EP1103008A1 - Device with capacitive electrodes for measuring subsurface electric characteristics - Google Patents

Device with capacitive electrodes for measuring subsurface electric characteristics

Info

Publication number
EP1103008A1
EP1103008A1 EP99936711A EP99936711A EP1103008A1 EP 1103008 A1 EP1103008 A1 EP 1103008A1 EP 99936711 A EP99936711 A EP 99936711A EP 99936711 A EP99936711 A EP 99936711A EP 1103008 A1 EP1103008 A1 EP 1103008A1
Authority
EP
European Patent Office
Prior art keywords
electrodes
measuring
measurement
electrode
injection
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99936711A
Other languages
German (de)
French (fr)
Inventor
Richard Lagabrielle
Virginie Leroux
Jean-Luc Sorin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Laboratoire Central des Ponts et Chaussees
Original Assignee
Laboratoire Central des Ponts et Chaussees
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Laboratoire Central des Ponts et Chaussees filed Critical Laboratoire Central des Ponts et Chaussees
Publication of EP1103008A1 publication Critical patent/EP1103008A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/18—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging
    • G01V3/20—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with propagation of electric current
    • G01V3/24—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with propagation of electric current using ac

Definitions

  • the present invention relates to a device for measuring electrical characteristics in the basement with capacitive electrodes.
  • An object of the present invention is to provide a device for measuring the electrical characteristics of the subsoil from a borehole, a device which can be used in particular when no means is available to ensure electrical continuity by conduction between the electrode (s) placed in the borehole (s) and the basement for which the measurements are to be made.
  • the device for electric prospecting in drilling with capacitive electrodes which comprises at least two injection electrodes and a current generator for injecting current through them into the ground, as well as two electrodes for measure and means for measuring the potential difference between them, is characterized in that: said current generator delivers an alternating current whose frequency is preferably between 5 and 100 kHz at a voltage of less than 1000 volts,
  • At least one of the four electrodes is intended to be placed in a borehole and has a substantially cylindrical and electrically conductive external surface, and in that it further comprises:
  • This coupling is of sufficient quality for the measurements carried out to be usable for recognizing the electrical characteristics of the subsoil to be prospected.
  • At least one of said injection electrodes is intended to be placed in drilling. It is then substantially cylindrical and has an electrically conductive external surface.
  • the device for measuring the intensity of the injected current and the injection electrode are mounted on the same component which is intended to be placed in the borehole in the desired position or positions, according to the measurements to be performed.
  • At least one of said measurement electrodes is intended to be placed in a borehole. It is then substantially cylindrical and has an external electrically conductive surface and is integral with a part of the voltage measurement device. This arrangement makes it possible to improve the accuracy of the measurement of the potential difference between the two measurement electrodes.
  • FIG. 1 is a simplified view of a first embodiment of the measurement device by capacitive coupling
  • Figures 2, 3, 4, 5, 6 and 7 illustrate in a simplified manner other possibilities of configuration of the injection and potential electrodes.
  • Figure 8 is a perspective view of a preferred embodiment of an electrode. intended to be placed in a borehole
  • FIG. 9 is a view in vertical section of the electrode of FIG. 8.
  • the installation firstly comprises an injection electrode 16 which is placed in the first borehole 12 and suspended from a cable 18.
  • the second injection electrode is constituted by a metal stake 20 driven into the ground and the distance of which compared to drilling 12 can be considered infinite in the electric sense of the term.
  • the injection electrodes 16 and 20 are connected to an alternating current generator 22.
  • To the injection electrode 16 placed in the borehole 12 is associated a device for measuring the intensity of the current 24.
  • a device 26 makes it possible to know the position of the electrode 16 in the borehole 12.
  • a first measurement electrode 28 which is also suspended from the end of a cable 30 associated with means 32 for measuring the position of the electrode 28 in the borehole 14.
  • a second measurement electrode 34 is constituted by a metal stake stuck in the ground at a distance such that one can consider it as infinite from an electrical point of view.
  • a voltmeter or similar device 36 makes it possible to measure the difference in electrical potential between the measurement electrodes 28 and 34. It may include a part 36b taken along with the electrode 28 in the borehole 14.
  • a communication bus 40 makes it possible to connect the current generator 22, the devices 26 and 32 for measuring the depth of the electrodes and the voltmeter 36 to an interface circuit 42.
  • the interface circuit 42 therefore makes it possible to connect each of the parts mentioned in a central installation for managing the whole, which may advantageously be constituted by a microcomputer 44.
  • the holes 12 and 14 are for example tubes with a non-conductive material such as a plastic material or else these holes 12 and 14 are not filled with any conductive fluid. electricity.
  • the coupling between the electrodes 16, 20, 28, 34 and the basement in which one wishes to carry out measurements is of the capacitive type, at least as regards the electrodes 16 and 28.
  • the current generator with controllable frequency is associated with an amplifier which makes it possible to adapt the output voltage.
  • the electrodes 16 and 28 arranged in the boreholes 12 and 14 have a substantially cylindrical shape and their external face is made of an electrically conductive material. They are given suitable dimensions to optimize the capacitive coupling between these electrodes and the subsoil.
  • VZ -, which depends on the electrical properties of the subsoil and the geometric arrangement of the electrodes.
  • This processing can be carried out by the central device 44.
  • FIGs 8 and 9 we will describe a preferred embodiment of the capacitive electrodes of the invention.
  • These electrodes intended to be introduced into boreholes have substantially the shape of a cylinder 80 of length L and of diameter D. They are covered with a conductive material, therefore also of substantially cylindrical shape. They are surmounted by a compartment 81 containing a measuring instrument 91 electrically connected to the external conductive surface of the electrode.
  • This measuring device 91 will be a ammeter in the case where the cylinder 80 constitutes an injection electrode, it will be a voltmeter in the case where the cylinder is a measuring electrode.
  • the measuring device 91 is connected to terminals 92, which are themselves connected to external conductors which make it possible to trace the measurements made by the device 91 to the bus 40 and therefore to the processing device 44.
  • the diameter D of the electrodes is adapted to the diameter of the borehole and their length L is adapted accordingly so that their setting impedance allows the desired intensity to be injected.
  • the length L of the current or potential electrodes may be up to one meter, or even more, and their diameter will be between a few centimeters and about fifteen centimeters. Regarding the diameter, it must of course be less than the diameter of the borehole, without however being too much so that the capacitive coupling is of good quality.
  • the potential difference between the two potential electrodes will be measured by a device in two parts: on the one hand, a head with very high input impedance placed near the capacitive electrode in drilling, on the other hand a voltmeter allowing the measurement by comparison with the reference which is the potential of the other very distant electrode, as well as the compensation of the capacitive losses along the measurement cables.
  • the device for measuring the potential difference between the two measurement electrodes described above can be assembled in a single device.
  • the frequency of the current is from one to several tens of kHz, and the voltage delivered from several hundred volts.
  • This device can be used with capacitive drilling electrodes according to a large number of geometries. Of course in all cases the drilling electrodes can be mobile.
  • FIGS 2 to 7 illustrate different possible configurations for the measurement electrodes and the injection electrodes.
  • Figure 2 corresponds to Figure 1 and shows that the injection electrodes 16 and 28 for measurement can be moved in the holes 12 and 14 to perform different measurements.
  • FIG. 3 it is possible to carry out measurements between the injection 16 and measurement 28 electrodes placed in boreholes or between the electrode 16 and the measurement electrodes constituted by the metal stakes 50-51-52 etc. .
  • an injection electrode 16 and a measurement electrode 28 are arranged in the same borehole 12.
  • the other electrodes are constituted by stakes 60 and 61. This configuration corresponds to a pole-pole measurement in drilling (or pole-pole logging if the distance between the two electrodes is fixed).
  • the two injection electrodes 62 and 63 can be moved separately or together in a borehole 64, for example horizontal.
  • the measurement electrodes consist, on the one hand, of an infinitely distant conductive stake 65 and, on the other hand, of a series of metallic stakes 66 planted in the ground. The potential difference is measured at one of the stakes 66. For each position of the injection electrodes, as many measurements are obtained as there are stakes 66.
  • an injection electrode 16 is lowered into the borehole as well as a measurement electrode 28.
  • the current is injected by means of the electrode 16 and a stake 67 planted in the soil to a distance not infinite in the electric sense of the term of drilling.
  • the potential difference between the electrode 28 and a stake 68 planted on the ground surface is measured at a distance not infinite in the electrical sense of the term of drilling.
  • the four electrodes 70, 71, 72 and 73 are placed in drilling.
  • a current is injected through the electrodes 70 and 71.
  • the potential difference between the electrodes 72 and 73 is measured.
  • the measurements can then be, for example, of the dipole-dipole type in drilling or according to other geometries of the quadrupole, with spacings of multiple electrodes. If the distance between the electrodes is fixed, electrical logs can be produced. It is also possible to provide that only one measurement electrode is placed in the borehole, the injection electrodes and the other or the other measurement electrodes being disposed on the surface.
  • the instrumented part of the drilling electrodes can detach from it, and consequently, adapt to electrodes of various sizes and shapes chosen according to the drilling in which they are to be used.

Abstract

The invention concerns a electrical prospecting device in a borehole with capacitive electrodes comprising at least two injection electrodes (16, 20), at least two measuring electrodes (28, 34) and a current generator (22) for applying an electric current between the two injection electrodes. The current generator (22) delivers an alternating current whereof the frequency ranges from 5 kHz to 100 kHz under a voltage less than 1000 volts. At least one of the measuring or injection electrodes (16, 28) is arranged in a borehole (12, 14) and has an electricity conducting cylindrical outer surface. The device further comprises means (24) for measuring the intensity of the current passing through said injection electrodes, means for measuring the difference of potential between the two measuring electrodes (36, 36b), and means for processing the intensity measurements and the potential difference to deduce therefrom the characteristics of the subsurface where the borehole is located.

Description

Dispositif de mesure des caractéristiques électriques dans le sous-sol à électrodes capacitives. Device for measuring electrical characteristics in the basement with capacitive electrodes.
La présente invention a pour objet un dispositif de mesure des caractéristiques électriques dans le sous-sol à électrodes capacitives.The present invention relates to a device for measuring electrical characteristics in the basement with capacitive electrodes.
Les techniques de prospection électrique par courant continu ont montré depuis longtemps leur efficacité pour la prospection et la reconnaissance du sous- sol. Ces méthodes n'ont cessé de se développer pour la reconnaissance à partir de la surface du sol. En ce qui concerne la mise en oeuvre dans des forages, ces techniques ont pris les noms de diagraphie électrique, tomographie électrique, cylindre électrique ... Quelle que soit la technique particulière utilisée, elle est toujours fondée sur l'utilisation d'au moins quatre électrodes : deux électrodes (dites d'injection ou de courant) servant à injecter un courant d'intensité I dans le sol, deux autres électrodes (dites de mesure ou de potentiel) entre lesquelles on mesure la différence de potentiel qui en résulte. C'est la géométrie du quadripôle constitué par ces quatre électrodes et leur positionnement à la surface du sol et/ou dans un ou des forages qui détermine le nom de la technique particulière.The techniques of direct current electric prospecting have long shown their effectiveness for prospecting and reconnaissance of the subsoil. These methods have been continuously developed for reconnaissance from the ground surface. Regarding the implementation in drilling, these techniques have taken the names of electric logging, electric tomography, electric cylinder ... Whatever the particular technique used, it is always based on the use of at least four electrodes: two electrodes (called injection or current electrodes) used to inject a current of intensity I into the ground, two other electrodes (called measurement or potential) between which the resulting potential difference is measured. It is the geometry of the quadrupole formed by these four electrodes and their positioning on the ground surface and / or in one or more boreholes which determines the name of the particular technique.
Dans ces techniques de mesures électriques on désire reconnaître le sous- sol sur quelques dizaines de mètres d'épaisseur au maximum ; pour cela, on perce des forages. Le terrain est souvent hétérogène, altéré, et les forages doivent être tubes. En outre, ils sont souvent au moins en partie au-dessus du niveau de la nappe phréatique et ne contiennent alors pas d'eau. Par ailleurs ils ne comportent pas toujours un fluide conducteur de l'électricité.In these electrical measurement techniques, we want to recognize the subsoil a few tens of meters thick at most; for this, we drill holes. The terrain is often heterogeneous, altered, and the boreholes must be tubed. In addition, they are often at least partly above the level of the water table and therefore do not contain water. Furthermore, they do not always include an electrically conductive fluid.
En d'autres termes, dans ces situations, il n'est pas possible d'établir par couplage conductif une continuité du circuit électrique entre les différentes électrodes utilisées et le sous-sol dans lequel on veut effectuer ces mesures.In other words, in these situations, it is not possible to establish by conductive coupling a continuity of the electrical circuit between the different electrodes used and the subsoil in which one wishes to carry out these measurements.
Un objet de la présente invention est de fournir un dispositif de mesure des caractéristiques électriques du sous-sol à partir d'un forage, dispositif qui puisse être utilisé en particulier lorsqu'aucun moyen n'est disponible pour assurer la continuité électrique par conduction entre la ou les électrodes disposées dans le ou les forages et le sous-sol pour lequel on veut effectuer les mesures.An object of the present invention is to provide a device for measuring the electrical characteristics of the subsoil from a borehole, a device which can be used in particular when no means is available to ensure electrical continuity by conduction between the electrode (s) placed in the borehole (s) and the basement for which the measurements are to be made.
Pour atteindre ce but, selon l'invention, le dispositif de prospection électrique en forage à électrodes capacitives qui comprend au moins deux électrodes d'injection et un générateur de courant pour injecter à travers elles le courant dans le sol, ainsi que deux électrodes de mesure et des moyens pour mesurer la différence de potentiel entre elles, se caractérise en ce que : - ledit générateur de courant délivre un courant alternatif dont la fréquence est de préférence comprise entre 5 et 100 kHz sous une tension inférieure à 1000 volts,To achieve this object, according to the invention, the device for electric prospecting in drilling with capacitive electrodes which comprises at least two injection electrodes and a current generator for injecting current through them into the ground, as well as two electrodes for measure and means for measuring the potential difference between them, is characterized in that: said current generator delivers an alternating current whose frequency is preferably between 5 and 100 kHz at a voltage of less than 1000 volts,
- au moins une des quatre électrodes est destinée à être disposée dans un forage et présente une surface externe sensiblement cylindrique et conductrice de l'électricité, et en ce qu'il comprend en outre :at least one of the four electrodes is intended to be placed in a borehole and has a substantially cylindrical and electrically conductive external surface, and in that it further comprises:
- des moyens pour mesurer l'intensité traversant les électrodes d'injection- means for measuring the intensity passing through the injection electrodes
- des moyens pour mesurer la différence de potentiel entre les électrodes de mesure, etmeans for measuring the potential difference between the measurement electrodes, and
- des moyens pour traiter ladite mesure d'intensité et ladite mesure de différence de potentiel pour en déduire les caractéristiques électriques du sous-sol dans lequel est situé le forage.- Means for processing said intensity measurement and said potential difference measurement to deduce therefrom the electrical characteristics of the subsoil in which the borehole is located.
On comprend que grâce aux dispositions de l'invention on établit effectivement un couplage ohmique entre la ou les électrodes disposées dans le ou les forages et le sous-sol dans lequel on veut effectuer les mesures, bien qu'aucun moyen ne permet d'assurer par conduction la continuité électrique entre les électrodes et le sous-sol.It will be understood that, thanks to the provisions of the invention, an ohmic coupling is effectively established between the electrode (s) placed in the borehole (s) and the subsoil in which the measurements are to be made, although no means makes it possible to ensure by conduction the electrical continuity between the electrodes and the basement.
Ce couplage présente une qualité suffisante pour que les mesures effectuées soient exploitables pour la reconnaissance des caractéristiques électriques du sous- sol à prospecter.This coupling is of sufficient quality for the measurements carried out to be usable for recognizing the electrical characteristics of the subsoil to be prospected.
Selon un mode de réalisation préféré au moins une desdites électrodes d'injection est destinée à être placée en forage. Elle est alors sensiblement cylindrique et comporte une surface externe conductrice de l'électricité. Selon un autre mode préféré de mise en oeuvre le dispositif de mesure d'intensité du courant injecté et l'électrode d'injection sont montés sur un même composant qui est destiné à être placé dans le forage dans la ou les positions souhaitées, selon les mesures à effectuer.According to a preferred embodiment at least one of said injection electrodes is intended to be placed in drilling. It is then substantially cylindrical and has an electrically conductive external surface. According to another preferred embodiment, the device for measuring the intensity of the injected current and the injection electrode are mounted on the same component which is intended to be placed in the borehole in the desired position or positions, according to the measurements to be performed.
On comprend que grâce à cette disposition, la mesure de l'intensité du courant injecté peut être réalisée avec une grande précision, ce qui facilite l'interprétation des résultats.It is understood that thanks to this arrangement, the measurement of the intensity of the injected current can be carried out with great precision, which facilitates the interpretation of the results.
Selon une autre caractéristique préférée, au moins une desdites électrodes de mesure est destinée à être disposée dans un forage. Elle est alors sensiblement cylindrique et comporte une surface externe conductrice de l'électricité et est solidaire d'une partie du dispositif de mesure de tension. Cette disposition permet d'améliorer la précision de la mesure de la différence de potentiel entre les deux électrodes de mesure.According to another preferred characteristic, at least one of said measurement electrodes is intended to be placed in a borehole. It is then substantially cylindrical and has an external electrically conductive surface and is integral with a part of the voltage measurement device. This arrangement makes it possible to improve the accuracy of the measurement of the potential difference between the two measurement electrodes.
D'autres caractéristiques et avantages de l'invention apparaîtront plus clairement à la lecture de la description qui suit de plusieurs modes de réalisation préférés de l'invention donnés à titre d'exemples non limitatifs. La description se réfère aux figures annexées sur lesquelles : la figure 1 est une vue simplifiée d'un premier mode de réalisation du dispositif de mesure par couplage capacitif; les figures 2, 3, 4, 5, 6 et 7 illustrent de façon simplifiée d'autres possibilités de configuration des électrodes d'injection et de potentiel la figure 8 est une vue en perspective d'un mode préféré de réalisation d'une électrode destinée à être placée dans un forage la figure 9 est une vue en coupe verticale de l'électrode de la figure 8.Other characteristics and advantages of the invention will appear more clearly on reading the following description of several preferred embodiments of the invention given by way of non-limiting examples. The description refers to the appended figures in which: FIG. 1 is a simplified view of a first embodiment of the measurement device by capacitive coupling; Figures 2, 3, 4, 5, 6 and 7 illustrate in a simplified manner other possibilities of configuration of the injection and potential electrodes. Figure 8 is a perspective view of a preferred embodiment of an electrode. intended to be placed in a borehole FIG. 9 is a view in vertical section of the electrode of FIG. 8.
En se référant tout d'abord à la figure 1 on va décrire l'ensemble du dispositif de mesure selon un premier mode de mise en oeuvre où une électrode de mesure et une électrode d'injection sont disposées dans deux forages.Referring first to Figure 1 we will describe the entire measuring device according to a first embodiment where a measuring electrode and an injection electrode are arranged in two boreholes.
On va décrire en se référant à cette figure 1 l'ensemble d'un premier mode de réalisation du dispositif de mesure selon l'invention.Referring to this FIG. 1, a description will be given of the assembly of a first embodiment of the measuring device according to the invention.
On y a représenté la surface 10 du sol où ont été percés deux forages 12 et 14 dans la zone dont on veut déterminer les caractéristiques électriques.There is shown the surface 10 of the ground where two holes 12 and 14 were drilled in the area whose electrical characteristics are to be determined.
L'installation comprend tout d'abord une électrode d'injection 16 qui est disposée dans le premier forage 12 et suspendue à un câble 18. La deuxième électrode d'injection est constituée par un piquet métallique 20 enfoncé dans le sol et dont la distance par rapport au forage 12 peut être considérée comme infinie au sens électrique du terme. Les électrodes d'injection 16 et 20 sont reliées à un générateur de courant alternatif 22. A l'électrode d'injection 16 disposée dans le forage 12 est associé un appareil de mesure de l'intensité du courant 24. Le câble de sustentationThe installation firstly comprises an injection electrode 16 which is placed in the first borehole 12 and suspended from a cable 18. The second injection electrode is constituted by a metal stake 20 driven into the ground and the distance of which compared to drilling 12 can be considered infinite in the electric sense of the term. The injection electrodes 16 and 20 are connected to an alternating current generator 22. To the injection electrode 16 placed in the borehole 12 is associated a device for measuring the intensity of the current 24. The lift cable
18 comporte en outre de préférence des conducteurs électriques d'une part pour relier l'électrode au générateur 22 et d'autre part pour relier le système de mesure d'intensité au système de contrôle de l'ensemble de l'installation. De plus, un dispositif 26 permet de connaître la position de l'électrode 16 dans le forage 12.18 preferably further comprises electrical conductors on the one hand for connecting the electrode to the generator 22 and on the other hand for connecting the intensity measurement system to the control system of the entire installation. In addition, a device 26 makes it possible to know the position of the electrode 16 in the borehole 12.
Dans le forage 14 est disposée une première électrode de mesure 28 qui est également suspendue à l'extrémité d'un câble 30 associé à des moyens 32 de mesure de la position de l'électrode 28 dans le forage 14. Une deuxième électrode de mesure 34 est constituée par un piquet métallique fiché dans le sol à une distance telle qu'on peut la considérer comme infinie d'un point de vue électrique. Un voltmètre ou un dispositif analogue 36 permet de mesurer la différence de potentiel électrique entre les électrodes de mesure 28 et 34. Il peut comporter une partie 36b emmenée avec l'électrode 28 dans le forage 14.In the borehole 14 is disposed a first measurement electrode 28 which is also suspended from the end of a cable 30 associated with means 32 for measuring the position of the electrode 28 in the borehole 14. A second measurement electrode 34 is constituted by a metal stake stuck in the ground at a distance such that one can consider it as infinite from an electrical point of view. A voltmeter or similar device 36 makes it possible to measure the difference in electrical potential between the measurement electrodes 28 and 34. It may include a part 36b taken along with the electrode 28 in the borehole 14.
Un bus de communication 40 permet de relier le générateur de courant 22, les dispositifs 26 et 32 de mesure de profondeur des électrodes et le voltmètre 36 à un circuit d'interface 42. Le circuit d'interface 42 permet donc de relier chacune des parties mentionnées à une installation centrale de gestion de l'ensemble qui peut être avantageusement constituée par un microordinateur 44.A communication bus 40 makes it possible to connect the current generator 22, the devices 26 and 32 for measuring the depth of the electrodes and the voltmeter 36 to an interface circuit 42. The interface circuit 42 therefore makes it possible to connect each of the parts mentioned in a central installation for managing the whole, which may advantageously be constituted by a microcomputer 44.
Comme on l'a déjà indiqué, dans le cas de l'invention les forages 12 et 14 sont par exemple tubes avec un matériau non conducteur tel qu'un matériau plastique ou bien ces forages 12 et 14 ne sont remplis par aucun fluide conducteur de l'électricité.As already indicated, in the case of the invention the holes 12 and 14 are for example tubes with a non-conductive material such as a plastic material or else these holes 12 and 14 are not filled with any conductive fluid. electricity.
Comme on l'a déjà indiqué également, selon l'invention, le couplage entre les électrodes 16, 20, 28, 34 et le sous-sol dans lequel on veut effectuer des mesures est de type capacitif, au moins en ce qui concerne les électrodes 16 et 28.As already indicated also, according to the invention, the coupling between the electrodes 16, 20, 28, 34 and the basement in which one wishes to carry out measurements is of the capacitive type, at least as regards the electrodes 16 and 28.
Pour pouvoir effectuer les mesures dans des conditions optimales, le générateur de courant à fréquence commandable est associé à un amplificateur qui permet d'adapter la tension de sortie.To be able to carry out the measurements under optimal conditions, the current generator with controllable frequency is associated with an amplifier which makes it possible to adapt the output voltage.
Comme on l'expliquera plus en détail ultérieurement, les électrodes 16 et 28 disposées dans les forages 12 et 14 ont une forme sensiblement cylindrique et leur face externe est constituée d'un matériau conducteur de l'électricité. On leur donne des dimensions convenables pour optimiser le couplage capacitif entre ces électrodes et le sous-sol.As will be explained in more detail later, the electrodes 16 and 28 arranged in the boreholes 12 and 14 have a substantially cylindrical shape and their external face is made of an electrically conductive material. They are given suitable dimensions to optimize the capacitive coupling between these electrodes and the subsoil.
Grâce à la mesure, d'une part, de la différence de potentiel électrique V entre les électrodes 28 et 34, et d'autre part du courant I effectivement injecté par les électrodes 16 et 20, on peut en déduire une mesure d'impédance de transfertBy measuring, on the one hand, the difference in electrical potential V between the electrodes 28 and 34, and on the other hand the current I actually injected by the electrodes 16 and 20, it is possible to deduce a measurement of impedance therefrom. transfer
V Z = — , qui dépend des propriétés électπques du sous-sol et de la disposition géométrique des électrodes. Ce traitement peut être effectué par le dispositif central 44. En se référant maintenant aux figures 8 et 9 on va décrire un mode préféré de réalisation des électrodes capacitives de l'invention. Ces électrodes destinées à être introduites dans des forages ont sensiblement la forme d'un cylindre 80 de longueur L et de diamètre D. Elles sont recouvertes d'un matériau conducteur, de forme donc également sensiblement cylindrique. Elles sont surmontées d'un compartiment 81 contenant un instrument de mesure 91 relié électriquement à la surface externe conductrice de l'électrode. Cet appareil de mesure 91 sera un ampèremètre dans le cas où le cylindre 80 constitue une électrode d'injection, il sera un voltmètre dans le cas où le cylindre est une électrode de mesure. Bien entendu l'appareil de mesure 91 est relié à des bornes 92, elles-mêmes reliées à des conducteurs externes qui permettent de remonter les mesures effectuées par l'appareil 91 vers le bus 40 et donc vers le dispositif de traitement 44.VZ = -, which depends on the electrical properties of the subsoil and the geometric arrangement of the electrodes. This processing can be carried out by the central device 44. Referring now to Figures 8 and 9 we will describe a preferred embodiment of the capacitive electrodes of the invention. These electrodes intended to be introduced into boreholes have substantially the shape of a cylinder 80 of length L and of diameter D. They are covered with a conductive material, therefore also of substantially cylindrical shape. They are surmounted by a compartment 81 containing a measuring instrument 91 electrically connected to the external conductive surface of the electrode. This measuring device 91 will be a ammeter in the case where the cylinder 80 constitutes an injection electrode, it will be a voltmeter in the case where the cylinder is a measuring electrode. Of course, the measuring device 91 is connected to terminals 92, which are themselves connected to external conductors which make it possible to trace the measurements made by the device 91 to the bus 40 and therefore to the processing device 44.
Le diamètre D des électrodes est adapté au diamètre du forage et leur longueur L est adaptée en conséquence pour que leur impédance de prise permette d'injecter l'intensité voulue. La longueur L des électrodes de courant ou de potentiel pourra aller jusqu'à un mètre, voire plus, et leur diamètre sera compris entre quelques centimètres et une quinzaine de centimètres. En ce qui concerne le diamètre, il doit bien sûr être inférieur au diamètre du forage, sans toutefois l'être trop afin que le couplage capacitif soit de bonne qualité.The diameter D of the electrodes is adapted to the diameter of the borehole and their length L is adapted accordingly so that their setting impedance allows the desired intensity to be injected. The length L of the current or potential electrodes may be up to one meter, or even more, and their diameter will be between a few centimeters and about fifteen centimeters. Regarding the diameter, it must of course be less than the diameter of the borehole, without however being too much so that the capacitive coupling is of good quality.
Dans un mode préféré de mise en oeuvre, la différence de potentiel entre les deux électrodes de potentiel sera mesurée par un dispositif en deux parties : d'une part une tête à très haute impédance d'entrée disposée à proximité de l'électrode capacitive en forage, d'autre part un voltmètre permettant la mesure par comparaison à la référence qu'est le potentiel de l'autre électrode très éloignée, ainsi que la compensation des pertes capacitives le long des câbles de mesure.In a preferred embodiment, the potential difference between the two potential electrodes will be measured by a device in two parts: on the one hand, a head with very high input impedance placed near the capacitive electrode in drilling, on the other hand a voltmeter allowing the measurement by comparison with the reference which is the potential of the other very distant electrode, as well as the compensation of the capacitive losses along the measurement cables.
Dans les cas d'utilisation où les deux électrodes de potentiel sont proches, le dispositif de mesure de la différence de potentiel entre les deux électrodes de mesure décrit précédemment pourra être rassemblé en un seul appareil.In the cases of use where the two potential electrodes are close, the device for measuring the potential difference between the two measurement electrodes described above can be assembled in a single device.
De préférence, la fréquence du courant est de une à plusieurs dizaines de kHz, et la tension délivrée de plusieurs centaines de volts.Preferably, the frequency of the current is from one to several tens of kHz, and the voltage delivered from several hundred volts.
On peut utiliser ce dispositif à électrodes capacitives de forage selon un grand nombre de géométries. Bien entendu dans tous les cas les électrodes de forage peuvent être mobiles.This device can be used with capacitive drilling electrodes according to a large number of geometries. Of course in all cases the drilling electrodes can be mobile.
Les figures 2 à 7 illustrent différentes configurations possibles pour les électrodes de mesure et les électrodes d'injection.Figures 2 to 7 illustrate different possible configurations for the measurement electrodes and the injection electrodes.
La figure 2 correspond à la figure 1 et montre que les électrodes 16 d'injection et 28 de mesure peuvent être déplacées dans les forages 12 et 14 pour effectuer différentes mesures. On a une configuration pôle-pôle entre forages.Figure 2 corresponds to Figure 1 and shows that the injection electrodes 16 and 28 for measurement can be moved in the holes 12 and 14 to perform different measurements. We have a pole-pole configuration between boreholes.
Dans le cas de la figure 3, on peut effectuer des mesures entre les électrodes d'injection 16 et de mesure 28 disposées dans des forages ou entre l'électrode 16 et les électrodes de mesure constituées par les piquets métalliques 50-51-52 etc. Dans le cas de la figure 4, une électrode d'injection 16 et une électrode de mesure 28 sont disposées dans un même forage 12. Les autres électrodes sont constituées par des piquets 60 et 61. Cette configuration correspond à une mesure pôle-pôle dans un forage (ou diagraphie pôle-pôle si l'écartement entre les deux électrodes est fixe).In the case of FIG. 3, it is possible to carry out measurements between the injection 16 and measurement 28 electrodes placed in boreholes or between the electrode 16 and the measurement electrodes constituted by the metal stakes 50-51-52 etc. . In the case of FIG. 4, an injection electrode 16 and a measurement electrode 28 are arranged in the same borehole 12. The other electrodes are constituted by stakes 60 and 61. This configuration corresponds to a pole-pole measurement in drilling (or pole-pole logging if the distance between the two electrodes is fixed).
Dans le cas de la figure 5, les deux électrodes d'injection 62 et 63 peuvent être déplacées séparément ou ensemble dans un forage 64, par exemple horizontal. Les électrodes de mesure sont constituées, d'une part, par un piquet conducteur 65 infiniment éloigné et, d'autre part, par une série de piquets métalliques 66 plantés dans le sol. On mesure la différence de potentiel à un des piquets 66. Pour chaque position des électrodes d'injection, on obtient autant de mesures qu'il y a de piquets 66.In the case of FIG. 5, the two injection electrodes 62 and 63 can be moved separately or together in a borehole 64, for example horizontal. The measurement electrodes consist, on the one hand, of an infinitely distant conductive stake 65 and, on the other hand, of a series of metallic stakes 66 planted in the ground. The potential difference is measured at one of the stakes 66. For each position of the injection electrodes, as many measurements are obtained as there are stakes 66.
Dans le cas de la figure 6, une électrode d'injection 16 est descendue dans le forage ainsi qu'une électrode de mesure 28. Le courant est injecté au moyen de l'électrode 16 et d'un piquet 67 planté dans le sol à une distance non infinie au sens électrique du terme du forage. On mesure la différence de potentiel entre l'électrode 28 et un piquet 68 planté à la surface du sol à une distance non infinie au sens électrique du terme du forage.In the case of FIG. 6, an injection electrode 16 is lowered into the borehole as well as a measurement electrode 28. The current is injected by means of the electrode 16 and a stake 67 planted in the soil to a distance not infinite in the electric sense of the term of drilling. The potential difference between the electrode 28 and a stake 68 planted on the ground surface is measured at a distance not infinite in the electrical sense of the term of drilling.
Dans le cas de la figure 7, les quatre électrodes 70, 71, 72 et 73 sont placées en forage. Un courant est injecté à travers les électrodes 70 et 71. On mesure la différence de potentiel entre les électrodes 72 et 73. Les mesures peuvent être alors par exemple de type dipôle-dipôle en forage ou suivant d'autres géométries du quadripôle, à écartements d'électrodes muliples. Si l'écartement entre les électrodes est fixé, on peut réaliser des diagraphies électriques. Il est encore possible de prévoir que, seule une électrode de mesure soit disposée dans le forage, les électrodes d'injection et l'autre ou les autres électrodes de mesure étant disposées en surface.In the case of FIG. 7, the four electrodes 70, 71, 72 and 73 are placed in drilling. A current is injected through the electrodes 70 and 71. The potential difference between the electrodes 72 and 73 is measured. The measurements can then be, for example, of the dipole-dipole type in drilling or according to other geometries of the quadrupole, with spacings of multiple electrodes. If the distance between the electrodes is fixed, electrical logs can be produced. It is also possible to provide that only one measurement electrode is placed in the borehole, the injection electrodes and the other or the other measurement electrodes being disposed on the surface.
De préférence, la partie instrumentée des électrodes de forage peut s'en détacher, et par suite, s'adapter à des électrodes de tailles et formes diverses choisies selon le forage où elles doivent être mises en oeuvre. Preferably, the instrumented part of the drilling electrodes can detach from it, and consequently, adapt to electrodes of various sizes and shapes chosen according to the drilling in which they are to be used.

Claims

REVENDICATIONS
1. Dispositif de prospection électrique en forage à électrodes capacitives comprenant au moins deux électrodes d'injection, au moins deux électrodes de mesure, un générateur de courant pour appliquer un courant électrique entre deux électrodes d'injection et des moyens pour mesurer la différence de potentiel entre deux électrodes de mesure caractérisé en ce que :1. Electric prospecting device for drilling with capacitive electrodes comprising at least two injection electrodes, at least two measurement electrodes, a current generator for applying an electric current between two injection electrodes and means for measuring the difference of potential between two measuring electrodes characterized in that:
- ledit générateur de courant (22) délivre un courant alternatif dont la fréquence est de 5 kHz à 100 kHz sous une tension inférieure à 1000 volts- said current generator (22) delivers an alternating current whose frequency is from 5 kHz to 100 kHz at a voltage of less than 1000 volts
- au moins une des électrodes de mesure (28) ou d'injection (16) est destinée à être disposée dans un forage (12, 14) et présente une surface externe sensiblement cylindrique et conductrice de l'électricité (80),- at least one of the measurement (28) or injection (16) electrodes is intended to be placed in a borehole (12, 14) and has a substantially cylindrical and electrically conductive external surface (80),
- des moyens (24) pour mesurer l'intensité du courant traversant lesdites électrodes d'injection,- means (24) for measuring the intensity of the current passing through said injection electrodes,
- des moyens (26) pour mesurer la différence de potentiel entre lesdites électrodes de mesure, et- means (26) for measuring the potential difference between said measurement electrodes, and
- des moyens (44) pour traiter ladite mesure d'intensité et ladite mesure de différence de potentiel pour en déduire des caractéristiques du sous-sol dans lequel est situé le forage.- Means (44) for processing said intensity measurement and said potential difference measurement to deduce therefrom characteristics of the subsoil in which the borehole is located.
2. Dispositif selon la revendication 1 caractérisé en ce que ladite électrode d'injection sensiblement cylindrique et un dispositif de mesure d'intensité (24) sont montés sur un même composant destiné à être placé en forage.2. Device according to claim 1 characterized in that said substantially cylindrical injection electrode and an intensity measuring device (24) are mounted on the same component intended to be placed in drilling.
3. Dispositif selon l'une quelconque des revendications 1 et 2 caractérisé en ce que ladite électrode de mesure sensiblement cylindrique (80) présente une surface externe conductrice de l'électricité, et qu'elle est montée sur le même composant qu'une partie du dispositif de mesure de tension (36b), ce composant étant destiné à être placé en forage.3. Device according to any one of claims 1 and 2 characterized in that said substantially cylindrical measuring electrode (80) has an external electrically conductive surface, and that it is mounted on the same component as a part of the tension measurement device (36b), this component being intended to be placed in drilling.
4. Dispositif selon la revendication 3, caractérisé en ce que les moyens de mesure de différence de potentiel comprennent en outre une deuxième partie (36) permettant de comparer les potentiels des deux électrodes de mesure (28, 34) et de compenser les pertes dans les câbles les reliant, et des moyens de traitement des tensions mesurées.4. Device according to claim 3, characterized in that the potential difference measurement means further comprises a second part (36) making it possible to compare the potentials of the two measurement electrodes (28, 34) and to compensate for the losses in the cables connecting them, and means for processing the measured voltages.
5. Dispositif selon l'une quelconque des revendications 3 et 4, caractérisé en ce qu'une deuxième électrode de mesure (73) est destinée à être placée en forage, en ce que ladite électrode est cylindrique et présente une surface externe conductrice de l'électricité, et en ce que ladite deuxième électrode de mesure et ledit deuxième dispositif de mesure de tension sont montés sur un même composant destiné à être placé en forage.5. Device according to any one of claims 3 and 4, characterized in that a second measuring electrode (73) is intended to be placed in drilling, in that said electrode is cylindrical and has an external surface electrically conductive, and in that said second measurement electrode and said second voltage measurement device are mounted on the same component intended to be placed in drilling.
6. Dispositif selon l'une quelconque des revendications 1 à 5, caractérisé en ce qu'il comprend une deuxième électrode d'injection (71) destinée à être placée dans un forage, en ce que ladite deuxième électrode d'injection est sensiblement cylindrique et présente une surface externe conductrice de l'électricité, au moins la partie "amplificateur" du générateur de courant étant montée sur un même composant que l'électrode d'injection, composant destiné à être placé en forage. 6. Device according to any one of claims 1 to 5, characterized in that it comprises a second injection electrode (71) intended to be placed in a borehole, in that said second injection electrode is substantially cylindrical and has an electrically conductive external surface, at least the "amplifier" part of the current generator being mounted on the same component as the injection electrode, a component intended to be placed in drilling.
7. Dispositif selon l'une quelconque des revendications 1 à 6, caractérisé en ce qu'au moins une desdites électrodes (16, 28) est mobile dans au moins un des forages (12, 14) et en ce que ledit dispositif comprend en outre des moyens (26, 32) pour mesurer la position de chaque électrode mobile dans un forage.7. Device according to any one of claims 1 to 6, characterized in that at least one of said electrodes (16, 28) is movable in at least one of the boreholes (12, 14) and in that said device comprises in in addition to means (26, 32) for measuring the position of each movable electrode in a borehole.
8. Dispositif selon l'une quelconque des revendications 1 à 7 et selon lequel la partie instrumentée des électrodes de forage peut s'en détacher, et par suite, s'adapter à des électrodes de tailles et formes diverses choisies selon le forage où elles doivent être mises en oeuvre. 8. Device according to any one of claims 1 to 7 and according to which the instrumented part of the drilling electrodes can detach from it, and consequently, adapt to electrodes of various sizes and shapes chosen according to the drilling where they must be implemented.
EP99936711A 1998-08-07 1999-08-09 Device with capacitive electrodes for measuring subsurface electric characteristics Withdrawn EP1103008A1 (en)

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FR9810198 1998-08-07
FR9810198A FR2782170B1 (en) 1998-08-07 1998-08-07 DEVICE FOR MEASURING ELECTRICAL CHARACTERISTICS IN THE BASEMENT WITH CAPACITIVE ELECTRODES
PCT/FR1999/001958 WO2000008492A1 (en) 1998-08-07 1999-08-09 Device with capacitive electrodes for measuring subsurface electric characteristics

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FR2782170B1 (en) 2000-11-10

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