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Title:
METHOD AND APPARATUS FOR MONITORING OF THE MULTIPHASE FLOW IN A PIPE
Document Type and Number:
WIPO Patent Application WO/2016/050792
Kind Code:
A1
Abstract:
A monitoring apparatus for monitoring a multiphase flow in a pipe using magnetic induction tomography, the apparatus comprising: at least one annular 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.

Inventors:
HUNT ANDREW (GB)
BYARS MALCOLM (GB)
MCCANN DOMINIC PATRICK (GB)
Application Number:
PCT/EP2015/072469
Publication Date:
April 07, 2016
Filing Date:
September 29, 2015
Export Citation:
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Assignee:
IPHASE LTD (GB)
International Classes:
G01F1/74; G01F1/58; G01R33/422
Domestic Patent References:
WO1993004493A11993-03-04
Foreign References:
GB2507368A2014-04-30
EP2383582A22011-11-02
US20130229178A12013-09-05
GB2507368A2014-04-30
EP2379990A12011-10-26
EP2044470A12009-04-08
US20080258717A12008-10-23
US7276916B22007-10-02
Other References:
"MPFM Handbook", 2005
Attorney, Agent or Firm:
PETER DAVID JENKINS et al. (Bedford HouseJohn Street,London Greater, London WC1N 2BF, GB)
Download PDF:
Claims:
Claims

1. A monitoring apparatus for monitoring a multiphase flow in a pipe using magnetic induction tomography, the apparatus comprising: at least one annular 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.

2. An apparatus according to claim 1 wherein the annular screen is located radially inwardly of the at least one annular array of coils.

3. An apparatus according to claim 1 or claim 2 wherein the annular screen comprises a plurality of screen portions, each screen portion being located at a respective position in an axial direction along the pipe.

4. An apparatus according to claim 3 wherein the annular screen comprises a plurality of first electrically 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.

5. An apparatus according to claim 4 wherein each first electrically conducting screen portion comprises a metallic sheet, optionally of copper.

6. An apparatus according to any one of claims 3 to 5 wherein 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.

7. An apparatus according to claim 6 wherein the second electrostatic screen portion comprises a sheet of electrically insulating material carrying an array of electrically conducting elements, each electrically conducting element being connected to an electrical ground potential via an electrical resistance.

8. An apparatus according to claim 7 wherein each electrically conducting element is substantially planar and extends substantially along the sheet of electrically insulating material.

9. An apparatus according to claim 7 or claim 8 wherein 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.

10. An apparatus according to any one of claims 6 to 9 wherein the second electrostatic screen portion comprises a flexible printed circuit board.

1 1. An apparatus according to claim 1 or claim 2 wherein the annular screen comprises an array of electrically conducting coil elements, each coil element having a pair of electrical terminals selectively correctable to a source of electrical energy.

12. An apparatus according to claim 1 1 wherein the array of electrically conducting coil elements is on a sheet of electrically insulating material, each coil element extending substantially along the sheet of electrically insulating material.

13. An apparatus according to claim 1 1 wherein each coil element is substantially planar.

14. An apparatus according to any one of claims 1 1 to 13 wherein the apparatus further 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.

15. An apparatus according to claim 14 wherein the controller is adapted to modif an impedance connected to at least some of the respective selected coil elements in the array to modify the magnitude of the local electromagnetic field generated from the respective energized coil element.

16. An apparatus according to claim 14 or claim 15 wherein the controller is adapted to selectively switch electrical current through selected coil elements in the array to provide a composite electromagnetic field generated from the energized coils, when transmitting, and the energized coil elements having a controllable focal point within the pipe.

17. An apparatus according to claim 14 or claim 15 wherein 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, when receiving, from a controllable focal point within the pipe.

18. An apparatus according to claim 16 or claim 17 wherein the controller is adapted to scan the controllable focal point across a cross-section of the pipe and/or along a flow direction along the pipe.

19. An apparatus according to claim 18 wherein the controller is adapted to scan the controllable focal point across a plurality of points to provide a pixelated image of the multiphase flow.

20. An apparatus according to any one of claims 1 to 19 further comprising 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 from at least one other coil, the second screening device comprising an annular electrically conducting screen located around the pipe.

21. An apparatus according to claim 20 wherein the annular electrically conducting screen is located radially outwardly of the at least one annular array of coils.

22. An apparatus according to claim 20 or claim 21 wherein the annular electrically conducting screen comprises a metallic sheet, optionally of copper.

23. An apparatus according to any one of claims 20 to 22 wherein the annular electrically conductin screen is connected to an electrical ground potential via an electrical resistance.

24. An apparatus according to any one of claims 1 to 23 wherein the 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 field and generate an output electrical signal.

25. An apparatus according to claim 24 wherein each first coil is circumferentially offset, in a direction around the pipe, with respect to a respective adjacent second coil, to reduce or minimise direct electromagnetic coupling between the respective first and second coils.

26. An apparatus according to claim 24 or claim 25 wherein the first and second coils are provided on opposite sides of a second sheet of electrically insulating material.

27. An apparatus according to claim 26 wherein the first and second coils and the second sheet of electrically insulating material comprise a flexible printed circuit board.

28. A method of monitoring a multiphase flow in a pipe using magnetic induction tomography, the method comprising the steps of:

a. providing at least one annular 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,

b. flowing a multiphase flow along the pipe; c. transmitting an electromagnetic field from a first coil into the multiphase flow;

d. receiving by a second coil an electromagnetic field from the multiphase flow and generating 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.

29. A method according to claim 28 wherein the annular screen is located radially inwardly of the at least one annular array of coils.

30. A method according to claim 28 or claim 29 wherein the annular screen comprises a plurality of screen portions, each screen portion being located at a respective position in an axial direction along the pipe.

31. A method according to claim 30 wherein the annular screen comprises a plurality of first electrically 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.

32. A method according to claim 31 wherein each first electrically conducting screen portion comprises a metallic sheet, optionally of copper.

33. A method according to any one of claims 30 to 32 wherein 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.

34. A method according to claim 33 wherein the second electrostatic screen portion comprises a sheet of electrically insulating material carrying an array of electrically conducting elements, each electrically conducting element being connected to an electrical ground potential via an electrical resistance.

35. A method according to claim 34 wherein each electrically conducting element is substantially planar and extends substantially along the sheet of electrically insulating material.

36. A method according to claim 34 or claim 35 wherein 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.

37. A method according to any one of claims 33 to 36 wherein the second electrostatic screen portion comprises a flexible printed circuit board.

38. A method according to claim 28 wherein the annular screen comprises an array of electrically conducting coil elements, each coil element having a pair of electrical terminals selectively connectable to a source of electrical energy.

39. A method according to claim 38 wherein the array of electrically conducting coil elements is on a sheet of electrically insulating material, each coil element extending substantially along the sheet of electrically insulating material.

40. A method according to claim 39 wherein each coil element is substantially planar.

41. A method according to any one of claims 38 to 40 further comprising, in step (e), selectively switching electrical current through selected coil elements in the array to generate from each energized coil element a local electromagnetic field.

42. A method according to claim 41 wherein in step (e) an impedance connected to at least some of the respective selected coil elements in the array is modified to modify the magnitude of the local electromagnetic field generated from the respective energized coil element.

43. A method according to claim 41 or claim 42 wherein 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 coils, when transmitting, and the energized coil elements having a controllable focal point within the pipe.

44. A method according to claim 41 or claim 42 wherein in step (e) electrical current is selectively switched through selected coil elements in the array to provide a composite electromagnetic field received by the coils, when receiving, from a controllable focal point within the pipe.

45. A method according to claim 43 or claim 44 further comprising the step of (f) scanning the controllable focal point across a cross-section of the pipe and/or along a flow direction along the pipe.

46. A method according to claim 45 wherein the scanning of the controllable focal point is across a plurality of points to provide a pixelated image of the multiphase flow,

47. A method according to any one of claims 28 to 46 wherein in step (e) at least one second screening device screens 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 second screening device comprising an annular electrically conducting screen located around the pipe.

48. A method according to claim 47 wherein the annular electrically conducting screen is located radially outwardly of the at least one annular array of coils.

49. A method according to claim 47 or claim 48 wherein the annular electrically conducting screen comprises a metallic sheet, optionally of copper.

50. A method according to any one of claims 47 to 49 wherein the annular electrically conducting screen is connected to an electrical ground potential via an electrical resistance.

51. A method according to any one of claims 28 to 50 wherein the 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 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).

52. A method according to claim 51 wherein each first coil is circumferentially offset, in a direction around the pipe, with respect to a respective adjacent second coil, to reduce or minimise direct electromagnetic coupling between the respective first and second coils,

53. A method according to claim 51 or claim 52 wherein the first and second coils are provided on opposite sides of a second sheet of electrically insulating material.

54. A method according to claim 53 wherein the first and second coils and the second sheet of electrically insulating material comprise a flexible printed circuit board.

28

Description:
Method and apparatus for monitoring of the multiphase flow in a pipe

The present invention relates to a method of, and a monitoring apparatus for, monitoring a multiphase flow in a pipe using magnetic induction 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 conjunction with other techniques such as those mentioned in GB2507368A.

In the current state of the art the optimisation of production from subsea wells is difficult because flow from multiple wells is often comingled in subsea manifolds and transferred to surface through a single flowline. As a result, the flow from any one 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 surface then it is unknown from which well it is coming. The multiphase flowmeters in the market today are expensive and may not be reliable enough to be placed on each wellhead.

Multi-component flows are often loosely called multiphase. For example, a mixed flow of oil and water is not multiphase (it is one phase - liquid) but it is multi-component (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 multi-component and multiphase are used interchangeably to mean the same thing - a mixture of fluids and solids flowing in a pipe.

In the case of a multiphase flow with several components, the operator (for example, an oil company) requirement may be the volume or mass flowrate of some or all of components. In a typical oilfield flow the operator requires the measurement of the mass flow of gas, oil and often the water, but typically not specifically the solids. Although measurement of the flowrate or concentration of solids is a useful additional measurement and can help determine the health of the downhole 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, erosion. There are many applications of multiphase flowmeters in the oil industry for flows of gas, oil, water and solids: downhole, wellhead, platform, pipelines, subsea, wet gas, heavy oil, gas lift, tar sands etc. The further upstream in the process the more complex and demanding the conditions, so subsea and downhole 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 wellhead there is almost always some gas present. In addition, most wells produce some water and the amount increases through the life of the well until by the end of its life the well may be 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, but frequently this is associated with the production of light oil known as condensate and again later in life some water is likely to be produced.

Therefore both oil and gas wells generate multiphase 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 term 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 be used for the purposes of production enhancement.

It is very beneficial for both the reservoir and production engineers to have reliable measurements of the multiple phases in the production from a well. In addition 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 different problems to the production engineer. Real-time determination of these different and 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 separates the input flow into output flows of oil, gas and water with three independent single-phase flowmeters to measure each. In production this is still the prime measurement technique - here the flow needs to be separated anyway for use in the downstream process. For well testing, well monitoring and subsea completions however the separator is a large, expensive and not very accurate unit and is steadily being replaced by multiphase flowmeters. However, as already mentioned, multiphase flowmeters available in the market have many drawbacks that 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 Venturi element to the meter.

The oilfield environment is physically demanding - high pressure (up to 1000 bar), with high temperatures of the fluids (up to 250 degrees Celsius), variation of physical properties of the oil and gas (PVT), variation in salinity of the produced water, issues of ¾S 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 flowmeters available can be found in oil industry catalogues (see for example MPFM Handbook Revision 2 2005 ISBN-82-91341 -89-3) along with the technologies used in each. The essence of many of them is that the overall mass flow is estimated by a Venturi meter, in most the density is estimated using a gamma density meter and then some sort of electrical method is used to estimate the oil/water ratio. The common use of a gamma ray nuclear source is one particular requirement of devices that the industry 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 reliability issues. This is due to the fact that the pressure in the meter can be very high (1000s of PSI) but pressure drop across the Venturi is typically less than 0.1 PSI. As a result it is typical to have a delta pressure (dP) sensor rather than two absolute pressure sensors, one each side of the Venturi. It should also be noted that the Venturi imposes a restriction in the flow. Unfortunately, dP sensors can be a source of reliability issues, for example, a blockage or restriction of the pressure feed on one side of the sensor causes an overpressure resulting in the sensor failing. Large pressure transients cross the Venturi can have a similar result, it is not uncommon for these dP gauges to fail within a year or two of operation.

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 be 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 highly fluctuating in both space and time, it can be shown that there is an unbounded error if the average phase concentration is multiplied by the average phase velocity to get average phase volumetric flowrate, this error may easily be 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, current multiphase 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 way to reduce the slip velocity to zero is to completely homogenize the different phases before metering but this would necessitate significant separation problems downstream, otherwise accurate multiphase flowrate measurements must start with independent estimates of velocity and concentration of each component across the flow.

Another issue with the solutions presently available is that phase concentrations are averages and it is unknown how these phases are distributed in the flow. For example, a meter 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 bubbles or even a single bubble.

Finally, some prior art has attempted to address some of these issues, for example, see EP 2379990 Al Multiphase flowmeter. However, the resulting solution involves splitting the flow such that the meter has an obstruction in the flow stream. In many applications the measurement must be non-intrusive so that access to the pipeline is not impeded. The addition of an obstruction in the meter has significant disadvantages. For example, anything directly in the flow path has a tendency to erode, leading to early failure. The increased pressure drop can also impact production performance. Three-phase 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 pre-mixed before passing through the meter and it is 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 examples include the electromagnetic flowmeter, electrical capacitance tomography (ECT), electrical resistance tomography (ERT) 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 field can be used to measure certain physical parameters of the constituent components.

The present invention provides a monitoring apparatus for monitoring a multiphase flow in a pipe using magnetic induction tomography, the apparatus comprising: at least one annular 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 preferred embodiment, the annular screen comprises a plurality of screen portions, each screen portion being located at a respective position in an axial direction along the pipe.

Preferably, the annular screen comprises a plurality of first electrically 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 electrostatic screen portion comprises a sheet of electrically insulating material carrying an array of electrically conducting elements, each electrically conducting element being connected to an electrical ground potential via an electrical resistance. Typically, each electrically conducting element is substantially planar and extends substantially along the sheet of electrically insulating material.

In this specification the term "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 circumference of the pipe.

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 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 terminals selectively connectable to a source of electrical energy.

Preferably, the apparatus further 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 modify an impedance connected to at least some of the respective selected coil elements in the array to modify the magnitude of the local electromagnetic field generated from the respective energized coil element. In one embodiment, the controller is adapted to selectively switch electrical current through selected coil elements in the array to provide a composite electromagnetic field generated from the energized coils and the energized coil elements having a controllable focal 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 from a controllable focal point within the pipe. In either of these embodiments, the controller may be adapted to scan the controllable focal point across a cross-section of the pipe and/or along a flow direction along the pipe. The controller may be adapted to scan the controllable focal point across a plurality of points to provide a pixelated image of the multiphase flow.

In another preferred embodiment, the apparatus further comprises 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 from 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 electrically conducting screen comprises a metallic sheet, optionally of copper.

Preferably, the annular electrically conducting screen 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 transmit an electromagnetic field when energized by an input electrical signal and a second annular array of second coils arranged to receive an electromagnetic field and generate an output electrical signal.

Preferably, each first coil is circumferentially offset, in a direction around the pipe, with respect to a respective adjacent second coil, to reduce or minimise direct electromagnetic 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.

Preferably, the first and second coils and the second sheet of electrically insulating material comprise a flexible printed circuit board.

The present invention further provides a method of monitoring a multiphase flow in a pipe using magnetic induction tomography, the method comprising the steps of: a. providing at least one annular 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, b. flowing a multiphase flow along the pipe; c. transmitting an electromagnetic field from a first coil into the multiphase flow; d. receiving by a second coil an electromagnetic field from the multiphase flow and generating 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 screen is located radially inwardly of the at least one annular array of coils.

In one preferred embodiment, the annular screen comprises a plurality of screen portions, each screen portion being located at a respective position in an axial direction along the pipe. Preferably, the annular screen comprises a plurality of first electrically 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. Typically, each first 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 element being connected to an electrical ground potential via an electrical resistance.

Typically, each electrically conducting element is substantially planar and extends substantially along the sheet of electrically insulating material.

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 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 terminals selectively connectable to a source of electrical energy.

Preferably, the method further comprises, in step (e), selectively switching electrical current through selected coil elements in the array to generate from each energized coil element a local electromagnetic field.

Preferably, in step (e) an impedance connected to at least some of the respective selected coil 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 coils and the energized coil elements having a controllable focal point within the pipe.

In another embodiment, in step (e) electrical current is selectively switched through selected coil elements in the array to provide a composite electromagnetic field 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 cross-section 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 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 second screening device comprising an annular electrically conducting screen located around the pipe, and typically radially outwardly of the at least one annular array of coils.

Preferably, the annular electrically conducting screen comprises a metallic sheet, optionally of copper.

In another preferred embodiment, the annular electrically conducting screen 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 transmit an electromagnetic field when energized 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 circumferentially offset, in a direction around the pipe, with respect to a respective adjacent second coil, to reduce or minimise direct electromagnetic 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.

Preferably, the first and second coils and the second sheet o electrically insulating material comprise a flexible printed circuit board.

The present invention relates specifically to an improved method and apparatus for the use of MIT (Magnetic Induction Tomography), in particular in the application of MIT to measuring multiphase flows in the oil and gas and other industries. The 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 be used to compute the conductivity contrast between the object and the material that surrounds it. See for example EP 2044470 Al and US 20080258717. Magnetic induction has been used to measure components of a multiphase flow, see US7276916B2, but this application makes only one measurement across the flow.

MIT is mentioned as one of three combination elements in GB2507368A. 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 fluids from a well or group of wells during oil and gas exploration, production 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 additionally provided in this invention. These and other aspects of the present invention will now be 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 art;

Figure 4 shows a schematic sectional end view of an arrangement of transmitting and receiving coils and a screening device in accordance with an embodiment 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 embodiment of Figure 4; and

Figure 7 is a schematic plan view of the structure of a second screen which may be used in the embodiment of Figure 4.

Hereinafter, the present invention will now be described in more detail with reference to the accompanying figures, in which exemplary embodiments of the invention are shown. The invention may, however, be 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 be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.

Referring to Figure 1 there is shown a schematic of a multiphase flow, 1 1 , in a pipeline 10. In 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 13 and 14. Solid (e.g., sand) in the flow is illustrated as labelled 15. The figure illustrates that the flow in the pipeline, 10, has multiple 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 better understand these various flow regimes, the reasons for their existence and how they affect overall production performance, see for 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 Figure 2b is a view parallel to the flow. Referring to Figure 2a there are a plurality of coils, 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 2a antennae 313 is shown as a transmitter. A varying electric current is 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 313 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 interrogate 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 will in turn generate a secondary varying electromagnetic field that will propagate through the pipe where it will be 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 varying 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, for example, 12, 13 and 14, to be computed.

At any point in time there is one coil that is transmitting and all of the others are receiving. 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 forth. As an example, 313 is the first transmitter coil then the coil immediately next to it going clockwise becomes the next transmitter. After that, the next coil immediately next to and clockwise to it 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 that a complete cycle o 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 be 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 configuration can be provided whereby certain coils are always transmitters and others are always receivers. In other embodiments coils can be 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.

Referring to Figure 2b, it is shown that there are 2 sets of coils 36 and 317 that are separated 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 possible to cross correlate the measurements from these two sets, 36 and 317, in order to establish the time-of-flight of features that represent different phases in the multiphase flow 11. This is illustrated in Figure 2c where 31 1 shows two curves; one showing a feature passing coils 36 and the second the same feature passing electrodes 317. The 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 the time difference is longer illustrating that this phase is travelling slower than the first phase shown by 31 1. It will be understood by those skilled in the art that the features shown by 31 1 and 312 could in fact be derived by cross correlating 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 labelled 14. It will be appreciated that while Figure 2a shows 3 phases (12, 13 and 14); it is possible that more can be present and in particular solids (e.g. sand) can also be present. Also, these velocities can be obtained when the primary or continuous phase is either conducting (e.g. water) or non-conducting fluid (e.g. oil).

The electromagnetic measurement, 30, as described above will provide measurements where there is a conductivity contrast between the phases. This is possible when the different phases or constituents are flowing in a predominately conducting (e.g. water) or non-conducting (e.g. oil) primary phase 12.

Although the apparatus representing the state of the art shown in Figures 2a, 2b and 2c 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.

Figure 3 shows the same embodiment as in Figures 2a, 2b and 2c, but simplified and indicating the approximate electromagnetic field lines 320 when coil 36 is energised as a transmitter and coils 317 are receivers. As before 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 of water, represented by 321 , will influence the measurement as it cuts the electromagnetic field lines 320 even though it is nominally Outside' of the sensor. A similar element such as 13 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 differentiate between the effects 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 for monitoring a multiphase flow in a pipe using magnetic induction tomography.

The monitoring apparatus 400 comprises two annular arrays 402, 404 of coils disposed around a pipe 408 which defines therein an imaging space 406. In the first array 402, each 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. Preferably, the first 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 sheet of electrically insulating material 414 comprise a flexible printed circuit board.

In Figures 4 and 5 the monitoring apparatus 400, forming a cylindrical MIT sensor, has 8 electrode-pairs 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 PCB 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 electromagnetic field when energized by an input electrical signal and/or to receive an electromagnetic field and generate an output electrical signal. This may be provided by a flexible printed circuit board.

The monitoring apparatus 400 further 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 interfering 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 arrays 402, 404 of coils. The internal screening device 416 consists of a partially- 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 (ES) and the coil array (CA) for electromagnetic and electrostatic screening.

Referring to Figure 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 X-X 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 comprises a second electrostatic screen portion 424. The second screen portion 424 is aligned, in the axial direction X-X along the pipe 408, to at least one of the first and second annular arrays 402, 404 of the first 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 annular 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 electrically conducting screen 452 located around the pipe 408 and radially outwardly of the annular arrays 402, 404. Preferably, the annular electrically conducting screen 452 comprises a metallic sheet, typically of copper. The annular electrically conducting screen 452 is connected, as illustrated schematically, to the electrical 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 electrostatic screen portion 424 comprises a flexible printed circuit board. 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, but 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 from 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. The embodiment shows an array of 4 x 4 elements, but any desired number may be provided. Each "star" is earthed via a resistor which has a sufficiently low value to hold the screen at ground potential, while preventing any significant currents flowing to earth, which would otherwise act as an electrical short-circuit.

In this embodiment, any capacitive 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 between the coils 410, 412 and the imaging space 406. The electrostatic screen portion 424 provides a network of partially-earthed printed circuit board (PCB) tracks, which extend over 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 the screen surface. In contrast, the earthed metal screen formed by the first electrically conducting screen portions 420 acts as an electromagnetic screen because the electromagnetic field would cause large eddy currents to flow in the conducting screen portions 420 and these currents would generate a secondary electromagnetic field, which would cancel the primary field at the screen surface.

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 be used with a relatively short receiving coil, as a possible method for improving measurement sensitivity 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 transmitted electromagnetic field. In an alternative embodiment of the present invention as shown in Figure 7, there is provided a means o 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 electromagnetic screen when the coil-pair is in receiving mode. Such a means is provided by replacing the conducting regions of the inner screen of Figure 6 with a switchable electromagnetic screen which can be switched on and off using an array of coils which can be switched to be either open or short-circuited.

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 is 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, but 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 pair of electrical terminals 508, 510 selectively connectable is (for clarity of illustration as shown schematically for one element 504) to a source of electrical energy 512. A 4 X 4 array of elements 504 is shown but any number may be selected as desired.

The monitoring apparatus further comprises a controller 514 for selectively switching electrical current through selected coil elements 504 in the array 502 to generate from each energized coil element 504 a local electromagnetic field. Preferably, the controller 514 is adapted 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 electrical current through selected coil elements 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 controllable focal 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 controllable focal point across a cross-section of the pipe 408 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 multiphase flow.

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

In other embodiments each coil can be controlled independently of the others so that certain coils are on while others are off. The selective on/off switching of the coils can be changed in order to create a required screening characteristic for the array as a whole. Additionally, rather than each being either off or on by being either open or short-circuited, in an alternative arrangement the coil behaviour is changed by varying the impedance so that the coil can be gradually changed from open to short-circuit. The degree is controllable to change the coil electromagnetic 'transmissibility' characteristics. Each coil is controlled independently in 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 controllable. Electromagnetic energy passing through the array is focused at a given focal point or the array is controlled to receive electromagnetic energy from a given focal point. Such an array can then be controlled in real-time to scan across the flow cross-section and/or along the flow path as its focal point is moved. A pixelated image of the flow can thus be produced. In another embodiment a composite intelligent screen may be provided by printing the electrostatic "star" screen of Figure 6 on one side of an insulating cylinder and the electromagnetic "coil" screen of Figure 7 on the other side of the cylinder. With suitable switching, the function of the individual array elements could therefore be controlled remotely.

The monitoring apparatus 400 is used in a method of monitoring a multiphase flow in a pipe using magnetic induction tomography.

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

The 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.

The second screening device 450 screens the coils 410, 412 of the annular arrays 402, 404 from an interfering electromagnetic field emitted from at least one other coil 410, 412.

In the screening step using annular screen 500, electrical current is selectively switched through 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 504 in the array 502 is modified to modify the magnitude of the local electromagnetic field generated from the respective energized coil element 504. In one embodiment, the electrical current may be selectively switched through selected coil elements 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 controllable focal point within the pipe 408. In another embodiment, the electrical current may be selectively switched 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. The controllable focal point may be scanned across the array 502 of electrically conducting coil elements 504 to scan the generated electromagnetic field across a cross-section of the pipe 408 and/or along a flow direction along the pipe 408. Tthe scanning of the controllable focal point may be across a plurality of points to provide a pixelated image of the multiphase flow.

When the MIT monitoring apparatus 400 is used for flow measurement, the detector coils 410, 412 only "view" the area of the imaging space 406 at the same axial location as the coil arrays 402, 404 in order to maximise the axial resolution of the measurement system of the monitoring apparatus 400, In the embodiment of Figures 4 and 5, the cylindrical electromagnetic screen comprised of the plurality of first electrically conducting screen portions 420 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. Accordingly, the two copper cylinders of the first electrically conducting screen portions 420, located offset forwardly and rearwardiy, 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 screening of interfering electromagnetic fields increases the sensitivity of the electromagnetic induction tomography across the pipe and along the axis o the pipe as compared to known for monitoring multiphase flow in a pipe apparatus, and can provide lead to clearer and more precise imaging of 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 multiphase flow.

Various other embodiments of the monitoring apparatus and method of the present invention within the scope o the appended claims will readily be apparent to those skilled in the art.