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

Abstract

The invention discloses an electrical source transient electromagnetic data three-dimensional inversion method and device, and a storage medium. The method comprises the following steps: S1, collecting a vertical induced voltage and a horizontal electric field component of electrical source transient electromagnetic; s2, the first-order time derivatives of the Vz and the Ex are used for calculating the whole-period apparent resistivity; s3, performing time-frequency conversion to obtain frequency-apparent resistivity data of each measuring point; and S4, performing three-dimensional inversion on the frequency-apparent resistivity data by using a three-dimensional inversion algorithm of magnetotelluric.

Description

Technical Field

[0001] The 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 method is an advantageous means for deep geophysical exploration. At present, the processing methods of electrical source transient electromagnetic data are mainly limited to one-dimensional and quasi-two-dimensional. Three-dimensional inversion faces problems such as large amount of calculation, low efficiency, and inability to process multiple emission sources, which brings great challenges to the fine processing of electrical source transient electromagnetic 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 for electrical source transient electromagnetic data, and a storage medium, 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 solution:

[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, using Vz and Ex to calculate the apparent resistivity of the entire period;

[0008] Step S3, performing time-frequency conversion according to 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] Preferably, in step S2, the first-order derivatives of Vz and Ex with respect to time are calculated respectively. and And use the following formula to calculate the apparent resistivity ρ for the entire period:

[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] The acquisition module is 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 apparent resistivity of the entire period using Vz and Ex;

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

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

[0019] Preferably, the first calculation module calculates the first-order derivative of Vz and Ex with respect to time respectively. and And use the following formula to calculate the apparent resistivity ρ for the entire period:

[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 uses a three-dimensional inversion algorithm of magnetotelluric to perform three-dimensional inversion on the frequency-apparent resistivity data.

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

[0024] The present invention utilizes the two components of vertical induced voltage and horizontal electric field 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, thereby realizing 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

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

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

[0028] Figure 3 It is a three-dimensional model and a transmit-receive layout diagram;

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

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work 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] Embodiment 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, using Vz and Ex to calculate the apparent resistivity of the entire period;

[0036] Step S3, performing time-frequency conversion according to 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 present invention,

[0039] The expressions of the horizontal electric field Ex and vertical induced voltage Vz generated by the 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 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] The apparent resistivity ρ of the entire period is obtained:

[0047]

[0048] Among them, y is the vertical distance between the observation point and the emission source, and t is the time. This resistivity calculation formula can offset the emission source term and eliminate the influence of factors such as the emission source size, position, 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 dimensions using the mature three-dimensional inversion program in magnetotelluric method, such as ModEM. Figure 2 As shown in the figure, the specific steps include: (1) reading in the frequency, apparent resistivity data and initial model parameters after time-frequency conversion; (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 three-dimensional model of multiple anomalies shown in the figure has a background resistivity of 50Ω·m. A total of three anomalies are designed. The resistivity of the shallow and deep low-resistance anomalies is 10Ω·m, and the resistivity of the deep high-resistance anomaly is 250Ω·m. The size of the shallow anomaly is 600m×600m×250m, and the top surface is buried at a depth of 20m. The sizes of the two deep anomalies are 1200m×800m×500m, and the top surface is buried at a depth of 500m. The length of the transient electromagnetic emission source of the electrical source is 2km, and the sampling time range is 0.1ms~50ms. The survey line offset distance ranges from 500m to 1500m, with a total of 20 survey lines. The length of each survey line is 3km, and the point spacing is 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 using formula (1). Then, time-frequency conversion is performed using formula (2) to obtain frequency domain data. Finally, the open source program ModEM is used to perform three-dimensional inversion on the converted frequency domain data to obtain the three-dimensional inversion resistivity structure, as shown in Fig. Figure 4 shown.

[0058] The results show that the three-dimensional inversion method of transient electromagnetic data of electrical sources in the embodiment of the present invention can better restore the three-dimensional electrical structure of the real model, verifying the feasibility and effectiveness of the method. At the same time, compared with direct three-dimensional inversion of time domain data, the calculation efficiency can be improved by more than 5 times: the new method takes about 1 hour, and the traditional method takes about 5 hours.

[0059] Embodiment 2:

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

[0061] The acquisition module is 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 apparent resistivity of the entire period using Vz and Ex;

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

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

[0065] As an implementation method of the embodiment of the present invention, the first calculation module calculates the first-order derivative of Vz and Ex with respect to time respectively. and And use the following formula to calculate the apparent resistivity ρ for the entire period:

[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 magnetotelluric to perform three-dimensional inversion on the frequency-apparent resistivity data.

[0069] Embodiment 3:

[0070] An embodiment of the present invention further provides a storage medium, on which a computer program is stored, and when the computer program is run, a three-dimensional inversion method for electrical source transient electromagnetic data is executed.

[0071] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined 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, using Vz and Ex to calculate the apparent resistivity of the entire period; Step S3, performing time-frequency conversion according to the full-period apparent resistivity to obtain frequency-apparent resistivity data of each measuring point; Step S4: perform three-dimensional inversion on the frequency-apparent resistivity data.

2. The three-dimensional inversion method of electrical source transient electromagnetic data according to claim 1, characterized in that: In step S2, the first-order derivatives of Vz and Ex with respect to time are calculated respectively. and And use the following formula to calculate the apparent resistivity ρ for the entire period: Where y is the vertical distance between the observation point and the emission source, and t is the time.

3. The three-dimensional inversion method of electrical source transient electromagnetic data according to claim 2, 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.

4. A three-dimensional inversion device for electrical source transient electromagnetic data, characterized in that: include: The acquisition module is 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 apparent resistivity of the entire period using Vz and Ex; The second calculation module is used to perform time-frequency conversion according to the full-period apparent resistivity to obtain frequency-apparent resistivity data of each measuring point; Inversion module for 3D inversion of frequency-apparent resistivity data.

5. The three-dimensional inversion device for electrical source transient electromagnetic data according to claim 4, characterized in that: The first calculation module calculates the first-order derivative of Vz and Ex with respect to time respectively. and And use the following formula to calculate the apparent resistivity ρ for the entire period: Where y is the vertical distance between the observation point and the emission source, and t is the time.

6. The three-dimensional inversion device for electrical source transient electromagnetic data according to claim 5, characterized in that: The inversion module uses the three-dimensional inversion algorithm of magnetotelluric to perform three-dimensional inversion of frequency-apparent resistivity data.

7. 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 as described in any one of claims 1 to 3.

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