Three-dimensional inversion method and device for electrical source transient electromagnetic data, and storage medium

Abstract

The present invention discloses a three-dimensional inversion method and device for electrical source transient electromagnetic data, and a storage medium, comprising: step S1, collecting the vertical induced voltage and horizontal electric field components of the electrical source transient electromagnetic; step S2, calculating the full-period apparent resistivity using the first-order time derivatives of Vz and Ex; step S3, performing time-frequency conversion to obtain frequency-apparent resistivity data of each measuring point; and step S4, performing three-dimensional inversion on the frequency-apparent resistivity data using a three-dimensional inversion algorithm of magnetotelluric.

Description

Technical Field

[0001] The present invention belongs to the technical field of geophysical exploration, and in particular relates to a three-dimensional inversion method and device for electrical source transient electromagnetic data, and a storage medium. Background Art

[0002] The electrical source transient electromagnetic (ESEM) method is a promising tool for deep geophysical exploration. Currently, methods for processing ESET data are limited to one-dimensional and pseudo-two-dimensional methods. Three-dimensional inversion suffers from computational overhead, low efficiency, and an inability to process multiple sources, posing significant challenges to the precise processing of ESET data. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a three-dimensional inversion method and device, and a storage medium for electrical source transient electromagnetic data, which overcomes the influence of the emission source, improves the inversion efficiency, and provides a solution for the three-dimensional inversion of multi-source data.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A three-dimensional inversion method for electrical source transient electromagnetic data, comprising:

[0006] Step S1, collecting the vertical induced voltage Vz and horizontal electric field Ex components of the electrical source transient electromagnetic;

[0007] Step S2, calculating the apparent resistivity of the entire period using Vz and Ex;

[0008] Step S3, performing time-frequency conversion based on the full-period apparent resistivity to obtain frequency-apparent resistivity data of each measuring point;

[0009] Step S4: Perform three-dimensional inversion on the frequency-apparent resistivity data.

[0010] As a preference, in step S2, the first-order derivatives of Vz and Ex with respect to time are calculated respectively. and The full-period apparent resistivity ρ is calculated using the following formula:

[0011]

[0012] Where y is the vertical distance between the observation point and the emission source, and t is the time.

[0013] Preferably, in step S4, a three-dimensional inversion algorithm of magnetotelluric is used to perform three-dimensional inversion on the frequency-apparent resistivity data.

[0014] The present invention also provides a three-dimensional inversion device for electrical source transient electromagnetic data, comprising:

[0015] Acquisition module, used to collect the vertical induced voltage Vz and horizontal electric field Ex components of the electrical source transient electromagnetic;

[0016] The first calculation module is used to calculate the full-period apparent resistivity using Vz and Ex;

[0017] The second calculation module is used to perform time-frequency conversion based on the full-period apparent resistivity to obtain frequency-apparent resistivity data of each measuring point;

[0018] Inversion module, used for 3D inversion of frequency-apparent resistivity data.

[0019] As an example, the first calculation module calculates the first-order derivative of Vz and Ex with respect to time. and The full-period apparent resistivity ρ is calculated using the following formula:

[0020]

[0021] Where y is the vertical distance between the observation point and the emission source, and t is the time.

[0022] Preferably, the inversion module performs three-dimensional inversion on the frequency-apparent resistivity data using a three-dimensional inversion algorithm of magnetotellurics.

[0023] The present invention also provides a storage medium, on which a computer program is stored. When the computer program is run, the method for three-dimensional inversion of electrical source transient electromagnetic data is executed.

[0024] The present invention uses the vertical induced voltage and horizontal electric field components of electrical source transient electromagnetic to define the full-period apparent resistivity that can eliminate the influence of the emission source, and proposes an accurate time-frequency conversion relationship to realize the conversion of time domain signals to frequency domain data. The three-dimensional inversion technology in the magnetotelluric method is further used to invert the converted data, thereby realizing the rapid three-dimensional inversion of electrical source transient electromagnetic data. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0026] Figure 1 This is a flow chart of a three-dimensional inversion method for electrical source transient electromagnetic data according to an embodiment of the present invention;

[0027] Figure 2Flow chart for 3D inversion processing of converted frequency-apparent resistivity data;

[0028] Figure 3 It is a three-dimensional model and a transmitting-receiving arrangement diagram;

[0029] Figure 4 This is the three-dimensional inversion result. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1:

[0033] like Figure 1 As shown, an embodiment of the present invention provides a three-dimensional inversion method for electrical source transient electromagnetic data, comprising:

[0034] Step S1, collecting the vertical induced voltage Vz and horizontal electric field Ex components of the electrical source transient electromagnetic;

[0035] Step S2, calculating the apparent resistivity of the entire period using Vz and Ex;

[0036] Step S3, performing time-frequency conversion based on the full-period apparent resistivity to obtain frequency-apparent resistivity data of each measuring point;

[0037] Step S4: Perform three-dimensional inversion on the frequency-apparent resistivity data.

[0038] As an implementation method of the embodiment of the present invention,

[0039] The expressions of the horizontal electric field Ex and vertical induced voltage Vz generated by a horizontal electric dipole source on the surface of the Earth in a uniform half-space are:

[0040]

[0041] Where I is the emission current intensity, ds is the length of the dipole source, ρ is the resistivity, is the distance from the observation point (x, y) to the emission source (x', y'), the variable μ0=4×10 -7 H / A is the magnetic permeability;

[0042] For e x and v z Calculate the first-order derivative with respect to time t respectively:

[0043]

[0044] Then find the ratio of the two:

[0045]

[0046] Obtain the apparent resistivity ρ for the entire period:

[0047]

[0048] Where y is the vertical distance from the observation point to the emission source, and t is the time. This resistivity calculation formula can offset the emission source term, eliminating the influence of factors such as the emission source size, location, and shape.

[0049] As an implementation of an embodiment of the present invention, in step S3, the time-frequency conversion is performed using the following formula:

[0050] f=150 / t

[0051] Where f is the frequency.

[0052] As an implementation of the embodiment of the present invention, in step S4, a three-dimensional inversion algorithm of magnetotelluric is used to perform three-dimensional inversion on the frequency-apparent resistivity data.

[0053] Furthermore, the converted frequency-apparent resistivity data are processed in three-dimensional inversion using the mature three-dimensional inversion program in the magnetotelluric method, such as ModEM. Figure 2 As shown in FIG, the specific steps include: (1) reading in the frequency and apparent resistivity data after time-frequency conversion and the initial model parameters; (2) performing nonlinear conjugate gradient inversion, calculating the model change after each iteration, and updating the model; (3) judging whether the fitting residual data meets the requirements, if so, ending the inversion and outputting the model; if not, continuing to iterate and modify the model; (4) obtaining the inversion model that finally meets the fitting residual requirements, ending the inversion and outputting the inversion results.

[0054] It should be noted that the converted frequency domain data is similar to the transverse electric (TE) polarization field in the magnetotelluric method, so the TE inversion mode needs to be used in the inversion.

[0055] Numerical example:

[0056] Design as Figure 3The 3D model of multiple anomalies shown has a background resistivity of 50 Ω·m. Three anomalies were designed: shallow and deep low-resistance anomalies with resistivities of 10 Ω·m each, and a deep high-resistance anomaly with resistivity of 250 Ω·m. The shallow anomaly measures 600m × 600m × 250m, with a top buried depth of 20m. The two deep anomalies each measure 1200m × 800m × 500m, with a top buried depth of 500m. The electrical transient electromagnetic emission source is 2km long, with a sampling time range of 0.1ms to 50ms. The survey line offsets range from 500m to 1500m, with a total of 20 survey lines. Each line is 3km long, with a point spacing of 20m.

[0057] First, the three-dimensional model is forward modeled to obtain the Vz and Ex responses of all measuring points. Then, the full-period apparent resistivity is calculated. Then, time-frequency conversion is performed to obtain frequency domain data. Finally, the open source program ModEM is used to perform a three-dimensional inversion on the converted frequency domain data to obtain the three-dimensional inverted resistivity structure, as shown in the following figure. Figure 4 shown.

[0058] The results show that the 3D inversion method for electrical source transient electromagnetic data, implemented in this embodiment of the present invention, can effectively restore the 3D electrical structure of the real model, validating the method's feasibility and effectiveness. Furthermore, compared to direct 3D inversion of time-domain data, computational efficiency can be increased by more than five times: the new method takes approximately one hour, while the traditional method takes approximately five hours.

[0059] Example 2:

[0060] The present invention also provides a three-dimensional inversion device for electrical source transient electromagnetic data, comprising:

[0061] Acquisition module, used to collect the vertical induced voltage Vz and horizontal electric field Ex components of the electrical source transient electromagnetic;

[0062] The first calculation module is used to calculate the full-period apparent resistivity using Vz and Ex;

[0063] The second calculation module is used to perform time-frequency conversion based on the full-period apparent resistivity to obtain frequency-apparent resistivity data of each measuring point;

[0064] Inversion module, used for 3D inversion of frequency-apparent resistivity data.

[0065] As an implementation method of an embodiment of the present invention, the first calculation module calculates the first-order derivative of Vz and Ex with respect to time respectively. and The full-period apparent resistivity ρ is calculated using the following formula:

[0066]

[0067] Where y is the vertical distance between the observation point and the emission source, and t is the time.

[0068] As an implementation method of the embodiment of the present invention, the inversion module uses a three-dimensional inversion algorithm of magnetotellurics to perform three-dimensional inversion on the frequency-apparent resistivity data.

[0069] Example 3:

[0070] An embodiment of the present invention further provides a storage medium having a computer program stored thereon. When the computer program is run, the computer program executes a three-dimensional inversion method for electrical source transient electromagnetic data.

[0071] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A three-dimensional inversion method for electrical source transient electromagnetic data, characterized in that: include: Step S1, collecting the vertical induced voltage Vz and horizontal electric field Ex components of the electrical source transient electromagnetic; Step S2, calculating the apparent resistivity of the entire period using Vz and Ex; Step S3, performing time-frequency conversion based on the full-period apparent resistivity to obtain frequency-apparent resistivity data of each measuring point; Step S4, performing three-dimensional inversion on the frequency-apparent resistivity data; In step S2, the first-order derivative of Vz and Ex with respect to time is calculated respectively. and The full-period apparent resistivity ρ is calculated using the following formula: Where y is the vertical distance between the observation point and the emission source, and t is the time.

2. The three-dimensional inversion method for electrical source transient electromagnetic data according to claim 1, characterized in that: In step S4, a three-dimensional inversion algorithm of magnetotelluric is used to perform three-dimensional inversion on the frequency-apparent resistivity data.

3. A three-dimensional inversion device for electrical source transient electromagnetic data, characterized in that: include: Acquisition module, used to collect the vertical induced voltage Vz and horizontal electric field Ex components of the electrical source transient electromagnetic; The first calculation module is used to calculate the full-period apparent resistivity using Vz and Ex; The second calculation module is used to perform time-frequency conversion based on the full-period apparent resistivity to obtain frequency-apparent resistivity data of each measuring point; Inversion module, used for three-dimensional inversion of frequency-apparent resistivity data; The first calculation module calculates the first-order derivative of Vz and Ex with respect to time. and The full-period apparent resistivity ρ is calculated using the following formula: Where y is the vertical distance between the observation point and the emission source, and t is the time.

4. The three-dimensional inversion device for electrical source transient electromagnetic data according to claim 3, characterized in that: The inversion module uses the three-dimensional inversion algorithm of magnetotelluric to perform three-dimensional inversion on the frequency-apparent resistivity data.

5. A storage medium, characterized in that: The storage medium stores a computer program, which, when running, executes the three-dimensional inversion method for electrical source transient electromagnetic data according to any one of claims 1 to 2.

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