A geophysical method for detecting groundwater using a non-conventional transient electromagnetic method

Abstract

The application discloses a geophysical prospecting method for detecting underground water by using a non-conventional transient electromagnetic method, and belongs to the technical field of underground water detection. A , B , W , and a profile measurement work is arranged according to the determined underground water inlet and outlet W A , B and the water flow direction D W ; the observation equipment comprises a transient electromagnetic instrument system and a transmitting system, and the measurement is carried out on the induced voltage data of a single field source and the data of an additional field source; the development depth and position of the underground karst pipeline and other information are inferred through processing and inversion. The application relates to the technical field of underground water detection, and the geophysical prospecting method for detecting underground water by using the non-conventional transient electromagnetic method uses the electromagnetic induction principle and the property of the underground water as a good conductor, supplies alternating current into the underground water system to form a secondary field anomaly which changes with time and space, the secondary field anomaly has the characteristics of high amplitude and sharp change, has the similarity with the electromagnetic interference signal characteristics, and thus has great difference with the measurement anomaly of the transient electromagnetic instrument system, so that the anomaly caused by the underground karst pipeline can be easily identified, and the multi-solution property is reduced.

Description

Technical Field

[0001] This invention relates to the field of groundwater detection technology, specifically a geophysical method for detecting groundwater using a non-traditional transient electromagnetic method. Background Technology

[0002] Currently, groundwater investigation methods include drilling, pumping tests, and geophysical exploration. Compared to drilling and pumping tests, geophysical exploration technology has the advantages of being economical, non-destructive, rapid, and having a large coverage. It mainly relies on the difference in physical properties between the underground space filled with water or relatively filled with water and the surrounding medium, and then studies the changes in geophysical fields to infer the structure of the underground space. It mainly uses electrical methods, including high-density electrical resistivity tomography (EDT), transient electromagnetic methods (TEM), audio-frequency magnetotellurics (AFM), induced polarization methods, and combined profiling methods. Transient electromagnetic methods, high-density EDT, and ground-penetrating radar are mainly used to solve the distribution of shallow anomalies. Controlled-source AFM and AFM are mainly used to reveal the development of fault structures. Combined profiling methods and charging methods are mainly used to identify the planar location of steep water-bearing structures, fissures, and steep geological bodies with high resistance. All of the above methods are indirect methods for finding water. Nuclear magnetic resonance (NMR) can directly detect the presence of groundwater and is a direct method for finding water.

[0003] In actual exploration, the applicable conditions for each method differ: high-density electrical resistivity tomography, combined profiling, and nuclear magnetic resonance are significantly affected by topography, resulting in relatively shallow exploration depths; audio-frequency magnetotellurics and nuclear magnetic resonance have weak resistance to electromagnetic interference, limiting their application as a single method. In practice, multiple methods are often combined to cross-verify and reduce ambiguity, but in work areas with large exploration areas and unclear target boundaries, this increases exploration costs and time. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a geophysical method for detecting groundwater using non-traditional transient electromagnetic methods, which solves the problems of large limitations, long cycles, and high costs of existing groundwater detection methods.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention provides the following technical solution: a geophysical method for detecting groundwater using non-traditional transient electromagnetic methods, comprising the following operational steps:

[0008] S1: Thoroughly analyze the regional hydrogeological characteristics, including groundwater recharge, runoff, and discharge conditions, and combine this with drilling and basic geological data to determine the groundwater inlet / outlet W. A With W B Direction of water flow D W ;

[0009] S2: Using groundwater as a good conductor, according to the electromagnetic induction theorem, when an alternating electric field is supplied to the groundwater system, a primary magnetic field is generated. When the current is suddenly cut off, an induced eddy current field is excited and a secondary field that propagates in the medium and varies with time and space is generated. The energized karst pipe forms an electromagnetic field source.

[0010] S3: Perpendicular to the direction of groundwater flow (D) W Set up measurement profiles P1, P2, P3, P4...P i ..., each profile P i Measuring points P are arranged at the same intervals. i1 P i2 P i3 P i4 ...P ij ...;

[0011] S4: The observation equipment includes a transient electromagnetic instrument system and a transmission system;

[0012] S5: Before the power supply equipment supplies AC power to the groundwater system, measurements are carried out along the established measuring points using a transient electromagnetic instrument system to obtain the time-varying single-source induced voltage data SS at each measuring point. ij ;

[0013] S6: Electrodes A and B of the transmitting system are respectively placed at the groundwater inlet / outlet W. A With W B The transmitting system supplies alternating current to the groundwater through power supply equipment, operating synchronously with the transient electromagnetic system. Simultaneously, the transient electromagnetic instrument system conducts measurements along the deployed measuring points to obtain the SD data of the additional field source induced voltage at each measuring point after power supply. ij That is, the time-varying induced voltage data generated by different electric field sources transmitted through the underground medium;

[0014] S7: For each profile P i Additional field source induced voltage data SD at each measuring point ij Normalization processing is performed (divided by the single-source induced voltage data SS of the corresponding profile). ij Normalized additional field source induced voltage data (SDN) is obtained by averaging the values. ij ; Utilizing normalized additional field source induced voltage data SDN ij SS data of single-source induced voltage ij The difference is used to obtain the profile P for each section. i The induced voltage is abnormal; under normal circumstances, when there is a hidden karst pipeline, the measured induced voltage value changes significantly during the AC power supply to the groundwater system. The induced voltage anomaly profile curve of the measuring point in the influence range of the hidden karst pipeline shows a more dramatic change. Based on this characteristic, the induced voltage anomaly profile is delineated.

[0015] S8: For each profile P i Single-source induced voltage data SS ij Inversion was performed to obtain the single-field source apparent resistivity values ​​ρ for all profiles. S S i ; Using the mapping software Surfer, each profile P was analyzed i The apparent resistivity value ρ of a single field source S S i Interpolation is performed to generate an apparent resistivity profile anomaly map; the water-bearing karst conduit exhibits low resistivity characteristics relative to the surrounding rock, and the water-bearing development zone of the karst conduit is represented by a dense zone of low resistivity isolines or a low-value closed zone on the apparent resistivity profile map. Based on the above characteristics, the dense zone of low resistivity isolines or the low-value closed zone is delineated.

[0016] S9: Based on the hydrogeological characteristics of the work area, compare each profile P i The characteristics and distribution of induced voltage anomalies, dense low resistivity contours, or low-value closed zones in the delineated profiles are analyzed and compared to obtain the distribution and burial depth of karst conduits in each profile. Finally, by connecting the locations of karst conduits in all profiles, the planar location and direction of underground karst conduits can be deduced.

[0017] Preferably, W A W is the upstream point of the karst conduit. B This is the downstream point of the karst conduit.

[0018] Preferably, the transient electromagnetic instrument system generates a primary pulse magnetic field by inputting a step current into the ungrounded return line, and uses a coil to measure the time-varying secondary field (induced voltage data) generated by the underground geological body when the power is off.

[0019] Preferably, the transmitting system includes a power supply device, electrodes, and underground karst water runoff. The power supply device provides pulse power supply with a power supply current of about 1200A and a power supply pulse width of 4ms.

[0020] (III) Beneficial Effects

[0021] This invention provides a geophysical method for detecting groundwater using non-traditional transient electromagnetic methods. It offers the following advantages:

[0022] 1. This non-traditional transient electromagnetic method for detecting groundwater utilizes the principle of electromagnetic induction and the property of groundwater as a good conductor. Alternating current is supplied to the groundwater system to form a secondary field anomaly that varies with time and space. This secondary field anomaly is characterized by high amplitude and drastic changes, and has similar characteristics to electromagnetic interference signals. Therefore, it differs significantly from the anomalies measured by the transient electromagnetic instrument system, making it easier to identify anomalies caused by underground karst conduits and reducing ambiguity.

[0023] 2. This transient electromagnetic method is less affected by terrain, is not shielded by high-resistivity layers, and is sensitive to low-resistivity layers. With a point spacing of 20-40 meters, it can complete 50-80 measurement points per day. It is simple to operate and has fast data acquisition. The improved non-traditional transient electromagnetic method inherits its advantages. Compared with traditional methods or combinations of multiple methods, it controls the increase in detection costs and cycle time. At the same time, it can quickly determine the distribution and burial depth of karst conduits and delineate the distribution and burial depth of underground horizontal planes, thus improving detection efficiency and accuracy. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the detection process of the present invention;

[0025] Figure 2 This is a flowchart illustrating the operation of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] like Figure 1-2 As shown, this invention provides a technical solution: a geophysical exploration method for detecting groundwater using a non-traditional transient electromagnetic method, comprising the following operational steps:

[0028] S1: Thoroughly analyze the regional hydrogeological characteristics, including groundwater recharge, runoff, and discharge conditions, and combine this with drilling and basic geological data to determine the groundwater inlet / outlet W. A With W B Direction of water flow D W， Among them W A W is the upstream point of the karst conduit. B This is the downstream point of the karst conduit;

[0029] S2: Using groundwater as a good conductor, according to the electromagnetic induction theorem, when an alternating electric field is supplied to the groundwater system, a primary magnetic field is generated. When the current is suddenly cut off, an induced eddy current field is excited and a secondary field that propagates in the medium and varies with time and space is generated. The energized karst pipe forms an electromagnetic field source.

[0030] S3: Perpendicular to the direction of groundwater flow (D) W Set up measurement profiles P1, P2, P3, P4...P i ..., each profile P i Measuring points P are arranged at the same intervals. i1 P i2 P i3 Pi4 ...P ij ...;

[0031] S4: The observation equipment includes a transient electromagnetic instrument system and a transmission system. The transient electromagnetic instrument system generates a primary pulse magnetic field by inputting a step current into the ungrounded return line. When the power is off, it uses coils to measure the secondary field (induced voltage data) generated by the underground geological body that changes over time. The transmission system includes power supply equipment, electrodes, and underground karst water runoff. The power supply equipment provides pulse power supply with a power supply current of about 1200A and a power supply pulse width of 4ms.

[0032] S5: Before the power supply equipment supplies AC power to the groundwater system, measurements are carried out along the established measuring points using a transient electromagnetic instrument system to obtain the time-varying single-source induced voltage data SS at each measuring point. ij ;

[0033] S6: Electrodes A and B of the transmitting system are respectively placed at the groundwater inlet / outlet W. A With W B The transmitting system supplies alternating current to the groundwater through power supply equipment, operating synchronously with the transient electromagnetic system. Simultaneously, the transient electromagnetic instrument system conducts measurements along the deployed measuring points to obtain the SD data of the additional field source induced voltage at each measuring point after power supply. ij That is, the time-varying induced voltage data generated by different electric field sources transmitted through the underground medium;

[0034] S7: For each profile P i Additional field source induced voltage data SD at each measuring point ij Normalization processing is performed (divided by the single-source induced voltage data SS of the corresponding profile). ij Normalized additional field source induced voltage data (SDN) is obtained by averaging the values. ij ; Utilizing normalized additional field source induced voltage data SDN ij SS data of single-source induced voltage ij The difference is used to obtain the profile P for each section. i The induced voltage is abnormal; under normal circumstances, when there is a hidden karst pipeline, the measured induced voltage value changes significantly during the AC power supply to the groundwater system. The induced voltage anomaly profile curve of the measuring point in the influence range of the hidden karst pipeline shows a more dramatic change. Based on this characteristic, the induced voltage anomaly profile is delineated.

[0035] S8: For each profile P i Single-source induced voltage data SS ij Inversion was performed to obtain the single-field source apparent resistivity values ​​ρ for all profiles. S S i ; Using the mapping software Surfer, each profile P was analyzedi The apparent resistivity value ρ of a single field source S S i Interpolation is performed to generate an apparent resistivity profile anomaly map; the water-bearing karst conduit exhibits low resistivity characteristics relative to the surrounding rock, and the water-bearing development zone of the karst conduit is represented by a dense zone of low resistivity isolines or a low-value closed zone on the apparent resistivity profile map. Based on the above characteristics, the dense zone of low resistivity isolines or the low-value closed zone is delineated.

[0036] S9: Based on the hydrogeological characteristics of the work area, compare each profile P i The characteristics and distribution of induced voltage anomalies, dense low resistivity contours, or low-value closed zones in the delineated profiles are analyzed and compared to obtain the distribution and burial depth of karst conduits in each profile. Finally, by connecting the locations of karst conduits in all profiles, the planar location and direction of underground karst conduits can be deduced.

[0037] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0038] In summary, this non-traditional transient electromagnetic method for groundwater geophysical exploration utilizes the principle of electromagnetic induction and the good conductor property of groundwater to supply alternating current to the groundwater system, thereby forming a secondary field anomaly that varies with time and space. This secondary field anomaly is characterized by high amplitude and drastic changes, and has similar characteristics to electromagnetic interference signals. Therefore, it differs significantly from anomalies measured by transient electromagnetic instrument systems, making it easier to identify anomalies caused by underground karst conduits and reducing ambiguity.

[0039] It should be noted that all electrical components mentioned in this article are connected to an external main controller and 220V AC mains power. The main controller can be a conventional, known device such as a computer, and its control principles, internal structure, and control switching methods are all conventional methods of existing technology. These are directly cited here without further elaboration. In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A geophysical method for detecting groundwater using non-traditional transient electromagnetic methods, comprising the following operational steps: S1: Fully analyze the regional hydrogeological characteristics, including the groundwater recharge, runoff and discharge conditions in the area, and combine drilling and basic geological data to determine the groundwater inlet and outlet WA and WB, and the water flow direction DW; S2: Using groundwater as a good conductor, according to the electromagnetic induction theorem, when an alternating electric field is supplied to the groundwater system, a primary magnetic field is generated. When the current is suddenly cut off, an induced eddy current field is excited and a secondary field that propagates in the medium and varies with time and space is generated. The energized karst pipe forms an electromagnetic field source. S3: DW perpendicular to the direction of groundwater flow, set up measurement profiles P1, P2, P3, P4... Pi..., and set up measuring points Pi1, Pi2, Pi3, Pi4... Pij... at the same intervals along each profile Pi; S4: The observation equipment includes a transient electromagnetic instrument system and a transmission system; S5: Before the power supply equipment supplies AC power to the groundwater system, the transient electromagnetic instrument system is used to carry out measurement work along the set measurement points to obtain the single-field source induced voltage data SSij of each measurement point as time changes. S6: Electrodes A and B in the transmitting system are respectively placed at the groundwater inlet and outlet WA and WB. The transmitting system supplies AC power to the groundwater through the power supply equipment and works synchronously with the transient electromagnetic system. At the same time, the transient electromagnetic instrument system is used to carry out measurement work along the set measuring points to obtain the additional field source induced voltage data SDij of each measuring point after power supply, that is, the induced voltage data of different electric field sources transmitted through the underground medium that changes with time. S7: Normalize the additional field source induced voltage data SDij of each measuring point of each profile Pi to obtain normalized additional field source induced voltage data SDNij; use the difference between the normalized additional field source induced voltage data SDNij and the single field source induced voltage data SSij to obtain the induced voltage anomaly of each profile Pi; under normal conditions where there are hidden karst pipelines, the measured induced voltage anomaly value changes greatly during the AC power supply to the groundwater system. Therefore, the induced voltage anomaly profile curve of the measuring point in the influence range of the hidden karst pipeline shows a more dramatic change. Based on this characteristic, the profile induced voltage anomaly is delineated. S8: Invert the single-source induced voltage data SSij of each profile Pi to obtain the single-source apparent resistivity value ρSSi of all profiles; use the mapping software Surfer to interpolate the single-source apparent resistivity value ρSSi of each profile Pi to form an apparent resistivity profile anomaly map; the water-bearing karst conduit exhibits low resistivity characteristics relative to the surrounding rock, and the water-bearing development zone of the karst conduit is shown as a dense zone of low resistivity contour lines or a low-value closed zone on the apparent resistivity profile map. Based on the above characteristics, delineate the dense zone of low resistivity contour lines or the low-value closed zone. S9: Combining the hydrogeological characteristics of the work area, compare the characteristics and distribution of the profile induced voltage anomaly, dense low resistivity contour zones or low value closed zones delineated by each profile Pi, and obtain the distribution and burial depth of karst conduits for each profile through comparative analysis. Finally, connect the locations of karst conduits in all profiles to infer the planar location and direction of the underground karst conduits.

2. The geophysical exploration method for detecting groundwater using a non-traditional transient electromagnetic method according to claim 1, characterized in that: Where WA is the upstream point of the karst conduit and WB is the downstream point of the karst conduit.

3. The geophysical exploration method for detecting groundwater using a non-traditional transient electromagnetic method according to claim 1, characterized in that: The transient electromagnetic instrument system generates a primary pulse magnetic field by inputting a step current into the ungrounded return line. When the power is off, it uses a coil to measure the time-varying secondary field, i.e., the induced voltage data, generated by the underground geological body.

4. The geophysical exploration method for detecting groundwater using a non-traditional transient electromagnetic method according to claim 1, characterized in that: The transmission system includes power supply equipment, electrodes, and underground karst water runoff. The power supply equipment provides pulse power supply with a current of about 1200A and a pulse width of 4ms.

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