Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17D—PIPE-LINE SYSTEMS; PIPE-LINES
  • F17D5/00—Protection or supervision of installations
  • F17D5/02—Preventing, monitoring, or locating loss
  • F17D5/06—Preventing, monitoring, or locating loss using electric or acoustic means
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B47/00—Survey of boreholes or wells
  • E21B47/12—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling
  • E21B47/13—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling by electromagnetic energy, e.g. radio frequency

Definitions

• This invention relates to data transmission systems, methods of data transmission, signal receiving apparatus and methods of receiving signals all for use in pipeline systems, in particular wells.
• a data transmission system in which metallic structure of a pipeline system is used as a signal channel and earth is used as return comprising means for forming a current loop path having first and second conducting portions electrically connected to one another at spaced locations, the metallic structure comprising at least one of the conducting portions, and a local unit having transmitting means for applying a signal to one of the conducting portions whereby in use current flows around said loop generating a potential difference between earth and the metallic structure in the region of the loop and causing a signal to be propagated along the metallic structure away from the loop, wherein the means for forming the current loop path is arranged to ensure that the spaced locations are separated by at least a minimum distance selected to give desired transmission characteristics.
• a method of data transmission in which metallic structure of a pipeline system is used as a signal channel and earth is used as return comprising the steps of: forming a current loop path having first and second conducting portions electrically connected to one another at spaced locations, the metallic structure comprising at least one of the conducting portions; applying a signal to one of the conducting portions to cause a current to flow around said loop to generate a potential difference between earth and the metallic structure in the region of the loop and cause a signal to be propagated along the metallic structure away from the loop; and ensuring that the spaced locations are separated by at least a minimum distance selected to give desired transmission characteristics.
• the pipeline system may comprise an inner flow line and a surrounding casing.
• the pipeline system comprises a well having a production string and surrounding casing.
• the current flowing around the loop path in operation can be considered to make the system act as a dipole transmitter.
• Receiving means may be provided at a location remote from said current loop path for receiving the signals propagated along the metallic structure.
• the above arrangement has the advantages that wirelines can be avoided and a signal which will be detectable can be injected onto the metallic structure in practical situations using realistic current levels even when signalling along a production string from a position in which the string is located within a casing.
• the metallic structure as whole may be treated as a single conduction channel.
• the minimum distance can be chosen to suit the circumstances such that an acceptable level of signal is detectable at the desired location remote from the local unit, for example at the well head.
• a typical selected minimum distance may be 100 metres. It is preferred that the selected minimum distance is small relative to the overall length of the structure/well.
• one of the conducting portions comprises a portion of a production string.
• the transmitting means may be arranged to apply signals to the production string.
• one conducting portion comprises a portion of a flow line, for example a production string and the other conducting portion comprises a surrounding portion of casing.
• the means for forming a current loop path may comprise insulating spacer means for keeping the flow line spaced from the surrounding casing for the selected minimum distance.
• An insulating coating may be provided on the flow line and/or casing over the portion corresponding to the selected minimum distance.
• the spaced connections between the first and second conducting portions to complete the current loop path may comprise glancing contacts between the flow line and casing beyond the selected region. It will be appreciated that the costs involved in improving isolation between the flow line and casing over the selected minimum distance will be significantly lower than those involved in trying to isolate the string and casing along their whole length.
• one conducting portion comprises a portion of a pipeline or flowline and the other conducting portion comprises at least one electrically conductive elongate member connecting at least two pigs disposed within the pipeline or flowline.
• the spaced connections to complete the current loop path may be provided at the pigs .
• the local unit may be provided at one of the pigs .
• the transmitting means is arranged to apply signals to the elongate member.
• the local unit may comprise sensor means for measuring conditions in the region of the unit.
• the local unit may comprise receiving means for receiving incoming signals transmitted along the metallic structure or otherwise.
• the local unit may be arranged to act as a relay station. It will be appreciated that the relay station may be disposed on a cased section of production string and thus be used to improve the range of the data transmission system.
• the transmitting means applies signals substantially at the midpoint of the respective conducting portion. This tends to equalise the signal propagation characteristics away from the local unit in both directions along the metallic structure and is particularly suitable if the local unit is to function as a bi-directional relay station.
• the transmitting means may be arranged to apply signals at a point towards one end, preferably the opposite end, of the respective conducting portion.
• the transmitting means and/or the receiving means may comprise an isolation member disposed in series with the respective conducting portion.
• the transmitting means may comprise a signal generating means connected across the isolation member.
• the receiving means may comprise a signal measuring means, for example voltage measuring means, connected across the isolation member.
• the isolation member may be an isolation joint disposed in the string.
• the transmitting means and/or the receiving means may comprise inductive coupling means disposed around the respective conducting portion.
• the current loop path may act as a single turn winding of a transformer.
• the inductive coupling means may comprise a coil wound on a generally toroidal core which encircles the respective conducting portion.
• signal receiving apparatus for use with a data transmission system in which metallic structure of a pipeline system is used as a signal channel and earth is used as return, comprising a local unit having receiving means, means for providing electrical contact between the local unit and at least two spaced locations on a portion of the metallic structure and means for ensuring that the two spaced locations are separated by at least a minimum distance selected to give desired reception characteristics.
• a method for receiving a signal from the metallic structure of a pipeline system which is used as a signal channel in a data transmission system with earth as return, comprising the steps of providing a local unit having receiving means; providing electrical contact between the local unit and at least two spaced locations on a portion of the metallic structure; and ensuring that the spaced locations are separated by at least a minimum distance selected such to give desired reception characteristics.
• the means for providing electrical contact at spaced locations may comprise a portion of the production string and insulating spacer means provided to keep said string portion spaced from the corresponding portion of surrounding casing.
• An isolation joint may be provided in the string in the region of the local unit and a signal measuring means connected across it.
• the means for providing electrical contact at spaced locations may comprise at least one electrically conductive elongate member connecting at least two pigs disposed within the production string.
• signal receiving apparatus for use with a data transmission system in which metallic structure of a pipeline system is used as a signal channel, comprising a local unit having receiving means which comprises an inductive coupling.
• the signal channel may be split into two or more branches in the region of the local unit and the inductive coupling disposed around one of said branches.
• the inductive coupling is disposed around a production string disposed within a casing.
• One branch may comprise the production string and another branch may comprise the casing.
• the inductive coupling may comprise a toroid disposed around said one of the channels and/or a production string.
• a data transmission system in which metallic structure of a well including a production string and casing is used as a signal channel and earth is used as return comprising a local unit having receiving and/or transmitting means coupled to the string for receiving signals from and/or transmitting signals along the signal channel and insulating spacer means arranged to ensure that the production string and casing are spaced from one another for at least a selected minimum distance in the region of the local unit, said minimum distance being selected to give desired reception and/or transmission characteristics.
• the casing may comprise a plurality of separate sections, which may be screwed together. Mating surfaces at one or more joint between adjacent sections may be coated with an isolating medium. This can change the electrical characteristics of the metal structure and enhance performance.
• a data transmission system for use in pipeline systems which comprises, means for forming a current loop path comprising a portion of an inner conductive member and a corresponding portion of an outer conductive member electrically connected to one another at two spaced locations, the outer conducting member surrounding the inner conductive member and being part of the metallic structure of a pipeline system; an internal unit disposed within the outer member and having transmission means for injecting a signal into the current loop path; and an external unit disposed outside the outer member comprising inductive coupling means arranged to be linked by flux generated by current flowing around the loop path, the arrangement being such that in use the current flowing in said portion of the inner member does not match the current flowing in the corresponding portion of the outer member whereby signals are generated in the inductive coupling means so allowing communication from the internal unit to the external unit.
• a method of data transmission system for use in pipeline systems which comprises the steps of: forming a current loop path comprising a portion of an inner conductive member and a corresponding portion of an outer conductive member electrically connected to one another at two spaced locations, the outer conducting member surrounding the inner conductive member and being part of the metallic structure of a pipeline system; injecting a signal into the current loop path from an internal unit disposed within the outer member; and disposing an external unit outside the outer member which unit comprises inductive coupling means arranged to be linked by flux generated by current flowing around the loop path, and the arrangement being such that in use the current flowing in said portion of the inner member does not match the current flowing in the corresponding portion of the outer member whereby signals are generated in the inductive coupling means so allowing communication from the internal unit to the external unit .
• the inner and outer members will be generally co-axially arranged elongate members, the outer member being generally tubular.
• the spaced locations may separated by a selected minimum distance.
• the minimum distance is selected to give desired transmission characteristics.
• the data transmission system may be arranged for use in pipeline systems comprising a conductive flowline which acts as the outer member and a dedicated inner conductive member may be provided.
• the inner conductive member my comprise a conductive strop connected between two pigs .
• the electrical connections between the dedicated inner conductor and a flow line may be provided at the pigs.
• Cleaning brushes located on the pigs may act as contacts with the inner surface of the flowline.
• the data transmission system may be arranged for use in pipeline systems comprising an inner conductive flowline and an outer conductive casing.
• the outer member may comprise the casing and the inner member may comprise the flowline.
• the outer member particularly when a casing, may comprise a plurality of separate sections, which may be screwed together. Mating surfaces at one or more joint between adjacent sections may be coated with an isolating medium. This can change the electrical characteristics of the metal structure and enhance performance. It is preferred that no completely isolated joint is disposed in the casing between the spaced locations at which the casing and flowline electrically contact one another.
• the electrical connections between the flowline and casing may comprise glancing contacts and/or conductive packers. Where the spaced connections consist of glancing contacts it is possible to select a minimum separation between the connections. Where conductive packers are used the actual spacing between the packers, and hence the connections, may be chosen.
• the means for forming the current loop path may comprise an insulating layer provided on the outer surface of the inner flow line and/or the inner surface of the outer casing.
• the means for forming the current loop path may comprise insulating spacer means .
• connections and/or means used for insulating the portion of the flowline from the corresponding portion of the casing may be chosen to give desired transmission characteristics.
• the transmission means is arranged to apply signals to the inner flowline.
• An isolation joint may be provided in the flowline and the transmission means may be arranged to signal across the isolation joint .
• the inductive coupling means may comprise a toroid disposed around the casing in the region of the current loop. Preferably the inductive coupling means is disposed towards a midpoint between the spaced connections .
• the pipeline system comprises a cased section of a well, the production string being the flowline in such a case.
• Figure 1 schematically shows a subsea well including a data transmission system which comprises a first embodiment of the invention
• Figure 2 schematically shows a portion of the well shown in Figure 1 at which a relay station is disposed;
• Figure 3 shows a simplified equivalent circuit of a typical length of production string and casing of the well shown in Figure 1;
• Figure 4 shows a simplified equivalent circuit of the portion of the well shown in Figure 2 during reception of a signal
• Figure 5 shows a simplified equivalent circuit of the portion of the well shown in Figure 2 during transmission of a signal
• Figure 6 shows an alternative coupling method
• Figure 7 is a schematic view of part of a second embodiment of the invention.
• Figure 8 schematically shows a third embodiment of the present invention
• Figure 9 shows an equivalent circuit for the arrangement shown in Figure 8.
• Figures 1 and 2 schematically show a subsea well including a wireless or non-wireline data transmission system.
• the well comprises a production string 1 for extracting product from a formation F.
• the production string 1 joins a tree 2 at the mudline and is surrounded by casing 3 between the tree 2 and the formation F.
• the string 1 and casing 3 form part of the metallic structure of the well.
• Figure 1 shows the string 1 as being disposed centrally within the casing 3, in practice the string 1 and casing 3 will make glancing contact with one another at numerous positions along their lengths.
• the space between the string 1 and casing 3 is filled with brine (or alternatively another fluid which is denser than water) to help reduce the pressure acting on the packing ring 4 provided between the casing 3 and string 1 as they enter the formation F.
• brine or alternatively another fluid which is denser than water
• the well also comprises a number of data logging stations 5 provided on the string 1 at open well locations, that is within the formation.
• the data transmission system is arranged to allow data to be transmitted between the data logging stations 5 and the mudline or beyond by using the metallic structure of the well 1,3 as a signal channel.
• the distance between the data logging stations and the mudline may be in excess of 3000 metres.
• Data is received at and transmitted from the data logging stations 5 using existing non-wireline open well techniques, for example those described in the applicant's earlier application EP-A-0, 646 , 304. Whilst these techniques work in the open well and can transmit a signal along the cased section they cannot be used in practice to transmit from a position within the cased section. Only if the length of the cased section is not too great can signals be received directly at and sent directly from the mudline using the non-wireline techniques described in the above mentioned application; range and data rate being essentially determined by signal to noise ratio.
• the strength of the signal and/or range of the system is improved by providing a relay station 6 partway along the cased portion of the production string 1.
• the relay station 6 comprises transceiver means including an isolation joint 7 provided in the production string, signal generating means 8a used during transmission and signal measuring means 8b used during reception. Both the signal generating means and the signal measuring means are connected across the isolation joint 7.
• a plurality of insulating annular spacers 9 are provided around the production string 1 over a distance of the order of 100 metres in the region of the isolation joint 7. The distance over which the spacers 9 are provided is chosen such that signals can be effectively received and transmitted. The actual distance will depend on a number of factors relating to the components of the transmission system and the well itself .
• the spacers 9 are of a half shell type which are bolted together around the string 1.
• An insulating layer 9a is provided between each spacer and the string 1.
• a side view of one of the spacers 9 is shown and the remainder of the spacers 9 are shown in cross- section.
• the spacers 9 are arranged and positioned such that at each spacer 9 the string 1 is held towards the centre of the casing 3 and such that the string 1 will not contact with the casing 3 at any position between adjacent spacers 9. Beyond the last spacer 9 at each end of the plurality of spacers 9, the string 1 makes glancing contact 10 with the casing 3 as shown in Figure 2.
• each last spacer 9 and the respective glancing contact 10 will be random but its lower limit will be determined by characteristics of the well and spacers 9.
• the spacers 9 ensure that there is no contact between the string 1 and casing 3 for at least a selected minimum distance.
• the transmission and receiving characteristics of the system improve as the spacing between the glancing contacts 10 is increased.
• there is a trade off against the cost involved in lengthening the minimum distance In general the actual spacing between the glancing contacts 10 will be greater than the minimum distance but this simply serves to improve the system.
• the portions of the string 1 and casing 3 between the glancing contacts 10 are hereinafter referred to as the isolated portion of the string la and the corresponding portion of the casing 3a.
• Figure 3 shows an equivalent (lumped parameter) circuit for a typical length of the production string 1 and casing 3.
• the string 1 and casing 3 are respectively represented by series of resistors R s and R c .
• the leakage paths between the string 1 and casing 3 are represented by a series of resistors R g+b and the leakage paths between the casing 3 and remote earth E are represented by resistors R e and capacitors C e . If a signal is applied to the string 1 or casing 3 the strength of the signal will decrease with distance away from the source due to the losses through the leakage paths to remote earth E. Further, as mentioned above the potential of the string 1 and casing 3 will tend to equalise.
• Figure 4 shows a simplified equivalent circuit for the portions of the production string la and casing 3a in the region of the relay station 6 during reception of a signal. Except those 10 at either end of the portions la, 3a, the leakage paths due to glancing contacts have been removed. Thus the resistors R g+b are replaced by resistors R b of much higher value representing the leakage through brine alone. The resistance through the brine in the region of the relay station 6 is so large compared with that provided by the glancing contacts 10 at the ends of the isolated portion of string la that the effect of the brine can essentially be ignored.
• Figure 5 shows a simplified equivalent circuit for the portions of the production string la and casing 3a in the region of the relay station 6 during transmission.
• the leakage paths due to glancing contacts have been removed except those 10 at either end of the portions la, 3a.
• the resistors R g+b are replaced by resistors R b of much higher value representing the leakage through brine alone.
• the resistance through the brine in the region relay station 6 is so large compared with that provided by the glancing contacts 10 at the ends of the isolated portion of string la that the effect of the brine can be ignored.
• a current loop path can be considered to exist consisting of the isolated portion of the string la, the corresponding portion of the casing 3a and the glancing connection points 10.
• the two ends of this loop are of course also connected to the remainder of the string 1 and casing 3.
• the signal generating means 8a causes a current I to flow around the loop path. This flow of current I causes a potential difference to be set up between the glancing contacts 10 at opposite ends of the isolated portion of string la. This potential difference will be I x sumRc , where sumRc equals the total resistance of the casing between the glancing contacts 10.
• the magnitude of the potential difference between metallic structure and earth at each end of the isolated portion la will be ( I x sumRc )/2. Because a potential difference exists between the positions of the glancing contacts 10 and earth, a signal will tend to travel along the string 1 and casing 3 in each direction away from the relay station 6.
• Desired data for example that received from a data logging station, can be transmitted along the string 1 and casing 3 away from the relay station by encoding a suitable signal onto the string 1 by means of the mechanism described above.
• the resulting signal propagates away from the current loop path along the string and casing as a single conductor.
• the signal circuit is completed by an earth return and no wirelines are required.
• Appropriate receiving means at the mudline or at another relay station are used to detect the signal applied to the string 1 and casing 3 and extract the desired data.
• the receiving means may make use of an inductive coupling or be arranged to measure signals with respect to a separate earth reference.
• the range of the signal transmission system can be dramatically increased by providing a suitable number of relay stations within the casing 3.
• the relay stations are bi-directional so that the transmission range when transmitting signals down into the well as well as out of the well is increased.
• the isolation joint located centrally within the isolated portion la, the signals in each direction away from the relay station 6 will have substantially equal strength. However, if the isolation joint 7 is disposed towards one end of the isolated portion la, the potential difference generated at the other end of the isolated portion la will tend to be greater than (I x sumRc )/2. Thus if it is desired to increase the strength of the signal in one direction the isolation joint 7 may be disposed accordingly.
• the isolated portion of the production string la is provided with an insulating coating to further reduce conduction between the isolated portion la and the corresponding portion of the casing 3a.
• Figure 6 shows a coil 201 provided on a toroidal core 202 disposed around the production string portion la for use in an alternative method of applying a signal to and/or tapping a signal from the production string 1.
• inductive coupling is relied on and no isolation joint is used.
• the coil 201 is used to induce a current in the string 1 and the current loop path described above acts as a single turn transformer winding.
• a signal on the production string 1 induces a corresponding current in the coil 201 which can be detected.
• This method of reception does not rely on there being an isolated portion la of production string.
• This coupling method gives an advantage that it is possible to optimise impedance matching by appropriately choosing the turns ratio.
• Figure 7 shows a further embodiment of the invention suitable for use in a well of the type described above which comprises two pigs 301 connected by an electrically conductive strop 302 and disposed within the production string 1 which may or may not be cased.
• a first of the pigs 301 comprises a local station 303 having an isolation member 7 provided in series with the strop 302 and signal generating means 8a and signal measuring means 8b connected across the isolation member 7.
• Each of the pigs 301 has a contact 304 for contacting with an internal surface of the string 1. Signals may be transmitted and received in this embodiment in substantially the same way as described above in relation to the first embodiment.
• the strop 302 a portion of the string la and the contacts 304 form a current loop path.
• a potential difference between the string 1 and earth can be generated at each contact 304 allowing a signal to be transmitted.
• the strop 302 and contacts 304 allow the potential difference between two longitudinally spaced points on the string 1 to be measured so that a signal can be extracted from the string 1.
• signals may be sent to and from the first pig 301.
• signals may be sent from the pig 301 which allow the location of the pig 301 to be determined and/or which represent a quantity, such as wall thickness, measured by the pig 301.
• One possible mechanism for determining the location of the pig 301 would be to arrange trigger means at spaced locations along a pipeline which cause the pig 301 to send an appropriate signal. Another method would be to determine the time difference of arrival of the signal at each end of the pipeline.
• this system may be used whether the pigs 301 are within a cased or uncased section of string. Further the system may be used in other pipeline systems besides wells.
• more than two pigs may be used.
• Three pigs connected by two conductive members may be used and the local unit disposed at the central pig. This can facilitate equalisation of the transmission characteristics in both directions away from the local unit.
• Figure 8 schematically shows a third embodiment of the present invention which is a system for transmitting data from inside a section of a cased well to a substantially adjacent position outside of the casing.
• the 401 is surrounded by a metallic casing 403 which form part of a cased well.
• An isolation joint 407 is provided in the string 401 and an internal unit 408 including transmitting means (not shown) is connected across the isolation joint 407.
• generally annular electrically conductive packers 411 are provided between the string 401 and casing 403.
• the electrically conductive packers 411 are spaced by a selected distance L and provide a good electrical connection between the production string 401 and the casing 403.
• the portion 401a of the production string 401 between the spaced pair of packers 411 is provided with an insulating coating 409.
• the coating 409 helps to ensure that there is no conduction path or at least only a very poor conduction path between the string 401 and casing 403 at all points between the packers 411.
• An external unit 413 comprising receiving means (not shown) and a toroid 415 is provided outside of the casing 403 at a position which ic between the pair of spaced packers 411.
• the toroid 415 surrounds the casing 403 and is arranged to act as an inductive coupling means such that any net magnetic flux flowing through the toroid generates a signal which can be detected by the receiving means (not shown).
• the system is arranged to be used to transmit signals from the internal unit 408 to the external unit 413 by the mechanism described below.
• the insulated portion of the production string 401a, a corresponding portion of the casing 403a, and the pair of conductive packers 411 form a current loop path around which current may flow.
• the loop is imperfect such that there are other current flow paths and losses will occur.
• I. represents the current flowing through the insulated portion 401a of production string 401
• I c represents the current flowing in the corresponding portion of the casing 403a
• I ⁇ represents the leakage current to earth.
• Figure 9 shows a simplified equivalent circuit for the current loop path and the leakages to earth.
• the resistances of the portion of the production string 401a, the corresponding portion of the casing 403a and earth are represented by a resistors R s ,R e ,R e respectively.
• the level of signal obtained in the toroid 415 can be adjusted by making appropriate design choices. For example, the position of the toroid along the insulated portion of the string 401a and the position of the isolation joint 407 may be selected. Further, the spacing L between the conductive packers 411 may be changed, as may the length of the insulated portion of the production string 401a. The aim is to maximise the receivable signal by increasing the resistance of the casing loop R c relative to the leakage resistance R e as far as is practicable. In the first instance this may be achieved by increasing the spacing between the conductive packers .
• this system does not require insulation between the production string 401 and the casing 403 along the whole of the well's length, it is merely preferable along the length chosen to give the necessary transmitting characteristics .
• the technique is equally appropriate for other situations where it is desired to signal from within a conductive member which surrounds the transmitter.
• the system can be used to signal from within the casing of flow lines other than production strings and from within flow lines themselves providing that a suitable inner conductor is provided.
• this system can be used with apparatus along the lines of that shown in and described with reference to Figure 7. That is to say the current loop path may be formed by a portion of a flow line 1, two pigs 301 and an interconnecting conductive strop 302. If a toroid is then provided around the flow line 1 it will be possible to pick-up signals generated by the transmitting means 8a located in the pig 301 as it passes through the region of the toroid.
• this embodiment makes use of the same phenomenon as described above with reference to the first and second embodiments. However, in the present embodiment it is the effects which occur in the current loop path itself which are used rather than the current which leaks away from the current loop path along the production string and casing 1,3.
• the casing 3 of a well is typically made up of screwed together sections.
• some or all of the joints between the casing sections may be treated so as to cause a level of discontinuity in conductivity of the casing. This can typically be achieved by coating the mating surfaces at each joint with an isolating medium which does not prejudice the sealing requirements for the casing. Introducing such discontinuities can significantly change the electrical characteristics of the well as a whole. At least in some circumstances this may lead to improved performance of the relevant embodiments described above. For example the range of transmission systems shown in Figures 1 and 2 may be improved. Improvements can be achieved whether the discontinuities are provided in the region of the current loop path, i.e. between the spaced connections or away from that region.
• the present embodiments, and present invention in general, may function better if discontinuties exist between mating sections of casing this is not a requirement for operation.
• the system may be such that the casing is substantially electrically continous along its whole length or at least in the region of the loop. This is true for the casing of a well and the casing of any other pipeline as well for as any corresponding surrounding outer member such as the string in the embodiment shown in figure 7.

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• 2002
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