Method and system for electromagnetic frequency sounding of geothermal energy

Abstract

The application discloses a method and system for detecting geothermal energy by electromagnetic frequency sounding in an electromagnetic interference area, and comprises the following steps: collecting data of the electromagnetic interference area to predict key features of a target geological body, further determining the position and burying mode of field source AB electrodes, the transmitting-receiving distance between the field source AB electrodes and the MN electrodes in a detection area, and the direction and distance of the MN electrodes in the detection area; performing field test according to the position and burying mode of the field source AB electrodes, the transmitting-receiving distance, and the direction and distance of the MN electrodes in the detection area, and determining the parameter values of the key parameters according to the field test results; performing formal field production according to the parameter values of the key parameters, collecting complete data of the electromagnetic interference area; processing the complete data of the electromagnetic interference area to form a plurality of preliminary interpretation results, and finally interpreting the electromagnetic interference area in combination with the preliminary interpretation results. The application achieves the purpose of improving the applicability and result quality of the electromagnetic frequency sounding in the geothermal energy exploration.

Description

Technical Field

[0001] This invention relates to the field of geological exploration technology, specifically to a method and system for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones. Background Technology

[0002] The development and utilization of geothermal energy primarily serves industrial and agricultural production, residential life, and ecotourism, with development areas mostly located in and around highly urbanized regions. Urbanization brings dense populations, numerous buildings, numerous surface and underground engineering projects, and developed transportation, resulting in strong electromagnetic interference from fiber optic cables, high-voltage electricity, power lines, and the operation of mechanical equipment. These conditions make geothermal energy exploration difficult, rendering many geophysical exploration methods and technologies, such as gravity methods, magnetic methods, seismic methods, and magnetotellurics, ineffective.

[0003] Although artificial source electromagnetic frequency sounding can yield relatively good exploration results, on the one hand, the dense human-made buildings on the ground limit the construction of electromagnetic frequency sounding for geothermal energy exploration, affecting exploration efficiency and the quality of the collected exploration data. On the other hand, strong electromagnetic interference seriously affects the data from electromagnetic frequency sounding, thus affecting the results of geothermal energy exploration. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a method and system for electromagnetic frequency sounding in electromagnetic interference zones to detect geothermal energy. This method addresses the technical problems of existing technologies being limited by human-made structures and subject to electromagnetic interference when detecting geothermal energy, which affects exploration efficiency and the quality of collected exploration data. The goal is to improve the applicability and quality of electromagnetic frequency sounding in geothermal energy exploration.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows: A method for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones includes the following steps: Collect data on electromagnetic interference zones and predict key features of the target geological body based on the data on electromagnetic interference zones; Based on the data of the electromagnetic interference zone and the prediction results of the key features, determine the location and burial method of the field source AB electrode, the transmit / receive distance between the detection zone MN electrode and the field source AB electrode, and the direction and distance of the detection zone MN electrode; Field tests were conducted based on the location and burial method of the field source AB electrode, the transmit / receive distance, and the direction and distance of the detection area MN electrode, and the parameter values ​​of each key parameter were determined based on the field test results. Formal field production was conducted based on the parameter values ​​of the key parameters, and complete data of the electromagnetic interference zone was collected. The complete data of the electromagnetic interference zone is processed to form several preliminary interpretation results, and the electromagnetic interference zone is finally interpreted by combining the several preliminary interpretation results.

[0006] As a preferred embodiment of the present invention, when predicting the key features of the target geological body based on data from the electromagnetic interference zone, the method includes: Collect and analyze topographic, geological, hydrogeological, geothermal, and geophysical data of the electromagnetic interference zone to predict the maximum depth, apparent resistivity, and minimum frequency of the target geological body to be detected.

[0007] As a preferred embodiment of the present invention, predicting the lowest frequency at which the target geological body is detected includes: The minimum frequency at which the target geological body is detected is predicted using a depth calculation formula, specifically as follows: As shown in Equation 1:

[0008] In the formula, D is the effective detection depth in m, ρ is the formation resistivity in Ω·m, and f is the frequency in Hz.

[0009] In a preferred embodiment of the present invention, determining the location and embedding method of the field source AB electrode includes: The location of the interference source in the field source AB electrode layout area and the location of the field source AB electrode and the local electrical inhomogeneity in the electromagnetic interference interval are obtained; The field source AB electrodes are arranged to avoid the locations of the interference sources and the local electrical inhomogeneities. The actual grounding point of the field source AB electrode is set in a damp soil location. The distance between the A electrode and the B electrode is 1 to 3 km and multiple points are connected in parallel. The distance between adjacent electrode points is not less than 3 m.

[0010] In a preferred embodiment of the present invention, determining the transmit / receive distance between the detector region electrode MN and the source electrode AB includes: Determine whether the site conditions are limited. If so, set the transmit / receive distance to be greater than 3 times the detection depth. If not, set the transmit / receive distance to be greater than 2 times the detection depth.

[0011] In a preferred embodiment of the present invention, determining the direction and distance of the detector region MN electrode includes: Obtain the orientation of the field source AB electrode, and match the orientation of the detection region MN electrode according to the orientation of the field source AB electrode; The positions of interference sources and obstacles in the detection area MN electrode layout region are obtained, and the positions of interference sources and obstacles are avoided when the detection area MN electrodes are laid out.

[0012] In a preferred embodiment of the present invention, determining the parameter values ​​of each key parameter based on the results of field tests includes: A test range is preset for different key parameters. Different operating frequencies, distances between the field source AB electrodes, transmission current, transmission-reception distance, and electrode spacing of the detection area MN electrodes are selected in the test range to obtain several field test results. Based on the several field test results, appropriate parameter values ​​are selected for different key parameters. The key parameters include the operating frequency, the distance between the field source AB electrodes, the transmission current, the transmission-reception distance, and the electrode spacing of the detection area MN electrodes.

[0013] As a preferred embodiment of the present invention, during formal field production, the following is included: Obtain the frequency of the deepest target geological body, and set the data acquisition frequency according to the frequency of the deepest target geological body; The electromagnetic interference zone is detected based on the data acquisition frequency and the parameter values ​​of each key parameter. During the detection process, the position and orientation of the MN electrode in the detection zone are adjusted in a timely manner according to the position of the interference source and obstacles. Electromagnetic interference zone data is collected, the root mean square error of the electromagnetic interference zone data is obtained, and the original electric field-frequency curve is established. The quality of the electromagnetic interference region data is determined based on the root mean square error and the original electric field-frequency curve. If the quality is acceptable, the acquisition of complete electromagnetic interference region data is completed.

[0014] In a preferred embodiment of the present invention, the final interpretation of the electromagnetic interference zone includes: Electromagnetic interference suppression and filtering processes are performed on the complete data of the electromagnetic interference zone to obtain denoised data. Using the electric field data in the denoised data, and based on the positions of the field source AB electrode and the detector area MN electrode, the apparent resistivity over the entire period is obtained. Based on the apparent resistivity over the entire period, multi-frequency curves and apparent resistivity-frequency pseudo-section diagrams are plotted, dual-frequency induced polarization amplitude parameters are extracted, and a preliminary interpretation of the fracture structure and substrate is performed. Based on the multi-frequency curve and the apparent resistivity-frequency pseudo-section diagram, appropriate parameters are selected for static displacement correction. The multi-frequency curve and apparent resistivity pseudo-section diagram after static displacement correction are plotted to further interpret the fracture structure and the substrate, and the preliminary interpretation results of the fracture structure and the substrate are obtained. Electromagnetic frequency sounding parameters were extracted to perform preliminary interpretation and inversion of aquifer interfaces. The electromagnetic interference zone was then given a final interpretation based on the preliminary interpretation results of the fracture structure and the basement.

[0015] A system for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones includes: Prediction unit: used to collect data on the electromagnetic interference zone and predict the key features of the target geological body based on the data on the electromagnetic interference zone; Electrode setting unit: used to determine the position and embedding method of the field source AB electrode, the transmit / receive distance between the detection area MN electrode and the field source AB electrode, and the direction and distance of the detection area MN electrode based on the data of the electromagnetic interference zone and the prediction results of the key features; Parameter determination unit: used to conduct field tests based on the location and burial method of the field source AB electrode, the transmit / receive distance, and the direction and distance of the detection area MN electrode, and to determine the parameter values ​​of each key parameter based on the field test results; Interpretation Unit: Used to conduct formal field production based on the parameter values ​​of the key parameters, collect complete data of the electromagnetic interference area; process the complete data of the electromagnetic interference area to form several preliminary interpretation results, and combine the several preliminary interpretation results to perform the final interpretation of the electromagnetic interference area.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention forms a set of technical processes for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones. It can effectively solve the technical problems of existing technologies being limited by human buildings and electromagnetic interference when detecting geothermal energy, and improve the applicability and quality of electromagnetic frequency sounding in geothermal energy exploration. (2) This invention provides a basic guarantee for the development and utilization of geothermal energy and gives full play to the role of geophysical exploration technology in achieving the national "dual carbon" goal.

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0018] Figure 1 - This is a tectonic unit division map of the Guanzhong Basin, the study area of ​​this invention; Figure 2 - is a schematic diagram of the fracture in the study area according to an embodiment of the present invention; Figure 3 - is a physical diagram of the wide-area electromagnetic instrument signal transmitter device according to an embodiment of the present invention; Figure 4 - is a schematic diagram showing the location of the electromagnetic frequency sounding points in the study area according to an embodiment of the present invention; Figure 5 - is a multi-frequency curve of the potential difference between the receiving electrodes MN of line 1 in an embodiment of the present invention; Figure 6 - is the apparent resistivity-frequency pseudo-section diagram of line 1 in an embodiment of the present invention; Figure 7 - is the apparent resistivity-frequency pseudo-section diagram of line 1 after static displacement correction according to an embodiment of the present invention; Figure 8 - is a cross-sectional view of the inverted resistivity of line 1 in an embodiment of the present invention; Figure 9 - is a simulated seismic profile of line 1 in an embodiment of the present invention; Figure 10 - is a transient electromagnetic resistivity cross-sectional view of line 1 in an embodiment of the present invention; Figure 11 - This is an amplitude-frequency curve extracted using two frequencies in one line according to an embodiment of the present invention; Figure 12 - is a simulated seismic profile of the two lines in an embodiment of the present invention; Figure 13 - This is a flowchart illustrating the steps of a method for detecting geothermal energy in an electromagnetic interference zone using electromagnetic frequency sounding, according to an embodiment of the present invention. Detailed Implementation

[0019] The method for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones provided by this invention, such as... Figure 13 As shown, it includes the following steps: Step S1: Collect data on the electromagnetic interference zone and predict the key features of the target geological body based on the data on the electromagnetic interference zone; Step S2: Based on the data of the electromagnetic interference zone and the prediction results of key features, determine the location and burial method of the field source AB electrode, the transmit / receive distance between the detection zone MN electrode and the field source AB electrode, and the direction and distance of the detection zone MN electrode; Step S3: Conduct field tests based on the location and burial method of the field source AB electrode, the transmit / receive distance, and the direction and distance of the detector MN electrode, and determine the parameter values ​​of each key parameter based on the field test results; Step S4: Conduct formal field production based on the parameter values ​​of key parameters and collect complete data of the electromagnetic interference area; Step S5: Process the complete data of the electromagnetic interference area to form several preliminary interpretation results, and combine these preliminary interpretation results to make a final interpretation of the electromagnetic interference area.

[0020] In step S1 above, when predicting the key features of the target geological body based on data from the electromagnetic interference zone, the following steps are included: Collect and analyze topographic, geological, hydrogeological, geothermal, and geophysical data of the electromagnetic interference zone to predict the maximum depth, apparent resistivity, and minimum frequency of the target geological body to be detected.

[0021] Furthermore, when predicting the minimum frequency at which the target geological body can be detected, this includes: The minimum frequency of detecting the target geological body is predicted using the depth calculation formula, as shown in Formula 1: (1) In the formula, D is the effective detection depth in m, ρ is the formation resistivity in Ω·m, and f is the frequency in Hz.

[0022] In step S2 above, determining the location and installation method of the field source AB electrode includes: Obtain the location of the interference source in the field source AB electrode layout area, as well as the location of the field source AB electrode and the local electrical inhomogeneities in the electromagnetic interference zone; The field source AB electrodes are arranged to avoid the locations of interference sources and local electrical inhomogeneities; The actual grounding point of the field source AB electrode is set in a damp soil area. The distance between the A electrode and the B electrode is 1-3 km and multiple points are connected in parallel. The distance between adjacent electrode points is not less than 3 m.

[0023] Furthermore, the electrode materials can be selected from multiple metal rods or multiple metal plates, meshes, foils, etc., and can be driven into the ground by hammering or buried in several electrode pits. The placement of the field source AB electrodes should avoid high-voltage lines, mines (tunnels), buried pipelines, streams, and parallel fracture structures as much as possible to reduce electromagnetic interference. The placement of the field source AB electrodes should also consider avoiding known mines, lakes, caves, and other local electrical inhomogeneities between the AB electrodes and the detection area (data acquisition area).

[0024] In step S2 above, determining the transmit / receive distance between the detector region electrode MN and the source electrode AB includes: Determine if the site conditions are limited. If so, set the transmit / receive distance to be greater than 3 times the detection depth. If not, set the transmit / receive distance to be greater than 2 times the detection depth.

[0025] Furthermore, given that the transmit / receive distance meets the above conditions, the transmit / receive distance should be minimized as much as possible to improve the signal-to-noise ratio of the collected data.

[0026] In step S2 above, determining the direction and distance of the detector region MN electrode includes: Obtain the orientation of the field source electrode AB, and match the orientation of the detector electrode MN according to the orientation of the field source electrode AB. The positions of interference sources and obstacles in the MN electrode deployment area of ​​the detection zone are obtained, and the MN electrodes are deployed in the detection zone while avoiding the positions of interference sources and obstacles.

[0027] Furthermore, while avoiding interference sources and obstacles, try to detect electromagnetic interference from known high-voltage lines, power lines, optical fibers, etc., in the detection area vertically.

[0028] In step S3 above, when determining the parameter values ​​of each key parameter based on the field test results, the following is included: For different key parameters, a test range is preset. Within the test range, different operating frequencies, distances between the field source AB electrodes, transmission current, transmission-reception distance, and electrode spacing of the detector area MN electrodes are selected to obtain several field test results. Based on these field test results, appropriate parameter values ​​are selected for different key parameters. Key parameters include operating frequency, distance between the source AB electrodes, transmission current, transmission-reception distance, and electrode spacing of the detector region MN electrodes.

[0029] Furthermore, field tests are conducted based on the design and engineering layout. The goal of the field tests is to select appropriate parameter values ​​to complete the target mission of the detection.

[0030] In step S4 above, during formal field production, the following is included: Obtain the frequency of the deepest target geological body, and set the data acquisition frequency based on the frequency of the deepest target geological body; The electromagnetic interference zone is detected based on the data acquisition frequency and the parameter values ​​of each key parameter. During the detection process, the position and orientation of the MN electrode in the detection zone are adjusted in a timely manner according to the location of the interference source and obstacles. Electromagnetic interference zone data is collected, the root mean square error of the electromagnetic interference zone data is obtained, and the original electric field-frequency curve is established. The quality of the data in the electromagnetic interference area is determined based on the root mean square error and the original electric field-frequency curve. If the data is satisfactory, the acquisition of complete data in the electromagnetic interference area is completed.

[0031] Furthermore, in order to extract the frequency parameters of the dual-frequency induced polarization amplitude, the data acquisition frequency should have two frequencies that are less than the frequency required to detect the deepest geological target.

[0032] Specifically, during formal field production, data quality monitoring and adjustment of the MN electrode orientation are crucial. This requires monitoring the electric field data at each frequency, ensuring the root mean square error of multiple superimposed field data meets design requirements, plotting the apparent resistivity curve for the entire period based on the day's field data at each measurement point, and randomly checking the original electric field-frequency curves to evaluate data quality. Based on the sources of electromagnetic interference and obstacles in the field, the position and orientation of the MN electrodes must be adjusted promptly to suppress electromagnetic interference from voltage lines, power lines, and optical fibers. Complete data must be collected for the electromagnetic interference zone, and the coordinates of each M and N electrode must be measured for subsequent data processing.

[0033] In step S5 above, the final interpretation of the electromagnetic interference zone includes: Electromagnetic interference suppression and filtering processes are applied to the complete data in the electromagnetic interference zone to obtain denoised data. Using the electric field data in the denoised data, and based on the positions of the field source electrode AB and the probe electrode MN, the apparent resistivity for the entire period is obtained. Multi-frequency curves and apparent resistivity-frequency pseudo-section diagrams are plotted based on the apparent resistivity for the entire period. The frequency parameters of the dual-frequency induced polarization amplitude are extracted, and a preliminary interpretation of the fracture structure and the substrate is performed. Based on the multi-frequency curves and apparent resistivity-frequency pseudo-section diagrams, appropriate parameters are selected for static displacement correction. The multi-frequency curves and apparent resistivity pseudo-section diagrams after static displacement correction are plotted, and the fracture structure and basement are further preliminarily interpreted to obtain the preliminary interpretation results of the fracture structure and basement. Electromagnetic frequency sounding parameters were extracted to perform preliminary interpretation and inversion of aquifer interfaces. Finally, the electromagnetic interference zone was interpreted by combining the preliminary interpretation results of fault structures and the basement.

[0034] Furthermore, the final explanation includes: tectonics, aquifer interfaces, and anomalies in water-rich areas.

[0035] The system for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones provided by this invention includes: a prediction unit, an electrode setting unit, a parameter determination unit, and an interpretation unit.

[0036] The prediction unit is used to collect data on the electromagnetic interference zone and predict the key features of the target geological body based on the data on the electromagnetic interference zone.

[0037] The electrode setting unit is used to determine the location and embedding method of the field source AB electrode, the transmit / receive distance between the detection area MN electrode and the field source AB electrode, and the direction and distance of the detection area MN electrode based on the data of the electromagnetic interference zone and the prediction results of key characteristics.

[0038] The parameter determination unit is used to conduct field tests based on the location and burial method of the field source AB electrode, the transmit / receive distance, and the direction and distance of the detector MN electrode, and to determine the parameter values ​​of each key parameter based on the field test results.

[0039] The interpretation unit is used to conduct formal field production based on the parameter values ​​of key parameters and collect complete data of the electromagnetic interference area; it processes the complete data of the electromagnetic interference area to form several preliminary interpretation results, and combines these preliminary interpretation results to perform the final interpretation of the electromagnetic interference area.

[0040] The following examples further illustrate the present invention, but the scope of the invention is not limited thereto. Example (Application of Electromagnetic Frequency Sounding in Geothermal Energy Detection in Hancheng, Shaanxi) I. Geological conditions for geothermal energy 1. Stratigraphy The geothermal energy reservoir in Hancheng, Shaanxi Province, is located in the Ordovician limestone of the Paleozoic era, overlain by the Carboniferous and Permian strata of the Paleozoic era, the Triassic strata of the Mesozoic era, and the Neogene and Quaternary strata of the Cenozoic era, with a caprock thickness of approximately 2500 m. A brief description of the strata from oldest to youngest is as follows: (1) Paleozoic Ordovician (O) This area forms the basement, deeper in the north and shallower in the south, thicker in the north and thinner in the south. The upper part is mainly composed of thin, tabular, and shale-like limestone, interbedded with tuff and breccia limestone; the middle and lower parts are mainly limestone and dolomite, locally interbedded with marl, calcareous shale, and siliceous dolomite.

[0041] (2) Paleozoic Carboniferous System (C) This area forms the basement, deeper in the north and shallower in the south, thicker in the north and thinner in the south. The upper part consists of light gray sandy mudstone interbedded with claystone, containing coal seams, and the bottom of the sandy mudstone contains Shanxi-type pyrite nodules; the lower part consists of light gray claystone interbedded with coal seams, gray-black massive mudstone, and gray sandy mudstone.

[0042] (3) Paleozoic Permian (P) Buried beneath the Triassic system, it is deeper in the north and shallower in the south, and thicker in the north and thinner in the south. The upper part is mainly composed of dark red mudstone, gray-green fine sandstone, gray-black mudstone, siltstone, and medium-coarse sandstone; the lower part is mainly composed of variegated mudstone, dark gray and blackish-gray medium-fine sandstone, siltstone, and sandy mudstone.

[0043] (4) Mesozoic Triassic (T) Buried beneath Neogene strata, it is deeper in the north and shallower in the south, and thicker in the north and thinner in the south. The upper part is mainly composed of purplish-red, brownish-red, and grayish-green siltstone, mudstone, and thin-layered sandstone in yellowish-green, grayish-green, and purplish-gray; the lower part is mainly composed of grayish-green sandstone with well-developed cross-bedding, interbedded with brownish-red mudstone.

[0044] (5) Newly Recent Series (N) Buried beneath the Quaternary system, it is deeper in the north and shallower in the south, and thicker in the north and thinner in the south. The lithology is mainly purplish-red clay, interbedded with cemented and semi-cemented silty sand and gravel layers, containing a large number of calcareous nodules.

[0045] (6) The Fourth Department of the New Generation (Q) It mainly consists of Pleistocene and Holocene strata, overlying Neogene strata. The lithology is mainly light yellow and grayish-yellow silty clay and silty clay, interbedded with medium and fine sand and gravel layers.

[0046] 2. Structural features The study area is tectonically located at the junction of the southeastern edge of the Ordos Block and the Fenwei Graben, specifically as follows: Figure 1 As shown, the Pucheng Uplift is subdivided into the Weihe Graben Basin, and is adjacent to the Gushi Depression in the south, with the Kouzhen-Guanshan Fault as the boundary.

[0047] According to regional geological data, the Hancheng Fault F1 is a well-developed fault in the area, specifically as follows: Figure 2As shown. The Hancheng Fault F1 is the largest fault in the region. This piedmont fault extends 26 kilometers from Yumenkou in the northeast to Xinzhuang in Longtingyuan in the southwest, running through the entire region. It is mainly a normal fault, with the fault plane exhibiting a gently wavy pattern along its strike and dip. The strike is NE20-50°, the dip is southeast, the dip angle is greater than 60°, and the displacement exceeds 500 meters. This fault forms the boundary between the Beishan Mountains and the Guanzhong Plain. The area southeast of the fault has continuously subsided, accumulating hundreds of meters of thick Quaternary loose sediments. The terrain is gentle, forming the northeastern part of the Weihe Graben, which has good caprock heat storage conditions. The terrain northwest of the fault is high and steep, consisting of thick rock strata and overlying Quaternary loose sediments forming a fault block topography. The strata exposed west of the fault are mainly Ordovician limestone and Triassic sandstone and mudstone.

[0048] II. Implementation of Electromagnetic Frequency Depth Sounding 1. Field construction The electromagnetic frequency sounding exploration was carried out in three phases over the course of a year, using a wide-area electromagnetic instrument system jointly developed by Hunan Jishan High Technology Co., Ltd. and Central South University. The main equipment included a wide-area electromagnetic transmitter, a wide-area electromagnetic receiver, and a high-power generator.

[0049] 1.1 Launch site source The wide-area electromagnetic transmitter consists of three parts: a high-power diesel AC generator, a rectifier-inverter, and a pseudo-random signal transmission controller. The transmitter system, through the rectifier cabinet and under the action of the pseudo-random signal generator, generates a high-energy pseudo-random signal and supplies power underground, specifically as follows... Figure 3 As shown.

[0050] The signal source of the wide-area electromagnetic transmitter is 2 n The sequence pseudo-random signal allows for the selection of different signal frequencies according to exploration needs, and currently can transmit seven frequencies simultaneously, fulfilling the requirement of simultaneous measurement at multiple frequencies and greatly improving exploration efficiency. The main technical specifications are as follows: 1) Voltage range: <1000V; 2) Current range: <200A; 3) Frequency range: 0.0117~8192HZ.

[0051] Four different field sources were used in the three explorations, with the distance between the transmitting electrodes A and B being approximately 1 km in each exploration. Electrodes A and B consisted of 18 aluminum foil plates (approximately 1m × 1m), which were buried in 18 electrode pits dug. The pits were at least 0.6m deep, and the distance between adjacent pits was at least 3m. Conductive liquid (sodium chloride solution) was poured onto the aluminum foil plates to reduce the grounding resistance of the AB field sources, resulting in a final transmitting current of approximately 120A.

[0052] 1.2 Data Acquisition The wide-area electromagnetic exploration receiving system mainly consists of a wide-area electromagnetic instrument receiver, receiving electrodes, and a computer workstation. The specific specifications of the wide-area electromagnetic instrument receiver are as follows: 1) Analog-to-digital converter resolution: 24-bit; 2) Analog-to-digital converter speed: greater than 600KSPS; 3) Signal input range: -37.5mV to +37.5mV; 4) Signal frequency range: 0.0117Hz~10KHz; 5) Detection sensitivity: ≥0.05mV; 6) Potential difference measurement accuracy: ±0.5%; 7) Input impedance: 3MΩ; 8) Fixed gain: 100x.

[0053] The Ordovician limestone in the study area is about 2900m deep, and the geothermal energy detection depth requirement is 4000m. Therefore, the 11, 9, 7, 5, 3 and 1 frequency groups of the 7-frequency wave of the wide-area electromagnetic instrument were selected for power supply and data acquisition. The highest frequency is 8192Hz and the lowest frequency is 0.0117Hz, for a total of 40 frequency points.

[0054] 2. Project Layout Figure 4 This is a schematic diagram showing the location of electromagnetic frequency sounding points in the study area. Figure 4 It can be seen that the three construction projects were conducted at certain distances from each other. The first construction site was located in the northeastern urban-rural fringe area of ​​Hancheng City, with one survey line (named Line 1) 3km long, a point spacing and MN electrode spacing of 100m, and 31 frequency sounding points. One transmitting source was located in the southwest of the city, with a transmit-receive distance of approximately 12km, and the area between the source and receiver points was Hancheng City. Transient electromagnetic exploration was also conducted simultaneously, with a point spacing of 25m and 121 measuring points.

[0055] The second construction site was located approximately 1.2 km southwest of the first site, already within the urban area. Two measurement lines (designated lines 2 and 3) were laid out along the streets of the city, forming a broken line. The point spacing and MN electrode spacing varied from 50 to 100 meters, and 64 frequency sounding points were completed. One transmitting source was located not far from the first source location, with a transmit-receive distance of approximately 11 km. The area between the source and the receiving point was the urban area of ​​Hancheng City.

[0056] The third survey site was located south of the first and second sites, approximately 2.4 km from the second site. Situated between the urban area and the Yellow River, it involved three survey lines (named lines 4, 5, and 6), with a point spacing and MN electrode spacing of approximately 100 m, completing 51 frequency sounding points. The third survey utilized two field sources and conducted exploration studies using multiple methods.

[0057] III. Geothermal Energy Exploration Results Figure 5 This is a multi-frequency curve of the potential difference (normalized transmit current) between the receiving electrodes M and N of line 1, showing three frequency bands from top to bottom. A high-voltage line is present at point 2750, and the voltage in the high-frequency band is significantly higher than that in the 2000-2500 band. In the low-frequency band, the multi-frequency curve shows that the voltage at smaller points is higher than that at larger points. The undulating shape of the curve reflects the high-resistivity basement of the Ordovician limestone, with shallower burial depth in the northwest and greater burial depth in the southeast.

[0058] Figure 6 It is the apparent resistivity-frequency pseudo-profile of line 1, from Figure 6 It can be seen that the static displacement of measuring points such as 800, 1200, 1700, 2400, and 2600 is obvious. Figure 7 This is a pseudo-section of apparent resistivity-frequency after static displacement correction of line 1. The corrected apparent resistivity contour lines basically reflect the undulations of the strata and provide a more intuitive display of the shallow in the northwest and deep in the southeast of the high resistivity basement of the Ordovician limestone.

[0059] Figure 8 This is the inversion resistivity profile of line 1. Figure 8 The data provides resistivity at different locations in the underground space. Based on the resistivity distribution characteristics, an electrical stratification interpretation is performed. The strata above elevations of -1700 to -1400 m have low resistivity, which is interpreted as the lower boundary of the Cenozoic (Neogene) strata. The Ordovician limestone has an elevation between -2750 and -2250 m, with a significant low resistivity anomaly at point 1500, which is interpreted as a fault.

[0060] Figure 9 This is a simulated seismic profile of the first line. Figure 9 The chosen reference level is 450m. Using the resulting pseudo-seismic profile for visualization allows for a more precise interpretation of electrical stratigraphic boundaries, faults, and other structural features. Three faults were identified near the Ordovician limestone interface: one large fault and two small faults. Figure 10 This is a transient electromagnetic resistivity profile of line 1. Figure 10 This can roughly explain the location of the top interface of Ordovician limestone and explain four water-rich anomaly zones in Ordovician limestone.

[0061] Figure 11 The amplitude-frequency curve is extracted using two frequencies for line 1. The amplitude-frequency at point 800 is the largest, exceeding the average value of 0.46. The amplitude-frequency near point 2000 is the second largest, with three measuring points having values ​​greater than 0.46, indicating areas with relatively high water content.

[0062] Based on the inverted resistivity profile, simulated seismic profile, dual-frequency amplitude curves, and transient electromagnetic exploration results, the geothermal well location was recommended to the client at borehole 2000. Following this recommendation, the client drilled borehole DRJ3 at borehole 2000, reaching a depth of 2904m at the Ordovician limestone top interface, with a wellhead water yield of 60m³.3 The water output was 82℃ / h, exceeding expectations in both flow rate and temperature, and has already been used for geothermal heating. The wellhead water temperature of DRJ1, located 400 meters away from DRJ3, was only 56℃.

[0063] Figure 12 This is a simulated seismic profile of the second line. Figure 12 The Ordovician limestone is buried at a depth of about 2800m, which is shallower than that of Line 1. The undulating morphology of the top interface of the Ordovician limestone and the bottom interface of the Cenozoic strata is similar to that of Line 1, generally showing a higher elevation in the northwest and a lower elevation in the southeast.

[0064] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones, characterized in that, Includes the following steps: Collect data on electromagnetic interference zones and predict key features of the target geological body based on the data on electromagnetic interference zones; Based on the data of the electromagnetic interference zone and the prediction results of the key features, determine the location and burial method of the field source AB electrode, the transmit / receive distance between the detection zone MN electrode and the field source AB electrode, and the direction and distance of the detection zone MN electrode; Field tests were conducted based on the location and burial method of the field source AB electrode, the transmit / receive distance, and the direction and distance of the detection area MN electrode, and the parameter values ​​of each key parameter were determined based on the field test results. Formal field production was conducted based on the parameter values ​​of the key parameters, and complete data of the electromagnetic interference zone was collected. The complete data of the electromagnetic interference zone is processed to form several preliminary interpretation results, and the electromagnetic interference zone is finally interpreted by combining the several preliminary interpretation results. The final interpretation of the electromagnetic interference zone includes: Electromagnetic interference suppression and filtering processes are performed on the complete data of the electromagnetic interference zone to obtain denoised data. Using the electric field data in the denoised data, and based on the positions of the field source AB electrode and the detector area MN electrode, the apparent resistivity over the entire period is obtained. Based on the apparent resistivity over the entire period, multi-frequency curves and apparent resistivity-frequency pseudo-section diagrams are plotted, dual-frequency induced polarization amplitude parameters are extracted, and a preliminary interpretation of the fracture structure and substrate is performed. Based on the multi-frequency curve and the apparent resistivity-frequency pseudo-section diagram, appropriate parameters are selected for static displacement correction. The multi-frequency curve and apparent resistivity pseudo-section diagram after static displacement correction are plotted to further interpret the fracture structure and the substrate, and the preliminary interpretation results of the fracture structure and the substrate are obtained. Electromagnetic frequency sounding parameters were extracted to perform preliminary interpretation and inversion of aquifer interfaces. The electromagnetic interference zone was then given a final interpretation based on the preliminary interpretation results of the fracture structure and the basement.

2. The method for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones according to claim 1, characterized in that, When predicting key features of the target geological body based on data from the electromagnetic interference zone, the following are included: Collect and analyze topographic, geological, geothermal, and geophysical data of the electromagnetic interference zone to predict the maximum depth, apparent resistivity, and minimum frequency of the target geological body to be detected.

3. The method for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones according to claim 2, characterized in that, When predicting the minimum frequency at which the target geological body can be detected, the following are included: The minimum frequency at which the target geological body is detected is predicted using a depth calculation formula, as shown in Formula 1: D=365 （1）； In the formula, D is the effective detection depth in m, ρ is the formation resistivity in Ω·m, and f is the frequency in Hz.

4. The method for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones according to claim 1, characterized in that, When determining the location and installation method of the field source AB electrodes, the following should be included: The location of the interference source in the field source AB electrode layout area and the location of the field source AB electrode and the local electrical inhomogeneity in the electromagnetic interference area are obtained; The field source AB electrodes are arranged to avoid the locations of the interference sources and the local electrical inhomogeneities. The actual grounding point of the field source AB electrode is set in a damp soil location. The distance between the A electrode and the B electrode is 1 to 3 km and multiple points are connected in parallel. The distance between adjacent electrode points is not less than 3 m.

5. The method for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones according to claim 1, characterized in that, When determining the transmit / receive distance between the detector electrode MN and the source electrode AB, the following is included: Determine if the site conditions are limited. If so, set the transmit / receive distance to be greater than 3 times the detection depth. If not, set the transmit / receive distance to be greater than 2 times the detection depth.

6. The method for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones according to claim 1, characterized in that, When determining the orientation and distance of the MN electrode in the detection region, the following are included: Obtain the orientation of the field source AB electrode, and match the orientation of the detection region MN electrode according to the orientation of the field source AB electrode; The positions of interference sources and obstacles in the detection area MN electrode layout region are obtained, and the positions of interference sources and obstacles are avoided before the detection area MN electrodes are laid out.

7. The method for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones according to claim 1, characterized in that, When determining the values ​​of key parameters based on field test results, the following should be included: A test range is preset for different key parameters. Different operating frequencies, distances between the field source AB electrodes, transmission current, transmission-reception distance, and electrode spacing of the detection area MN electrodes are selected in the test range to obtain several field test results. Based on the several field test results, appropriate parameter values ​​are selected for different key parameters. The key parameters include the operating frequency, the distance between the field source AB electrodes, the transmission current, the transmission-reception distance, and the electrode spacing of the detection area MN electrodes.

8. The method for electromagnetic frequency sounding to detect geothermal energy in an electromagnetic interference zone according to claim 1, characterized in that, During formal field production, this includes: Obtain the frequency of the deepest target geological body, and set the data acquisition frequency according to the frequency of the deepest target geological body; The electromagnetic interference zone is detected based on the data acquisition frequency and the parameter values ​​of each key parameter. During the detection process, the position and orientation of the MN electrode in the detection zone are adjusted in a timely manner according to the position of the interference source and obstacles. Electromagnetic interference zone data is collected, the root mean square error of the electromagnetic interference zone data is obtained, and the original electric field-frequency curve is established. The quality of the electromagnetic interference zone data is determined based on the root mean square error and the original electric field-frequency curve. If the quality is acceptable, the acquisition of complete electromagnetic interference zone data is completed.

9. A system for electromagnetic frequency sounding to detect geothermal energy in electromagnetic interference zones, characterized in that, A method for implementing the electromagnetic frequency sounding method for geothermal energy detection in an electromagnetic interference zone as described in any one of claims 1-8, comprising: Prediction unit: used to collect data on the electromagnetic interference zone and predict the key features of the target geological body based on the data on the electromagnetic interference zone; Electrode setting unit: used to determine the position and embedding method of the field source AB electrode, the transmit / receive distance between the detection area MN electrode and the field source AB electrode, and the direction and distance of the detection area MN electrode based on the data of the electromagnetic interference zone and the prediction results of the key features; Parameter determination unit: used to conduct field tests based on the location and burial method of the field source AB electrode, the transmit / receive distance, and the direction and distance of the detection area MN electrode, and to determine the parameter values ​​of each key parameter based on the field test results; Interpretation Unit: Used to conduct formal field production based on the parameter values ​​of the key parameters, collect complete data of the electromagnetic interference area; process the complete data of the electromagnetic interference area to form several preliminary interpretation results, and combine the several preliminary interpretation results to perform the final interpretation of the electromagnetic interference area.

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