic induction tomography, the apparatus eoirpns ng at least one anm lar array of coils disposed around a pipe, each coil being adapted to transmit an electromagnetic field when energized by an input electrical signal and/or to receive an electromagnetic field and generate an output electrical signal. and at least one screening device for screening at least one of the coils of at least one of the annular arrays from an interfering electromagnetic field emitted from at least one other coil, the screening device comprising an annular screen located around the pipe.

Typically, the annular screen is located radially inwardly of the at least one annular array of coils.

In one peferred embodiment, the ann flat scicer comprises a phiralit) of screen portinns eaci screen portion being located a a respect ye nositon in an axial dsection along the pipe Pieferabh, the ann'a. srcon on'puses a plura ity of first eleLtnuaiIy conducting screen portions, each first screen portion being offset, in an axial direction along the pipe, relative to at least one annular array of coils. More preferably, each first electrically conducting screen portion comprises a metallic sheet, optionally of copper.

Preferably, the annular screen comprises a second electrostatic screen portion aligned, in an axial direction along the pipe, to at least one annular array of coils. More preferably, the second electiostatw screen portion Compnsu a sheet of e1e&tru ally nulatirg material c rymg an array of eketrically conducting elements, each electrically conducting element being connected to an electrical ground potential via an electrical resistance, Typically, each electrically conducting clement is substantially planar and extends substantially along the sheet of electrically insulating material.

In this specification the tenn "planar" encompasses an element having a curvature so as to be oriented in a curved direction associated with and around the corresponding curvature of the circumlerence of the pipe.

Preferably, each electrically conducting element comprises a plurality of electrically conductive spurs extending fro n a central prt of me electucafly conducting element, tao spurs being mutually electrically insulated apart from at the central part.

Preferably, the second electrostatic screen portion comprises a flexible printed circuit board.

In another preferred embodiment, the annular screen comprises an array of electrically conducting coil elements on a sheet of electrically insulating material, each coil element being substantially planar and extending substantially along the sheet of electrically insulating material, each coil element having a pair of electrical temunals selectively connectable to a source of electrical energy.

Preferably, the apparatus ffirther comprises a controller for selectively switching electrical current through selected coil elements in the array to generate from each energized coil element a local electromagnetic field, More preferably, the controller is adapted to modfty an impedance connected to at least some of the respective sciected coil elements in the array to modify the rnagmtudc of the local electromagnetic field generated from the respective energized coil element.in one embodiment, the controller is adapted to selectively s-witch elecfrical current through selected coil elements in the array to provide a composite electromagnetic tie d geneiated lion rhe eneigized coils and the eneigized coil elementc having a controllable fbcal point within the pipe.

In another embodiment, the controller is adapted to selectively switch electrical current through selected coil elements in the array to provide a composite electromagnetic field received by the coils flo ii a controllable ibeal punt withm ih pipe In either of these embodiments, the controller may be adapted to scan the controllable fhcal point across a crosssection of the pipe and/or along a flow dEtection along the pipe. The controller may be adapted to scan the controllable foca' point across a plurality of points to provide a. oixeiated image of the multiphase flow.

In another preferred embodiment, the apparatus further compnscs at least one second screening device for screening at least one of the coils of at least one of the annular arrays from an interfering electromagnetic field emitted 1' cm at least one other coil, the second screening device comprising an annular electrically conducting screen located around the pipe and radially outwardly of the at least one annular array of coils.

Preferably, the annular eEectrica] Ey conducting screen comprises a metallic sheet, optionally of copper.

Preferably, the annular electrically conducting screen is connected to an electrical ground potential ia an electncal resistance In another prcfened embodiment. thc at least one annular array of coils comprises a first annular array of first coils arranged to transmit an electromagnetic field when energized by an input electrical signal and a second annular array of second coils arranged to receive an electromagnetic fied and generate an output ekctrical signal.

PreferaHy. each first coil is circurnferentially offset, in a direction around the pipe, wilt respect to a respective adjacent second coil, to reduce or minimise direct electromagietic coupling between the respective first and second coils.

Preferably, the first and second coils are provided on opposite sides of a second sheet of electrically insulating material Preferaby, the first and second coils dnd the second sheet of electrically insulating material comprise a flexible printed circuit board.

The present invention further provides a method of monitoring a rntdtiphase flow in a pipe asing magnctic mduction tomogapny, the irethod compns ng tht steus of a providing at Icast one annu'ai array of co Is disnosed aound a p pe, each coil being anapled to transmrt an electromagncac ibId when encrgved by an input clectnci signal and,or to receive an electromagnetic field and generate an output electrical signal, b. flowing a multiphase flow along the pipe; c, transmitting an electromagnetic field from a first coil into the muitiphase flow; d. receiving by a second coil an electromagnetic field from the multiphase flow and generaüng an output electrical signal therefrom; and e. screening, during at least step (d), at least one of the coils of at least one of the annular arrays from an interfering electromagnetic field emitted from at least one other coil, by a screening device comprising an annular screen located around the pipe.

Typically, the annular sueen is ocated radially nwaidiy of the at least one anrular array of coils.

In one preferred embodiment, the annular screen comprises a plurality of screen portions, each screen portion being locatcd at a respective position in an axial direction along the pipe.

Preferably. the annular screen comprises a plurality of first electrically conducting screen porti'ns, eacn first sreon portico being offset, in an axial direction along the pipe, rciatie to at least ore ann,a an of coils fymcaiy, each that electrically conducting screen portion comprises a metallic sheet, optionally of copper.

Preferably. the annular screen comprises a second electrostatic screen portion being aligned, in an axial direction along the pipe, to at least one annular array of coils, More preferably, the second electrostatic screen portion comprises a sheet of electrically insulating material carrying an array of electrically conducting elements, each electrically conducting eiemen.t being connected to an electrical ground potential via an electrical resistance.

Typically, each electrically conducting element is substantially planar and extends uh\tant1fly along the sheet of ell. ctn ally in'ulating matci ml Preferably, each electrically conducting element comprises a plurality of electrically conductive spurs extending from a central part of the electrically conducting element, the spurs being mutually electrically insulated apart from at the central part.

Preferably, the second electrostatic screen portion comprises a flexible printed circuit board.

in another preferred ernbodimenL, the annular screen comprises an array of electrically conducting coil elements on a sheet of electrically insulating material, each coil element being substantially planar and extending substantially along the sheet of electrically insulating a material, each coil element having a pair of electrical terminals selectively connectable to a source of electucal energy Preferably, the method thiTher comprises, in step (e), selectively switdhing electrical current through selected coil elements in the array to generate from each energized. coil element a local

electromagnetic field.

Preferably in rep e) an npcdarcc connected te r least some of the respect e selected coi elements in the array is modified to modify the magnitude of the local electromagnetic field generated from the respective energized coil element.

In one embodiment, in step (e) electrical, current is selectively switched through selected coil elements in the array to provide a composite electromagnetic field generated. from the energized cods and the entrgized coil clernent having a cnrnrnllable oca1 pant ttnrn the ppe In another embodiment, in step (e) electrical current is selectively switched through selected coil elements in the array to provide a composite electromagnetic held received by the coils from a controllable focal point within the pipe.

Preferably, the method further comprises the step of' (f) scanning the controllable focal point across a crosssection of the pipe and/or along a flow direction along the pipe. Optionally, the scanning of the controllable focal point is across a plurality of points to provide a pixelated image of the multiphase flow.

in another preferred embodiment, in step (e) at least one second screening device screens at east one of the cotls of at least one of the annular an'avs horn an anterfenng electromagnetic field emitted from at least one other coil, the second screening device conwdsing an annular electrically conducting screen located around the pipe, and typically radially outwardly of the at least one annular array of coils, Preferably, tte annular electrically conducting screen comprises a metallic sheet, optionally of copper in nothei preterred embodiment the annn1r e]ccmcalty cond..rctmg crecn is connected to an electrical ground potential via an electrical resistance, In another preferred embodiment, the at least one annular array of coils comprises a first annular array of first coils arranged to transm tan elccronagnenc field then ene gized by an input electrical signal in step (c) and a second annular array of second coils arranged to receive an electromagnetic field and generate an output electrical signal in step (d).

Preferably, each first coil is circur.nfbrentiafly offset, in a direction around the ripe. with respect to a respective adjacent second coil, to reduce or minimise direct electromagnetic coupling, between the resoective first and second coils.

Preferably, the first and second coils are provided on opposite sides of a second sheet of electrically insulating material, Preferably. the first and second coils and the second sheet of electrically insulating material comprise a fiexihk printed circuit hoard, The present invention relates spectically to an unproved method and apparatus for the use of MTT (Magnetic Induction Tomography), in particular in the application of MIT to measuring muluphase flows in the oil and gas and other industries 1 he principle of MIT is that electric coils are excited with alternating current that results in the coils producing varying electromagnetic fields, The object of interest is placed within these fields and the varying field induces varying currents within the object that is dependent on the conductivity of the object.

The varying currents in the object produce secondary electromagnetic fields that can be received by the same or other coils, The received secondary electromagnetic field in conjunction with the primary imposed electromagnetic field can use he used to compute the conductivity contrast between the object and the material that surrounds it See for example EP 2044470 Al and U.s 20080254717. Magnetic induction has been. used to measure components of a niuhiphase flow see US 12 169lo82 but this application makes only one measurement ross the flow MIT is mentioned as one of three combination elements in 0B2507368A. The present invention relates to an apparatus to improve the measurements of such a system.

The preferred embodiments of this invention disclose a method to measure the flow of mixtures of fl,nds from a we I or gioup ot wells cunng oil and gas exploratiot, produc ion or transportation operations. Through these listed aspects of this invention, the inventors have provided different embodiments, which cover some of the potential applications of the multiphase flowmeter described. However, it is understood that this is a subset of the potential applications and those skilled in the art will appreciate that there can be many others which are additionaily pro ided i tits unent on These and other aspects of the present invention will now he described, by way of examples, with reference to the accompanying drawings, in which: Figure 1 illustrates multiphase flow through a pipeline; Figures 2a, 2b and 2c show schematics of an electromagnetic measurement that is in accordance with an embodiment of the state of the art; Figure 3 shows the approximate electromagnetic field lines of the coils used in the state of the Figure 4 shows a schematic sectional end view of an arrangement of transmitting and receiving coils and a screening device in. accordance with an enthodiment of the present invention; Figure 5 shows a schematic sectional side view of the arrangement of transmitting and receiving coils and screening device of Figure 4; Figure 6 is a schematic plan view of the structure of a first screen which may be used in the enihodiment of Figure 4; and Figure 7 is a schematic plan view of the structure of a second screen which maybe used in the embodiment of Figure 4, Hereinafter, the present invention will now he described in more detail with reference to the accompanying figures, in which exemplary embodiments of the invention are shown. The invention may. however, he embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will he thorough and complete, and will fully convey t.h.e concept of the invention to those skilled in the art, Refernng to F g'n'e 1 there is shown a schenthc ot a rn. Itiphase flow, 11, in a pipe'ine C) ir Figure 1, 12, illustrates the primary or continuous phase of the flow, e.g., oil. water or gas.

Within this primary phase there is schematically shown two other constituents to the flow labelled i3 and 14. Solid (eg., sand) in the flow is illustrated as labelled 15. The figure illustrates that the flow th the pipeline, 10, has muitipk phases including solids, Clearly this figure is a simplistic and the distribution of these phases can vary significantly depending on the concentrations of each phase and the flow regime. The structure of such multiphase flows can be very complex and there are many industry papers that attempt to explain this complexity and bctttr understand these vanous flow regin cc the. reasons foi neu exicte CC zi d how they affect overall production performance. see hr example Hunt et al 2010, In Figures 2a. 2b and 2c is shown a schematic of a measurement element, 30, representing the state of the art. Figure 2a shows a cross-section that is taken perpendicular to the flow and Thgure 2n is a siexs patallel to the flow Rcfcmng o Fig-nrc 2a there arc i plurality of cci s 36. arranged around the circumference of the instrument. In Figure 2a the continuous or primary fluid phase or constituent is labelled 12 e.g., oil. Two other phases or constituents are shown diagrammatically as 13 and 14; these could be gas and water, respectively. Each of the antennae 36 can act as either a transmitting or receiving coil and can change between the two modes In Figure 3a antennae 11 is shosn ass tranmdter A aiyu g electric cuirent s Passed through the coil 313 as illustrated by the sign wave 37. Although this varying signal is shown as a sine wave it could be of another form, e.g,, square wave and all other potential forms are provided in this invention. The varying electric current passing through the coil 3 13 will generate a varying electromagnetic flux through the multiphase fluid 11 that is within the pipe.

The electromagnetic flux lines are schematically shown and one is labelled 314 for illustration purposes. Depending on the physical properties of the different phases that the flux lines niterrogate and in particular the conductivity contrast between. e.g.. phases 12 and 14, a varying current is induced in the second phase, 14. This is shown schematically and labelled 315 in Figure 2a, This induced current svill in turn generate a secondary varying electromagnetic field that will propagate through the pipe where it will he pickup by the other antennae that are used as receivers, This secondary varying electromagnetic field is shown as dashed lines and labelled 316 in Figure 2a and will induce vrrying currents in the receiver coils, This is shown schematically in one coil on Figure 2a and labelled 38. Comparing 37 and 38 with appropriate processing, for example, the phase shift between the signals, allows the conductivity contrast between the materials, thr example. 12. 13 and 14, to be computed.

At an point in time there is one coil tat is transmnttng and all of the others ate recei ing Once all the receiver coils signals have been processed, one or more of the other coils becomes the transmitter and again the remainder are receivers and so forthi As an example, 313 is the first transmitter coil then the coil immediately next to it going clockwise becomes the next ttansmittcr Atle that, the next coil imwee aels next ro and clockw se o becomes the transmitter, This continues around all the coils and eventually 313 will become the transmitter coil once more, in Figure 2a it will be appreciated by those skilled in the art that the sequencing can take place in any order and tha.i a complete cycle of measurements, that is, where every coil has been the transmitter once, can occur very rapidly with, e.g., 500 to 5000 measurement cycles every second. This frequency being primarily limited only by the processing power available that can he scaled as needed, it will also be appreciated by those skilled in the art that after one complete cycle of measurements a mesh of properties is produced that can be processed to provide a mesh or image of the fluids phases across the section of the pipe.

Although this description describes each coil being either a transmitter or receiver, clearly, a contguration can he provided whereby certain coils are always transmitters and others arc always receivers. In other embodiments coils can he enclosed within other coils so that dedicated transmitter and receiver coils are at the same location, Those skilled in the art will appreciate that many combinations are possible and all such combinations are provided in this invention, Refenrg to Thgwe 2b it is shown that LI crc axe 2 et of cc Ic 36 and 317 that ate separatee by a known fixed distance 39. Both sets operate in the same fashion and provide independent meshes or images of the flow at two points along the pipe 10. it is possihk to cross correlate the measurements from these two sets. 36 and 317. in order to establish the timeof-flight of features that represent different phases in the niultiphase flow 11. This is illustrated in Figure 2c where 311 shows two curves; one showing a feature passing coils 36 and the second the same feature passing electrodes 3 1 7. l"he time difference between the features provides the time it takes for this phase to travel from 36 to 317, that is, the distance 39, Those skilled in the art will appreciate that the velocity of this phase is easily computed from this information, In Figure 2c, 312 illustrates features that result from a different phase in the flow and in this case me nic difference is longer uIusrahng tha this wasc is t"aelhng slower than the first phase shown by 311, It will he understood by those skilled in the art that the features shown by 311 and 312 could in fact he derived by cross con'elating the mesh elements at the same location in the cross section of the pipe such that a velocity profile across the cross section of the pipe is obtained, That is, a mesh or image of velocities is produced that can be used to establish the velocity differences between the primary/continuous phase, phase labelled 13 and the phase labciled 14 It wi I be ppreuatcd mat while Figrre 2a shows 3 phases (12 13 anc 14) it is possible that more can be present and in particular solids (e.g. sand) can also be present. Also.

LI ese ye ocities can be obtained yhen the pnmary or continuous phase is erher conducting (e g wa Cr) or noricondactmg flrnd (e g oil) The elccnon"aguetic measciement 33, as described above wid provide measurements where there m a conductivity contrast eeen the phases Pus s possihie when the different phases or constituents are flowing in a predominately conducting (e.g. water) or noncondueting (e.g. oil) primaiy phase 12, Although the apparatus representing the state of the art shown in Fignres 2a, 2b and 2e can make the measurements described there are significant limitations in some aspects of the measurement. These restrictions will be discussed with regard to Figure 3.

iiguie 3 ci ow, the arre eTuhodirnent as in F gures 2a 2h and 2c, but smipife and indicating the approximate electromagnetic field lines 320 when coil 36 is energised as a transmitter and coils 317 are receivers, As hefbre transmitter 313 is a transmitter for a period of time, then the next coil of the array 36 is energised as transmitter in sequence around the pipe. in each case the electromagnetic field lines seen from a side view will have a similar form to 320.

A significant limitation of this embodiment of the state of the art is that the electromagnetic field lines 320 extend for an unlimited length of the pipe so that an element of multiphase flow, such as a bubble ol' water, represented by 321, will influence the measunnient as it cuts the electromagnetic field lines 320 even though it is nominally outside' of the sensor, Asirnilar element such as 1 3 will have a larger effect on the measurement as the electromagnetic field lines are closer together towards the centre of the sensor, but the measurement cannot di.tThrentiate between the efiècts of the two elements of multiphase flow, in Figures 4 and 5 is shown a preferred embodiment of the monitoring apparatus of the present invention, the apparatus being t'br monitoring a multiphase flow in a pipe using magnete induction tomography.

The monitoring apparatus 400 comprises two annular arrays 402, 404 of coils disposed around a pipe 4Ot which dciii cc therein n imaging spie 406 in t"e fisi arTd% 402, cah first coil 410. and indicated as TX. is adapted to transmit an electromagnetic field when energized by an input electrical signal, and in the second array 404 each second coil 412 and indicated as RX, is adapted to receive an electromagnetic field and generate an output electrical signal.

Preferably, each first coil 410 is circumferentially offset, indicated by the angle a. in a direction around the pipe 408, with respect to a respective adjacent second coil 412, to reduce or minimise direct electromagnetic coupling between the respective first and second coils 410, 412.

Preferahy, the flrst and second coils 410. 412 are provided on opposite sides of a sheet of electrically insulating material 414, Typically, the first and second coils 410,412 and the heet of electrically insulating material 414 comprise a flexible printed circuit hoard, In Figures 4 and 5 the monitoring apparatus 400, thnning a cylindrical MIT sensor, has 4 electrodepairs provided by the first and second coils 410, 412. The MIT sensor coil arrays 402, 404 are formed by pairs of transmitting (TX) and receiving (RX) coils 410, 412 printed on two sides of a flexible P03 laminate formed into a cylinder. The coils 410, 412 in each pair are offset by the angle a selected to minimise the direct coupling between the TX and RX coils within each pair.

In an alternative embodiment (not illustrated) there is a single annular array of coils, and each coil is adapted to transmit an dectromagnetic field when energized by an input electrical signal and/or to receive an electromagnetic field and generate an output electrical signal. [his may be provided by a flexible printed circuit hoard, The monitoring apparatus 400 farther comprises a screening device 416 for screening at least one of the coils 410, 412 of at least one of the annular arrays 402, 404 from an imerfering electromagnetic field emitted from at least one other coil 410, 412. The screening device 416 comprises an annular screen 418 located around the pipe 408 and radially inwardly of the annular rays 102 W4 of cot s he mteial scree. ng deice 416 con'sts o2 a part ally earthed electrostatic screen (ES) in the opposite the coil array (CA) location, with earthed conductive metal, e.g. solid copper, screens (CS) on opposite sides, with respect to the axial direction of the pipe 408, of the electrostatic screen dES) and the coil array (CA) for electromagnetic and electrostatic screening.

Referring to ligure 5, the annular screen 418 comprises a plurality of first electrically conducting screen portions 420. Each first screen portion 420 is offset, in the axial direction XX along the pipe 408, relative to at least one of the first and second annular arrays 402, 404 of the first and second coils 410, 412, Preferably, the first electrically conducting screen portions 420 comprise a metallic sheet, typically of copper.

The annular screen 418 also comurises a second electrostatic screen portion 424. The second screen portion 424 is ahgned, in the axia direction XX along the pipe 408, to at least one of the first and second atuiar arrays 402, 404 of the tirst and second coils 410, 412.

The monitoring apparatus 400 further comprises at least one second screening device 450 for screening at least one of the coils 410, 412 of the armuar arrays 402, 404 from an interfering electromagnetic field emitted from at least one other coil 402, 404, The second screening device 450 comprises an annular electricafly conducting screen 452 located around the pipe 408 arId radially outwardly of the annular arrays 402, 404. Preferably, the annular electrically conducting screen 452 c.mpuses a nieta I c sheet typica ly of coper ilte annular eketncall.

conducting screen 452 is connected, as illustrated schematically, to the &ectrieal ground potential 432 via the electrical resistance 434. The earthed cylindrical metallic electromagnetic screen 450 is located around the outside of the sensor to minimise external interfering signals from being received by the RX coils.

Referring to Figure 6, in one embodiment the second electrostatic screen portion 424 comprises a sheet 426 of electrically insulating material carrying an array 428 of electrically conducting elements 430. Preferably, the second electrostaric screen portion 424 comprises a flexible printed circuit hoard. Each electrically conducting element 430 is (for clarity of illustration as shown schematically for one element 430) connected to an electrical ground potential 432 via an electrical resistance 434. Typically, each electrically conducting element is substantially planar, hut including any curvature of the annular screen 420, and extends substantially along the sheet 426 of electrically insulating material. Each electrically conducting element 430 comprises a plurality of electrically conductive spurs 436 extending from a central part 438 of the electrically conducting element 430. The spurs 436 are mutually electrically insulated apart tram at the central part 438 In the arrangement shown in Figure 6, the second electrostatic screen portion 424 is constructed from an array of star" screening elements. T he embodiment shows an array of 4 x 4 elements, hut any desired number may he provided. Each star" is earth.ed via a resistor which has a sufficiently low value to hold the screen at ground potential, while preventing any significant cwrents flowing to earth, wrncn would otherwise a as an eiecna shortcir,uit In this embodiment, any canacitive coupling between the transmitting coils 410, TX and receiving coils 412, RX in the magnetic induction tomography (MIT) arrays 402, 404 can be minimised or eliminated by locating the cylindrical electrostatic screen portion 424 hctween the c nls 410 412 and (he irnagir g space 406 The electrostatic screen poror 42 provides a network of partialvearthed piured circr' board (PCB) tracks thich extend oer the area of the imaging space 406 but do not create any closed current paths (or loops). The absence of any closed current paths avoids the generation of eddy currents at high frequency electromagnetic, fields, for example 10MHz, which would. generate a secondary electromagnetic field, which in turn would cancel the primary electromagnetic field at die screen surface, in contrast, the earthed metal screen thrrned by the first electrically conducting scicen portions 420 acts a.s an electromagnetic screen because the electromagnetic field would cause large eddy currents to flow in the conducting screen portions 420 and these currents would gererate a secondary electromagnetic flod, u hioh would cancel ie pnxna.y field at the screen sm face In an MIT system, separate transmitting and receiving coils are typically used. to minimise switching complexity and so, in principle, an axially-long transmitting coil may he used with a relatively short receiving coil, as a possible method for improving measurement sensjtivity and axial resolution. However, in the screen arrangement of Figures 4, 5 and 6, if the axial length of the transmitting coil 410 is increased this would short out part of the lransmitted electrornagneuc field In an 1terna we emhodrnen of the prcent invention as shown n Figure 7, there is provided a means of making the region in front of the transmitting coil 410 transparent to electromagnetic fields when this coil 410 is excited, while making it act as an e1ecn'ornagnetc screen wheit the ccihpa" s m ieLewng mode Such a means is provided h, replacing the conducting regions of the imier screen of Figure 6 with a switchabIe electromagnetic screen which can be switched on and off using an array of coils which can he switched to be either open or shortcircuited.

Figure 7 illustrates an electromagnetic "intelligent" screen array which may be used as an alternative as the annular screen 418 of Figures 4 and 5. Referring to Figure 7, the annular screen 418 i.s provided by annular screen 500 which comprises an array 502 of electrically conducting coil elements 504 on a sheet 506 of electrically insulating material. Each coil element 504 is substantially planar, hut including any curvature of the annular screen 500. and extends substantially along the sheet 506 of electrically insulating material. Each coil element 504 has a pthr of electrical terminals 508, 510 selectively connectable is (for clarity of tilustration as shown schcmatically br one element 504) to a source of clectncal energy 512 A 4 X 4 array of elements 504 is shown but any number may be selected as desired.

The monitoring apparatos further comprises a controller 514 fhr selectively switching electrical current through selected cod elemerts 504 u the array 502 to generate Cacti energiLed coil element 504 a local elect omag ietic fiele P"efurahly, the cont"oller 14 s arhipled to modify an impedance connected to at least some of the respective selected coil elements 504 in the array 502 to modify the magnitude of the local electromagnetic field generated from the respective energized coil element 504, In one embodiment, the controller 514 is adapted to selectively switch e!ectiicai current through selected coil demerits 504 in the array 502 to provide a composite electromagnetic field generated from the energized coils 410, when transmitting, and the energized coil elements 504 having a controllaHe rocal point within the pipe 408. In another embodiment, the controller 514 is adapted to selectively switch electrical current through selected, coil elements 504 in the array 502 to provide a composite electromagnetic field received by the coils 412, when receiving, from a controllable focal point within the pipe 408. Typically, in either embodiment, the controller 514 is adapted to scan the controflahie focal point across a crosssection of the pine 40$ and/or along a flow direction along the pipe 408, and the scanning may scan the controllable focal point across a plurality of points to provide a pixelated image of the muitiphase flow.

Thus each of the coil elements 504 in the array 502 consists of a. coil which can he shorted by connecting together the pair of electrical terminals 508. 510, When this is done, eddy currents will be genetatud in the coil element 504 thuh will generate a local eectrornagnetic fi&d which will cancel the incident electromagnetic field.

In other ernhodunents each coil can he controlled independently of' the others so that certain coils are on while others are off, The selective on/off switching of the coils can he changed in order to create a required screening characteristic for the array as a whole. Additionally, rathcr than each being either off or on by being either open or shorteircuited, in an alternative arrangement the coil behaviour is changed by vaidng the impedance so that the cofl can he graduaHy changed from open to shortcireuit. The degree is controflable to change the coil electromagnetic transmissibi1ity' characteristics. Each coil is controlled independently i.n order to achieve a required screening or transmissibility behaviour for the array as a whole. For example, the array could be controlled to act as an electromagnetic lens' whose focal point is controIidbe. Eectroxnagnetic energy passing through the array is focused at a given foca point or the arra.y is controlled to receive electromagnetic energy from a given focal point. Such an array can then be controlled in reahtime to scan across the flow crossseetion andIor along the flow path as its foc& point is moved, A pixelated image of the flow can thus be produced, In another embodiment a composite intelligent screen may he provided by printing the electrostatic "star" screen oft Figure 6 on one side of an insulating cylinder and the electromagnetic "coil" screen of Figure 7 on the other side of the cylinder. \Vith suitahk switching, the function of the individual array elements could therefore be controlled remotely, The monitor ng apparatus 400 is used in a method of monitoring a muhiphase flow in a pipe using magnetic induction tomography.

In the method, a multiphase flow is flowed along the pipe 408, An electromagnetic field is tranmitted from. first cod 410 nto the multipiase flow The plural first uul' 410 are sequentially driven with the same signal, and in turn each of the first coils 410 becomes an active transmitter for a period of time.

ftc second coils 412 receive an electromagnetic field from the multiphase flow and generating an output electrical signal therefrom. During at least the receiving step, and typically during both the transmitting and receiving steps, at least one of the coils 410.412 of the annular arrays 402, 404 is screened from an interfering electromagnetic field emitted from at least one other coil 410, 412, by the screening device 416, which comprises the annular screen 420, 500.

I'he second screening device 450 screens the coils 4l 0,412 of the annular arrays 402, 404 iron, an interfering electromagnetic field emitted from at least one other coil 410, 412.

In hc screcnug s4ep usmg ann Lii screen 500, electncal currert is selectively svi:hd througn selected coil elements 504 in the array 502 to generate from each energized coil element 504 a local electromagnetic field. Typically, an impedance (not shown) connected to at least some of the respective selected coil elements 304 in the array 502 is modified to modi' the magnitude of the local electromagnetic field generated from the respective energized coil element 504. In one embodiment, the electrical current ma.y be selectively switched through selected coil elements 504 in t.he array 502 to prcvide a composite electromagnetic field generated from the energized coils 410, when transmitting, and the energized coil elements 504 having a controllable focal point within the pipe 408. In another embodiment, the electrical current may be selectRely itchcd throug'i selected co I elements 504 in the array 502 to provide a composite electromagnetic field received by the coils 412, when receiving, from a controllable focal point within the pipe 408, The controllable focal point maybe scanned across the array 502 of electrically conducting coil elements 504 to scan the generated electromagnetic field across a crosssection of the pipe 408 and/or along a flow direction along the pipe 408.

Tthe scaing of the controllable focal point may he across a plurality of points to provide a pixelated image of the muhiphase flow.

When the MIT monitoring apj.aratus 400 is used for flow measurement, the detector coils 41. (1, 413 only uview the area of the imaging space 406 at the same axial location as the coil arrays 4(12,404 in order to naxrrise he axial resolution oftFe measuremen system of the moritonng apparatus 400, In the embodiment of Figures 4 and 5, the cylindrical electromagnetic screen compnsed of the plurality of first electncaily conducting screen ortons 4.20 is located between the coils 410,412 and the imaging space 406. At an electromagnetic field frequency of 10MHz, the copper sheet of the first electrically conducting screen portions 420 acts as a good electromagnetic screen..kccordingy. the two copper cylinders of the first electrically conducting screen portions 420 located offset forwardly and rearwardly, in the flow direction along the pipe 408. relative to the coil arrays 402, 404. act to prevent the detector coils 410, 412 from seeing eddy current fields generated away from the axial location of the coil arrays 410, 412.

The scieemng o interfering electromagnenc fieks uiyeises the sei,sitri ity of the electromagnetic induction tomography across the pipe and along the axis of the pipe as compared to known for monitoring multiphase flow in a pipe apparatus, and can provide lead to clearer and more precise imaging cxf the flow than possible by the current state of the art. in particular the present invention can provide more accurate measuring of the transit velocity of elements of the rnultiphase flow.

Various other embodiments of the monitoring apparatus and method of the present invention within tlic scope. fthc appu ccc claims wil readily be apparent to those ski,led in tie art