Static displacement correction method for long wire artificial source electromagnetic method based on vertical magnetic field

Abstract

The present application belongs to the field of geophysical exploration, and specifically discloses a long-wire artificial source electromagnetic method static displacement correction method based on a vertical magnetic field, which comprises the following steps performed in sequence: S1, simultaneously observing a vertical magnetic field (Hz) and a horizontal electric field (Ex) at the same point; S2, calculating the apparent resistivity of the horizontal electric field (Ex) and the vertical magnetic field (Hz) in the whole area; S3, translating the apparent resistivity curve of the horizontal electric field (Ex) in the logarithmic domain, and calculating the static correction coefficient of the horizontal electric field (Ex); and S4, correcting the horizontal electric field (Ex) to be corrected based on the static correction coefficient. The horizontal electric field (Ex) refers to the horizontal electric field parallel to the long-wire source. The present application does not depend on subjective judgment of the static displacement and artificial selection of the filtering parameters, and improves the precision of the static correction of the horizontal electric field (Ex). The present application is suitable for static displacement correction of the horizontal electric field (Ex) observed by the long-wire artificial source electromagnetic method.

Description

Technical Field

[0001] This invention belongs to the field of geophysical exploration technology, specifically a static displacement correction method based on a long-conductor artificial source electromagnetic method using a vertical magnetic field. Background Technology

[0002] The long-conductor artificial source electromagnetic method is an important artificial source electrical exploration method. This method uses a grounded long-conductor source (the transmitter cannot be treated as an electric dipole) for excitation. By observing and studying the distribution of the ground electromagnetic field (usually the horizontal electric field (Ex) and vertical magnetic field (Hz) parallel to the source), it studies the electrical characteristics of the earth and thus solves related geological problems. Because this method uses a long-conductor source for excitation, it has the characteristics of strong excitation energy, large exploration depth, and high signal-to-noise ratio, and is widely used in energy, groundwater, and mineral exploration fields.

[0003] In practical applications of this method, the electric field components often exhibit static displacement due to the influence of shallow electrically inhomogeneous bodies. This static displacement manifests as a vertical stripe-like false anomaly on the profile. Because static displacement distorts the electromagnetic characteristics of the profile, it severely affects the processing and interpretation of electromagnetic exploration data. Therefore, static correction of the electric field components is a crucial step in electromagnetic exploration data processing. Conventional correction methods include logarithmic domain curve translation, spatial filtering, and median filtering. However, these methods either rely on subjective judgment of the static displacement or on manual selection of filtering parameters. Due to the complexity of static displacement, accurate judgment or selection is difficult, resulting in low static correction accuracy. Therefore, improving the accuracy of static correction of the electric field components is an important problem that needs to be solved in electromagnetic exploration data processing. Summary of the Invention

[0004] The purpose of this invention is to provide a static displacement correction method based on a long conductor artificial source electromagnetic method using a vertical magnetic field, so as to improve the static correction accuracy of the electric field components.

[0005] To achieve the above objectives, the present invention employs the following technical methods:

[0006] A static displacement correction method based on a long conductor artificial source electromagnetic method with a vertical magnetic field includes the following steps performed sequentially:

[0007] S1. The long-conductor artificial source electromagnetic method is used to detect geological targets. The vertical magnetic field (Hz) and horizontal electric field (Ex) are observed at the same point to obtain observation data.

[0008] S2. Calculate the apparent resistivity of the horizontal electric field (Ex) and the apparent resistivity of the vertical magnetic field (Hz) over the entire region based on the observation data.

[0009] S3. Translate the apparent resistivity curve of the horizontal electric field (Ex) over the entire logarithmic domain so that its high-frequency band is aligned with the high-frequency band of the apparent resistivity curve of the vertical magnetic field (Hz) over the entire region, and calculate the static correction coefficient of the horizontal electric field (Ex).

[0010] S4. Based on the static correction coefficients of the horizontal electric field (Ex) obtained in step S3, the horizontal electric field (Ex) to be corrected is corrected to obtain the statically corrected horizontal electric field (Ex).

[0011] As a limitation: the method for calculating the apparent resistivity of the horizontal electric field (Ex) over the entire region in step S2 is as follows:

[0012] Under uniform half-space conditions, with a grounded long wire as the emission source, the observed horizontal electric field (Ex) at point p on the ground is:

[0013]

[0014] In formula (1): l is the half-length of the source, x is the x-coordinate of the observation point p, r1 is the distance from the observation point p to one end of the source, r2 is the distance from the observation point p to the other end of the source, r is the distance from the observation point p to the integrating electric dipole dζ; I is the emission current; ρ is the resistivity of the ground; k1 is the propagation wavenumber of the ground. ω is the angular frequency, μ0 is the permeability of air, and i is the imaginary unit;

[0015] Based on formula (1), the apparent resistivity of the horizontal electric field (Ex) over the entire region is calculated using an iterative method.

[0016] As a further limitation: Based on formula (1), the iterative method for calculating the apparent resistivity of the horizontal electric field (Ex) over the entire region is as follows: From formula (1), the iterative calculation formula for the apparent resistivity of the horizontal electric field (Ex) over the entire region can be derived as follows:

[0017]

[0018] In formula (2): |E xω | represents E xω The amplitude, |F e | represents F e The amplitude;

[0019] Based on formula (2), the iterative method is used to solve the problem, which yields the apparent resistivity of the horizontal electric field (Ex) over the entire region.

[0020] As a limitation: the method for calculating the apparent resistivity of the vertical magnetic field (Hz) over the entire region in step S2 is as follows:

[0021] Under uniform half-space conditions, with a grounded long wire as the emission source, the observed vertical magnetic field (Hz) at point p on the ground is:

[0022]

[0023] In formula (3): y is the vertical coordinate from the observation point p to the source, i is the imaginary unit, ω is the angular frequency, μ0 is the permeability of air, ρ is the resistivity of the earth, I is the emission current, l is the half-length of the source, r is the distance from the observation point p to the integrating electric dipole dζ, and k1 is the propagation wavenumber of the earth.

[0024] Based on formula (3), the apparent resistivity of the vertical magnetic field (Hz) over the entire region is calculated using an iterative method.

[0025] As a further limitation: Based on formula (3), the iterative method for calculating the apparent resistivity of the vertical magnetic field (Hz) over the entire area is as follows: From formula (3), the iterative calculation formula for the apparent resistivity of the vertical magnetic field (Hz) over the entire area can be derived:

[0026] ρ=|H z | / |F z | (4)

[0027] In formula (4): |H z | indicates H z The amplitude, |F z | represents F z The amplitude;

[0028] Based on formula (4), the iterative method is used to solve the problem, which yields the apparent resistivity of the vertical magnetic field (Hz) over the entire area.

[0029] As a limitation: the static correction coefficient of the horizontal electric field (Ex) in step S3 is calculated as follows:

[0030] f = ρ c / ρ o

[0031] In the formula: f is the static correction coefficient of the horizontal electric field (Ex), ρ c ρ is the apparent resistivity of the horizontal electric field (Ex) over the entire region after translation; o Let be the apparent resistivity of the horizontal electric field (Ex) before translation.

[0032] As a limitation: In step S4, the method for correcting the horizontal electric field (Ex) to be corrected is to multiply the horizontal electric field (Ex) to be corrected by the static correction coefficient to obtain the statically corrected horizontal electric field (Ex). The specific calculation formula is as follows:

[0033] E c=E0×f

[0034] In the formula: E c The horizontal electric field (Ex) after static correction, E o Let f be the horizontal electric field (Ex) before static correction, and f be the static correction coefficient of the horizontal electric field (Ex).

[0035] The beneficial effects achieved by this invention, due to the adoption of the above-described solution, compared with the prior art, are as follows:

[0036] This invention provides a static displacement correction method based on a long-conductor artificial source electromagnetic method using a vertical magnetic field. The method uses a vertical magnetic field (Hz) that is unaffected by static displacement to perform static correction on the horizontal electric field (Ex). This method does not rely on subjective judgment of static displacement or manual selection of filter parameters, thus improving the accuracy of static correction of the horizontal electric field (Ex).

[0037] This invention is applicable to static displacement correction of the horizontal electric field (Ex) observed by the electromagnetic method of a long-conductor artificial source. Attached Figure Description

[0038] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0039] Figure 1 This is a flowchart of the static displacement correction method in this embodiment;

[0040] Figure 2 This is a schematic diagram of the simulation observation device in this embodiment;

[0041] Figure 3 The amplitude curves of the vertical magnetic field (Hz), the horizontal electric field (Ex) without static displacement, and the horizontal electric field (Ex) with static displacement are shown in the time-frequency electromagnetic forward modeling of this embodiment.

[0042] Figure 4 The apparent resistivity curves of the vertical magnetic field (Hz) and the horizontal electric field (Ex) including static displacement are calculated for this embodiment, and the apparent resistivity curves of the horizontal electric field (Ex) after translation are aligned with the high-frequency band of the apparent resistivity curve of the vertical magnetic field (Hz).

[0043] Figure 5 The graph shows the amplitude curve of the horizontal electric field (Ex) after static correction based on the static displacement correction method of this embodiment, and compares it with the simulated amplitude curves of the vertical magnetic field (Hz), the horizontal electric field (Ex) with static displacement, and the horizontal electric field (Ex) without static displacement.

[0044] Figure 6 This is a profile of the horizontal electric field (Ex) amplitude obtained from an exploration area in the Ordos Basin.

[0045] Figure 7 This is an amplitude profile of the vertical magnetic field (Hz) observed in a certain exploration area of ​​the Ordos Basin.

[0046] Figure 8 This is the amplitude profile of the horizontal electric field (Ex) after static correction using the static displacement correction method of this embodiment. Detailed Implementation

[0047] The present invention will be further described below with reference to embodiments. However, those skilled in the art should understand that the horizontal electric field (Ex) in the present invention refers to the horizontal electric field parallel to the long conductor source. The present invention is not limited to the following embodiments. Any improvements and equivalent changes made based on the specific embodiments of the present invention are within the scope of protection of the claims of the present invention.

[0048] Example: Static displacement correction method based on long conductor artificial source electromagnetic method with vertical magnetic field

[0049] A static displacement correction method based on a long conductor artificial source electromagnetic method with a vertical magnetic field is illustrated in the flowchart below. Figure 1 As shown, the steps are performed sequentially:

[0050] S1. The long-conductor artificial source electromagnetic method is used to detect geological targets. The vertical magnetic field (Hz) and horizontal electric field (Ex) are observed at the same point to obtain observation data.

[0051] S2. Calculate the apparent resistivity of the horizontal electric field (Ex) and the apparent resistivity of the vertical magnetic field (Hz) over the entire region based on the observation data.

[0052] The method for calculating the apparent resistivity of the horizontal electric field (Ex) over the entire region is as follows:

[0053] Under uniform half-space conditions, using a grounded long wire as the emission source, the horizontal electric field (Ex) is observed at point p on the ground. The observed horizontal electric field (Ex) is:

[0054]

[0055] In formula (1): l is the half-length of the source, x is the x-coordinate of the observation point p, r1 is the distance from the observation point p to one end of the source, r2 is the distance from the observation point p to the other end of the source, r is the distance from the observation point p to the integrating electric dipole dζ; I is the emission current; ρ is the resistivity of the ground; k1 is the propagation wavenumber of the ground. ω is the angular frequency, μ0 is the permeability of air, and i is the imaginary unit;

[0056] Based on formula (1), the apparent resistivity of the horizontal electric field (Ex) over the entire region is calculated using an iterative method, as follows:

[0057] From formula (1), the iterative calculation formula for the apparent resistivity of the horizontal electric field (Ex) over the entire region can be derived as follows:

[0058]

[0059] In formula (2): |E xω | represents E xω The amplitude, |F e | represents F e The amplitude;

[0060] Based on formula (2), the iterative method is used to solve the problem, which yields the apparent resistivity of the horizontal electric field (Ex) over the entire region.

[0061] The method for calculating the apparent resistivity of the vertical magnetic field (Hz) over the entire region is as follows:

[0062] Under uniform half-space conditions, using a grounded long wire as the emission source, the vertical magnetic field (Hz) is observed at point p on the ground. The observed vertical magnetic field (Hz) is:

[0063]

[0064] In formula (3): y is the vertical coordinate from the observation point p to the source, i is the imaginary unit, ω is the angular frequency, μ0 is the permeability of air, ρ is the resistivity of the earth, I is the emission current, l is the half-length of the source, r is the distance from the observation point p to the integrating electric dipole dζ, and k1 is the propagation wavenumber of the earth.

[0065] Based on formula (3), the apparent resistivity of the vertical magnetic field (Hz) over the entire region is calculated using an iterative method, as follows:

[0066] From formula (3), the iterative calculation formula for the apparent resistivity of the vertical magnetic field (Hz) over the entire region can be derived:

[0067] ρ=|H z | / |F z | (4)

[0068] In formula (4): |H z | indicates H z The amplitude, |F z | represents F z The amplitude;

[0069] Based on formula (4), the iterative method is used to solve the problem, which yields the apparent resistivity of the vertical magnetic field (Hz) over the entire area.

[0070] S3. Translate the apparent resistivity curve of the horizontal electric field (Ex) over the entire logarithmic domain so that its high-frequency band is aligned with the high-frequency band of the apparent resistivity curve of the vertical magnetic field (Hz) over the entire region, and calculate the static correction coefficient of the horizontal electric field (Ex).

[0071] The static correction coefficient for the horizontal electric field (Ex) is calculated as follows:

[0072] f = ρ c / ρ o (5)

[0073] In formula (5): f is the static correction coefficient of the horizontal electric field (Ex), ρ c ρ is the apparent resistivity of the horizontal electric field (Ex) over the entire region after translation; o Let be the apparent resistivity of the horizontal electric field (Ex) before translation.

[0074] S4. Based on the static correction coefficient of the horizontal electric field (Ex) obtained in step S3, the horizontal electric field (Ex) to be corrected is multiplied by the static correction coefficient to obtain the statically corrected horizontal electric field (Ex). The specific calculation formula is as follows:

[0075] E c =E0×f (6)

[0076] In the formula: E c The horizontal electric field (Ex) after static correction, E o The horizontal electric field (Ex) before static correction.

[0077] The effectiveness of this embodiment was tested based on simulated data:

[0078] Assume the half-space medium has a five-layer electrical structure, with resistivities of 100 Ω·m, 10 Ω·m, 100 Ω·m, 10 Ω·m, and 100 Ω·m for the first to fifth layers, and thicknesses of 400 m, 100 m, 3000 m, and 500 m for the first to fourth layers, respectively; the simulation observation device is as follows: Figure 2 As shown: the transmitter AB is 10000m long and emits 100A current. The observation point p is located at a distance S 10000m off the perpendicular bisector of the transmitter's long conductor. Figure 3 The amplitude curves of the vertical magnetic field (Hz), the horizontal electric field (Ex) without static displacement, and the horizontal electric field (Ex) with static displacement are shown in the forward modeling of time-frequency electromagnetic fields. Figure 4 The apparent resistivity curves for the entire region calculated for the vertical magnetic field (Hz) and the horizontal electric field (Ex) including static displacement, and the apparent resistivity curves for the entire region of the horizontal electric field (Ex) after translation and alignment with the high-frequency band of the apparent resistivity curve for the entire region of the vertical magnetic field (Hz). Figure 5The figure shows the amplitude curve of the horizontal electric field (Ex) after static correction based on the static displacement correction method of this embodiment, and compares it with the simulated amplitude curves of the vertical magnetic field (Hz), the horizontal electric field (Ex) with static displacement, and the horizontal electric field (Ex) without static displacement. As can be seen from the figure, the amplitude curve of the corrected horizontal electric field (Ex) almost completely overlaps with the amplitude curve of the horizontal electric field (Ex) without static displacement, indicating that the static correction effect of the static displacement correction method of this embodiment is good.

[0079] This embodiment was applied in an exploration area in the Ordos Basin, where the surface topography is highly undulating and the surface geoelectric conditions are complex. The observed horizontal electric field (Ex) amplitude profile is as follows. Figure 6 As shown, there is a severe static effect, with numerous longitudinal strip-shaped false anomalies on the profile, severely distorting the electrical distribution characteristics of the profile; the amplitude profile of the vertical magnetic field (Hz) is as follows. Figure 7 As shown, there is almost no static effect; therefore, the static displacement correction method of this embodiment was used for static correction. The amplitude profile of the horizontal electric field (Ex) after static correction is shown in the figure. Figure 8 As shown, the static displacement correction method of this embodiment effectively reduces the influence of static effects after static correction, and clearly shows the distribution of electrical characteristics of the profile.

Claims

1. A static displacement correction method based on a long conductor artificial source electromagnetic method using a vertical magnetic field, characterized in that, This includes the following steps performed sequentially: S1. The long-conductor artificial source electromagnetic method is used to detect geological targets. The vertical magnetic field (Hz) and horizontal electric field (Ex) are observed at the same point to obtain observation data. S2. Calculate the apparent resistivity of the horizontal electric field (Ex) and the apparent resistivity of the vertical magnetic field (Hz) over the entire region based on the observation data. S3. Translate the apparent resistivity curve of the horizontal electric field (Ex) over the entire logarithmic domain so that its high-frequency band is aligned with the high-frequency band of the apparent resistivity curve of the vertical magnetic field (Hz) over the entire region, and calculate the static correction coefficient of the horizontal electric field (Ex). S4. Based on the static correction coefficients of the horizontal electric field (Ex) obtained in step S3, the horizontal electric field (Ex) to be corrected is corrected to obtain the statically corrected horizontal electric field (Ex).

2. The static displacement correction method based on a long conductor artificial source electromagnetic method using a vertical magnetic field as described in claim 1, characterized in that, The method for calculating the apparent resistivity of the horizontal electric field (Ex) over the entire region in step S2 is as follows: Under uniform half-space conditions, with a grounded long wire as the emission source, the observed horizontal electric field (Ex) at point p on the ground is: In formula (1): l is the half-length of the source, x is the x-coordinate of the observation point p, r1 is the distance from the observation point p to one end of the source, r2 is the distance from the observation point p to the other end of the source, r is the distance from the observation point p to the integrating electric dipole dζ; I is the emission current; ρ is the resistivity of the ground; k1 is the propagation wavenumber of the ground. ω is the angular frequency, μ0 is the permeability of air, and i is the imaginary unit; Based on formula (1), the apparent resistivity of the horizontal electric field (Ex) over the entire region is calculated using an iterative method.

3. The static displacement correction method based on a long conductor artificial source electromagnetic method using a vertical magnetic field as described in claim 2, characterized in that, Based on formula (1), the iterative method is used to calculate the apparent resistivity of the horizontal electric field (Ex) over the entire region as follows: From formula (1), the iterative calculation formula for the apparent resistivity of the horizontal electric field (Ex) over the entire region can be derived as follows: In formula (2): |E xω | represents E xω The amplitude, |F e | represents F e The amplitude; Based on formula (2), the iterative method is used to solve the problem, which yields the apparent resistivity of the horizontal electric field (Ex) over the entire region.

4. The static displacement correction method based on a long conductor artificial source electromagnetic method using a vertical magnetic field as described in claim 1, characterized in that, The method for calculating the apparent resistivity of the vertical magnetic field (Hz) over the entire region in step S2 is as follows: Under uniform half-space conditions, with a grounded long wire as the emission source, the observed vertical magnetic field (Hz) at point p on the ground is: In formula (3): y is the vertical coordinate from the observation point p to the source, i is the imaginary unit, ω is the angular frequency, μ0 is the permeability of air, ρ is the resistivity of the ground, I is the emission current, l is the half-length of the source, r is the distance from the observation point p to the integrating electric dipole dζ, and k1 is the propagation wavenumber of the ground. Based on formula (3), the apparent resistivity of the vertical magnetic field (Hz) over the entire region is calculated using an iterative method.

5. The static displacement correction method based on a long conductor artificial source electromagnetic method using a vertical magnetic field as described in claim 4, characterized in that, Based on formula (3), the iterative method is used to calculate the apparent resistivity of the vertical magnetic field (Hz) over the entire area as follows: From formula (3), the iterative calculation formula for the apparent resistivity of the vertical magnetic field (Hz) over the entire area can be derived as follows: p=|H z | / |F z | (4) In formula (4): |H z | indicates H z The amplitude, |F z | represents F z The amplitude; Based on formula (4), the iterative method is used to solve the problem, which yields the apparent resistivity of the vertical magnetic field (Hz) over the entire area.

6. The static displacement correction method based on a long conductor artificial source electromagnetic method using a vertical magnetic field according to claim 1, characterized in that, The method for calculating the static correction coefficient of the horizontal electric field (Ex) in step S3 is as follows: f=ρ c / r o In the formula: f is the static correction coefficient of the horizontal electric field (Ex), ρ c ρ is the apparent resistivity of the horizontal electric field (Ex) over the entire region after translation; o Let be the apparent resistivity of the horizontal electric field (Ex) before translation.

7. The static displacement correction method based on a long conductor artificial source electromagnetic method using a vertical magnetic field according to claim 1, characterized in that, In step S4, the method for correcting the horizontal electric field (Ex) to be corrected is to multiply the horizontal electric field (Ex) to be corrected by the static correction coefficient to obtain the statically corrected horizontal electric field (Ex). The specific calculation formula is as follows: AND c =And o ×f In the formula: E c The horizontal electric field (Ex) after static correction, E o Let f be the horizontal electric field (Ex) before static correction, and f be the static correction coefficient of the horizontal electric field (Ex).

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