A method and system for obtaining horizontal electric field apparent resistivity variation trend in different directions of horizontal layered earth

Abstract

The application discloses a method and system for obtaining horizontal electric field apparent resistivity variation trend in different directions of horizontal layered earth, comprising: establishing two-layer G-type cross-section model, two-layer D-type cross-section model, three-layer H-type cross-section model and three-layer K-type cross-section model; obtaining G-type cross-section model, D-type cross-section model, H-type cross-section model and K-type cross-section model full-period apparent resistivity curves defined by different direction horizontal electric field according to two-layer G-type, two-layer D-type, three-layer H-type and three-layer K-type cross-section model; analyzing G-type cross-section model, D-type cross-section model, H-type cross-section model and K-type cross-section model full-period apparent resistivity curves to obtain relevant analysis results; establishing horizontal layered earth model of a region to be explored according to the analysis results, and obtaining horizontal electric field apparent resistivity variation trend in different directions of the region to be explored based on the horizontal layered earth model. The application achieves the purpose of suppressing electromagnetic interference and avoiding obstacles.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geological exploration, in particular to a method and system for obtaining horizontal electric field apparent resistivity variation trend in different directions of horizontal layered earth. BACKGROUND

[0002] In the geothermal energy exploration of horizontal layered earth, the electromagnetic frequency sounding exploration methods include controllable source audio frequency magnetotelluric sounding method and wide area electromagnetic method. The controllable source audio frequency magnetotelluric sounding method collects Ex parallel to the field source AB and Hy perpendicular to Ex, calculates apparent resistivity and inverts stratum resistivity through Ex / Hy, so as to perform geological, hydrogeological and geothermal energy geological interpretation. However, in the actual sounding exploration process, electromagnetic and obstacle interference exist, so that the collected data deviates greatly from the real data.

[0003] The electromagnetic interference includes random electromagnetic interference and active electromagnetic interference. The active electromagnetic interference seriously affects the electromagnetic frequency sounding data quality, such as high-voltage line, telephone line and communication optical fiber. The random electromagnetic interference can be inhibited through multiple data collection and stacking (averaging), but the electromagnetic interference caused by high-voltage line and other linear sources cannot be effectively inhibited through instrument notch, increased transmission current and multiple data collection and averaging, and even fails. The frequency of telephone line is generally 300-3400 Hz, and the frequency of optical fiber is higher. The interference affects the high-frequency electromagnetic frequency sounding data, and affects the interpretation of shallow geology and stratum. The induced electric field caused by current in high-voltage line and the electrostatic field caused by high voltage seriously interfere with the electromagnetic frequency sounding data of electric field with frequency not less than 50 Hz, and affect the geological interpretation of the shallow layer.

[0004] Another problem disturbing the electromagnetic frequency sounding is that it is difficult to measure the horizontal electric field Ex parallel to the field source AB when there are water ponds, buildings, factories, mines and enterprises and other human facilities on the ground (collectively referred to as obstacles) and in complex topographic conditions, or it is impossible to achieve, so that the electric field data cannot be obtained or the electric field data has a large error. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the present application provides a method and system for obtaining horizontal electric field apparent resistivity variation trend in different directions of horizontal layered earth, which is used to solve the technical problem of electromagnetic and obstacle interference in the geological exploration of horizontal layered earth, so as to achieve the purpose of inhibiting electromagnetic interference and avoiding obstacles.

[0006] To solve the above problems, the technical scheme adopted by the present application is as follows:

[0007] A method for obtaining horizontal electric field apparent resistivity variation trend in different directions of horizontal layered earth, characterized in that it comprises the following steps:

[0008] establishing a two-layer G-type cross-section model, a two-layer D-type cross-section model, a three-layer H-type cross-section model and a three-layer K-type cross-section model;

[0009] obtaining G-type cross-section model full-period apparent resistivity curves, D-type cross-section model full-period apparent resistivity curves, H-type cross-section model full-period apparent resistivity curves and K-type cross-section model full-period apparent resistivity curves defined by horizontal electric fields in different directions according to the two-layer G-type cross-section model, the two-layer D-type cross-section model, the three-layer H-type cross-section model and the three-layer K-type cross-section model;

[0010] analyzing the G-type cross-section model full-period apparent resistivity curves, the D-type cross-section model full-period apparent resistivity curves, the H-type cross-section model full-period apparent resistivity curves and the K-type cross-section model full-period apparent resistivity curves to obtain relevant analysis results;

[0011] establishing a horizontal layered earth model of a to-be-explored area according to the analysis results, and obtaining variation trends of horizontal electric field apparent resistivity of the to-be-explored area in different directions based on the horizontal layered earth model.

[0012] As a preferred embodiment of the present application, when establishing the two-layer G-type cross-section model and the two-layer D-type cross-section model, the following steps are included:

[0013] obtaining positions of transmitting field sources A point and B point and a position of a receiving point MN;

[0014] obtaining a shallow resistivity, a shallow thickness and a basement resistivity;

[0015] establishing the two-layer G-type cross-section model and the two-layer D-type cross-section model according to the positions of the transmitting field sources A point and B point, the position of the receiving point MN, the shallow resistivity, the shallow thickness and the basement resistivity.

[0016] As a preferred embodiment of the present application, when establishing the three-layer H-type cross-section model and the three-layer K-type cross-section model, the following steps are included:

[0017] obtaining positions of transmitting field sources A point and B point and a position of a receiving point MN;

[0018] obtaining shallow-to-deep three-layer resistivities, a cover layer thickness and an intermediate layer thickness;

[0019] establishing the three-layer H-type cross-section model and the three-layer K-type cross-section model according to the positions of the transmitting field sources A point and B point, the position of the receiving point MN, the shallow-to-deep three-layer resistivities, the cover layer thickness and the intermediate layer thickness.

[0020] As a preferred embodiment of the present application, when obtaining the full-period apparent resistivity curves of each cross-section model, the method comprises:

[0021] According to each cross-section model, the full-period apparent resistivity in the horizontal electric field X direction is forward modeled to obtain the full-period apparent resistivity curve in the horizontal electric field X direction of each cross-section model.

[0022] As a preferred embodiment of the present application, when obtaining the full-period apparent resistivity curves of each cross-section model, the method further comprises:

[0023] According to each cross-section model, the full-period apparent resistivity in the horizontal electric field Y direction is forward modeled to obtain the full-period apparent resistivity curve in the horizontal electric field Y direction of each cross-section model.

[0024] As a preferred embodiment of the present application, when obtaining the full-period apparent resistivity curves of each cross-section model, the method further comprises:

[0025] According to each cross-section model, the full-period apparent resistivity in the direction of 30 degrees to the horizontal electric field X axis is forward modeled to obtain the full-period apparent resistivity curve in the direction of 30 degrees to the horizontal electric field X axis of each cross-section model.

[0026] As a preferred embodiment of the present application, when obtaining the full-period apparent resistivity curves of each cross-section model, the method further comprises:

[0027] According to each cross-section model, the full-period apparent resistivity in the direction of 60 degrees to the horizontal electric field X axis is forward modeled to obtain the full-period apparent resistivity curve in the direction of 60 degrees to the horizontal electric field X axis of each cross-section model.

[0028] As a preferred embodiment of the present application, when analyzing the full-period apparent resistivity curves defined by the horizontal electric field in different directions of each cross-section model, the method comprises:

[0029] the frequency point when the full-period apparent resistivity curves defined by the horizontal electric field in different directions of each cross-section model appear bifurcation, the change trend, the apparent resistivity when tending to be fixed and the corresponding frequency point thereof are obtained;

[0030] whether each cross-section model can reflect the change characteristics of the formation resistivity is determined according to the frequency point when the bifurcation appears, the change trend, the apparent resistivity when tending to be fixed and the corresponding frequency point thereof;

[0031] If yes, the cross-section model is considered to be an effective cross-section model.

[0032] As a preferred embodiment of the present application, when the horizontal layered earth model is established according to the related analysis results, the method comprises:

[0033] electrical layers are divided based on each effective cross-section model and according to the measured resistivity logging curve;

[0034] According to the electrical layering result, a horizontal layered earth model is established, and the full-period apparent resistivity in the X direction of the horizontal electric field, the Y direction of the horizontal electric field, the direction of 30 degrees to the X axis of the horizontal electric field, and the direction of 60 degrees to the X axis of the horizontal electric field is forward calculated according to the horizontal layered earth model to obtain a full-period apparent resistivity curve of the horizontal layered earth model;

[0035] According to the full-period apparent resistivity curve of the horizontal layered earth model, the variation trend of the horizontal electric field apparent resistivity in different directions of the to-be-explored area is obtained.

[0036] A system for obtaining the variation trend of the horizontal electric field apparent resistivity in different directions of a horizontal layered earth includes:

[0037] A model establishing unit is configured to establish a two-layer G-type cross-section model, a two-layer D-type cross-section model, a three-layer H-type cross-section model, and a three-layer K-type cross-section model.

[0038] A curve establishing unit is configured to obtain a full-period apparent resistivity curve of a G-type cross-section model defined by the horizontal electric field in different directions, a full-period apparent resistivity curve of a D-type cross-section model, a full-period apparent resistivity curve of an H-type cross-section model, and a full-period apparent resistivity curve of a K-type cross-section model according to the two-layer G-type cross-section model, the two-layer D-type cross-section model, the three-layer H-type cross-section model, and the three-layer K-type cross-section model.

[0039] A variation trend obtaining unit is configured to analyze the full-period apparent resistivity curve of the G-type cross-section model, the full-period apparent resistivity curve of the D-type cross-section model, the full-period apparent resistivity curve of the H-type cross-section model, and the full-period apparent resistivity curve of the K-type cross-section model to obtain relevant analysis results, establish a horizontal layered earth model of a to-be-explored area according to the analysis results, and obtain the variation trend of the horizontal electric field apparent resistivity in different directions of the to-be-explored area based on the horizontal layered earth model.

[0040] Compared with the prior art, the present application has the following advantages:

[0041] The present application establishes a horizontal layered earth model to obtain a full-period apparent resistivity curve of a horizontal layered earth model defined by the horizontal electric field in different directions, further uses the full-period apparent resistivity curve of the horizontal layered earth model to obtain the variation trend of the horizontal electric field apparent resistivity in different directions of a to-be-explored area in the horizontal layered earth, and determines whether the variation of the horizontal electric field apparent resistivity in different directions reflects the electrical characteristics of the stratum of the to-be-explored area, so that electromagnetic interference is suppressed and obstacles are avoided through the measurement of the horizontal electric field in different directions.

[0042] The present application will be further described in detail below in combination with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a G-type cross-section model full-period apparent resistivity curve diagram defined by different direction horizontal electric field of the embodiment of the present application;

[0044] Figure 2 is a D-type cross-section model full-period apparent resistivity curve diagram defined by different direction horizontal electric field of the embodiment of the present application;

[0045] Figure 3 is a H-type cross-section model full-period apparent resistivity curve diagram defined by different direction horizontal electric field of the embodiment of the present application;

[0046] Figure 4 is a K-type cross-section model full-period apparent resistivity curve diagram defined by different direction horizontal electric field of the embodiment of the present application;

[0047] Figure 5 is a horizontal layered earth model full-period apparent resistivity curve diagram defined by different direction horizontal electric field of the embodiment of the present application;

[0048] Figure 6 is a schematic diagram of electric field suppression electromagnetic interference of the embodiment of the present application in varying measurement direction;

[0049] Figure 7 is an engineering layout diagram of wide-area electromagnetic detection of geothermal energy for developing hot spring tourism in a certain place in Shaanxi of the embodiment of the present application;

[0050] Figure 8 is an M, N electrode layout diagram of avoiding small-area water body on the ground of the embodiment of the present application;

[0051] Figure 9 is a comparison diagram of processing effect of different direction horizontal electric field measurement and adding new M, N electrode defined measurement point data of the embodiment of the present application;

[0052] Figure 10 is a method step diagram of obtaining horizontal electric field apparent resistivity variation trend in different directions of horizontal layered earth of the embodiment of the present application. DETAILED DESCRIPTION

[0053] The method for obtaining horizontal electric field apparent resistivity variation trend in different directions of horizontal layered earth provided by the present application, as shown in the figure, comprises the following steps: Figure 10

[0054] Step S1: establishing two-layer G-type cross-section model, two-layer D-type cross-section model, three-layer H-type cross-section model and three-layer K-type cross-section model;

[0055] ​Step S2: obtaining the G-type section model full-period apparent resistivity curve, the D-type section model full-period apparent resistivity curve, the H-type section model full-period apparent resistivity curve and the K-type section model full-period apparent resistivity curve defined by the horizontal electric field in different directions according to the two-layer G-type section model, the two-layer D-type section model, the three-layer H-type section model and the three-layer K-type section model;

[0056] Step S3: analyzing the G-type section model full-period apparent resistivity curve, the D-type section model full-period apparent resistivity curve, the H-type section model full-period apparent resistivity curve and the K-type section model full-period apparent resistivity curve to obtain relevant analysis results;

[0057] Step S4: establishing a horizontal layered earth model of the area to be explored according to the analysis results, and obtaining the variation trend of the horizontal electric field apparent resistivity in different directions of the area to be explored based on the horizontal layered earth model.

[0058] In the above step S1, when establishing the two-layer G-type section model and the two-layer D-type section model, it includes:

[0059] The positions of the transmitting field sources A point and B point and the position of the receiving point MN are obtained;

[0060] The shallow resistivity, the shallow thickness and the basement resistivity are obtained;

[0061] The two-layer G-type section model and the two-layer D-type section model are established according to the positions of the transmitting field sources A point and B point, the position of the receiving point MN, the shallow resistivity, the shallow thickness and the basement resistivity.

[0062] In the above step S1, when establishing the three-layer H-type section model and the three-layer K-type section model, it includes:

[0063] The positions of the transmitting field sources A point and B point and the position of the receiving point MN are obtained;

[0064] The shallow-to-deep three-layer resistivity, the cap layer thickness and the intermediate layer thickness are obtained;

[0065] The three-layer H-type section model and the three-layer K-type section model are established according to the positions of the transmitting field sources A point and B point, the position of the receiving point MN, the shallow-to-deep three-layer resistivity, the cap layer thickness and the intermediate layer thickness.

[0066] In the above step S2, when obtaining the full-period apparent resistivity curves of each section model, it includes:

[0067] The full-period apparent resistivity of the horizontal electric field X direction is forward calculated according to each section model to obtain the full-period apparent resistivity curve of the horizontal electric field X direction of each section model.

[0068] In the step S2, when obtaining the full period apparent resistivity curves of each cross section model, further comprising:

[0069] According to each cross section model, the full period apparent resistivity in the Y direction of the horizontal electric field is forward calculated to obtain the full period apparent resistivity curve in the Y direction of the horizontal electric field of each cross section model.

[0070] In the step S2, when obtaining the full period apparent resistivity curves of each cross section model, further comprising:

[0071] According to each cross section model, the full period apparent resistivity in the 30 degree direction of the X axis of the horizontal electric field is forward calculated to obtain the full period apparent resistivity curve in the 30 degree direction of the X axis of the horizontal electric field of each cross section model.

[0072] In the step S2, when obtaining the full period apparent resistivity curves of each cross section model, further comprising:

[0073] According to each cross section model, the full period apparent resistivity in the 60 degree direction of the X axis of the horizontal electric field is forward calculated to obtain the full period apparent resistivity curve in the 60 degree direction of the X axis of the horizontal electric field of each cross section model.

[0074] In the step S3, when analyzing the full period apparent resistivity curves defined by the different directions of the horizontal electric field of each cross section model, comprising:

[0075] Obtaining the frequency points when the full period apparent resistivity curves defined by the different directions of the horizontal electric field of each cross section model appear bifurcation, the change trend, the apparent resistivity when tending to be fixed and the corresponding frequency points;

[0076] According to the frequency points when appearing bifurcation, the change trend, the apparent resistivity when tending to be fixed and the corresponding frequency points, judging whether each cross section model can reflect the change characteristics of the formation resistivity;

[0077] If yes, considering that each cross section model is an effective cross section model.

[0078] In the step S4, when establishing the horizontal layered earth model according to the related analysis results, comprising:

[0079] Based on each effective cross section model, and according to the measured resistivity logging curve, the electrical layering is performed;

[0080] According to the electrical layering results, the horizontal layered earth model is established, and the full period apparent resistivity curves of the horizontal layered earth model are obtained by forward calculating the full period apparent resistivity in the X direction of the horizontal electric field, the Y direction of the horizontal electric field, the 30 degree direction of the X axis of the horizontal electric field and the 60 degree direction of the X axis of the horizontal electric field;

[0081] According to the horizontal layered earth model full period apparent resistivity curve, the horizontal electric field apparent resistivity variation trend in different directions of the area to be explored is obtained.

[0082] The system for obtaining the horizontal electric field apparent resistivity variation trend in different directions of the horizontal layered earth provided by the application comprises a model establishing unit, a curve establishing unit and a variation trend obtaining unit.

[0083] The model establishing unit is used for establishing a two-layer G-type cross-section model, a two-layer D-type cross-section model, a three-layer H-type cross-section model and a three-layer K-type cross-section model.

[0084] The curve establishing unit obtains a G-type cross-section model full period apparent resistivity curve, a D-type cross-section model full period apparent resistivity curve, a H-type cross-section model full period apparent resistivity curve and a K-type cross-section model full period apparent resistivity curve defined by the horizontal electric field in different directions according to the two-layer G-type cross-section model, the two-layer D-type cross-section model, the three-layer H-type cross-section model and the three-layer K-type cross-section model.

[0085] The variation trend obtaining unit is used for analyzing the G-type cross-section model full period apparent resistivity curve, the D-type cross-section model full period apparent resistivity curve, the H-type cross-section model full period apparent resistivity curve and the K-type cross-section model full period apparent resistivity curve, obtaining relevant analysis results, establishing a horizontal layered earth model of the area to be explored according to the analysis results and obtaining the horizontal electric field apparent resistivity variation trend in different directions of the area to be explored based on the horizontal layered earth model.

[0086] The following examples are further illustrations of the application, but the scope of the application is not limited thereto. Example 1 (establishment of a G-type cross-section model full period apparent resistivity curve)

[0087] The parameters of the G-type cross-section model are as follows: the coordinates of A point of the transmitting field source are (-500, 0), the coordinates of B point are (500, 0), the receiving point MN is located at (2480, 4300), the shallow layer resistivity is 50 ohm·m, the shallow layer thickness is 200 m and the base resistivity is 500 ohm·m. Figure 1 is a G-type cross-section model full period apparent resistivity curve defined by the horizontal electric field in different directions provided by the application, Figure 1 which contains the apparent resistivity curves in the horizontal electric field X direction (AB-Ex), the Y direction (AB-Ey), the direction of 30 degrees to the X axis and the direction of 60 degrees to the X axis. Figure 1It can be seen that when the frequency is higher than 100 Hz, the four curves are basically coincident; when the frequency is between 10-100 Hz, the four curves are divergent, but the change trend is consistent; when the frequency is less than 10 Hz, the apparent resistivity of the horizontal electric field in Y direction and the direction of 60 degrees with the X axis begins to tend to a fixed value, and the apparent resistivity of the horizontal electric field in X direction and the direction of 30 degrees with the X axis still slowly increases; when the frequency is less than 1 Hz, the apparent resistivity of the electric field in the four directions all tends to a fixed value, which are 511, 357, 279 and 337 ohm·m respectively. It can be seen that the apparent resistivity curves defined by the electric field in the four directions all reflect the change characteristics of the formation resistivity, and can detect the high-resistance basement layer under 200 meters.

[0088] The detection depth is according to the skin depth It is estimated that when the exploration depth is less than 300 m, the root mean square relative error of the apparent resistivity defined by the electric field in the four directions is less than 5%, and when the exploration depth is less than 1000 meters (the frequency is greater than 24 Hz), the root mean square error of the apparent resistivity at all frequencies is 9.60%, which is shown in Table 1:

[0089] Table 1 Comparison table of apparent resistivity of G-type section

[0090]

[0091]

[0092]

[0093] Example 2 (establishment of apparent resistivity curve of D-type section model)

[0094] The parameters of the D-type section model are that the coordinates of the transmitting field source A point are (-500, 0), the coordinates of the B point are (500, 0), the receiving point MN is located at (2480, 4300), the shallow layer resistivity is 500 ohm·m, the shallow layer thickness is 200 meters, and the basement resistivity is 50 ohm·m. Figure 2 is the apparent resistivity curve diagram of the D-type section model defined by the horizontal electric field in different directions of the present application, which is obtained by Figure 2 It can be seen that the four curves are basically coincident, and the final apparent resistivity tends to a fixed value of 50 ohm·m, and the total root mean square relative difference of the apparent resistivity in the four directions at all frequencies is 2.72%. It is proved that the low-resistance basement can be detected in the four directions, and has the same frequency sounding function.

[0095] Example 3 (establishment of apparent resistivity curve of H-type section model)

[0096] H-type cross-section model parameters: transmitting field source A point coordinates (-500, 0), B point coordinates (500, 0), receiving point MN is located at (2480, 4300), three layers from shallow to deep resistivity is 100, 10, 200 ohm-m respectively, cover layer thickness is 200 meters, middle layer thickness is 50 meters. Figure 3 is the H-type cross-section model full-time apparent resistivity curve chart defined by different direction horizontal electric field of the present application, which is obtained by Figure 3 It can be seen that when the frequency is higher than 50Hz, the four curves are basically coincided, the apparent resistivity curve form is consistent with D-type cross-section; when the frequency is 7-50Hz, the four curves appear differentiation phenomenon, which is that the full-time apparent resistivity of horizontal electric field with 60 degree direction to X axis has a false minimum value, then the change trend is consistent, the full-time apparent resistivity of the four curves increases with the decrease of frequency; when the frequency is less than 7Hz, the full-time apparent resistivity of AB-Ey, AB-Ex60 begins to tend to a fixed value, the full-time apparent resistivity of AB-Ex, AB-Ex30 still increases slowly; finally, the apparent resistivity of four direction horizontal electric field all tends to a fixed value, which is 208.3, 161.6, 138.0, 155.7 ohm-m respectively. The four directions all reflect the change characteristics of H-type cross-section stratum resistivity, that is, the four direction horizontal electric field can all detect the high resistance basement under 250 meters.

[0097] Example 4 (establishment of K-type cross-section model full-time apparent resistivity curve)

[0098] K-type cross-section model parameters: transmitting field source A point coordinates (-500, 0), B point coordinates (500, 0), receiving point MN is located at (2480, 4300), three layers from shallow to deep resistivity is 50, 500, 50 ohm-m respectively, cover layer thickness is 200 meters, middle layer thickness is 100 meters. Figure 4 is the K-type cross-section model full-time apparent resistivity curve chart defined by different direction horizontal electric field of the present application, when the frequency is higher than 10Hz, the four curves are basically coincided; when the frequency is 0.1-10Hz, the apparent resistivity appears cross change; when the frequency is less than 0.1Hz, the four curves all tend to a fixed value, which is 45.8, 55.4, 60.2, 56.6 ohm-m respectively. The four directions all reflect the change characteristics of stratum resistivity from shallow to deep low-high-low, that is, the four direction horizontal electric field can all detect the low resistance basement under 300 meters. From the numerical analysis, when the detection depth is within 848m, the root mean square relative difference of the four direction apparent resistivity is mostly within 2%, the total root mean square relative difference is 5.66%, which is shown in Table 2.

[0099] Table 2 K-type cross-section full-time apparent resistivity comparison table

[0100]

[0101]

[0102]

[0103] After comparing and analyzing the full-period apparent resistivity curves of the above-mentioned examples 1-4, the following analysis results can be obtained:

[0104] (1) In the high frequency band, the apparent resistivity sounding curves of the horizontal electric field in the four directions are basically coincident;

[0105] (2) In the medium frequency band, the apparent resistivity sounding curves of the horizontal electric field in the four directions appear bifurcation phenomenon, but the change rule is consistent, which can reflect the electrical property change characteristics of the stratum;

[0106] (3) In the low frequency band, when the frequency is lower than a certain frequency, the full-period apparent resistivity curves will tend to a certain fixed value, but the starting frequency of the full-period apparent resistivity defined by the horizontal electric field in different directions is different. The starting frequency of the apparent resistivity curve of the horizontal electric field X direction (AB-Ex) tending to a fixed value is the lowest. From this point, it can be analyzed that when the frequency is low to a certain extent, the skin depth is close to or even greater than the transmitting-receiving distance, so changing the frequency no longer has the effect of sounding depth;

[0107] In addition, the D-type section and the K-type section are both low-resistance base, the bifurcation points of the apparent resistivity curves in the four directions of the K-type section are inconsistent, while the bifurcation points of the apparent resistivity curves in the four directions of the D-type section are basically consistent. Overall, the relative error of the total root mean square of the apparent resistivity of the horizontal electric field in the four directions of the D-type section and the K-type section (low-resistance base) is less than that of the G-type section and the H-type section (high-resistance base).

[0108] Example 5 (Establishment of Full-period Apparent Resistivity Curve of K-type Section Model)

[0109] According to the resistivity logging curve of a certain mine in Shanxi Jinkuang, the electrical property is stratified, and a horizontal layered earth model is established. The model parameters are shown in Table 3. The forward is carried out in the directions of AB-Ex, AB-Ex30, AB-Ex60 and AB-Ey, and the full-period apparent resistivity is calculated, to obtain the full-period apparent resistivity curve of the horizontal layered earth model of a certain mine in Shanxi Jinkuang, as shown in Figure 5 .

[0110] Table 3 Model parameters of stratified electrical properties of a certain mine in Shanxi Jinkuang

[0111] Depth (m) Thickness (m) Resistivity (Ohm-m) Formation 60 60 18 Cenozoic, Upper Shihezi Formation 172 112 50 Upper Shihezi Formation 220 48 91 Upper Shihezi Formation 262 42 36 Upper Shihezi Formation 326 64 93 Lower Shihezi Formation 346 20 56 Lower Shihezi Formation 416 70 152 Shanxi Formation, Taiyuan Formation 516 100 180 Taiyuan Formation 536 20 20 Taiyuan Formation, Benxi Formation 1000 Ordovician

[0112] The parameters of the horizontal layered earth model are as follows: the coordinates of the transmitting field source A point are (-500, 0), and the coordinates of the B point are (500, 0), the receiving point MN is located at (2480, 4300), the transmitting-receiving distance is 4.9 km, and the included angle between the electrodes AB and OMN (O is the midpoint of AB) is 60°. TheFigure 5 It can be seen that the apparent resistivity curves of the four directions are substantially coincident when the frequency is higher than 100 Hz; the apparent resistivity curves of the four directions appear bifurcation when the frequency is 10-100 Hz, and the apparent resistivity curves of the four directions all tend to a fixed value at a low frequency, which indicates that the apparent resistivity changes of the four directions all reflect the electrical characteristics of the strata in the detection area.

[0113] Example 6 (measuring electromagnetic interference in different directions of horizontal electric field)

[0114] The electromagnetic interference is mainly generated by electromagnetic induction, and the electromagnetic noise of a parallel linear interference source is hundreds of times of the noise in the direction of a vertical linear interference source. Therefore, the present application determines whether the apparent resistivity changes in different directions of horizontal electric field all reflect the electrical characteristics of the strata in the detection area, and further suppresses the electromagnetic noise by changing the measurement direction of the electric field to improve the signal-to-noise ratio of the original data.

[0115] Figure 6 Fig. 1 is a schematic diagram of suppressing electromagnetic interference by changing the measurement direction of the electric field. As shown in Fig. 1, the electromagnetic interference is mainly generated by electromagnetic induction, and the electromagnetic noise of a parallel linear interference source is hundreds of times of the noise in the direction of a vertical linear interference source. Figure 6 It can be seen that there is a high-voltage line (left) parallel to the transmission source AB, and there is a high-voltage line (right) oblique to the transmission source AB. In the prior art of scalar CSAMT exploration or 2n sequence pseudo-random wide-area electromagnetic exploration, the electric field parallel to or oblique to the high-voltage line is obviously seriously interfered by the high-voltage line. Similarly, in order to measure the electric field of point O in the figure, the positions of M and N are changed to M' and N', so that the direction of M'N' is perpendicular to the high-voltage line, but the center point O remains unchanged, and then the original data with interference of the high-voltage line reduced by hundreds of times can be collected.

[0116] In this way, when Ex is parallel or oblique to the linear electromagnetic interference sources such as high-voltage lines, telephone lines and communication optical fibers, the apparent resistivity changes in different directions of horizontal electric field can all reflect the electrical characteristics of the strata in the detection area, and then the electric field in the vertical direction of the linear interference source can be measured to achieve the purpose of suppressing electromagnetic interference.

[0117] Example 7 (measuring electromagnetic interference in different directions of horizontal electric field)

[0118] Figure 7 Fig. 2 is an engineering layout diagram of wide-area electromagnetic exploration of geothermal energy for developing hot spring tourism in a certain place in Shaanxi. The loess gully is developed in the exploration area, and the two sides of the gully are steep cliffs, and the terrain is complex. The MN electrodes can only be arranged in the gully. The transmission field source AB is parallel to the blue line in the figure, and is mostly oblique to the direction of the gully. If the electric field Ex component is measured, the MN electrodes can only be laid discontinuously one by one, which is extremely inconvenient for construction. When the different direction electric field is measured, the MN electrodes can be laid to collect data, and the electromagnetic frequency sounding can be carried out by measuring the different direction horizontal electric field, so as to greatly improve the field construction efficiency.

[0119] Besides the complex terrain, village buildings and large area of water surface have great influence on construction, Figure 8 is to avoid the small area of water surface M, N electrode layout. Figure 8 The intersection in the middle is the M, N electrode position of the 304 line, in addition to the complete data obtained by the curved measuring line, the new M, N electrode can also be defined by crossing the continuous M, N electrode, such as Figure 8 indicated by the circle point. Figure 9 is the comparison chart of the processing effect of different direction horizontal electric field measurement and the addition of new M, N electrode defined measuring point data, which can be seen from Figure 9 , they all reflect the electrical characteristics of the formation, but the high resistivity trap shown in the original resistivity contour map is not obvious in the complex condition processing map (right). The exploration area also carried out three-dimensional seismic exploration, and the resistivity section map obtained by adding new M, N electrode defined measuring point data processing shows the DF2 fault of three-dimensional seismic interpretation obviously. That is to say, different direction measurement electric field electromagnetic frequency sounding can not only avoid obstacles, but also can carry out measuring point encryption, data homing processing, so as to improve the use rate of original data.

[0120] The above-mentioned embodiments are only preferred embodiments of the present application, which cannot be used to limit the scope of protection of the present application, and any non-essential changes and substitutions made by those skilled in the art on the basis of the present application shall belong to the scope of protection required by the present application.

Claims

1. A method for obtaining the trend of apparent resistivity variation of horizontal electric field in different directions of horizontal layered earth, characterized in that, The method comprises the following steps: establishing a two-layer G-type cross-section model, a two-layer D-type cross-section model, a three-layer H-type cross-section model and a three-layer K-type cross-section model; obtaining G-type cross-section model full-period apparent resistivity curves, D-type cross-section model full-period apparent resistivity curves, H-type cross-section model full-period apparent resistivity curves and K-type cross-section model full-period apparent resistivity curves defined by horizontal electric fields in different directions according to the two-layer G-type cross-section model, the two-layer D-type cross-section model, the three-layer H-type cross-section model and the three-layer K-type cross-section model; analyzing the G-type cross-section model full-period apparent resistivity curves, the D-type cross-section model full-period apparent resistivity curves, the H-type cross-section model full-period apparent resistivity curves and the K-type cross-section model full-period apparent resistivity curves to obtain relevant analysis results, specifically including: obtaining frequency points at which the full-period apparent resistivity curves defined by horizontal electric fields in different directions of each cross-section model appear to branch, variation trends, apparent resistivities when tending to be fixed and corresponding frequency points thereof; judging whether each cross-section model can reflect the variation characteristics of the formation resistivity according to the frequency points at which the full-period apparent resistivity curves appear to branch, the variation trends, the apparent resistivities when tending to be fixed and corresponding frequency points thereof; if yes, regarding each cross-section model as an effective cross-section model; and performing electrical layering based on each effective cross-section model and according to a measured resistivity logging curve; establishing a horizontal layered earth model of a to-be-explored area according to the analysis results and obtaining variation trends of horizontal electric field apparent resistivities in different directions of the to-be-explored area based on the horizontal layered earth model.

2. The method of claim 1, wherein the method is characterized by, When establishing the two-layer G-type cross-section model and the two-layer D-type cross-section model, the method comprises the following steps: obtaining positions of transmitting field sources A point and B point and a position of a receiving point MN; obtaining a shallow layer resistivity, a shallow layer thickness and a basement resistivity; establishing the two-layer G-type cross-section model and the two-layer D-type cross-section model according to the positions of the transmitting field sources A point and B point, the position of the receiving point MN, the shallow layer resistivity, the shallow layer thickness and the basement resistivity.

3. The method of claim 1, wherein the method is characterized by: When establishing the three-layer H-type cross-section model and the three-layer K-type cross-section model, the method comprises the following steps: obtaining positions of transmitting field sources A point and B point and a position of a receiving point MN; obtaining shallow-to-deep three-layer resistivities, a cover layer thickness and an intermediate layer thickness; establishing the three-layer H-type cross-section model and the three-layer K-type cross-section model according to the positions of the transmitting field sources A point and B point, the position of the receiving point MN, the shallow-to-deep three-layer resistivities, the cover layer thickness and the intermediate layer thickness.

4. The method of claim 1, wherein the method is characterized by: When obtaining full-period apparent resistivity curves of each cross-section model, the method comprises the following steps: forwarding full-period apparent resistivities of a horizontal electric field X direction according to each cross-section model to obtain full-period apparent resistivity curves of the horizontal electric field X direction of each cross-section model.

5. The method of claim 4, wherein the method is characterized by: When obtaining full-period apparent resistivity curves of each cross-section model, the method further comprises the following steps: forwarding full-period apparent resistivities of a horizontal electric field Y direction according to each cross-section model to obtain full-period apparent resistivity curves of the horizontal electric field Y direction of each cross-section model.

6. The method of claim 5, wherein the trend of apparent resistivity variation of horizontal electric field in different directions of horizontal layered earth is obtained. When obtaining full-period apparent resistivity curves of each cross-section model, the method further comprises the following steps: According to each section model, the full-period apparent resistivity in the direction of 30 degrees to the horizontal electric field X axis is forward calculated to obtain the full-period apparent resistivity curve of each section model in the direction of 30 degrees to the horizontal electric field X axis.

7. The method of claim 6, wherein the method is characterized by: When the full-period apparent resistivity curve of each section model is obtained, the following is further included: According to each section model, the full-period apparent resistivity in the direction of 60 degrees to the horizontal electric field X axis is forward calculated to obtain the full-period apparent resistivity curve of each section model in the direction of 60 degrees to the horizontal electric field X axis.

8. The method of claim 7, wherein the trend of apparent resistivity variation of horizontal electric field in different directions of horizontal layered earth is obtained. When the horizontal layered earth model is established according to the analysis result, the following is included: The horizontal layered earth model is established according to the electrical layering result, and the full-period apparent resistivity curves of the horizontal layered earth model in the X direction of the horizontal electric field, the Y direction of the horizontal electric field, the direction of 30 degrees to the horizontal electric field X axis and the direction of 60 degrees to the horizontal electric field X axis are forward calculated to obtain the full-period apparent resistivity curve of the horizontal layered earth model; The horizontal electric field apparent resistivity variation trend in different directions of the area to be explored is obtained according to the full-period apparent resistivity curve of the horizontal layered earth model.

9. A system for obtaining the trend of apparent resistivity variation of horizontal electric field in different directions in a horizontal layered earth, characterized in that, The following is included: The model establishing unit is configured to establish a two-layer G-type section model, a two-layer D-type section model, a three-layer H-type section model and a three-layer K-type section model; The curve establishing unit is configured to obtain the full-period apparent resistivity curve of the G-type section model, the full-period apparent resistivity curve of the D-type section model, the full-period apparent resistivity curve of the H-type section model and the full-period apparent resistivity curve of the K-type section model defined by the horizontal electric field in different directions according to the two-layer G-type section model, the two-layer D-type section model, the three-layer H-type section model and the three-layer K-type section model; The variation trend obtaining unit is configured to analyze the full-period apparent resistivity curve of the G-type section model, the full-period apparent resistivity curve of the D-type section model, the full-period apparent resistivity curve of the H-type section model and the full-period apparent resistivity curve of the K-type section model to obtain the analysis result, and the analysis result specifically includes: obtaining the frequency point when the full-period apparent resistivity curve of each section model defined by the horizontal electric field in different directions appears bifurcation, the variation trend, the apparent resistivity when the variation trend tends to be fixed and the corresponding frequency point; The variation trend obtaining unit is configured to analyze the full-period apparent resistivity curve of the G-type section model, the full-period apparent resistivity curve of the D-type section model, the full-period apparent resistivity curve of the H-type section model and the full-period apparent resistivity curve of the K-type section model to obtain the analysis result, and the analysis result specifically includes: obtaining the frequency point when the full-period apparent resistivity curve of each section model defined by the horizontal electric field in different directions appears bifurcation, the variation trend, the apparent resistivity when the variation trend tends to be fixed and the corresponding frequency point; The variation trend obtaining unit is configured to analyze the full-period apparent resistivity curve of the G-type section model, the full-period apparent resistivity curve of the D-type section model, the full-period apparent resistivity curve of the H-type section model and the full-period apparent resistivity curve of the K-type section model to obtain the analysis result, and the analysis result specifically includes: obtaining the frequency point when the full-period apparent resistivity curve of each section model defined by the horizontal electric field in different directions appears bifurcation, the variation trend, the apparent resistivity when the variation trend tends to be fixed and the corresponding frequency point;

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