WO2015118332A1

WO2015118332A1 - Measurement device and method

Info

Publication number: WO2015118332A1
Application number: PCT/GB2015/050320
Authority: WO
Inventors: Changhua QIU; Kent WEI
Original assignee: Industrial Tomography Systems Plc
Priority date: 2014-02-07
Filing date: 2015-02-05
Publication date: 2015-08-13
Also published as: GB201615078D0; GB2537792A; GB201402183D0

Abstract

A measurement device has a body defining an external periphery and comprises a two-dimensional array of electrodes disposed generally parallel to said external periphery of the body, an energisation source arranged to energise at least one of said electrodes, and a monitor arranged to measure an electrical parameter at least one of said electrodes. The energisation of an electrode by said energisation source causes an electric field to be established between at least one pair of electrodes, said electric field extending about said external periphery externally of said body.

Description

Measurement Device And Method

The present invention relates to a measurement device and method. More particularly, but not exclusively, the invention relates to a tomography apparatus for measuring the composition of material within in body to be imaged, such as, for example, a pipe.

Tomography refers to the use of some form of penetrating wave to image a region of interest. Generally, an image is constructed by the combination of a plurality of image sections. Tomography is often applied to industrial processes. In such applications tomography may involve the imaging of industrial systems, for example process pipes. The tomographic imaging enables various process parameters to be deduced relating to the contents of the process pipes. Tomography may thus be used to aid process control. The penetrating waves may be generated by electric or magnetic fields. Electrical resistance tomography (ERT) uses electrodes placed around the region of interest to monitor resistivity within the region of interest, and can be used for example to monitor characteristics of mixtures of conductive fluids in pipes. Electrical capacitance tomography (ECT) also uses electrodes placed around the region of interest, but monitors electrical permittivity within the material of interest. ECT can thus be used to distinguish between materials having different electrical permittivities.

Known tomography apparatus and methods provide a ring of electrodes spaced apart around the periphery of a body to be imaged. Various combinations of the electrodes are energised, and signals are detected from either those electrodes which are energised, or other ones of the electrodes, depending on the energisation scheme used. Both resistance and capacitance tomography may be used in such an arrangement. Known tomography apparatus are either formed as an integral part of, or attached to, the body to be imaged (i.e. the body within which measurements are required). In some situations this is straightforward, for example where a pipeline is easily accessible above ground. However, where the intended measurement location is not accessible, for example where the measurement location is within an existing oil-well below the ground, known tomography apparatus cannot be used unless installed during the commissioning of the oil-well.

It is an object of the present invention to provide a tomography apparatus which overcomes one or more of the problems associated with known tomography apparatus, discussed above or otherwise.

According to a first aspect of the invention there is provided a measurement device having a body defining an external periphery and comprising: a two-dimensional array of electrodes disposed generally parallel to said external periphery of the body; an energisation source arranged to energise at least one of said electrodes; and a monitor arranged to measure an electrical parameter at at least one of said electrodes; wherein energisation of an electrode by said energisation source causes an electric field to be established between at least one pair of electrodes, said electric field extending about said external periphery externally of said body.

The provision of an electric field extending about the external periphery, externally of the body of the probe allows those parts of the electric field which extend beyond the body to interact with material which is external to the body of the probe. By measuring an electrical parameter at an electrode in response to the energisation of an electrode, it is possible to deduce information about the material which surrounds the body of the probe, by virtue of the interaction of that material with the established electric field. Such a measurement device can thus be inserted into a cavity, for example a pipe, in order to perform measurements within that pipe, without having to rely on any measurement apparatus which is provided integrally with, or external to, the pipe. Such a measurement device can thus be used in any cavity within which measurements are required to be taken, whether or not any such measurement was envisaged or provided for at the time of creation or installation of that cavity. The measurement device may be a tomography probe.

The term energisation is used to refer to the application of some form of electrical stimulation to an electrode. The term excitation may alternatively be used to refer to the application of an electrical stimulation to an electrode. Depending on the application, the electrical stimulation may be an AC stimulation, a DC stimulation, or a combination of an AC and DC stimulation.

The electrical parameter at an electrode may be an electrical potential with respect to a known or fixed electrical potential. The electrical parameter may be a current flowing to or from the electrode, or the magnitude or direction of a current flowing to or from the electrode. The electrical parameter may be the phase relationship of a signal at the electrode relative to a known reference phase. The electrical parameter may be the frequency of a signal at the electrode.

The plurality of electrodes comprising an array provides a systematic arrangement of the electrodes. This allows the geometric relationship between electrodes to be related to different signals which are measured at different ones of the electrodes, and thus to properties of the material surrounding the measurement device.

The plurality of electrodes comprising a two-dimensional array provides a systematic arrangement of the electrodes in two dimensions. The two-dimensional array may further be arranged in three-dimensional space such that one or both of the dimensions of the array are not flat. For example, one of the dimensions of the array may be wrapped around a curved surface of the body of the measurement device. Such an arrangement allows the measurements taken at the electrodes to be used to build up a three-dimensional image of a property of the material surrounding the measurement device. Alternatively, a two-dimensional image, or series of two-dimensional images, may be generated. The or each two-dimensional image may be an image of a plane.

The body of the measurement device may be elongate, extending along a longitudinal axis. The measurement device may have a substantially circular cross section. The or each two-dimensional image may be an image of a plane which is perpendicular to the longitudinal axis.

An elongate body allows the measurement device to extend along a pipe (or other cavity) in which measurements are to be taken. A circular cross section has rotational symmetry, meaning that measurements taken between any two angularly separated points around the circumference of the circle will have the same geometric relationship as any other two points having the same angular separation. This may simplify calculations relating to properties of the material surrounding the measurement device. A circular cross section also provides a smooth outer shape around which material can easily flow. The electrode array may be configured to as to extend generally parallel to said longitudinal axis and generally parallel to said external periphery.

The electrode array extending along and around the body of the measurement device allows a relationship to be determined between the measurements taken and the geometry of the measurement device. Measurement data collected can thus be used to determine information about properties of the material around the measurement device and related to the position of the material having those properties with respect to the known position of the electrodes. The array which extends generally parallel to said external periphery may alternatively be considered to be circumferentially disposed around the body of a probe having a circular cross section. Equivalently, where the probe cross section is non-circular, the array which extends generally parallel to said external periphery may be considered to be disposed around a perimeter of the body. However it should be understood that the terms disposed around the body, circumferentially disposed around the body, and disposed around the perimeter of a body, are not intended to limit the positioning of any such electrodes to being at the external periphery of the probe. For example, the electrodes may be disposed on an internal surface of a probe body, the external surface defining the external periphery of the probe. Similarly, the electrodes may be disposed on an external surface of a portion of the probe which is itself enclosed within a further probe body which defines the external periphery of the probe.

The measurement device may further comprise an earth screen. An earth screen may be provided to electrically screen the effects of regions of the probe, or material around the probe, which are not intended to be measured by a particular measurement. The earth screen may comprise an earth grid, the earth grid extending between at least some of the plurality of electrodes. The earth grid may extend between each of the plurality of electrodes. An earth grid extending between at least some of the electrodes may improve the resolution of each measurement, reducing the effect of adjacent electrodes on a measurement in which they are not intended to be involved.

The earth screen may comprise an inner screen, the inner screen being provided internally of and substantially parallel to the external periphery of the body and the array and being electrically isolated from the plurality of electrodes.

The provision of an inner screen prevents any electric field from extending directly between electrodes where the direct route between those electrodes would extend through the body of the measurement device.

The earth screen may comprise at least one peripheral screen, the at least one peripheral screen being provided around the body of the measurement device adjacent a first end of said array.

A peripheral screen reduces the extent to which an electric field which is established between electrodes from extends further along the body of the probe than those electrodes, effectively focussing the measurements in a region of interest around the body of the measurement device.

The measurement device may comprise at least 4 electrodes. Preferably, the measurement device may comprise at least 12 electrodes. More preferably, the measurement device may comprise at least 24 electrodes. Providing a larger number of electrodes provides a larger number of measurement combinations, allowing a higher resolution image to be created of the material surrounding the measurement device.

Each of the plurality of electrodes may have an area of at least about 10 mm². For example, each of the plurality of electrodes may have an area between 10 mm² and 100 mm². Such electrodes may be suitable for electrical resistance tomography. Alternatively or additionally, each of the plurality of electrodes may have an area of around 600 mm², for example having dimensions of 20 mm x 30 mm. Such electrodes may be suitable for electrical capacitance tomography.

The measurement device may further comprise a processor.

Providing a processor within the measurement device allows processing to be carried out within the measurement device close to the location at which measurements are collected. This allows a processed data item to be transmitted or stored, which may involve less data than the raw measurement data. This may provide an advantage where communications with or data storage within a measurement device are limited in bandwidth or capacity respectively, or are unreliable. The processor may be configured to generate data representative of composition of a material surrounding the measurement device. This allows the measurement device to provide, as an output, data which is representative of the composition of the material surrounding the measurement device. Such data may be easily interpreted, rather than raw measurement data, which may require further processing to be interpreted.

The data may comprise a measure of the electrical permittivity of the material surrounding the measurement device. The permittivity of the material may be indicative of the composition of the material. This allows the measurement device to perform electrical capacitance tomography measurements.

The data may comprise a measure of the resistivity of the material surrounding the measurement device. The resistivity of the material may be indicative of the composition of the material. This allows the measurement device to perform electrical resistance tomography measurements.

The data may comprise a plurality of values, each of the plurality of values being associated with a different location around the measurement device. This allows a map of a property of the material around the measurement device to be developed. Such a map may be easily interpreted, rather than raw measurement data, which may require further processing to be interpreted. The data may comprise a plurality of data items, each of the plurality of data items being associated with a different time. This allows, for example, a series of images of the material around the measurement device to be output, which readily indicates to a user properties such as the composition of the material around the measurement device, and its movement.

The processor may be configured to calculate a parameter indicative of a flow rate of material surrounding the measurement device based upon said plurality of data items. A flow rate may be useful in determining an operational characteristic of an industrial process which is being measured.

The measurement device may comprise an inner body and an outer body, an external surface of the outer body defining the external periphery of the measurement device. The array may be disposed between the inner body and the external periphery. The array may be disposed adjacent a surface of the inner body. The array may be disposed adjacent a surface of the outer body. A first plurality of electrodes may be disposed adjacent a surface of the inner body and a second plurality of electrodes may be disposed adjacent a surface of the outer body.

Separate inner and outer bodies may allow the outer body to form a protective layer, improving the durability of the device. The inner body may itself be used to separate components within the measurement device. For example, the electrodes may be disposed on an outer surface of the inner body, while an inner screen may be disposed on an inner surface of the inner body. Electrodes provided on an outer surface of the inner body may be used for electrical capacitance tomography measurements. Electrodes provided on an outer surface of the outer body may be used for electrical resistance tomography measurements or electrical capacitance tomography measurements.

According to a second aspect of the invention there is provided a method of determining the composition of a material within a cavity, the method comprising: providing a measurement device within the cavity, the measurement device having a body defining an external periphery and comprising: a two-dimensional array of electrodes disposed generally parallel to said external periphery of the body; an energisation source arranged to energise at least one of said electrodes; and a monitor arranged to measure an electrical parameter at at least one of said electrodes; applying an energisation to an electrode by said energisation source, said applying an energisation causing an electric field to be established between at least one pair of electrodes, said electric field extending about said external periphery externally of said body; measuring, by the monitor, a signal at at least one of said electrodes; and calculating data representative of composition of the material within the cavity around the measurement device based upon the measured signal. The method may further comprise: measuring, by the monitor, a second signal at a second one of said electrodes; calculating data representative of composition of the material around the measurement device based upon the second signal.

Measurements of signals at different ones of the plurality of electrodes allows data representative of composition of the material around the measurement device to be related to the positions of the electrodes.

Calculating data representative of composition of the material around the measurement device based upon the measured signal and the second signal may comprise calculating the electrical permittivity of the material around the measurement device.

Calculating data representative of composition of the material around the measurement device based upon the measured and second signals may comprise calculating a plurality of values, each of the values representing the electrical permittivity of the material at a respective location around the measurement device.

The method may further comprise calculating a plurality of data items representative of composition of the material around the measurement device, each of the data items representing the electrical permittivity of the material around the measurement device at a respective point in time.

It will be appreciated that features of the first aspect of the invention may be combined with the second aspect of the invention. According to a third aspect of the invention there is provided a measurement device having a body defining an external periphery and comprising: a plurality of electrodes; an energisation source arranged to energise at least one of said electrodes; and a monitor arranged to measure an electrical parameter at at least one of said electrodes; wherein energisation of an electrode by said energisation source causes an electric field to be established between at least one pair of electrodes, said electric field extending about said external periphery externally of said body.

According to a fourth aspect of the invention there is provided a method of determining the composition of a material within a cavity, the method comprising: providing a measurement device within the cavity, the measurement device having a body defining an external periphery and comprising: a plurality of electrodes; an energisation source arranged to energise at least one of said electrodes; and a monitor arranged to measure an electrical parameter at at least one of said electrodes; applying an energisation to an electrode by said energisation source, said applying an energisation causing an electric field to be established between at least one pair of electrodes, said electric field extending about said external periphery externally of said body; measuring, by the monitor, a signal at at least one of said electrodes; and calculating data representative of composition of the material within the cavity around the measurement device based upon the measured signal.

It will be appreciated that features of the first and second aspects of the invention may be combined with the third and fourth aspects of the invention. Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a part-cutaway perspective view of a tomography probe according to an embodiment of the invention;

Figure 2 is a cross-sectional view of the tomography probe shown in Figure 1 ;

Figure 3 is a part-cutaway perspective view of the tomography probe shown in Figure 1 inserted into a pipe; Figure 4 is a schematic view of a controller within the tomography probe shown in Figure 1 ;

Figure 5 is a cross-sectional view of the tomography probe shown in Figure 1 inserted into a pipe;

Figure 6 is a flow chart which illustrates processing carried out in accordance with an embodiment of the invention; and Figure 7 is a schematic view of a controller which controls the tomography probe shown in Figure 1 .

Referring to Figure 1 , a measurement device 1 according to an embodiment of the invention is shown. The measurement device 1 is a tomography probe, having a plurality of electrodes 2. The probe 1 has a generally cylindrical shape. The plurality of electrodes 2 are arranged around the probe 1 in an array. The plurality of electrodes 2 are arranged as an array which extends around (i.e. circumferentially) and along (i.e. axially) the probe 1 . The probe 1 comprises an outer body 3 and an inner body 4. The outer body 3 surrounds and encloses the inner body 4, defining an external periphery of the probe 1 . The outer body 3 may be formed from an insulator. For example, the outer body 3 may be formed from polypropylene. The inner body 4 may be formed from an insulator. For example, the inner body 4 may be formed from glass. The plurality of electrodes 2 are disposed on an outer surface of the inner body 4 and are therefore also enclosed by the outer body 3. The outer body 3 has a continuous outer surface, being generally cylindrical in shape having a hemi-spherical first end formed integrally with the cylindrical body. A second end of the outer body is sealed with an end-cap 5 (shown removed for clarity). A probe controller 6 is provided within the probe 1 . The probe controller 6 is arranged to carry out processing described in more detail below.

The array of electrodes 2 may be considered to be a two-dimensional array. A first dimension of the array extends along (i.e. axially) the probe 1 , and a second dimension extends around (i.e. circumferentially) the probe 1 . Each electrode in the array may thus be uniquely addressed by reference to its position around and along the probe 1 . The array of electrodes 2 comprises four rows of six electrodes 2. That is, each of the four rows of electrodes 2 comprises six electrodes 2 which are evenly spaced around the circumference of the inner body 4. A first row of electrodes 2_{1 :1} , 2_{1 :2}, 2_{1 :3}, 2 , 2_{1 :5}, 2_{1 :6} is disposed around the probe 1 at a first axial position. A second row of electrodes 22,1 , 2_2,6 is disposed around the probe 1 at a second axial position, displaced along the length of the probe 1 from the first row of electrodes 2_{1 :1} , ... 2_{1 :6}. Third and fourth rows of electrodes 2_3J , ... 2_3,6, 2_4J , ... 2_4β are disposed around the probe 1 at respective third and fourth axial positions, each being further displaced along the length of the probe 1 than the previous row.

As described above, a row of electrodes consists of six electrodes arranged around the probe 1 . The electrodes 2 may also be referred to as being arranged in columns of electrodes 2. A column of electrodes 2 consists of one electrode of each of the rows of electrodes 2 arranged in a linear fashion along the length of the probe 1 . For example, a first column of electrodes consists of the electrodes 2_{1 :1} , 2₂,i , 2_3:1 and 2_4J , and so on.

Each of the electrodes within the two-dimensional array may also be referred to by its respective coordinates in three-dimensional space. For example, using a cylindrical coordinate system (the three dimensions being radial distance, height and angular position), each of the electrodes has the same radial distance coordinates i.e. the radius of the inner body 4). Each of the electrodes within a given row will have the same height coordinate, but a different angular position. On the other hand, each of the electrodes within a given column will have the same angular position, but a different height coordinate. For ease of reference, in the description below the electrodes will be referred to by their index within a two-dimensional array, as described above.

An earth screen is also provided in the region around each of the electrodes 2. The earth screen comprises an earth grid 7, which extends around the probe 1 , on the outer surface of the inner body 4, and between each of the electrodes 2. The earth screen further comprises an inner screen 8 which extends around an inner surface of the inner body 4. The inner screen 8 is electrically isolated from the electrodes 2 by the inner body 4. The earth screen further comprises an upper screen 9, which extends around the outer surface of the inner body 4 above the electrodes 2 and a lower screen 10 which extends around the outer surface of the inner body below the electrodes 2. It is noted that the terms upper and lower refer only to the relative positions of the screens 9, 10 when arranged as shown in Figure 1 . The upper and lower screens 9, 10 may both be referred to as peripheral screens, extending, as they both do, around the inner body 4 of the probe 1 adjacent a respective end of the array of electrodes 2. In general, the peripheral screens extend in an axial direction along the inner body 4 of the probe 1 further than the electrodes 2 (i.e. above or below the electrodes 2).

Figure 2 shows a cross section of the probe 1 in the plane A, as indicated on Figure 1 . The arrangement of the row of electrodes 2_1:1 , ... 2_{1 6} around the outer surface of the inner body 4 can be seen with a portion of the earth grid 7 present between each of the adjacent electrodes (i.e. between electrodes 2_1:1, and 2_{1 2}, 2_{1 2} and 2_{1 3}, and so on. The inner screen 8 is disposed on the inner surface of the inner body 4 and is shown as a continuous layer. The inner screen 8 is thus separated from, and electrically isolated from, the electrodes 2 by a wall of the inner body 4. The inner body 4 is formed from an insulating material.

Referring to Figure 3, the probe 1 is shown inserted into a cavity. The cavity is a pipe 11 , the material contained within which is to be examined. Any material contained or flowing within the pipe 1 1 surrounds the probe 1 , coming into contact with the outer surface of the outer body 3. The probe 1 is connected to a controller 12 by a cable 13. The cable 13 extends from the probe 1 , exiting the probe 1 through the end cap 5, and extending along the pipe 1 1 to an access location, where the probe 1 can be inserted into or retrieved from the pipe 1 1 . When the probe 1 is within the pipe 1 1 , the cable 13 can extend from the pipe 1 1 to the controller 12, which remains outside the pipe 1 1 .

The probe 1 may form part of a tool which is inserted into the pipe 1 1 . Alternatively, the probe 1 may be a separate unit. Actuators within the tool or probe 1 may be controlled by signals sent along the cable 13, allowing the tool or probe to be positioned as desired. Alternatively, the tool or probe 1 may be tethered by wires, and/or manipulated by external actuators so as to be positioned into a desired location. Typically a probe may be deployed at the centre of a pipe

In use, with the probe 1 within the pipe 1 1 , electrical capacitance tomography (ECT) measurements are carried out using the probe 1 . The ECT measurements comprise applying a predetermined energisation to selected ones of the electrodes 2, and measuring the capacitance between pairs of the electrodes 2. For example, an energisation may be applied to the electrode 2_1:1 and the capacitance measured between the energised electrode 2_1:1 and another electrode (e.g. between the electrode 2_1:1 and the electrode 2_1:2). The same energisation and measurement process is then repeated between the electrodes 2_1:1 and 2_1:3. The process is continued until the capacitance between the energised electrode and each of the other electrodes has been measured. Some electrode combinations may be excluded from this measurement process, examples of which are described below. Each electrode may be energised in turn and a set of measurements between that electrode and each of the other electrodes taken. During each energisation and measurement, an electric field is established between the energised electrode and the measured electrode, which extends within at least a part of the material surrounding the probe i.e. the electric field established by the energisation extends about the external periphery, externally of the body of the probe.

It will be appreciated that the electrodes 2, which are disposed on the outer surface of the inner body 4 of the probe 1 , are enclosed within the outer body 3. However, the electric field established when the above described energisation is applied to the electrodes 2 extends through the outer body 3 and into the material surrounding the probe 1 .

Figure 4 shows the probe controller 6 in further detail. It can be seen that the probe controller 6 comprises a CPU 6a which is configured to read and execute instructions stored in a volatile memory 6b which takes the form of a random access memory. The volatile memory 6b stores instructions for execution by the CPU 6a and data used by those instructions. For example, in use, the measured capacitance values may be stored in the volatile memory 6b.

The probe controller 6 further comprises non-volatile storage in the form of a solid state drive 6c. The measured signals and measured capacitance values may be stored on the solid state drive 6c. The probe controller 6 further comprises an I/O interface 6d to which are connected peripheral devices used in connection with obtaining the measured signals. More particularly, an energisation source 14 and a monitor 15 are connected to the I/O interface 6d. The energisation source 14 is arranged to apply an AC waveform to the energised electrode. The monitor 15 is arranged to detect a signal which is transmitted from the energised electrode and the measured electrode.

A network interface 6h allows the probe controller 6 to be connected to the controller 12, so as to receive and transmit data from and to the controller 12. The CPU 6a, volatile memory 6b, solid state drive 6c, I/O interface 6d, and network interface 6h, are connected together by a bus 6i.

The energisation involves the application of an AC waveform to the energised electrode by the energisation source 14 (shown in Figure 4), and the monitoring of the signal which is detected at a measured electrode by the monitor 15 (shown in Figure 4). The detected signal is used to determine the capacitance between the energised electrode and the measured electrode. The AC waveform may be a sinusoidal signal having a frequency of around 1 MHz. The AC waveform may, for example, have a peak-peak amplitude of 18 V. The monitor may detect the voltage amplitude at the measured electrode caused by the waveform applied to the energised electrode. Alternative energisation frequencies, amplitudes, or detection techniques may be used depending on the particular application, or the properties of the material surrounding the probe.

The probe controller 6 controls the energisation source 14 so as to generate and apply the energisation to the electrodes as described above. The probe controller 6 further controls the monitor 15 so as to monitor the signal received at the measured electrode (in response to the energisation of the energised electrode). The measured signal, in combination with characteristics of the known energisation, is used by the probe controller 6 to determine a capacitance value associated with pair of energised electrode and measured electrode, and the material present around and between those electrodes.

In use, during each of the energisations and capacitance measurements, the various parts of the earth screen (i.e. the earth grid 7, the inner screen 8, the upper screen 9 and the lower screen 10) are connected to earth. This reduces the impact on the capacitance measurement of regions of material which are not between the two electrodes involved in that measurement. The earth screen reduces the extent to which the electric field generated by the applied energisation spreads around the probe 1 .

In use, during each of the energisations and capacitance measurements, the electrodes which are not involved in a measurement are left floating, so as to not interfere with the measurement process.

For the 6x4 array described herein, the above described process results in 552 (24x23) combinations of electrodes. However, it will be appreciated that the capacitance between two electrodes will be the same as the capacitance between the reverse combination of the same electrodes. For example, the capacitance between the electrodes 2_{1 :1} and 2_{1 :3} is the same as the capacitance between the electrodes 2_{1 :3} and 2_{1 :1}. The number of unique electrode combinations is thus 276. Any reverse measurements (i.e. those which have already been performed with the energisation originating from another electrode) are excluded from the measurement sequence performed as they do not provide any information which is not already available - and doing so reduces the number of combinations, and therefore the time taken to perform the measurements, by one-half. In general, the number of unique measurements depends on the number of electrodes used. The number of unique measurements can be calculated as (N(N-1 ))/2, where N is the number of electrodes.

Figure 5 shows a cross section of the probe 1 when within the pipe 1 1 . The first row of electrodes 2_{1 :1} , ... 2_{1 :6} is shown. The measurements between the various pairs of electrodes are shown, each measurement being denoted by a line e. For example, the measurement between electrodes 2_{1 :1} and 2_{1 2} is shown by a line ei,i-i ,₂, and so on.

The lines e are representative of the electric field which is established between the energised electrode and the measured electrode during each measurement. It can clearly be seen that for each measurement the electric field extends beyond a part of the external periphery of the probe 1 , and thus into any material within the pipe 1 1 which is surrounding the probe 1 . The lines e between the electrodes 2 show schematically the distance from the probe 1 that the electric field extends, and thus the distance from the probe 1 that the pair of electrodes can 'see'. The capacitance between a pair of adjacent electrodes (e.g. the electrodes 2_1:1 and 2_1:2) is most strongly influenced by the material immediately surrounding each of those electrodes. However, as the separation between the pairs of electrodes is increased, the capacitance between the electrodes is influenced to a greater extent by material which is further from each of the electrodes. For example, the capacitance between the non-adjacent electrodes 2_1:1 and 2_1:3 is influenced by material which is further from the probe 1 , as denoted by the line θ_υ._{1 ι3}.

The measurements shown in Figure 5 represent just four of the twenty-three possible measurements involving the electrode 2_1:1. A possible fifth measurement between the electrodes 2_1:1 and 2_1:4 is not shown, due to this measurement being discarded, as described below. Six further measurements involving the electrode 2_1:1 and also involving an electrode within the second row of electrodes are also performed. The electrodes in the third and fourth rows, when combined with the electrode 2_1:1, also contribute a further six measurements each. Once each of the twenty-three measurements involving the electrode 2_1:1 have been performed, the twenty-two remaining measurements involving the electrode 2_2:1 will be performed, and so on until all of the unique 276 measurements have been performed.

The number of measured capacitance values which are further processed may further be reduced by discarding any opposite measurements. That is, measurements between electrodes 2 which are directly opposite one another on the probe 1 may be discarded. Such measurements may be susceptible to high levels of noise, the signal being weak when having to travel around the entire probe body. For example, the capacitance measurement between the between the electrodes 2_1:1 and 2_1:4, may be discarded. The symmetry of the probe 1 means that the signal received from the energisation of the electrode 2_1:1 at the electrode 2 would have travelled an equal distance in each direction (i.e. clockwise and anti-clockwise) around the probe, and would thus convey information about the material on both sides of the probe, which would not assist with determining the properties of the material around the probe in a particular location. The above described discarding of certain ones of the measurements between electrodes further reduces the number of unique measured capacitance values subsequently processed, as described in more detail below. It is further noted that the earth screen, and in particular the inner screen 8 acts to prevent the electric field between the electrodes 2_1:1 and 2_1:4, from extending directly between those electrodes i.e. across the centre of the probe 1. The presence of the earth screen thus reduces any impact on the capacitance measurements of the contents of the probe 1.

The effect described above with reference to adjacent and non-adjacent electrodes within a first row of electrodes around the probe (electrodes 2_1:1 to 2_{1 6}) is also applicable along the probe. For example electrodes 2_1:1 and 2₂,i are also adjacent electrodes, whereas electrodes 2_1:1 and 2_{4 1} are non-adjacent electrodes. Further, the capacitance between combinations of non-adjacent electrodes which are in neither the same row nor the same column (e.g. electrodes 2_1:1 and 2^), is influenced by the material which is even further from the probe.

In general terms, the capacitance measurements between adjacent electrodes provide an indication of the electrical permittivity of the material close to the probe, whereas capacitance measurements between electrodes further apart from one another provide an indication of the permittivity of the material further away from the probe. Thus, by combining the measured capacitance values from each of the pairs of the electrodes, information regarding the electrical permittivity of the material surrounding the probe can be deduced. The use of a two dimensional array of electrodes which are disposed around and along the probe allows a map of the electrical permittivity of the material surrounding the probe to be generated. Each unique pair of electrodes provides a capacitance with a unique geometric relationship to the material surrounding the probe, allowing the electrical permittivity map to be built up from the combined measurements. The electrical permittivity map may be a two-dimensional map, for example mapping a plane which is perpendicular to the probe 1 . Alternatively, the electrical permittivity map may be a three-dimensional map, for example mapping the volume which surrounds the probe 1 . In the following description, where the generation of a three-dimensional map is referred to, it will be appreciated that a two-dimensional map may also, or alternatively, be generated.

Once each of the energisations and corresponding capacitance measurements has been carried out, the measured capacitance values are processed by the probe controller 6. The processing carried out by the probe controller 6 takes as an input the measured capacitance values and generates data representative of composition of the material around the probe. For example the data may be representative of the proportions of oil and water. As described above, the measured capacitance values are related to the electrical permittivity of the material surrounding the probe 1 . Further, where the likely composition of the material is known, or at least it is known that the material is likely to be composed of distinct materials (e.g. oil and water) each with distinct electrical permittivities, then the electrical permittivity can be used to generate data which is representative of the proportions of oil and water around the probe.

It will be appreciated that the processing carried out by the probe controller 6 may generate data at various levels of abstraction. For example, the probe controller 6 may simply output a representation of the signals which are measured by the monitor. Alternatively the probe controller 6 may output a capacitance value associated with each pair of electrodes. Alternatively, the probe controller 6 may output an electrical permittivity map generated from the capacitance values. In a further alternative, a three-dimensional map of the electrical permittivity of the material surrounding the probe 1 can be used to generate a three-dimensional map of the composition of the material surrounding the probe.

Known algorithms exist for converting individual capacitance measurements to a three- dimensional map of the electrical permittivity. These algorithms can be applied by the controller 6 to generate the three-dimensional map of the electrical permittivity of the material surrounding the probe, and/or the three-dimensional map of the composition of the material surrounding the probe.

Figure 6 illustrates processing which may be carried out in order to generate a three- dimensional map of the electrical permittivity from individual capacitance measurements. The processing allows a three-dimensional map of the electrical permittivity of material surrounding the probe 1 to be generated based upon the geometry of the probe 1 , the arrangement of the electrodes 2, the environment within which the probe 1 operates, and the capacitance measurements.

At step S1 , data D1 which relates to the geometry of the probe and the arrangement of the electrodes 2 is used to generate a model of the field around the probe caused by the energisation of each of the electrode combinations, in the presence of a material having a known permittivity. When compared to conventional tomography systems, step S1 involves modelling the field extending about the external periphery, externally of the probe 1 , rather than extending internally within a sensor which is disposed around a pipe. The effect of this change in configuration is that the field around the probe 1 may be modelled to extend infinitely far from the probe 1 . However, it will be appreciated that the strength of the field around the probe 1 reduces as the distance from the probe increases. As such, it may be possible to assume that the field strength is effectively zero at a predetermined distance from the probe 1 .

At step S2, data D2 which relates to a known change to the properties of the material around the probe 1 is used, with the model of the field around the probe 1 generated at step S1 , to model the perturbation of the field caused by the known change. The known change may, for example, involve changing the assumed permittivity of a portion of the material around the probe 1 .

The processing at step S2 may be repeated a number of times in order to generate a plurality of models of the perturbed field around the probe in response to a plurality of known changes. The processing at step S2 thus generates a solution to a field problem, resulting in a set of relationships between a field applied between each pair of electrodes 2, and a distribution of permittivity in the material around the probe 1 .

At step S3, data D3 which relates to boundary measurements for each electrode combination is used to modify the solution to the field problem generated at step S2 in order to take into account the boundaries of the material around the probe 1 . The boundary measurements effectively define the boundaries of the three-dimensional map of the electrical permittivity which will be generated from the individual capacitance measurements, and may take into account interface effects between the electrodes and material surrounding the probe.

At step S4, data D4 which relates to the individual capacitance measurements is used in combination with the boundary modified solution to the field problem to generate data D5 which relates to the permittivity distribution of portions of the material around the probe 1 . The step S4 uses known algorithms to solve the inverse problem. That is, the measurement data D4 is used to generate the model parameters which would give rise to such capacitance measurements, the model parameters being the permittivity distribution of portions of the material around the probe 1 (i.e. data D5), which can be processed to produce the three-dimensional map of the electrical permittivity. The processing described with reference to Figure 6 may be carried out by the probe controller 6. Alternatively, the processing steps S1 to S3 may be carried out in advance of the measurement data being collected, either by the probe controller 6 or another processor. Where the processing is carried out in advance of the measurement data being collected, the boundary modified solution to the field problem may be generated and stored, for example within the solid state drive 6d of the probe controller 6, until it is required to be used to generate the data D5, when the measurement data D4 is available.

Further processing may be carried out by the probe controller 6. For example the data D5 generated by the processing described above may be further processed to generate data which is representative of the proportions of oil and water in the material surrounding the probe 1 . The data may be a plurality of values, each of which is representative of the proportions of oil and water in a respective location within the material surrounding the probe 1. The plurality of values may be a mesh.

When the probe 1 is located in a pipe 1 1 through which material is flowing, the measurements and processing described above may be repeated, so as to generate a plurality of data items which are representative of the proportions of oil and water in the material surrounding the probe 1 as a function of time (i.e. a time series of data items, each of the data items representing the material surrounding the probe at a respective point in time). The generated plurality of data items can be used to obtain information about changes in the composition of the material flowing through the pipe 11 . Alternatively, or additionally, the generated plurality of data items can be used to obtain information about the flow rate of the material flowing through the pipe 1 1.

Measurements may be collected at a rate depending on any or all of the following:

- the requirements of the specific application;

- the rate of change of the properties of the material around the probe; and

- the processing, data collection and/or data storage capabilities of the probe. For example, a probe may collect measurements at around 5 to 10 Hz. That is, 5 to 10 sets of measurements may be collected every second. Alternatively, measurements may be collected at a rate of around 300 Hz by a probe coupled with a separate data collection instrument, which reduces the processing and data storage load on a controller within the probe.

The data which is representative of the composition of the material surrounding the probe may be transmitted from the probe controller 6 to the controller 12, where further processing takes place. The transmission of data between the probe controller and the controller 12 may be along the cable 13. The cable 13 may also provide power to the probe 1 . Alternatively, or in addition to power provided by the cable 13, batteries (not shown) within the probe 1 may provide power to the probe.

In some embodiments the probe may by a considerable distance from the controller 12. For example, a probe may be deployed 1000 metres from the controller 12 within an oil-well. In such embodiments, the transmission of data along the cable 13 may be restricted to an extremely low data bandwidth. For example, a data rate of around 50 bits per minute may be possible. As such, the probe controller 6 being located within the probe 1 allows processing to be carried out within the probe, and only the data to be transmitted to the controller 12, rather than the measured capacitance values.

Depending on the application, any processing carried out within the probe may occur under extremely harsh operating conditions. For example, the temperature within an oil-well may be in excess of 100 °C, for example between 140 °C and 160 °C. The probe controller 6 should therefore be capable of reliable operation in such conditions.

Figure 7 shows the controller 12 in further detail. It can be seen that the controller 12 comprises a CPU 12a which is configured to read and execute instructions stored in a volatile memory 12b which takes the form of a random access memory. The volatile memory 12b stores instructions for execution by the CPU 12a and data used by those instructions. For example, in use, the data or plurality of data items may be stored in the volatile memory 12b.

The controller 12 further comprises non-volatile storage in the form of a hard disc drive 12c. The data or plurality of data items may be stored on the hard disc drive 12c. The controller 12 further comprises an I/O interface 12d to which are connected peripheral devices used in connection with the controller 12. More particularly, a display 12e is configured so as to display output from the controller 12. The display 12e may, for example, display a representation of the data or plurality of data items. Additionally, the display 12e may display images generated by processing of the data or plurality of data items. Input devices are also connected to the I/O interface 12d. Such input devices include a keyboard 12f and a mouse 12g which allow user interaction with the controller 12. A network interface 12h allows the controller 12 to be connected to an appropriate computer network so as to receive and transmit data from and to other computing devices, for example to the probe controller 6. The CPU 12a, volatile memory 12b, hard disc drive 12c, I/O interface 12d, and network interface 12h, are connected together by a bus 12i.

In some embodiments, for example where the transmission of data is less restricted than in the example described above, the processing of the measured capacitance values described above may be carried out within a processor which is not located within the probe (e.g. within the CPU 12a of the controller 12). In such embodiments, the measured capacitance values may be transmitted along the cable 13. Further, in some embodiments, and in particular where there is no communication possible with the probe, the measured capacitance values may be stored within the probe for subsequent processing when the probe is extracted from the pipe, or when the probe is able to communicate with a computer remote from the probe (e.g. the controller 12). In some embodiments, the probe controller 6 may generate data or a plurality of data items as described above, and store the generated data or a plurality of data items within non-volatile storage within the probe (e.g. the SSD 6c) for subsequent extraction and use. The probe may thus be operated in a data-logging capacity.

In some embodiments, the energisation source 14 and monitor 15 may be controlled by a capacitance monitor unit which comprises a separate controller from the probe controller 6. In such an embodiment, the capacitance monitor unit communicates with the probe controller 6. Alternatively, a capacitance monitor unit may be provided within the probe 1 , and the probe controller may be omitted. The controller 12 then may communicate directly with the capacitance monitor unit. The plurality of electrodes 2 described above are intended for use in ECT. The area of each of the electrodes 2 is large, so as to provide a large capacitance signal. For example, each of the electrodes 2 may be around 30 mm by 20 mm. Each of the electrodes 2 may be separated from each adjacent electrode 2 by about 2 mm. Larger electrodes than this may be used so as to provide higher sensitivity. Alternatively, smaller electrodes may be used to provide higher spatial resolution. The electrode size may vary within a probe, and will be selected based upon the requirements of a particular application. The thickness of the electrodes 2 may, for example, be greater than approximately 0.1 mm. The earth grid 7, which extends between the electrodes, may, for example, have a width of around 1 mm to 2 mm.

In an embodiment a probe may further comprise electrodes for use in electrical resistance tomography (ERT). An array of further electrodes may be provided to provide additional sensing capabilities. For example, array of further electrodes may be arranged around the external periphery of the probe (i.e. on an external surface of the outer body 4) to provide additional sensing capabilities. It will be appreciated that electrodes for ERT should be provided on the external surface of the outer body, rather than being enclosed within the outer body, so as to be in direct electrical contact with the material flowing within the pipe, allowing current to flow between the electrodes and the material flowing within the pipe. This is in contrast to the electrodes for ECT, which may be enclosed within the outer body, and thus will not be in direct electrical contact with the material flowing within the pipe. Electrodes for use in ERT are typically smaller than those used for ECT. For example, each of the further electrodes may be about 10 mm by 10 mm. Each of the further electrodes may be separated from each adjacent electrode by about 10 mm. As described above with reference to electrodes for use in ECT measurements, larger electrodes than this may be used so as to provide higher sensitivity. Alternatively, smaller electrodes may be used to provide higher spatial resolution. The electrode size may vary within a probe, and will be selected based upon the requirements of a particular application. The thickness of the further electrodes may, for example, be greater than approximately 0.1 mm. Where used within a pipe, the array of circumferential further electrodes may be provided towards the 'upstream' end of the probe. That is, material flowing along the pipe will encounter the further electrodes before passing the electrodes 2 disposed around the probe. This may be beneficial where a probe will disturb the flow within a pipe, allowing the further electrodes to effectively look at the material flowing within the pipe before the disturbance caused by the probe.

Further electrodes for ERT may be included in different regions of the probe. For example, a second array of further electrodes may be provided downstream from the electrodes 2 in addition to, or instead of, the upstream further electrode array described above.

It will be appreciated that while a two-dimensional array of electrodes 2 comprising 24 electrodes is described above for use in ECT, in embodiments of the invention alternative arrangements and numbers of electrodes may be used. For example, a linear array of electrodes may be disposed around a probe. Alternatively, a linear array of electrodes may be disposed along a probe.

Similarly, electrodes for ERT may be included in alternative quantities or arrangements. In some embodiments, a probe may comprise electrodes for ERT, and no electrodes for ECT.

Where electrodes are provided for ERT, resistance measurements are carried out between pairs of the electrodes. The measured resistance values are then processed by the probe controller 6 in a similar way to that described above with reference to the measured capacitance values. Data which is representative of the composition of the material surrounding the probe is then generated.

The descriptions above relating to the measurement, processing, storage and transmission of data relating to ECT measurements are applicable to ERT measurements. In general terms, in either ECT or ERT, an energisation is applied to at least one electrode, and a signal is measured at least one electrode.

Where electrodes are provided for ERT measurements, an earth grid may not be provided between the further electrodes. An earth grid may, however, be provided but not connected to earth. For example, in some embodiments electrodes may be used at a first time for ERT measurements (without an earth grid), and may at a second time be used for ECT measurements (with an earth grid). In such embodiments, having an optional earth grid may be advantageous.

It will further be appreciated that while a regularly spaced two-dimensional electrode array having both rows and columns is described above, in some embodiments the array may have irregular spacing between electrodes, or irregular sizing of electrodes. Further, adjacent rows or columns in an array may be offset with respect to one another. For example, a second row of electrodes may be offset with respect to a first row of electrodes such that each electrode edge within the first row is positioned approximately mid-way along an electrode within the second row.

In some embodiments alternative probe geometries may be used. A probe may have a non-circular cross section. For example a probe may have a square, hexagonal or octagonal cross section. Alternatively, a probe may have non-regular cross section.

In some embodiments a probe may not have a hemi-spherical end. For example a probe may have a conical end. A probe may have a flat end.

In some embodiments a probe may not comprise an outer body. In such embodiments, all electrodes may be present on the external periphery of the probe. This may result in higher sensitivity, when compared to a probe having an outer body which encloses the electrodes. On the other hand, a probe having an outer body may be more durable than a probe which omits an outer body. Hence, the configuration of a probe may be selected depending on the conditions in which the probe is expected to be operated (e.g. taking into account the competing requirements of durability or sensitivity).

In some embodiments, a probe may be deployed within a pipe-line or an oil-well.

In some embodiments, for example that described above, a probe may be used to discriminate between oil and water. Alternatively, a probe may be used to discriminate between other materials such as, for example, gas and oil, water and gas, or water and slurry. Further, a probe may be used where either fresh or salt water is present. In some embodiments, a probe may be used to determine a composition of a material around the probe. Alternatively, a probe may be used to detect or measure furring up within a pipe-line.

It is will be appreciated by one of ordinary skill in the art that the invention has been described by way of example only, and that the invention itself is defined by the claims. Numerous modifications and variations may be made to the exemplary design described above without departing from the scope of the invention as defined in the claims. For example, the precise shape and configuration of the various components may be varied.

The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as "preferable", "preferably", "preferred" or "more preferred" in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be considered as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language "at least a portion" and/or "a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary.

Claims

CLAIMS:

A measurement device having a body defining an external periphery and comprising:

a two-dimensional array of electrodes disposed generally parallel to said external periphery of the body;

an energisation source arranged to energise at least one of said electrodes; and

a monitor arranged to measure an electrical parameter at at least one of said electrodes;

wherein energisation of an electrode by said energisation source causes an electric field to be established between at least one pair of electrodes, said electric field extending about said external periphery externally of said body.

A measurement device according to claim 1 wherein the body is elongate, extending along a longitudinal axis.

A measurement device according to claim 2 wherein the electrode array is configured so as to extend generally parallel to said longitudinal axis.

A measurement device according to any preceding claim further comprising earth screen.

5. A measurement device according to claim 4 wherein the earth screen comprises an earth grid, the earth grid extending between at least some of the plurality of electrodes.

6. A measurement device according to any preceding claim wherein the array is disposed internally of said external periphery.

7. A measurement device according to claim 5 or 6 as it depends upon claim 5 wherein the earth screen comprises an inner screen, the inner screen being provided internally of and substantially parallel to the external periphery of the body and the array and being electrically insulated from the electrodes.

8. A measurement device according to any one of claims 5 to 7 wherein the earth screen comprises at least one peripheral screen, the at least one peripheral screen being provided around the body of the measurement device adjacent a first end of said array.

9. A measurement device according to any preceding claim comprising at least 4 electrodes.

10. A measurement device according to any preceding claim wherein each of the plurality of electrodes has an area of at least about 10 mm².

1 1 . A measurement device according to any preceding claim further comprising a processor.

12. A measurement device according to claim 1 1 wherein the processor is configured to generate data representative of composition of a material surrounding the measurement device.

13. A measurement device according to claim 12 wherein the data comprises a measure of the electrical permittivity of the material surrounding the measurement device.

14. A measurement device according to claim 13 wherein the data comprises a measure of the resistivity of the material surrounding the measurement device.

15. A measurement device according to any one of claims 12 to 14 wherein the data comprises a plurality of values, each of the plurality of values being associated with a different location around the measurement device.

16. A measurement device according to any one of claim 12 to 15 wherein the data further comprises a plurality of data items, each of the plurality of data items being associated with a different time.

17. A measurement device according to claim 16 wherein the processor is configured to calculate a parameter indicative of a flow rate of material surrounding the measurement device based upon said plurality of data items. 18. A measurement device according to any preceding claim comprising an inner body and an outer body, an external surface of the outer body defining the external periphery of the measurement device.

19. A measurement device according to claim 18, wherein the array is disposed between the inner body and the external periphery.

20. A measurement device according to claim 19 wherein the array is disposed adjacent a surface of the inner body. 21 . A method of determining the composition of a material within a cavity, the method comprising:

providing a measurement device within the cavity, the measurement device having a body defining an external periphery and comprising: a two- dimensional array of electrodes disposed generally parallel to said external periphery of the body; an energisation source arranged to energise at least one of said electrodes; and a monitor arranged to measure an electrical parameter at at least one of said electrodes;

applying an energisation to an electrode by said energisation source, said applying an energisation causing an electric field to be established between at least one pair of electrodes, said electric field extending about said external periphery externally of said body;

measuring, by the monitor, a signal at at least one of said electrodes; and

calculating data representative of composition of the material within the cavity around the measurement device based upon the measured signal.

22. A method according to claim 21 further comprising:

measuring, by the monitor, a second signal at a second one of said electrodes; calculating data representative of composition of the material around the measurement device based upon the second signal.

23. A method according to claim 22 wherein calculating data representative of composition of the material around the measurement device based upon the measured signal and the second signal comprises calculating the electrical permittivity of the material around the measurement device.

24. A method according to claim 23 wherein calculating data representative of composition of the material around the measurement device based upon the measured and second signals comprises calculating a plurality of values, each of the values representing the electrical permittivity of the material at a respective location around the measurement device.

25. A method according to claim 24 further comprising calculating a plurality of data items representative of composition of the material around the measurement device, each of the data items representing the electrical permittivity of the material around the measurement device at a respective point in time.