DE2932566A1 - SYSTEM FOR GEOPHYSICAL EXAMINATIONS OR THE LIKE WITH NON-POLARIZING ELECTRODES - Google Patents

Description

System for geophysical investigations or the like with no

polarizing electrodes.

Electrical procedures for geophysical surveys are known for a long time. If one disregards the method that works with self-potential, the systems use usually either an AC or DC power source for introducing an electric current into the ground between two spaced electrodes. The resulting Potential drop is either between these electrodes or measured at a distance from these other electrodes

When a pesticide ladder such as a metal stake or the like. in the Soil is brought in, cause the chemical components contained in the particular place in the earth and the concentration and the nature of the ions in the water contained in the pores of the Eras cause a change in the potentials applied to the Electrode contacts produce and also affect the grounding Resistance between the conductor and the earth. These two phenomena are commonly called polarization. It was before Years ago it was found that when the earth is supplied with an alternating current instead of a direct current, the degree of polarization when the electrodes touch the ground is significantly reduced. However, if the distance between the elec-

. a few trodden was taller than about a meter (a / feet) a phenomenon known as the "skin effect", i.e. the induction effect of the alternating current flowing through the floor a significant change in the path of current flow, significantly different from that observed when Direct current was used. In general, the "skin effect" created the main or intermediate path of current flow through the earth, so that he is more

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path between the current electrodes was limited than in the Pail in which direct current was used.

In various developments it was found that if deep penetration with direct current electrode arrangements was desired, it was possible to address the polarization problem by accepting the occurrence of polarization on the current electrodes and ^{scoring points by using so-called "porous cup electrodes 11"} at the contact between which the potential was measured.This arrangement is described in detail in geophysical books, e.g. in the book by JJJakosky "Exploration Geophysics" published by Times-Mirror-Press, Los Angeles, 1940. Essentially a permeable ceramic pot was used, usually in the form of a straight cylinder with an open top. The inside of the pot contained a saturated solution of salts of some metals and an electrode made of this particular metal was immersed in the solution in such a way that a surface contact as extensive as possible was achieved. Under normal Condition These electrodes could be inserted into the earth's surface with relatively negligible polarization voltages between them. Of course, they could not be used for electrical borehole probing because the hydrostatic pressure of the borehole fluid surrounding these electrodes forced that well fluid into the pot. In borehole probing, the usual method is therefore to use a relatively narrow distance between current and potential electrodes, metal electrodes and an alternating current potential, the frequency of which was usually above the 50 - 60 Hz current range, but was usually only a few 100 Hz, e.g. 400 Hz .

In addition to the non-polarizing porous electrodes described above, despite extensive searches in the literature (including the electrical surface investigation

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gen and borehole probing patents), no other Kind of a system with non-polarizing electrodes can be found.

The invention basically relates to the use of pairs of solid conductors, between which on contact with the ground an alternating current bias flows as individual electrodes

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for electrical geophysics '. Investigations or borehole probes. According to the invention, the use of a direct current is preferred as the measuring current, even if an alternating current with a low frequency, for example not above 20 or 30 Hz, can also be used. The alternating current bias of each pair of electrodes is at least in the range of the magnitude of the direct current or the alternating current with a very low frequency that is used for the measurements and is preferably somewhat greater than this measurement current. The frequency of the alternating current bias must differ considerably from that in the Hesskreis in order to simplify the measurement, ie to ensure that the bias current does not affect the reading instruments 100 Hz, for example 400-600 Hz, but preferably not above about 1000 Hz.

The invention thus relates to a system for electrical geophysical Investigation and borehole probing, in which a potential is applied to the earth, through which a " Direct current or an alternating current of low frequency is set in flow between adjacent electrodes, whereby the Potential between electrodes in contact with the ground is measured. Difficulties have emerged due to the electrode cliemie on the contact areas of the Electrodes with the ground. This phenomenon is usually called polarization, with frequent changes in potential at the Electrode contact point are caused. It was found that it is possible to have pairs of relatively close together lying solid conductor electrodes instead of the previously

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used to use single electrodes, with an alternating current between the two electrodes of each pair, which greatly reduces the polarization and creates a direct current or a low frequency AC potential is applied between two such pairs, either for abandoning one Measuring current into the ground or to determine the amount between other, similarly arranged pairs of pesticide electrodes, which are in contact with the earth and are also biased with alternating current resulting in potential. Of the The alternating bias current is at least in the range of the magnitude and preferably somewhat larger than the direct current an electrode.

The invention is explained in more detail below with reference to the drawings using two exemplary embodiments. Form the drawings part of this description and should be viewed in conjunction with it. In these drawings, like denotes Identical elements are referenced.

In the drawings show:

Fig. Is a schematic representation of a borehole probing process according to one embodiment of the invention,

FIG. 2 shows a circuit diagram of the arrangement used in FIG. 1 for borehole probing, and FIG

Fig. 3 is an oblique view of a schematic representation of a second embodiment for electrical surface probing.

Fig. 1 shows, very schematically, an arrangement of the devices according to the invention which are used for electrical borehole probing in a manner in which the illustrated system of non- polarizing electrodes has particular advantages. It was known that in most types of borehole probes that use resistivity, the electrode spacing was in the order of centimeters.

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tern (of inches), but seldom rose to a meter (2 or 3 feet). Since the penetration depth of the current used when carrying out the measurements (to a certain extent depending on the electrode design) is generally two to three times this value with regard to the electrode spacing, it can be seen that the electrical effects measured on the potential electrodes are no longer the Adjacent rock formations cover as an area from 1 m (3 feet) to perhaps 3 m (10 feet). In the petroleum industry it is sometimes desirable to use a well probing system in which the effective depth of penetration of the probing system is significantly greater, particularly when attempting to be perpendicular to the axis of the borehole at a depth of 30-300 meters (100-1000 feet) ) or the like. to investigate. This is the case, for example, when the side boundary of a salt dome is to be localized in the neighborhood. In this case, an ultra-long distance electrical survey method (Ulsel) in which the distance between the current electrode and the first potential electrode is in the range of 30-300 m (100,000 feet) or more must be used. In Pig. 1, which shows such an Ulsel system, the unlined section 11 of a borehole 12 is to be undercut using an electrical cable 13 which carries a current electrode 14 at the lower end of the cable, above which a first potential _{electrode 15 at a distance L 1} and a second potential electrode 16 is arranged at a distance Lg above this. The second current electrode 18 lies in the area of the borehole mouth and is, for example, inserted into the ground on the surface of the earth 17 (see position of the electrode 18). The electrical cable 13 is a multi-conductor cable, the conductors of which, as is known, are well insulated from one another and from possible penetration of the borehole fluid in the region 19 in the borehole 11. It is also understood that when this arrangement is used, the length L ₂ is usually a multiple of the length L ^,

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ORIGINAL INSPECTED

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eg 5 to> is 50 times L _1. In this Pail, the potential difference between electrodes 15 and 16 as a result of the current flow between electrodes 14 and 18 can be regarded as a first approximation, which is mainly determined by the specific resistance of the nature of the surrounding mountains in a sphere with the electrode 14 as the center and a radius with a length approximately between L ^ and Lp is influenced.

According to the invention, each of the electrodes has this arrangement actually of two contaminant conductor sections (e.g. 21 and 22 for electrode 15) electrically connected by a middle insulator 23 are separated.

From the circuit diagram according to Pig. 2 is better to see that each of the two contaminant conductor electrodes paired to form electrodes 14, 15, 16 and 18, with a potential of individual secondary windings 24-27 of a power transformer 28 is acted upon, the corresponding with an alternating current source 29 is fed. Since these electrodes are in contact with the earth, they do not have an infinite electrical resistance possessed, an alternating current or bias current flows between the two conductors forming the electrode 14, and in the same way alternating currents flow between the pairs forming the electrodes 15, 16 and 18.

The size of the individual bias currents are not of particular importance Meaning. According to the invention, it was found that it is very desirable that the as Yorspannungsstron serving alternating current flowing from a contaminant conductor of a part e.g. of the electrode 15, in the area the size of the measuring current and preferably slightly larger than is this measurement current at the electrode. In Pig. The embodiment shown in FIG. 2 is a direct current source as the read current source 30 (also shown in Pig. 1), which is connected to the electrodes in such a way that it is between

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see the center turns 31 and 32 of the secondary windings 24 "or 27. It was found that under these circumstances the pair of solid conductors that make up the electrode 14 and that forming the electrode 18 acts as a substantially non-polarizing electrode which is very satisfactorily conducts direct current from direct current source 30 between electrodes 14 and 18. The direction of the Power source polarity 30 hai, none under these circumstances special meaning.

If one of these electrode pair arrangements is used as a potential measuring electrode instead of being used as an electrode to apply the measurement current into the ground, the peak value of the AC bias potential should be be at least in the range of the potential difference to be measured, and preferably the rms The bias potential must be at least as large as the Hess potential. So it's supposed to be in Pig. 1 and 2 the potential between the secondary windings 25 and 26 of the transformer have a peak value of at least in the region of the direct current potential between the center turns of these secondary windings, and in particular the rms voltage of each of these secondary windings should be be as large as the DC potential.

In the same way, the middle turns 33 and 34 form the secondary windings 25 and 26 of transformer 28 supplying the AC bias current give up on the electrodes 16 and 14, the electrodes between which the direct current potential is measured in this well probing equipment. These mean windings are correspondingly with the DC voltage tape recorder 35 connected. As is known, the recording tape runs on which the potential drop of the electrode 15 and 16 is recorded for observation, usually in synchronism with the movement of the electrodes in the borehole. For example, the cable 13 can run over a turning roller 36 which diverts the cable onto the receiving thread 37. A mechanical one Output from the axis of the turning roller 36 is then to

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Drive of the recording tape used. This is indicated by the dashed line 38 in Pig. I shown.

The ends of the conductors of the cable 13 are in the secondary windings of the current transformer 28 by means of slip rings (only partially shown) connected to the receiving thread 37, as is also known. Pig. 1 shows this only schematically. The electric Connections are in Pig. 2 shown more clearly.

Of course, a very low frequency alternating current source can be used in place of the direct current source 30 which has a small advantage. In this pail the DC recorder can be read by means of an AC writing potentiometer that works on this frequency.

The power source 30 and the writer 35 can be included in each pail operated at a frequency below that of the electrical current source 29 will. As explained above, for example, the alternating current source 29 has a frequency of 400-1000 Hz, while the current source preferably a direct current source or a source of electrical current is not over 30 Hz.

It is understandable that there is the 7 / echselstrom as a bias voltage is applied to electrodes located at a relatively close distance (preferably the one separating the electrodes 21 and 22 is located For example, insulator 23 in the range of about 30 cm (1 ft.), And preferably In the area of just a few inches, a very small amount of pressure is necessary to generate a bias current to give up with the same size as that of the fed Direct current. In the arrangement shown, a power supply of only a few watts is usually necessary. From it is it can be seen that the distance between the electrode members of each pair is in the range of 1/50 or less of the distance between adjacent electrodes, e.g. the distance L *.

Fig. 3 shows a second embodiment of the invention, the

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is applied to another common submersion arrangement. Here forms the surface of the earth indicated by the reference number 40 is an interface for the current flow between two pairs 41 and 42 of solid, conductive, closely spaced electrodes which are inserted into the surface 40 were driven in. Two other pairs of like electrodes 43 and 44 are used to set the potential between the middle one Third of the distance between the electrodes 41 and 42 to be recorded. Like in Pig. 3 are the secondary windings 45, 46, 47 and 48 of four transformers 49-52 are connected to the electrode pairs 41, 43, 44 and 42, respectively. The primary windings of these transformers are connected in parallel to an alternating current source 54, so that an alternating current bias flows between the electrodes forming the electrode pairs. As stated earlier, it is desirable that this bias current is of the same magnitude or greater than the amplitude of the reading current, which in this Case is abandoned on the central turns 55 and 58 of the secondary windings 45 and 48 of the transformers. this is the Current measured by ammeter 59 which is shown connected in series with DC dynamo 60 · The The strength of the direct current signal can be controlled by a variable resistor 61 can be set or regulated. A potentiometer 62 or another means of accurately determining the potential is between center windings 56 and 57. This is one arrangement for electrical surface inspection called the "Wenner" or "Gish-Rooney" arrangement. The electrodes according to the invention can of course also be used with any other system for surface investigation.

As with the embodiment described first, it is desirable that the frequency of the bias potential coming from the AC power source 54 compared to that of the the dynamo used to deliver the ilesstrom is high, If, as shown in Fig. 3, direct current for the measuring

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circuit is used, the AC power source 54 may have a power frequency of 50-60 Hz, for example. On the other hand, if a low frequency alternating current source is used in place of the direct current dynamo 60, e.g., at a frequency in the range from 10-30 Hz, it is desirable that the frequency of the AC power source 54 be at least 100 Hz, preferably lies in the range of 400 - 1000 Hz.

In practice, the electrode pairs can constructively consist of two rods connected to one another with an insulating strip between they can be assembled in a sandwich manner, so that this compound or "sandwich bar" can be made in one operation can be used instead of driving two piles separately as shown in FIG.

In any case, the arrangement shown in FIG. 3 is an embodiment of an electrical investigation system in which non-polarizing electrodes are used for introducing the electrical current I into the ground. In the previous embodiment, it is preferable, compared to the distance between adjacent electrodes, to provide small distances between the two electrode elements that form the pair of electrodes. The distance between the two electrode elements 41 is preferably not more than 2 ^c / ° of the distance from the electrode 41, e.g. to the electrode 43.Although in both embodiments the measuring circuits are applied to the middle turns of the secondary coils of the transformer generating the bias current, it is of course, it is not essential that a center loop be used as long as the circuit is connected to the pair of electrodes.

There have been a number of changes in the arrangement of the devices which are equivalent to those already illustrated and described became. Of course, these embodiments are also within the scope of the invention, which by the claims is reproduced.

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Claims (10)

Dr. F. Zumstein Sr. - Di, U. Actmenn Cr. R. Koenigsberger Dipl.-Phys. R. Holzbauer - Dipl.-Ing. F. Klingseisen - Dr. F. Zumstein jun. PATENT LAWYERS APPROVED REPRESENTATIVES AT THE EUROPEAN PATENT OFFICE REPRESENTATIVES BEFORE THE EUROPEAN PATENT OFFICE 2332566 Standard Oil Company, Chicago 111. (T.St.A.) Claims: 1. Combined system for geophysical investigations, borehole soundings or the like. with non-polarizing Electrodes, marked by, - A first - adjacently arranged pair of electrodes connected to opposite ends of a first secondary winding a '.Techbelstromtransformer are connected, - second, third and fourth adjacently arranged pairs of electrodes, which are connected in the same way as the connection of the first pair of metal electrodes to the second, third and fourth secondary windings of the alternating current transformer, - a source of depolarization alternating current connected to the primary winding of the alternating current transformer, a direct current source in connection with an intermediate point of the first and fourth secondary windings for generating a read current in the earth between the first pair of electrodes and the fourth pair of electrodes, the first and fourth pairs of electrodes at a distance L from one another. 030007/0928 2332566 lying far away - a direct current measuring device in series with the direct current source for measuring the measuring current, and - A DC voltage measuring device in connection with an intermediate point of the second and third secondary windings for measuring a potential difference in the earth, the by the flow of the measuring current between the second spot trodenpaar and the third pair of electrodes is effected, the second and the third pair of electrodes between the first and fourth pairs of electrodes are so spaced that the DC voltage measurement in conjunction with the DC current measurement provides an indication of the resistivity of the earth between the second and third pairs of electrodes there and the depolarizing alternating current source generates a depolarizing alternating current which is between the adjacent pairs of electrodes flows. 2. Combined system for geophysical investigation, Borehole sounding or the like. with non-polarizing electrodes, marked by, -a first adjacent pair of electrodes that are connected to the opposite ends of a first secondary winding of an alternating current transformer is connected, - Second, third and fourth adjacent pairs of electrodes, which are in the same way as the connection of the first Electrode pairs are connected to the second, third and fourth secondary windings of the AC transformer, - a source of a depolarizing alternating current, the connected to the primary winding of the AC transformer, - one connected between the first and fourth secondary windings Low frequency alternating current source for generation 030007/0928 " ³ " 2332566 of a measuring current in the earth between the first pair of electrodes and the fourth pair of electrodes, the first and fourth pair of electrodes being at a distance L from one another, - one in none with the low frequency AC power source Horizontal low frequency alternating current measuring device for measuring of the measuring current, and a low-frequency AC voltage measuring device connected between the second and third secondary windings for measuring a potential difference in the earth caused by the flow of the Hes current zv / ischen the second pair of electrodes and the third pair of electrodes, the second and third pair of electrodes being between the first and fourth pair of electrodes are spaced apart, and wherein the low frequency AC voltage measurement in conjunction with the Low frequency ac measurement an indication of the specific resistance of the soil between the second and third pair of electrodes, and the depolarizing Alternating current source generates a depolarizing alternating current, which flows between the adjacent pairs of electrodes. 3. System according to claim 1 or 2, characterized in that each of the adjacent electrode pairs are at a distance of not more than 0.1 L from one another. 4- system according to claim 1 or 2, characterized in that the depolarizing alternating current is essentially a large one equal to that of the measuring current. 5. System according to claim 2, characterized in that the frequency of the depolarizing alternating current is not 030007/0928 2332566 is less than ten times the measuring current. ■ 6 · Procedures for geophysical surveys, borehole probing Or the like., With a non-polarizing electrode system is used, characterized by the following steps « - connecting a first pair of adjacently disposed electrodes to opposite ends of an inherited one Secondary winding of an AC transformer, - connecting second, third and fourth pairs of adjacent ones Electrodes in the same way as the connection of the first pair of electrodes with the second, third or fourth Secondary windings of the AC transformer, - applying a source of depolarizing alternating current to the primary winding of the alternating current transformer, - Applying a current source between the first and fourth secondary windings to generate a measuring current in the earth between the first pair of electrodes and the fourth pair of electrodes, the first and fourth pair of electrodes in are at a distance L from each other, - Connecting a current measuring device in series with this current source for measuring the size of the measuring current , - Connecting a voltage measuring device between the second and third secondary winding for measuring a potential difference in the earth caused by the flow of the measuring current between aem second and third pair of electrodes with the second and third pair of electrodes spaced between the first and fourth pair of electrodes lie, - Determination of the specific resistance in the soil between the second and third pairs of electrodes by calculating the ratio of the voltage measurement to the current measurement, where 030007/0928 - 5 - 2532566 *. the specific resistance due to the depolarization of the four pairs of electrodes caused by the depolarization alternating current flowing between the pairs of adjacently arranged electrodes is accurately measured. 7 method according to claim 6, characterized in that a direct current source is used as the measuring current source. 8 method according to claim 6, characterized in that a low-frequency alternating current source is used as the measuring current source. 9 method according to claim 8, characterized in that the depolarizing 7 / echs eist rom source with one frequency works much larger than the frequency of the Hesstromquelle. 10. The method according to any one of claims 6-9, characterized in that each of the pairs of adjacently arranged electrodes are at a distance of no more than 0.1 L from one another. 11 «The method according to any one of claims 6-9, characterized in that the depolarizing alternating current has a magnitude essentially equal to that of the measuring current. 12 method according to claim 8, characterized in that the frequency of the depolarizing current does not fall below ten times that of the measuring current source. 030007/0928