An exploration device and calculation method based on frequency domain electromagnetic method

Abstract

The present invention discloses a prospecting device and a calculation method based on the frequency-domain electromagnetic method. The prospecting device includes an electromagnetic transmitting device, three electromagnetic receiving devices, a controller, and a fixing device. The three electromagnetic receiving devices are all arranged on the same horizontal plane as the electromagnetic transmitting device. The controller is electrically connected to the electromagnetic transmitting device and the three electromagnetic receiving devices respectively. The three electromagnetic receiving devices and the electromagnetic transmitting device are fixed on the same horizontal plane through the fixing device. The calculation method includes calculating the horizontal gradient of the induced electromotive force of the secondary field, the conductivity, and the horizontal gradient · conductivity. By calculating the parameter of the horizontal gradient · conductivity, the present invention highlights and amplifies low-resistivity abnormal geological bodies such as metals and water-containing structures, which is more conducive to the accurate judgment of abnormal geological bodies. By using one transmitting coil and three receiving coils to realize the transceiver integration of the frequency-domain electromagnetic method detection device, the device is more portable.

Description

Technical Field

[0001] The present invention belongs to the technical field of geophysical exploration, and specifically relates to an exploration device and a calculation method based on frequency domain electromagnetic method. Background Art

[0002] The active source portable frequency domain electromagnetic method has been applied in urban geological exploration and environmental geological surveys, and good results have been achieved. Currently, the main equipment capable of carrying out the active source portable frequency domain electromagnetic method are the Gem-2 series products of Geophex Company in the United States and the EM34 series products produced in Canada. The Gem-2 product calculates PPM (which does not represent any physical meaning) through 1 transmitting coil, 1 reference coil and 1 receiving coil, and judges the detected abnormal object by comparing the numerical size of PPM. The EM34 product approximately calculates the conductivity through 1 transmitting coil and 1 receiving coil, and detects geological bodies by comparing the magnitudes of the approximate conductivities. The above equipment can identify abnormal geological bodies, such as faults, lithological interfaces, etc. When passing through abnormal geological bodies, the detected values will change significantly compared with those of normal geological bodies, and thus the abnormal geological bodies can be identified. Conductivity is an inherent electrical property parameter of geological bodies, that is, the conductivities of different geological bodies usually have differences, and the conductivity of the same stratum also has a certain variation range. When passing through a fault or a lithological interface, the horizontal gradient usually changes greatly and the conductivity increases. At present, the frequency domain electromagnetic method equipment does not comprehensively consider horizontal gradient detection and conductivity detection, and it is difficult to achieve more accurate identification and judgment of abnormal geology detection.

[0003] In view of this, the present invention is specifically proposed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide an exploration device and a calculation method based on frequency domain electromagnetic method. The basic concept of the technical solution adopted by the present invention to solve the above technical problems is:

[0005] An exploration device based on frequency domain electromagnetic method includes an electromagnetic emission device, three electromagnetic reception devices, and a controller. The three electromagnetic reception devices are all arranged on the same horizontal plane along with the electromagnetic emission device, and the controller is electrically connected to the electromagnetic emission device and the three electromagnetic reception devices respectively.

[0006] Furthermore, it further includes a fixing device, and the three electromagnetic reception devices are fixed on the same horizontal plane with the electromagnetic emission device through the fixing device.

[0007] Further, the electromagnetic emission device is a transmitting coil, and the electromagnetic receiving device is a receiving coil. The fixing device includes an upper long strip skeleton, a lower long strip skeleton, and a coil skeleton. The upper long strip skeleton and the lower long strip skeleton are arranged in parallel, the coil skeleton is fixed on the upper long strip skeleton and the lower long strip skeleton, and the transmitting coil and the receiving coil are respectively wound on the coil skeleton.

[0008] Further, the three electromagnetic receiving devices are respectively a first receiving coil, a second receiving coil, and a third receiving coil. The first receiving coil and the transmitting coil are arranged in concentric circles, the diameter of the transmitting coil is larger than the diameter of the first receiving coil, and the centers of the second receiving coil and the third receiving coil are both arranged on the same straight line as the center of the transmitting coil, and are respectively arranged on both sides of the transmitting coil.

[0009] Further, the coil skeleton includes a transmitting coil skeleton, a first receiving coil skeleton, a second receiving coil skeleton, and a third receiving coil skeleton. The transmitting coil is wound on the transmitting coil skeleton, the first receiving coil, the second receiving coil, and the third receiving coil are sequentially wound on the first receiving coil skeleton, the second receiving coil skeleton, and the third receiving coil skeleton, and the centers of the first receiving skeleton, the second receiving skeleton, and the third receiving skeleton are arranged in a straight line.

[0010] Further, the upper long strip skeleton, the lower long strip skeleton, and the coil skeleton are all made of PVC material. The transmitting coil uses a single-core wire, and the receiving coils all use enameled wires.

[0011] Further, the number of turns of the first receiving coil is 600 turns, and the number of turns of the second receiving coil and the third receiving coil are both 900 turns.

[0012] Further, the inner diameter of the transmitting coil skeleton is 480 mm, the outer diameter is 500 mm. The inner diameters of the first receiving coil skeleton, the second receiving coil skeleton, and the third receiving coil skeleton are all 230 mm, and the outer diameters are all 250 mm. The distance between the center of the second receiving coil and the center of the transmitting coil is 500 mm. The second receiving coil and the third receiving coil are symmetrically arranged on both sides of the transmitting coil. The thicknesses of the upper long strip skeleton and the lower long strip skeleton are both 20 mm, and the distance between adjacent two sides is 100 mm.

[0013] The calculation method for geological exploration using the exploration device includes the following steps:

[0014] Step 1, supply power to the transmitting coil through the external frequency transmitter of the controller;

[0015] Step 2, data acquisition, synchronously measure the potentials of the first receiving coil, the second receiving coil, and the third receiving coil;

[0016] Step 3, preliminary data processing, perform Fourier transform on the measured data;

[0017] Step 4, calculate the induced electromotive force horizontal gradient Hg, conductivity σ, and horizontal gradient - conductivity Hm of the secondary field, including the following steps:

[0018] Step 401, the first receiving coil collects the induced electromotive force V1, the second receiving coil collects the induced electromotive force V2, and the third receiving coil collects the induced electromotive force V3;

[0019] Step 402, calculate the induced electromotive force horizontal gradient Hg of the secondary field, and the formula is as follows:

[0020]

[0021] In the formula, Hs2 represents the secondary field magnetic field intensity of the second receiving coil, Hs3 represents the secondary field magnetic field intensity of the third receiving coil, and L represents the distance between the second receiving coil and the third receiving coil;

[0022] Step 403, calculate the conductivity, which can be approximately calculated by the following formula:

[0023]

[0024] In the formula, ω is the angular frequency; μ0 is the magnetic permeability in vacuum; s is the distance between the transmitting and receiving coils; Hp3 represents the primary field magnetic field intensity of the third receiving coil;

[0025] Step 404, calculate the horizontal gradient - conductivity Hm:

[0026] Hm = Hg·σ;

[0027] Step 5, the controller analyzes and processes the data and feeds it back to realize the judgment of abnormal geological detection.

[0028] Further, the transmission frequency of the frequency transmitter is 100Hz - 10kHz.

[0029] Further, the number of turns of the second receiving coil and the third receiving coil is the same, and the induced electromotive force of the primary field is equal, then:

[0030] V3 - V2 = Hp3 + Hs3 - Hp2 - Hs2 = Hs3 - Hs2

[0031] When the transmitting coil is powered, it satisfies:

[0032]

[0033] Hp1 = Hp2 + Hp3

[0034] Hp2 = Hp3

[0035] At this time, the primary field induced electromotive forces generated inside and outside the transmitting coil are equal; the induced electromotive force of the secondary field is proportional to the number of turns of the coil, then:

[0036] Hp1 = Hp2 + Hp3 = 2Hp3

[0037]

[0038] Hs2 + Hs3 = 3Hs1

[0039] Hs3 = Hs2

[0040]

[0041] Inside the coil, it can be considered that Hp2 >> Hs2, then:

[0042] Hp1 - Hs1 ≈ Hp1

[0043]

[0044]

[0045] Among them, n_inner is the number of turns of the first receiving coil, n_outer is the number of turns of the second receiving coil and the third receiving coil, is the magnetic flux of the primary field of the first receiving coil, is the magnetic flux of the primary field of the second receiving coil and the third receiving coil, Hp1 is the magnetic field intensity of the primary field of the first receiving coil, Hp2 is the magnetic field intensity of the primary field of the second receiving coil, Hp3 is the magnetic field intensity of the primary field of the third receiving coil, Hs1 is the magnetic field intensity of the secondary field of the first receiving coil, Hs2 is the magnetic field intensity of the secondary field of the second receiving coil, and Hs3 is the magnetic field intensity of the secondary field of the third receiving coil.

[0046] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0047] The present invention realizes the integration of receiving and transmitting of the frequency domain electromagnetic method detection device by using one transmitting coil and three receiving coils, and the device is simple and portable; the present invention highlights and amplifies abnormal geological bodies through the calculation of the horizontal gradient · conductivity parameter, which is more conducive to the accurate judgment of abnormal geological bodies. The structure of the present invention is simple and convenient for calculation and operation.

[0048] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings. Description of the Drawings

[0049] The accompanying drawings, as a part of this application, are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation to the present invention. Obviously, the accompanying drawings in the following description are only some embodiments. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. In the drawings:

[0050] Figure 1 is a schematic structural diagram of the system of the present invention;

[0051] Figure 2 is a schematic diagram of the system principle of the present invention;

[0052] Figure 3 is a schematic diagram of the data waveform of the first embodiment of the present invention.

[0053] In the figure: 1. Transmitting coil; 2. First receiving coil; 3. Second receiving coil; 4. Third receiving coil; 5. Upper long strip skeleton; 6. Lower long strip skeleton; 7. Transmitting coil skeleton; 8. First receiving coil skeleton; 9. Second receiving coil skeleton; 10. Third receiving coil skeleton.

[0054] It should be noted that these accompanying drawings and text descriptions are not intended to limit the scope of the concept of the present invention in any way, but to illustrate the concept of the present invention to those skilled in the art by referring to specific embodiments. Detailed Embodiments

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0056] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0057] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0058] Embodiment 1

[0059] As Figures 1 to 3 shown, an exploration device based on frequency domain electromagnetic method described in this embodiment includes an electromagnetic emission device, three electromagnetic reception devices, and a controller. The three electromagnetic reception devices are all arranged on the same horizontal plane as the electromagnetic emission device, and the controller is electrically connected to the electromagnetic emission device and the three electromagnetic reception devices respectively. The controller is electrically connected to the electromagnetic emission device, so that the electromagnetic emission device can emit electromagnetic waves of a certain frequency. The electromagnetic reception device receives the signal emitted by the electromagnetic emission device. The controller obtains the magnetic field intensity of the electromagnetic reception device, records and analyzes the data, and judges the geological state through calculation. By introducing the horizontal gradient into the measurement and calculation of conductivity, and comprehensively considering horizontal gradient detection and conductivity detection, abnormal geological bodies can be effectively highlighted and amplified, which is more conducive to the accurate judgment of abnormal geological bodies.

[0060] In order to better install and fix the electromagnetic emission device and the three electromagnetic reception devices, and also facilitate the later adjustment and maintenance, the exploration device further includes a fixing device. The three electromagnetic reception devices are fixed to the electromagnetic emission device on the same horizontal plane through the fixing device. Through the fixing device, the transceiver integration of the frequency domain electromagnetic method detection device is realized, and at the same time, the device is simple and portable. On the premise of ensuring the effectiveness of the exploration device, in order to reduce the complexity of the device and make the exploration device simple in structure and convenient to install, preferably, the electromagnetic emission device is the transmitting coil 1, the electromagnetic reception device is the receiving coil, and the fixing device includes an upper long strip skeleton 5, a lower long strip skeleton 6, and a coil skeleton. The upper long strip skeleton 5 and the lower long strip skeleton 6 are arranged in parallel. The coil skeleton is fixed on the upper long strip skeleton 5 and the lower long strip skeleton 6. The transmitting coil 1 and the receiving coil are respectively wound on the coil skeleton. The parallel arrangement of the upper long strip skeleton 5 and the lower long strip skeleton 6 can play a good role in fixing and supporting the coil skeleton. The transmitting coil 1 and the receiving coil are wound on the coil skeleton, which can make it more convenient to fix the coil, and it is easier to control the thickness and number of turns of the coil winding. When installing and debugging the device, the distance between the coils is easy to control, and it is more convenient for later adjustment and maintenance.

[0061] To facilitate the exploration device in collecting geological data and making accurate judgments on abnormal geology, preferably, the three electromagnetic receiving devices are respectively the first receiving coil 2, the second receiving coil 3, and the third receiving coil 4. The first receiving coil 2 and the transmitting coil 1 are arranged in concentric circles, and the diameter of the transmitting coil 1 is greater than that of the first receiving coil 2. The centers of the second receiving coil 3 and the third receiving coil 4 are both set on the same straight line as the center of the transmitting coil 1, and are respectively arranged on both sides of the transmitting coil 1. With the centers on the same straight line, it is more convenient to measure when making judgments on the input data. Among them, the coil skeleton includes a transmitting coil skeleton 7, a first receiving coil skeleton 8, a second receiving coil skeleton 9, and a third receiving coil skeleton 10. The transmitting coil 1 is wound around the transmitting coil skeleton 7, and the first receiving coil 2, the second receiving coil 3, and the third receiving coil 4 are successively wound around the first receiving coil skeleton 8, the second receiving coil skeleton 9, and the third receiving coil skeleton 10. The centers of the first receiving skeleton, the second receiving skeleton, and the third receiving skeleton are arranged in a straight line. After the transmitting coil 11 emits electromagnetic waves, the receiving coil can receive the induced electromotive force formed by the primary field and the secondary field. The controller performs a fast Fourier transform on the received induced electromotive force and converts it into amplitude data corresponding to the frequency.

[0062] To avoid the influence of the fixing device on the exploration data, preferably, the upper long strip skeleton 5, the lower long strip skeleton 6, and the coil skeleton are all made of PVC material. The PVC material has stable properties, is not easily corroded by acids and alkalis, and is relatively heat-resistant. Preferably, the inner diameter of the transmitting coil skeleton 7 is 480 mm, the outer diameter is 500 mm, the inner diameters of the first receiving coil skeleton 8, the second receiving coil skeleton 9, and the third receiving coil skeleton 10 are all 230 mm, and the outer diameters are all 250 mm. The distance between the center of the second receiving coil 3 and the center of the transmitting coil 1 is 500 mm. The second receiving coil 3 and the third receiving coil 4 are symmetrically arranged on both sides of the transmitting coil 1. The thicknesses of the upper long strip skeleton 5 and the lower long strip skeleton 6 are both 20 mm, and the distance between adjacent two sides is 100 mm. The transmitting coil 1 uses a single-core wire, and the receiving coils all use enameled wires to increase the accuracy of the detected data. Preferably, the number of turns of the first receiving coil 2 is 600 turns, and the number of turns of the second receiving coil 3 and the third receiving coil 4 are both 900 turns.

[0063] The calculation method for geological exploration using the described exploration device includes the following steps:

[0064] Step 1, supply power to the transmitting coil 1 through the external frequency transmitter of the controller;

[0065] Step 2, data collection, synchronously measure the induced electromotive forces V1, V2, and V3 of the first receiving coil 2, the second receiving coil 3, and the third receiving coil 4;

[0066] Step 3, preliminary data processing, perform Fourier transform on the measured data;

[0067] Step 4, calculate the induced electromotive force horizontal gradient Hg, conductivity σ, and horizontal gradient - conductivity Hm of the secondary field, including the following steps:

[0068] Step 401, the first receiving coil 2 collects the induced electromotive force V1, the second receiving coil 3 collects the induced electromotive force V2, and the third receiving coil 4 collects the induced electromotive force V3;

[0069] Step 402, calculate the induced electromotive force horizontal gradient Hg of the secondary field, and the formula is as follows:

[0070]

[0071] In the formula, Hs2 represents the magnetic field strength of the secondary field of the second receiving coil, Hs3 represents the magnetic field strength of the secondary field of the third receiving coil, and L represents the distance between the second receiving coil and the third receiving coil;

[0072] Step 403, calculate the conductivity, which can be approximately calculated by the following formula:

[0073]

[0074] In the formula, ω is the angular frequency; μ0 is the magnetic permeability in vacuum; s is the distance between the transmitting and receiving coils; Hp3 represents the magnetic field strength of the primary field of the third receiving coil;

[0075] Step 404, calculate the horizontal gradient - conductivity Hm:

[0076] Hm = Hg · σ;

[0077] Conduct an experiment on the ground where an iron pipe is buried underground. Uniformly select 57 measurement points for measurement experiments. Through the calculation of the controller, the obtained data is shown in Table 1 below:

[0078] Table 1

[0079]

[0080]

[0081] Step 5, the controller analyzes and processes the data and feeds it back to realize the judgment of abnormal geological detection.

[0082] The waveform diagram detected by the experiment is as Figure 3As shown, it can be seen from the figure that if only the horizontal gradient Hg of the induced electromotive force of the secondary field is calculated, within the range without metal, there will still be large fluctuations in the data, and the deviation of the data will cause mistakes in geological judgment; if only the conductivity σ of the secondary field is calculated, there will still be large data fluctuations within the range without abnormal geology. When calculating the horizontal gradient - conductivity Hm, it can suppress the interference anomalies caused by the same formation and highlight and amplify the low-resistivity abnormal geological bodies caused by metals, water-bearing structures, etc., which is more conducive to the accurate judgment of abnormal geological bodies.

[0083] The above are only the preferred embodiments of the present invention, and there is no limitation to the present invention in any form. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art of this patent, without departing from the scope of the technical solution of the present invention, can make some changes or modifications using the technical content prompted above as equivalent embodiments of equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the present invention.

Claims

1. An exploration device based on frequency domain electromagnetic method, characterized in that: It includes an electromagnetic emission device, three electromagnetic receiving devices, and a controller. The three electromagnetic receiving devices are all arranged on the same horizontal plane as the electromagnetic emission device. The controller is electrically connected to the electromagnetic emission device and the three electromagnetic receiving devices respectively, and calculates the induced electromotive force horizontal gradient · conductivity Hm of the secondary field. The three electromagnetic receiving devices are respectively a first receiving coil (2), a second receiving coil (3), and a third receiving coil (4). The first receiving coil (2) and the transmitting coil (1) are arranged in concentric circles. The diameter of the transmitting coil (1) is larger than that of the first receiving coil (2). The centers of the second receiving coil (3) and the third receiving coil (4) are both set on the same straight line as the center of the transmitting coil (1), and are respectively arranged on both sides of the transmitting coil (1).

2. The exploration device based on the frequency-domain electromagnetic method according to claim 1, characterized in that: It further includes a fixing device. The three electromagnetic receiving devices and the electromagnetic emission device are fixed on the same horizontal plane through the fixing device.

3. The exploration device based on the frequency-domain electromagnetic method according to claim 2, characterized in that: The electromagnetic emission device is a transmitting coil (1), and the electromagnetic receiving device is a receiving coil. The fixing device includes an upper long strip skeleton (5), a lower long strip skeleton (6), and a coil skeleton. The upper long strip skeleton (5) and the lower long strip skeleton (6) are arranged in parallel. The coil skeleton is fixed on the upper long strip skeleton (5) and the lower long strip skeleton (6). The transmitting coil (1) and the receiving coils are respectively wound on the coil skeleton.

4. The exploration device based on the frequency-domain electromagnetic method according to claim 3, characterized in that: The coil skeleton includes a transmitting coil skeleton (7), a first receiving coil skeleton (8), a second receiving coil skeleton (9), and a third receiving coil skeleton (10). The transmitting coil (1) is wound on the transmitting coil skeleton (7). The first receiving coil (2), the second receiving coil (3), and the third receiving coil (4) are successively wound on the first receiving coil skeleton (8), the second receiving coil skeleton (9), and the third receiving coil skeleton (10). The centers of the first receiving coil skeleton (8), the second receiving coil skeleton (9), and the third receiving coil skeleton (10) are arranged in a straight line.

5. The exploration device based on the frequency-domain electromagnetic method according to claim 3, characterized in that: The upper long strip skeleton (5), the lower long strip skeleton (6), and the coil skeleton are all made of PVC material. The transmitting coil (1) uses a single-core wire, and the receiving coils all use enameled wires.

6. The exploration device based on the frequency-domain electromagnetic method according to claim 1, wherein: The number of turns of the first receiving coil (2) is 600 turns, and the number of turns of the second receiving coil (3) and the third receiving coil (4) are both 900 turns.

7. An exploration device based on the frequency-domain electromagnetic method according to claim 4, characterized in that: The inner diameter of the transmitting coil skeleton (7) is 480 mm, and the outer diameter is 500 mm. The inner diameters of the first receiving coil skeleton (8), the second receiving coil skeleton (9), and the third receiving coil skeleton (10) are all 230 mm, and the outer diameters are all 250 mm. The distance between the center of the second receiving coil (3) and the center of the transmitting coil (1) is 500 mm. The second receiving coil (3) and the third receiving coil (4) are symmetrically arranged on both sides of the transmitting coil (1). The thicknesses of the upper long strip skeleton (5) and the lower long strip skeleton (6) are both 20 mm, and the distance between adjacent two sides is 100 mm.

8. A calculation method for geological exploration using the exploration device according to any one of claims 1-7, characterized in that, It includes the following steps: Step 1, supply power to the transmitting coil (1) through an external frequency transmitter of the controller. Step 2, data acquisition, synchronously measure the potentials of the first receiving coil (2), the second receiving coil (3), and the third receiving coil (4); Step 3, preliminary data processing, perform Fourier transform on the measured data; Step 4, calculate the induced electromotive force horizontal gradient Hg, conductivity σ, and horizontal gradient · conductivity Hm of the secondary field, including the following steps: Step 401, the first receiving coil (2) acquires the induced electromotive force V1, the second receiving coil (3) acquires the induced electromotive force V2, and the third receiving coil (4) acquires the induced electromotive force V3; Step 402, calculate the induced electromotive force horizontal gradient Hg of the secondary field, and the formula is as follows: In the formula, Hs2 represents the magnetic field intensity of the secondary field of the second receiving coil (3), Hs3 represents the magnetic field intensity of the secondary field of the third receiving coil (4), and L represents the distance between the second receiving coil (3) and the third receiving coil (4); Step 403, calculate the conductivity, which can be approximately calculated by the following formula: In the formula, ω is the angular frequency; μ0 is the magnetic permeability in vacuum; s is the distance between the receiving and transmitting coils; Hp3 represents the primary field magnetic field intensity of the third receiving coil (4); Step 404, calculate the horizontal gradient · conductivity Hm: Hm = Hg · σ; Step 5, the controller analyzes and processes the data and feeds it back to realize the judgment of abnormal geological detection.

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