JP2015028458A - Electric specific resistance survey data acquisition method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for acquiring electric specific resistance survey data, in which an actual natural potential is previously measured without feeding current before transmitting a rectangular wave current for an electric specific resistance survey to a survey region, and the level of accuracy of survey data is increased so as to predict error characteristics and reliability by acquiring the electric specific resistance survey data by a system for acquiring an electric resistance in each of a normal direction and a reverse direction between a positive current transmission section and a negative current transmission section using this natural potential, thereby increasing accuracy and reliability in an underground electric specific resistance image to be actually acquired.SOLUTION: The electric specific resistance survey data acquisition method includes: (a) a step of measuring a natural potential of a survey region; (b) a step of adding a rectangular wave transmission current to the survey region and calculating a normal direction resistance value for a positive current transmission section and a reverse direction resistance value for a negative current transmission section; and (c) a step of calculating the average value between the normal direction resistance value and the reverse direction resistance value so as to use for an electric resistance value of electric specific resistance survey data.

Description

  The present invention relates to a method for acquiring electrical resistivity exploration data, and more specifically, an actual natural potential is first measured without current supply before a rectangular wave current transmission for electrical resistivity exploration to the exploration region, By using this to acquire electrical resistivity exploration data by acquiring forward and reverse electrical resistance in the positive current transmission section and negative current transmission section, respectively, the accuracy of the exploration data is improved, and the error characteristics Further, the present invention relates to a method for acquiring electrical resistivity exploration data, which can predict the reliability and can improve accuracy and reliability in an actually acquired underground electrical resistivity image.

  The electrical resistivity exploration method is a non-destructive inspection method that can provide a continuous form of electrical resistivity distribution in the underground, and its utility has been proven in various fields. Sometimes.

Currently, most electrical resistivity surveys use (+) ON-OFF-(-) ON-OFF (or (+) ON-(-) ON) to remove the natural potential value during electrical resistivity survey. The transmission current waveform (square wave: square wave) as shown in FIG. 1 is used. On the other hand, as shown in FIG. 1, the potential values are measured in the (+) ON section and (-) ON section (each in the forward direction). The potential value V ₊ and the reverse potential value V ₋ ), and the measured potential value V _dc and the natural potential value V _sp can be calculated from the following formula <1>.

  In FIG. 1, the upper graph is a waveform of a transmission current for acquiring electrical resistivity survey data, and the lower graph is a graph showing a waveform of a measured potential.

From this, under the assumption that the transmission current is the same in the (+) ON section and the (−) ON section (I = I ₊ (Forward Current) = I ₋ (Backward Current)), 2> can be calculated.

  However, when acquiring the electrical resistivity survey data, if the current transmission waveform and the measured potential waveform are examined, the above assumptions often do not hold, and the electricity acquired in the (+) ON section and (-) ON section Resistance values show different values.

V _sp calculated by the above formula <1> at the time of current transmission in electrical resistivity survey is defined as SP (estimated SP: SPr), and the natural potential value without current transmission is measured SP (measured SP: SPm). In this case, the predicted SP (SPr) must be the same as the measured SP (SPm) in the classic method for acquiring electrical resistivity survey data. However, as shown in FIG. 2, the value of the predicted SP (SPr) acquired in the electrical resistivity exploration process varies depending on the relative distance from the current transmission source, and this is because the predicted SP (SPr) is the transmission current. It is shown that it is not a potential value that is not related to and thus is different from the measured SP (SPm). FIG. 2 is a graph showing a change in the natural potential value calculated by the distance from the current transmission dipole to the potential measurement dipole in the electric resistivity search of the dipole array method, and each curve is the same potential electrode dipole. Shows the change in predicted self-potential calculated for.

  As shown in FIG. 3, the predicted SP (SPr) and the measured SP (SPm) coincide in many cases, and this provides the basis that the existing search data acquisition method is effective. FIG. 3 is a graph showing the relationship between the measured SP (SPm) measured without current transmission and the predicted SP (SPr) obtained by calculation from the electrical resistivity measurement data. However, as shown in FIG. 3, there is a difference that does not become ridiculous in many parts. This is a predicted SP (SPr) value that is different from the actual value in Formula <1>, which is an existing electrical resistivity search protocol. Therefore, there is a problem that the measured resistance value has a difference from the actual underground electrical resistance value.

  The present invention has been devised in order to solve the above-described problems, and its purpose is to provide a current without supplying a rectangular wave current for electric resistivity exploration to the exploration region. By measuring the actual natural potential first, and using this to obtain electrical resistivity exploration data by the method of acquiring the forward and reverse electrical resistance in the positive current transmission section and the negative current transmission section, respectively, To provide an electrical resistivity exploration data acquisition method that can improve the accuracy and reliability of exploration data, predict error characteristics and reliability, and increase the accuracy and reliability in the actual acquired electrical resistivity image. It is in.

  According to the present invention, there is provided an electrical resistivity exploration material acquisition method for conducting electrical resistivity exploration through a current electrode and a potential electrode for an exploration region, comprising: (a) measuring a natural potential value in the exploration region; ) Adding a rectangular wave transmission current to the exploration area to calculate a forward resistance value for a positive current transmission interval and a reverse resistance value for a negative current transmission interval; and (c) reverse to the forward resistance value. There is provided a method for acquiring electrical resistivity search data, comprising the step of calculating an average value of the resistance value and using it for the electrical resistance value of electrical resistivity search data.

  Preferably, the step (a) is characterized in that an actual natural potential is measured for an exploration region in a state where no current is supplied before current transmission of a rectangular wave.

  Preferably, in the step (b), (b-1) a rectangular wave transmission current is added to the search area, a potential value and a transmission current amount for a positive current transmission section are measured, and a potential value for a negative current transmission section. And (b-2) calculating a forward resistance value by the difference between the potential value for the positive current transmission section and the natural potential value, and calculating the potential value and the natural value for the negative current transmission section. The method includes a step of calculating a reverse resistance value based on a difference from the potential value.

  Preferably, in the step (b-2), the forward resistance value and the reverse resistance value are calculated by the following formula <3>.

Here, R _f is a forward resistance value, V ₊ is a potential value for a positive current transmission section, V ^SPm is a natural potential value, I ₊ is a transmission current amount for a positive current transmission section, and R _b is a reverse resistance value. , V ₋ is a potential value for a negative current transmission section, and I ₋ is a transmission current amount for a negative current transmission section.

  Preferably, after the step (c), (d) a material error value is calculated by dividing a difference between the forward resistance value and the reverse resistance value by an average resistance value, and the material error value is set as a material weight value. The method further includes a step of performing a reverse calculation for acquiring the underground video.

  Preferably, in the step (d), the material weighting value according to the material error value is given to the target search material for back calculation so as to be inversely proportional to the size of the material error value.

  According to the present invention, the actual natural potential is first measured without current supply before the current transmission of the rectangular wave for the electrical resistivity exploration with respect to the exploration region, and the positive current transmission interval and By acquiring electrical resistivity exploration materials by acquiring forward and reverse electrical resistance in the negative current transmission section respectively, it is possible to improve the accuracy of the exploration materials and predict error characteristics and reliability. In addition, there is an effect that the accuracy and reliability of the actually acquired underground electrical resistivity image can be improved.

  In particular, in acquiring electrical resistivity survey data, the effect of the change in the measured resistance value due to unknown causes other than the spontaneous potential reaction and the change in the magnitude of the transmission current in two sections according to the positive current and negative current transmission in the current transmission waveform There is also an effect that can be taken into account.

It is a graph which shows the transmission current (upper) and measurement electric potential (lower) waveform for acquisition of electrical resistivity survey data according to the conventional technology. It is a graph which shows the change of the natural potential value calculated by the distance of an electric potential measurement dipole from the electric current transmission dipole in the electrical resistivity search (dipole arrangement) according to the prior art. It is a graph for demonstrating the relationship between prediction SP (SPr) and measurement SP (SPm). 1 is a schematic diagram of a system to which an electrical resistivity survey data acquisition method according to the present invention can be applied. It is a graph for demonstrating the relationship between a forward direction electrical resistance and a reverse direction electrical resistance. It is a graph which shows the difference of the data error and two electric resistance values by the electrical specific resistance back calculation. It is a figure for demonstrating the effect of the data weight value application by the electrical resistivity reverse calculation using the difference of a forward direction and a reverse direction electrical resistance. 5 is a flowchart for explaining a method for acquiring electrical resistivity search data according to the present invention.

  Hereinafter, a method for acquiring electrical resistivity search data according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 4 is a schematic diagram of a system to which the electrical resistivity search data acquisition method according to the present invention can be applied.

  Referring to FIG. 4, the electrical resistivity survey system has two or more current electrodes (C1, C2) and potential electrodes (P1, P2), and the transmission current management unit 10, the potential measurement unit 20, The search material calculation unit 30, the search control unit 40, and the reverse calculation processing unit 50 can be included.

  The electrical resistivity survey is to identify the electrical resistivity distribution in the underground and clarify the underground structure, and usually uses the potential difference between specific points caused by the current flowing from the current electrode. Thus, the electrical properties of the underground will be estimated.

  For this reason, the transmission current management unit 10 connected to the power supply supplies power to the current electrodes (C1, C2) to transmit current to the search region, and is connected to the potential electrodes (P1, P2). The exploration potential measuring unit 20 including the electrometer that has been measured measures the potential difference and reads the value divided by the current that caused the potential difference to flow, that is, the resistance value.

  In such electrical resistivity exploration, after flowing a certain current underground, the potential difference is measured to determine the apparent resistivity, and this is interpreted to interpret the subsurface geological structure, fracture zone, crack zone, groundwater, etc. The electrode arrangement method used for the electrical resistivity survey is as follows: monopole (Pole-Pole), monopole-dipole (Pole-Dipole), dipole (Dipole-Dipole), shram Schlumberger, Wenner, modified Pole-Pole, and modified Dipole-Dipole arrays are possible.

Currently, most electrical resistivity surveys use (+) ON-OFF-(-) ON-OFF (or (+) ON-(-) ON) to remove the natural potential value during electrical resistivity survey. The transmission current waveform (rectangular wave: square wave) is used, but when exploring the electrical resistivity, if the current transmission waveform and the measured potential waveform are examined, the transmission current is (+) ON section and (-) ON section In many cases, the assumption that they are the same (I = I ₊ = I ₋ ) does not hold, and the electrical resistance values acquired in the (+) ON section and the (−) ON section show different values. Become.

  The present invention is to improve this, and the self-potential (SP) material is acquired immediately before acquiring the electrical resistivity survey data, and based on this, the forward resistance (+) for the ON current transmission section ( The forward resistance and the backward resistance for the (−) ON current transmission interval are acquired.

  That is, the electrical resistivity search method according to the present invention can be described as shown in FIG.

First, in step S10, the natural potential (SP) of the exploration area is measured to acquire the natural potential value. At this time, it is preferable that the corresponding search area has no current transmission for electrical resistivity search. Here, the acquired natural potential is referred to as a measured SPm (measured SP), and V ^SPm indicates a natural potential value measured in a state without current transmission immediately before transmitting the current waveform of FIG.

  Next, in step S20, a rectangular wave transmission current (see FIG. 1) is transmitted through the current electrode to the search region that has acquired the natural potential value.

  Next, in step S30, the forward resistance for the positive current transmission interval of the rectangular wave transmission current and the backward resistance for the negative current transmission interval are calculated.

More specifically, in step S30, a rectangular wave transmission current is added to the search region, a potential value (V ₊ ) and a transmission current amount (I ₊ ) for a positive current transmission interval are measured, and a potential for a negative current transmission interval is measured. The forward resistance value is calculated from the step of measuring the value (V ₋ ) and the transmission current amount (I ₋ ), the difference between the potential value for the positive current transmission interval and the natural potential value, and for the negative current transmission interval. A step of calculating a reverse resistance value according to a difference between the potential value and the natural potential value is included.

Therefore, in FIG. 1, the measured electrical resistances for positive current and negative current transmission are defined as forward resistance and reverse resistance, and the forward resistance value (R _f ) and reverse resistance value (R _b ) are as follows: The numerical formula <3> is used.

Here, V ^SPm represents a natural potential value measured in the absence of current transmission immediately before transmitting the current waveform of FIG. 1, and V ₊ and V ₋ are positive current (I ₊ ) and negative current (I, respectively). _- ) Represents the potential value measured in the transmission interval. Such a difference between the two electric resistance values represents the distortion of the search data due to causes other than the natural potential (SP) in the electrical resistivity search.

  Next, in step S40, an average value of the forward resistance value and the reverse resistance value is calculated and used as the electrical resistance value of the electrical resistivity search data. In the actual electrical resistivity survey, the measured value is the average of the above forward resistance value and reverse resistance value, and is multiplied by the geometric factor according to the electrode arrangement used, and the apparent electrical resistivity value is used. (Apparent thermally) will be used as exploration data.

  Also, in step S50, the material error value is calculated by dividing the difference between the forward resistance value and the reverse resistance value by the average resistance value described above, and the material error value is used as the material weight value to acquire the underground image. Perform reverse calculations.

More specifically, the average value of these two measured values is used as the electrical resistivity survey data, and the difference between the two resistance values is divided by the above-mentioned average resistance value to calculate the data error value. As a result, it is possible to acquire a more precise underground structure image by performing a reverse calculation using values (data weighting). Here, it can be confirmed that the average value of the forward resistance and the reverse resistance is almost similar to the existing resistance value (R ^O = (V ⁺ −V ⁻ ) / (I ⁺ + I ⁻ )). It was.

  That is, the present invention relates to a method of exploring electrical resistivity universally used for underground exploration. Specifically, a self-potential is measured immediately before transmitting current when acquiring electrical resistivity exploration data, A positive current ((+) with respect to a current transmission waveform in a normal electrical resistivity search consisting of (+) ON-OFF-(-) ON-OFF (or (+) ON-(-) ON) ON) is measured and the forward current (Forward Resistance) is calculated by measuring the potential and the transmission current amount, and the reverse resistance ((−) ON) is measured by measuring the potential and the transmission current amount. Calculate Backward Resistance and use it for exploration data.

  At this time, the exploration data uses the average of the two resistance values, and is added here to quantify the error in the electrical resistivity exploration data from the difference between the forward and reverse resistances. It can be used for backward calculation of exploration materials, and more accurate underground images can be acquired.

  An example of exploration data measured by such a method is shown in FIG. 5, and in FIG. 3, a large number of data 2 is similar to the prediction SP (SPr) and measurement SP (SPm) representing similar values. Although the two resistance values appear to be similar, it can be confirmed that there is a large difference between the two values in a considerable portion.

  The distortion that causes the difference between the two resistance values includes causes that cannot be taken into account when acquiring electrical resistivity survey data, and includes mechanical problems that occur during acquisition of search data or noise with time-varying characteristics. . Therefore, the distortion or reliability of the electrical resistivity search data can be evaluated using the difference between the two electrical resistance values.

  Here, in order for the exploration method according to the present invention to be practical, in the case of a material with a large distortion of the material regardless of the cause of the difference between the two electrical resistance values, FIG. 6 shows data errors (data misfits) and differences between two electrical resistance values (Discrepancies) in the reverse calculation of electrical resistivity. When the difference between the two resistance values is small, the correlation between the document error and the difference between the two resistance values cannot be seen well, but the document error tends to increase as the difference between the two electrical resistance values increases. Since it is shown, it can be interpreted that the difference between the two electric resistance values reflects the error included in the material.

  As a result, a low weighting value is given to a material with a large difference between the forward resistance and the reverse resistance, which causes a material error to increase in the reverse calculation process of the electrical resistivity, and a high weighting value is given when these differences are small. The accuracy of the back calculation result can be improved.

  That is, an objective function that minimizes the data error is used as in the following formula <4>.

Here, m is a model vector, E is a material error vector, and W is a material weight matrix that is a diagonal matrix (that is, W = diag (w _i )) (p is 1 or 2).

  Using such a material error, a material weight matrix such as W in the above formula <4> is created, and the back calculation reflecting the error characteristics of the search material can be performed using this material weight matrix. The above formula <4> is an objective function for minimizing the material error, and it tries to minimize it in the reverse calculation process. However, the exploration material is given a weight value, and more important and highly reliable material ( A high weighting value is given to a material which has a small difference between the forward resistance and the reverse resistance, and a low weighting value is given in the opposite case.

  A back-calculation experiment was performed on the exploration data obtained by such a method, and FIG. 7 shows the result. FIG. 7 is a diagram for explaining the effect of applying the material weight value using the difference between the forward and reverse electrical resistances in the reverse calculation of the electrical resistivity.

  In FIG. 7, (a) shows a case in which no material editing is performed on the exploration material, and (b) shows a result of performing the reverse calculation except for the exploration material with a large error. The left side shows a case where no weight value is given to the material, and the right side shows a reverse calculation result obtained by applying the weight value to the material. It can be seen that the RMS error in the final back calculation result is calculated to be much smaller through the application of the material weight value even when the material having a large material error is not excluded, thereby providing a more reliable underground structure image.

  The electrical resistivity search data acquisition method according to the present invention is an electrical resistivity search data obtained by removing a natural potential using a transmission current waveform (rectangular wave) that alternately transmits positive current and negative current in electrical resistivity search. Measures the actual natural potential without current supply before current transmission, and uses this to acquire forward and reverse electrical resistance in the positive current transmission section and negative current transmission section, respectively. Follow the method. In this way, by measuring both forward and reverse electrical resistance, it is possible to predict the error characteristics and reliability of the exploration data, and this is the basis for applying the material weight value to the reverse calculation process of the exploration data. It is possible to improve the accuracy and reliability of the underground electrical resistivity image that is actually acquired by using the above. Also, when acquiring exploration data, it is possible to directly measure the actual natural potential value and to measure the natural potential more accurately than the natural potential exploration data obtained by calculation from the potential value measured during current transmission using the conventional method. It is.

  As described above, the optimal embodiment has been disclosed in the drawings and specification. Although specific terms are used herein, they are merely used for the purpose of describing the present invention and limit the scope of the present invention as defined in the meaning or claims. It was not used for that purpose. Accordingly, those skilled in the art can understand that various modifications and other equivalent embodiments are possible from this. Therefore, the true technical protection scope of the present invention should be determined by the technical idea of the appended claims.

DESCRIPTION OF SYMBOLS 10 Transmission current management part 20 Potential measurement part 30 Exploration material calculation part 40 Exploration control part 50 Back calculation process part

Claims (6)

An electrical resistivity exploration data acquisition method for conducting electrical resistivity exploration through a current electrode and a potential electrode in an exploration area,
(A) measuring the natural potential value of the exploration area;
(B) adding a rectangular wave transmission current to the exploration region to calculate a forward resistance value for a positive current transmission interval and a reverse resistance value for a negative current transmission interval;
(C) calculating an average value of the forward resistance value and the reverse resistance value and using the average value for the electrical resistance value of the electrical resistivity survey data;
A method for acquiring electrical resistivity survey data, comprising:   2. The electrical resistivity search data according to claim 1, wherein the step (a) measures an actual natural potential with respect to a search area in the absence of current supply before current transmission of a rectangular wave. Acquisition method. The step (b)
(B-1) adding a rectangular wave transmission current to the exploration region, measuring a potential value and a transmission current amount for a positive current transmission section, and measuring a potential value and a transmission current amount for a negative current transmission section;
(B-2) The forward resistance value is calculated from the difference between the potential value for the positive current transmission section and the natural potential value, and the reverse resistance value is calculated from the difference between the potential value and the natural potential value for the negative current transmission section. A step of calculating
The method for acquiring electrical resistivity search data according to claim 1, wherein: In the step (b-2),
The method for obtaining electrical resistivity search data according to claim 3, wherein the forward resistance value and the reverse resistance value are calculated by the following formula <3>.

Here, R _f is a forward resistance value, V ₊ is a potential value for a positive current transmission section, V ^SPm is a natural potential value, I ₊ is a transmission current amount for a positive current transmission section, and R _b is a reverse resistance value. , V ₋ is a potential value for a negative current transmission section, and I ₋ is a transmission current amount for a negative current transmission section. After step (c),
(D) calculating a material error value by dividing a difference between the forward resistance value and the backward resistance value by an average resistance value, and performing a backward calculation for acquiring an underground image using the material error value as a material weight value; The electrical resistivity survey data acquisition method according to claim 1, further comprising:   6. The electrical resistivity according to claim 5, wherein, in the step (d), the material weight value according to the material error value is given to the target search material for back calculation so as to be inversely proportional to the size of the material error value. Exploration material acquisition method.