Novel multi-channel natural potential daily variation correction method

Abstract

The invention relates to the technical field of geophysics, and discloses a novel multi-channel natural potential daily variation correction method, which comprises the following steps: S1, fully collecting geological data of a natural potential collection work area and an adjacent area thereof, dividing different rock stratums and numbering, and S2, respectively arranging daily variation observation stations on the different rock stratums; s3, recording the numerical value of each daily variation observation station; s4, processing the data recorded by the daily variation observation station; s5, selecting daily variation observation station data of the corresponding stratum according to the stratum where the mobile station is located, comparing the daily variation observation station data with the mobile station to obtain a daily variation attenuation coefficient, and S6, multiplying a measured value by the attenuation coefficient to obtain a natural potential value after daily variation correction. According to the invention, the periodic change of the natural electric field can be effectively observed, the accurate time and amplitude generated by random interference can be effectively observed, later data correction processing is facilitated, the natural potential correction precision of different stratums can be improved, and the method can be used in areas with serious human interference.

Description

Technical Field

[0001] The invention relates to the field of geophysical technology, and in particular to a new multi-channel natural potential diurnal variation correction method. Background Art

[0002] At present, the natural potential method is widely used to find oil and gas, sulfide deposits, metal mines and graphite mines. With the exploration and development of surface minerals, underground hidden mines are the focus of the next stage of prospecting. The signal that can be observed on the surface weakens with the increase of the buried depth of the ore body. Therefore, improving the accuracy of the natural potential results is the next development direction, and the accuracy of field data collection is directly related to the accuracy of the subsequent interpretation of the results.

[0003] At present, the observation of periodic changes in natural potential is carried out by setting up an observation station in the work area, and the observation pole spacing is consistent with the field point spacing. Feng Bing. Natural electric field and petroleum geological significance of Ordos Basin [D]. Beijing: China University of Geosciences (Beijing), 2010. The observation method of the same point spacing is used to eliminate the influence of time-varying electric field when conducting natural potential observation in Ordos Basin. The observation is carried out at a time interval of 10 minutes, which can effectively observe the periodic changes of natural potential, but cannot effectively observe the time and amplitude of random interference. During the rainy season in southern my country, the temperature and humidity changes are greater than those in the north. The cover layer in the southern mountainous areas is also thinner. Rainy days and sunny days alternate, which easily causes the moisture content of the stratum to change rapidly. In geologically complex areas, the water content of different lithologies is inconsistent, and the porosity and water conductivity of the strata are also inconsistent. With the change of time, the changes under the same temperature and humidity changes are bound to be inconsistent. Therefore, it is obviously inappropriate to use the statistical data observed by the same observation station to make daily changes to the changes in natural potential in a region.

[0004] To this end, the present application proposes a multi-reference channel natural potential diurnal variation observation method to solve the need for correction of natural potential diurnal variation in different rock formations in the same work area and improve the accuracy of correction of natural potential diurnal variation. Summary of the invention

[0005] The purpose of the present invention is to provide a new multi-channel natural potential diurnal variation correction method, which can improve the observation accuracy of natural potential periodic changes and improve the accuracy of natural potential diurnal variation correction, so as to solve the above-mentioned defects in the prior art.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a new multi-channel natural potential daily variation correction method.

[0008] A new multi-channel natural potential diurnal variation correction method includes the following steps:

[0009] S1. Fully collect geological data of the natural potential collection area and its neighboring areas, divide the distribution of different rock layers, and number them as D 1 , D 2 , D 3 ...Di;

[0010] S2. Arrange diurnal variation observation stations on the different rock layers divided in step S1. Specifically:

[0011] S21. Arrange the N pole of the diurnal variation observation station.

[0012] S22. M poles of diurnal variation observation stations are arranged in different rock layers and numbered M 1 、M 2 、M 3 …M i , corresponding to the numbers D 1 , D 2 , D 3 ...the rock formations of the Earth,

[0013] The pits for the N-pole electrode and the M-pole electrode should be free of debris such as gravel and grass. When the electrode burying point is very dry, water should be poured in advance in the pit.

[0014] S3. Record the value of each daily variation observation station;

[0015] S4, processing the data recorded by each diurnal variation observation station in step S3;

[0016] S5. According to the stratum where the mobile station is located, the daily variation observation station data of the corresponding stratum is selected. If the data collection of the daily variation observation station is synchronized with that of the mobile station, the daily variation attenuation coefficient can be obtained by directly dividing the observation value of the daily variation observation station at that time by the basic observation value of the daily variation observation station; if the data collection of the daily variation observation station is not synchronized with that of the mobile station, the daily variation observation station uses linear interpolation to obtain the observation value of the daily variation observation station at the same time as the mobile station and then divides it by the basic observation value of the daily variation observation station to obtain the daily variation attenuation coefficient;

[0017] S6. The natural potential value after daily variation correction can be obtained by multiplying the mobile station observation value by the daily variation attenuation coefficient obtained in step S5.

[0018] Preferably, in step S21, the N pole of the diurnal variation observation station needs to be selected where the height difference does not exceed 2m within a plane diameter of 20m, the potential difference between any two points does not exceed ±2mv, the nearby strata are stable, no large structures pass through, there are no rubble on the surface, there is soil within a depth of 1m, and no bedrock is exposed. It should be arranged at a location more than 200m away from water-rich ditches and seasonal ditches, and more than 500m away from high-voltage lines, transformers, and radio station grounding points.

[0019] Preferably, in step S22, the M pole of the daily change observation station needs to be selected with a height difference of no more than 2m within a plane diameter of 10m, located near the center of the stratum, with stable stratum and no obvious structure passing through, more than 200m away from water-rich ditches and seasonal ditches, and more than 500m away from high-voltage lines, transformers, and radio station grounding points.

[0020] Preferably, in step S22, at least one diurnal variation observation station is arranged in each of the different rock formations.

[0021] Preferably, in step S23, the anti-interference wire is a jointless, lightweight and high-strength wire with an internal resistance of less than 10Ω / km, the insulation resistance of the anti-interference wire is greater than 5MΩ / km, the anti-interference wire needs to be laid close to the ground to avoid electromagnetic field interference caused by the wire swinging with the wind, and when passing through railways and roads, measures such as fixing the two ends in the air or digging trenches to bury the wire are required to prevent damage to the wire and facilitate the passage of people, animals and vehicles.

[0022] Preferably, in step S3, the starting time nodes for recording the values ​​of each daily variable observation station are respectively starting to record before the official area measurement of the mobile station every day, and stopping to record after the official area measurement of the mobile station is finished;

[0023] Preferably, in step S3, the recording requirement of the value of each daily variable observation station is to read M at a time interval of 10s-60s. 1 N, M 2 N, M 3 N…M i The value of N is recorded.

[0024] Preferably, the method for processing the data recorded by each diurnal variation observation station in step S3 is to 1 N, M 2 N, M 3 N…M i The daily variation data recorded by N are respectively averaged at 5 or 7 points to reduce the noise level.

[0025] Preferably, when the data collection of the diurnal variation observation station is synchronized with the mobile station, the calculation formula of the diurnal variation attenuation coefficient value is as follows:

[0026] J=ΔU i / ΔU 基础 ;

[0027] When the data collection of the diurnal variation observation station is not synchronized with the mobile station, the calculation formula of the diurnal variation attenuation coefficient value is as follows:

[0028]

[0029] Among them, ΔUi is the daily variation observation value of a certain layer at a certain time, ΔU 基础 is the daily variation basic observation value selected for a certain stratum, ΔU x1 ,ΔU x2 It is the observation value of the daily variation observation station at a certain moment and the observation value of the daily variation observation station at the next moment (in mv); T is the daily variation observation period (in s), and J is the attenuation coefficient.

[0030] Preferably, the calculation formula of the natural potential value after daily variation correction is:

[0031] ΔU 改正后 =J*ΔU 移动 ,

[0032] Among them, ΔU 改正后 is the natural potential value after diurnal variation correction, ΔU 移动 Measure the natural potential value for the mobile station.

[0033] In summary, compared with the prior art, the solution of the present invention has the following beneficial effects:

[0034] The present invention can effectively observe the periodic changes of the natural electric field, and can also effectively observe the accurate time and amplitude of random interference, which is conducive to the subsequent data correction processing, can improve the accuracy of natural potential correction in different strata, and can also be used in areas with serious human interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a flow chart of a new multi-channel natural potential daily variation correction method in an embodiment of the present invention;

[0036] Figure 2 It is a layout diagram of a daily variation observation station for a new multi-channel natural potential daily variation correction method in an embodiment of the present invention.

[0037] Figure 3 It is a natural potential curve diagram of different water contents of formation A (left) and formation B (right) in the comparative example of the present invention;

[0038] Figure 4 It is the attenuation curve diagram of different strata in the comparative example of the present invention;

[0039] Figure 5 It is a comparison curve diagram of the actual correction value and the theoretical value of formation A (left) and formation B (right) in the comparative example of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solution of the present invention will be further described in detail below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0041] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0042] Example 1

[0043] A new multi-channel natural potential diurnal variation correction method includes the following steps:

[0044] S1. Fully collect geological data of the natural potential collection area and its neighboring areas, confirm the rock formation types of the work area and its neighboring areas, divide the distribution of different rock formations, and number them D 1 , D 2 , D 3 ...Di.

[0045] S2. Arrange at least one diurnal variation observation station on each of the different rock layers divided in step S1. Specifically:

[0046] S21. First, choose a location with a height difference of no more than 2m within a plane diameter of 20m, a potential difference of no more than ±2mv between any two points, stable strata nearby, no large structures passing through, no rubble on the surface, soil within 1m depth, no bedrock exposed, more than 200m away from water-rich ditches and seasonal ditches, and more than 500m away from high-voltage lines, transformers, and radio station grounding points to arrange the N-pole electrode of the diurnal variation observation station;

[0047] S22, then arrange the M pole electrodes of the daily change observation station in different rock formations at locations with a height difference of no more than 2m within a plane diameter of 10m, near the center of the formation, where the formation is stable and there is no obvious structure passing through, more than 200m away from water-rich ditches and seasonal ditches, and more than 500m away from high-voltage lines, transformers, and radio station grounding points, and number them M respectively. 1 、M 2 、M 3 …M i , corresponding to the numbers D 1 , D 2 , D 3 ...the rock formations of the Earth;

[0048] S23, connect M with anti-interference wire i , N-pole electrode, complete the daily variation observation station (M1 N, M 2 N, M 3 N…M i N), where the anti-interference wire is a jointless, light and high-strength wire with an internal resistance of less than 10Ω / km. This is because the wire has a small internal resistance, strong conductivity and small energy attenuation. The insulation resistance of the anti-interference wire is greater than 5MΩ / km. This is because the greater the insulation resistance, the greater the electric field strength that can be sustained. The anti-interference wire needs to be laid close to the ground to avoid electromagnetic field interference caused by the wire swinging with the wind. When passing through railways and highways, measures such as fixing the two ends in the air or digging trenches to bury the wire are required to prevent damage to the wire and facilitate the passage of people, animals and vehicles.

[0049] Among them, the pits of the N-pole electrode and the M-pole electrode must be free of debris such as gravel and grass. When the electrode burial point is very dry, water the pit in advance.

[0050] S3. Every day before the mobile station conducts formal area measurement, start recording the values ​​of each daily variable observation station arranged in step S2, and read the M at intervals of 10s-60s. 1 N, M 2 N, M 3 N…M i N The value of each daily variation observation station is recorded. After the mobile station finishes the formal area measurement every day, the value of each daily variation observation station is stopped.

[0051] It should be noted here that the smaller the time interval, the more short-period random interference can be observed, which is conducive to the subsequent judgment of data reliability.

[0052] S4, step S3 in the day change observation station M 1 N, M 2 N, M 3 N…M i The daily variation data recorded by N are respectively averaged at 5 or 7 points to reduce the noise level;

[0053] S5. According to the stratum where the mobile station is located, select the diurnal variation observation station data of the corresponding stratum. If the data collection of the diurnal variation observation station is synchronized with the mobile station, the diurnal variation attenuation coefficient can be obtained by directly dividing the observation value of the diurnal variation observation station at that time by the basic observation value of the diurnal variation observation station. The calculation formula of the diurnal variation attenuation coefficient is as follows:

[0054] J=ΔU i / ΔU 基础 ;

[0055] If the data collection of the daily variation observation station is not synchronized with that of the mobile station, the daily variation observation station uses linear interpolation to obtain the observation value of the daily variation observation station at the same time as the mobile station, and then divides it by the basic observation value of the daily variation observation station to obtain the daily variation attenuation coefficient. The calculation formula of the daily variation attenuation coefficient is as follows:

[0056]

[0057] Among them, ΔU i is the daily variation observation value of a certain layer at a certain time, ΔU 基础 is the daily variation basic observation value selected for a certain stratum, ΔU x1 ,ΔU x2 It is the observation value of the daily variation observation station at a certain moment and the observation value of the daily variation observation station at the next moment (in mv); T is the daily variation observation period (in s), and J is the attenuation coefficient.

[0058] S6. By subtracting the diurnal variation correction value obtained in step S5 from the measured value, the natural potential value after diurnal variation correction can be obtained. The calculation formula is:

[0059] ΔU 改正后 =J*ΔU 移动 ,

[0060] Among them, ΔU 改正后 is the natural potential value after diurnal variation correction, ΔU 移动 Measure the natural potential value for the mobile station.

[0061] Comparative Example 1

[0062] In the prior art, the simple expression of the self-potential anomaly caused by plasmoidal polarization is as follows:

[0063]

[0064] In the formula, the central burial depth of the anomaly is defined as z, the angle between the polarization axis and the ground is α, the resistivity of the surrounding rock is ρ1, the resistivity of the anomaly is ρ2, the comprehensive parameter of the maximum potential jump on the surface of the anomaly is Ur, and the parameter of the anomaly shape is q. Then the potential expression on the main section along the X-axis direction is formula (1). When the plate-like body is extended vertically infinitely, the q value is 1, and Ur is the comprehensive parameter of the maximum potential jump on the surface of the anomaly.

[0065] It can be seen from formula (1) that the natural electric field anomaly caused by the geological body is related to the resistivity of the geological body.

[0066] The factors affecting the resistivity of rocks mainly include mineral composition, content and distribution, resistivity of formation water, porosity and pore shape of rocks, porosity of rocks, humidity, etc. It is difficult to accurately calculate the resistivity of rocks. In actual operation, a large number of samples and classification statistics are used to determine the resistivity of a rock. In the same area, most rocks and ores can be regarded as composed of uniformly connected cements and mineral particles. The resistivity of cements is affected by the resistivity of cements, and the resistivity of cements is affected by humidity.

[0067] According to the improved Archie formula:

[0068] ρ=aΦ n-m θ -n ρ 0 …(2)

[0069] In the formula: ρ is the resistivity of rock; ρ0 is the resistivity of water in pores; θ is water content; φ is porosity; n is saturation index; m is porosity index; a is rock formation proportion coefficient. φ, n, m, and a are constant for the same region and lithology. In a certain period of time, only the water content changes. When the water content decreases, the resistivity of the rock increases.

[0070] To infer the relationship between water content and natural potential, substitute equation (2) into equation (1):

[0071]

[0072] By obtaining the relationship between water content and natural potential at a certain moment, it can be found that as the water content decreases, the natural electric field is in a state of attenuation, and the attenuation value is different in different rock formations.

[0073] The attenuation coefficient is obtained by calculating the ratio of the natural potential at a certain moment to the natural potential value at the next moment.

[0074]

[0075] In the formula, a1 and a2 are the ratio coefficients of surrounding rock and abnormal rock formation, φ1 and φ2 are the porosity of surrounding rock and abnormal rock formation, n1 and n2 are the saturation index of surrounding rock and abnormal rock formation, m1 and m2 are the porosity index of surrounding rock and abnormal rock formation, θ1 and θ1' are the water content of abnormal rock formation at a certain moment and the water content at the next moment, θ2 and θ2' are the water content of surrounding rock at a certain moment and the water content at the next moment. The attenuation coefficient is only related to φ, n, m, and θ, while φ, n, and m of the same area and lithology are fixed, and only θ is relatively variable, so the attenuation coefficient can be calculated based on this characteristic.

[0076] A model is now designed. When the surrounding rock is saturated with water, the resistivity is 3000Ω·m; when the water content is saturated, the resistivity of formation A is 100Ω·m, and Ur is the maximum potential jump on the surface of the abnormal body, which is -500mv; when the water content is saturated, the resistivity of formation B is 1000Ω·m, and Ur is the maximum potential jump on the surface of the abnormal body, which is -200mv.

[0077] Due to the decrease in water content, according to formula (3), the resistivity of the rock increases and the amplitude of the natural potential value decreases. The natural potential curves of formation A and formation B with different water contents are as follows: Figure 2 .

[0078] like Figure 3As shown, the daily variation observation stations of formation A and formation B are arranged at 50m. At different water content moments of formation A and formation B, their attenuation curves are inconsistent, indicating that the attenuation ratios of different formations are different relative to the starting value of the formation observation.

[0079] Now calculate the theoretical attenuation coefficient of formation A, select 30% tax content as the basic value of formation A, and when the water content drops from 30% to 15%, its attenuation coefficient J = -78.945 / -93.75 = 0.84208.

[0080] The natural potential value calculated by the attenuation coefficient when the water content of formation A is 15% is compared with the theoretical calculated value. Figure 4 According to the quality inspection requirements of the Technical Specifications for Natural Electric Field Method (DZ_T 0081-2017), the error value is calculated to be 0.03mv.

[0081] Use the same correction factor to correct layer B, such as Figure 5 As shown in (right), the shape of the corrected curve is significantly different from the theoretical value, with the maximum error reaching 8.12mv. The quality inspection requires that the overall error be calculated to be 2.17mv, and the larger the anomaly caused by the formation, the greater the correction error.

[0082] To sum up, when the moisture content of different strata changes rapidly, changes over time will inevitably lead to inconsistent changes in the strata under the same changes in temperature and humidity, resulting in anomalies. The larger the anomaly value caused by the stratum, the greater the error in the daily correction of the natural potential changes in a region using statistical data observed at the same observation station. The present application can effectively observe the periodic changes of the natural electric field by adopting a multi-channel natural potential daily change correction method, and can also effectively observe the exact time and amplitude of random interference, which is beneficial to the subsequent data correction processing, thereby improving the natural potential correction accuracy of different strata, and can also be used in areas with severe human interference.

[0083] The above-described embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A new multi-channel natural potential daily variation correction method, characterized in that: The steps include: S1. Collect geological data of the natural potential collection area and its neighboring areas, divide the distribution of different rock layers, and number them as D1, D2, D3...Di; S2. Arrange diurnal variation observation stations on the different rock layers divided in step S1. Specifically: S21. Arrange the N-pole electrode of the diurnal variation observation station. S22. Arrange the M-pole electrodes of the diurnal variation observation station in different rock layers and number them as M1, M2, M3…M i , corresponding to the rock layers numbered D1, D2, D3…Di, S23, connect M with anti-interference wire i , N pole; The pits for the N-pole electrode and the M-pole electrode should be free of gravel and grass. When the electrode burying point is very dry, water should be poured in advance in the pit. S3, record the value of each daily variation observation station; S4, processing the data recorded by each diurnal variation observation station in step S3; S5. According to the stratum where the mobile station is located, the daily variation observation station data of the corresponding stratum is selected. If the data collection of the daily variation observation station is synchronized with that of the mobile station, the daily variation attenuation coefficient can be obtained by directly dividing the observation value of the daily variation observation station at that time by the basic observation value of the daily variation observation station; if the data collection of the daily variation observation station is not synchronized with that of the mobile station, the daily variation observation station uses linear interpolation to obtain the observation value of the daily variation observation station at the same time as the mobile station and then divides it by the basic observation value of the daily variation observation station to obtain the daily variation attenuation coefficient; S6. The natural potential value after daily variation correction can be obtained by multiplying the mobile station observation value by the daily variation attenuation coefficient obtained in step S5.

2. A new multi-channel natural potential daily variation correction method as claimed in claim 1, characterized in that: In step S21, the N pole of the diurnal variation observation station needs to be selected within a plane diameter of 20m with a height difference of no more than 2m, the potential difference between any two points does not exceed ±2mv, the nearby strata are stable, no large structures pass through, there are no rubble on the surface, there is soil within a depth of 1m, and no bedrock is exposed. It should be arranged at a location more than 200m away from water-rich ditches and seasonal ditches, and more than 500m away from high-voltage lines, transformers, and radio station grounding points.

3. A new multi-channel natural potential daily variation correction method as claimed in claim 1, characterized in that: In step S22, the M pole of the daily change observation station needs to be selected with a height difference of no more than 2m within a plane diameter of 10m, located near the center of the stratum, with stable stratum and no obvious structure passing through, more than 200m away from water-rich ditches and seasonal ditches, and more than 500m away from high-voltage lines, transformers, and radio station grounding points.

4. A new multi-channel natural potential daily variation correction method as claimed in claim 1, characterized in that: In step S22, at least one diurnal variation observation station needs to be arranged in each of the different rock formations.

5. A new multi-channel natural potential daily variation correction method as claimed in claim 1, characterized in that: In step S23, the anti-interference wire is a jointless and lightweight wire with an internal resistance of less than 10Ω / km, the insulation resistance of the anti-interference wire is greater than 5MΩ / km, and the anti-interference wire needs to be laid close to the ground. When passing through railways and roads, measures such as fixing the two ends in the air or digging trenches to bury the wire are required.

6. A new multi-channel natural potential daily variation correction method as claimed in claim 1, characterized in that: In step S3, the starting time nodes for recording the values ​​of each daily variable observation station are respectively starting to record before the official area measurement of the mobile station every day, and stopping to record after the official area measurement of the mobile station is finished.

7. A new multi-channel natural potential daily variation correction method as claimed in claim 1, characterized in that: In step S3, the recording requirement of the values ​​of each daily variable observation station is to read M1N, M2N, M3N...M at a time interval of 10s-60s. i The value of N is recorded.

8. A new multi-channel natural potential daily variation correction method as claimed in claim 1, characterized in that: The method for processing the data recorded by each diurnal variation observation station in step S3 is to process M1N, M2N, M3N...M i The daily variation data recorded by N are respectively averaged at 5 or 7 points to reduce the noise level.

9. A new multi-channel natural potential daily variation correction method as claimed in claim 1, characterized in that: When the data collection of the diurnal variation observation station is synchronized with the mobile station, the calculation formula of the diurnal variation attenuation coefficient value is as follows: J=ΔU i / D 基础 ; When the data collection of the diurnal variation observation station is not synchronized with the mobile station, the calculation formula of the diurnal variation attenuation coefficient value is as follows: Among them, ΔU i is the daily variation observation value of a certain layer at a certain time, ΔU 基础 is the daily variation basic observation value selected for a certain stratum, ΔU x1 ,ΔU x2 It is the observation value of the daily variation observation station at a certain moment and the observation value of the daily variation observation station at the next moment (in mv); T is the daily variation observation period (in s), and J is the attenuation coefficient.

10. A new multi-channel natural potential daily variation correction method as claimed in claim 9, characterized in that: The calculation formula of the natural potential value after the daily variation correction is: D.U. 改正后 =J*ΔU 移动 , Among them, ΔU 改正后 is the natural potential value after diurnal variation correction, ΔU 移动 Measure the natural potential value for the mobile station.

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