CN110879410A - Multi-component seismic surface wave exploration method - Google Patents

Abstract

The invention belongs to the field of near-surface seismic exploration, and particularly relates to a multi-component seismic surface wave exploration method₁(ii) a Rolling and collecting multi-component surface wave seismic data; extracting Z component seismic data in the single-shot seismic record; step four, carrying out frequency dispersion curve f-v on the extracted Z component_RZijPerforming damped least squares inversion; step five, extracting H component seismic data in the single-shot seismic record, performing wave field transformation on the H component seismic record, and extracting an H component dispersion curve f-v_RHij(ii) a Step six, taking X for the extracted H component dispersion curve_z(v_SAnd h) taking the initial model, and performing iterative inversion according to the fourth step to obtain a final stratum inversion result X_H(v_S，h)。

Description

A Multicomponent Seismic Surface Wave Exploration Method

technical field

The invention belongs to the field of near-surface seismic exploration, in particular to a multi-component seismic surface wave exploration method.

Background technique

In multi-component seismic exploration, three-component geophones are used to obtain the fluctuation information of X, Y, and Z directions when the wave propagates in the medium. The signal-to-noise ratio and resolution of seismic recordings play an important role. This method has been effectively used in reflection seismic, but it is more practical for multi-channel transient surface wave exploration, because Rayleigh waves are inversely progressing ellipses near the medium interface. In the form of forward propagation, its energy is unequally distributed in the X and Z components, while the predecessors only used the Z component seismic records for dispersion imaging and inversion, due to factors such as random noise, near-field effects and P-waveguide waves Influence, the Rayleigh waves of various order modes are difficult to effectively identify and separate in the spectrogram, or even impossible to achieve. If the H-component information is combined for mutual restraint, the above problems can be effectively alleviated, and the H-component seismic signal attenuates faster and has a higher frequency. The high-velocity high-order Rayleigh waves are more prominent in the H-component spectrum than the fundamental-order mode in some frequency bands. Therefore, it is necessary to design and study a multi-component seismic surface wave exploration method for multi-component seismic surface wave exploration, which can be combined with The seismic surface wave information of X and Z components is subjected to dispersion imaging and inversion, which improves the accuracy of picking up dispersion curves and the accuracy of inversion results.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a multi-component seismic surface wave exploration method, which includes the acquisition of multi-component surface wave data, the imaging of dispersion energy and the joint inversion of H and Z component dispersion curves. Mutual constraints and complements of the multi-objective inversion objective functions of the two components of Z to improve inversion convergence efficiency and formation model parameter accuracy.

The technical scheme of the present invention is:

A multi-component seismic surface wave exploration method, comprising the following steps:

Step 1: Design the parameters of the multi-component surface wave exploration and observation system according to the actual situation of the study area, including the position of the survey line, the track spacing dx, the sampling rate t, the sampling length T, the arrangement length L, and the minimum offset distance x ₁ ;

Step 2: Rolling acquisition of multi-component surface wave seismic data;

Step 3, extract the Z component seismic data in the single shot seismic record, do the wave field transformation to the Z component seismic record, extract the Z component dispersion curve fv _RZij ;

Step 4. Perform damped least squares inversion on the extracted Z component dispersion curve fv _RZij to obtain a preliminary inversion stratigraphic model X _z (v _S , h);

Step 5, extract the H component seismic data in the single shot seismic record, carry out wave field transformation to the H component seismic record, extract the H component dispersion curve fv _RHij ;

Step 6: Take X _z (v _S , h) as the initial model for the extracted H component dispersion curve, and perform iterative inversion with reference to step 4 to obtain the final formation inversion result X _H (v _S , h).

In the first step, the minimum offset distance x ₁ is 5m; the track spacing dx is 2m, the sampling rate t is 2ms, the sampling length T is 400ms, and the arrangement length L is 48m.

The third step of extracting the Z-component seismic data in the single-shot seismic records includes: performing a two-dimensional Fourier transform on the Z-component seismic records, and converting the surface wave records from the x-t domain to the f-k domain, and the calculation formula is:

where f is the frequency and u(x, t) is the x-t domain seismic record;

where k is the wavenumber and U(f,k) is the f-k domain seismic record.

The step 3 further includes: generating an fv spectrum energy map according to k=f/v, and identifying its energy peak to obtain the measured Rayleigh wave Z component dispersion curve fv _RZij , where i=1,2,...N, where N is The number of measured phase velocities, j=1,2,...M, where M is the order of the picked-up Rayleigh wave dispersion curve.

In the fourth step, the damped least squares inversion of the extracted Z component dispersion curve fv _RZij includes: denoting the initial iteration number T as 1, and the inversion iteration formula is as follows:

Among them, I is the identity matrix, x ₀ is the initial model parameter of the inversion, μ is the damping factor, the present invention sets its initial value to 1, and A is the Jacobian matrix.

The step 4 further includes: based on the obtained parameter correction amount Δx, using the steepest descent method to obtain the optimal parameter correction step size λ, and the calculation formula is:

In the formula, g _i =( ^AT A+μI)Δx _i

Then, the parameters of the inversion model are corrected to x=x ₀ +λΔx, and T=T+1, and the above iteration formula is used for inversion until the preset number of iterations is reached, and the inversion result X _z (v _S , h) is recorded.

The step 5 to extract the H-component dispersion curve fv _RHij also includes: the fundamental-order dispersion becomes worse in resolution in some frequency bands, but the corresponding high-order dispersion shows higher resolution, so the fundamental-order dispersion is The combined application of the higher-order dispersion and the higher-order dispersion can improve the accuracy of the extracted dispersion curve fv _RHij .

The beneficial effects of the present invention are:

The multi-component surface wave exploration method designed by the invention can detect more abundant geological information of the underground medium, and avoids the problem of mode misjudgment caused by interference such as P-wave guided wave and leaky wave when collecting single-component surface wave data. The cross constraint of the two components of , Z can significantly improve the accuracy of extracting the dispersion curve. This method can detect more abundant geological information underground and significantly improve the accuracy of the inversion of stratigraphic parameters.

Description of drawings

1 is a flow chart of a multi-component seismic surface wave exploration method designed by the present invention;

Fig. 2 is the multi-component surface wave data acquisition scanning arrangement of the multi-component seismic surface wave exploration method designed by the present invention;

Fig. 3 is the acquisition Z-component surface wave seismic record of the multi-component seismic surface wave exploration method designed by the present invention;

Fig. 4 is the acquisition H-component surface wave seismic record of the multi-component seismic surface wave exploration method designed by the present invention;

Fig. 5 is the Z-component seismic record dispersion energy diagram of the multi-component seismic surface wave exploration method designed by the present invention and the extracted Z-component dispersion curve;

Fig. 6 is the H-component seismic record dispersion energy diagram of the multi-component seismic surface wave exploration method designed by the present invention and the extracted H-component dispersion curve;

FIG. 7 is a multi-component surface wave exploration formation inversion result of the multi-component seismic surface wave exploration method designed by the present invention.

Detailed ways

The present invention is further introduced below in conjunction with the accompanying drawings and embodiments: a multi-component seismic surface wave exploration method, comprising the following steps:

Step 1: Design the parameters of the multi-component surface wave exploration and observation system according to the actual situation of the study area, including the position of the survey line, the track spacing dx, the sampling rate t, the sampling length T, the arrangement length L, and the minimum offset distance x ₁ ;

Step 2: Rolling acquisition of multi-component surface wave seismic data; as shown in Figure 2;

Step 3: Extract the Z component seismic data in the single shot seismic record;

Step 4. Perform damped least squares inversion on the extracted Z component dispersion curve fv _RZij to obtain a preliminary inversion stratigraphic model X _z (v _S , h);

Step 5: Extract the H-component seismic data in the single-shot seismic record, as shown in Figure 4; perform wave field transformation on the H-component seismic record, and extract the H-component dispersion curve fv _RHij , as shown in Figure 6;

Step 6: Take X _z (v _S , h) as the initial model for the extracted H component dispersion curve, and perform iterative inversion with reference to step 4 to obtain the final formation inversion result X _H (v _S , h).

In the first step, the minimum offset distance x ₁ is 5m; the track spacing dx is 2m, the sampling rate t is 2ms, the sampling length T is 400ms, and the arrangement length L is 48m.

The step 3 to extract the Z component seismic data in the single shot seismic record includes: as shown in Figure 3

The two-dimensional Fourier transform is performed on the Z-component seismic records, and the surface wave records are converted from the x-t domain to the f-k domain. The calculation formula is:

where f is the frequency and u(x, t) is the x-t domain seismic record;

where k is the wavenumber and U(f,k) is the f-k domain seismic record.

The third step further includes: as shown in FIG. 5 , generating an fv spectrum energy diagram according to k=f/v, and identifying its energy peak value to obtain the measured Rayleigh wave Z component dispersion curve fv _RZij , where i=1,2 ,...N, N is the number of measured phase velocities, j=1,2,...M, M is the order of the picked-up Rayleigh wave dispersion curve.

In the fourth step, the damped least squares inversion of the extracted Z component dispersion curve fv _RZij includes: denoting the initial iteration number T as 1, and the inversion iteration formula is as follows:

Among them, I is the identity matrix, x ₀ is the initial model parameter of the inversion, μ is the damping factor, the present invention sets its initial value to 1, and A is the Jacobian matrix.

The step 4 further includes: based on the obtained parameter correction amount Δx, using the steepest descent method to obtain the optimal parameter correction step size λ, and the calculation formula is:

In the formula, g _i =( ^AT A+μI)Δx _i

Then, the parameters of the inversion model are corrected to x=x ₀ +λΔx, and T=T+1, and the above iteration formula is used for inversion until the preset number of iterations is reached, and the inversion result X _z (v _S , h) is recorded.

The step 5 to extract the H-component dispersion curve fv _RHij also includes: the fundamental-order dispersion becomes worse in resolution in some frequency bands, but the corresponding high-order dispersion shows higher resolution, so the fundamental-order dispersion is The combined application of the higher-order dispersion and the higher-order dispersion can improve the accuracy of the extracted dispersion curve fv _RHij .

In Figure 5, the Z-component seismic recording dispersion imaging and dispersion curve, it can be seen that the fundamental-order dispersion is dominant in the entire frequency band, and the resolution is high, while the resolution of the high-order dispersion is poor;

In Fig. 6, the H-component seismic recording dispersion imaging and dispersion curve, although the resolution of the fundamental-order dispersion becomes worse in some frequency bands, the corresponding higher-order dispersion shows a higher resolution. The two refer to each other. The combined application can improve the accuracy of the extracted dispersion curve, thereby improving the accuracy of the inversion results;

The multi-component surface wave dispersion inversion results in Fig. 7, Z _co represents the Z-component stratigraphic inversion results, H _co represents the H-component stratigraphic inversion results, that is, the multi-component surface wave exploration inversion results, which have higher inversion results precision.

A multi-component seismic surface wave exploration method proposed by the present invention is not limited to the above-mentioned embodiments, and other implementations obtained by those skilled in the art according to the technical solutions of the present invention satisfy the principles of the present invention. It belongs to the technical innovation category of the present invention.

Claims (7)

1. A multi-component seismic surface wave exploration method is characterized by comprising the following steps:

step one, designing parameters of the multi-component surface wave exploration observation system by combining the actual conditions of a research area, wherein the parameters comprise a survey line position, a track interval dx, a sampling rate T, a sampling length T, an arrangement length L and a minimum offset distance x₁；

Rolling and collecting multi-component surface wave seismic data;

extracting Z component seismic data in the single-shot seismic record, performing wave field transformation on the Z component seismic record, and extracting a Z component dispersion curve f-v_RZij；

Step four, carrying out frequency dispersion curve f-v on the extracted Z component_RZijPerforming damped least square inversion to obtain a preliminary inversion stratum model X_z(v_S，h)；

Step five, extracting H component seismic data in the single-shot seismic record, performing wave field transformation on the H component seismic record, and extracting an H component dispersion curve f-v_RHij；

Step six, taking X for the extracted H component dispersion curve_z(v_SAnd h) taking the initial model, and performing iterative inversion according to the fourth step to obtain a final stratum inversion result X_H(v_S，h)。

2. A method of multi-component seismic surface wave exploration, as claimed in claim 1, wherein: minimum offset x in step one₁Is 5 m; the track pitch dx is 2m, the sampling rate T is 2ms, the sampling length T is 400ms, and the arrangement length L is 48 m.

3. A method of multi-component seismic surface wave exploration, as claimed in claim 1, wherein: the third step of extracting Z-component seismic data in the single-shot seismic record comprises the following steps: and (3) performing two-dimensional Fourier transform on the Z-component seismic record, converting the surface wave record from an x-t domain to an f-k domain, and solving the formula as follows:

wherein f is frequency and u (x, t) is an x-t domain seismic record;

where k is the wavenumber and U (f, k) is the f-k domain seismic record.

4. A method of multi-component seismic surface wave exploration, as claimed in claim 3, wherein: the third step further comprises: generating an f-v frequency spectrum energy graph according to the k-f/v, and identifying the energy peak value of the f-v frequency spectrum energy graph to obtain an actually measured Rayleigh wave Z component frequency dispersion curve f-v_RZijWhere i is 1,2, … N, N is the number of measured phase velocities, j is 1,2, … M, and M is the order of the picked rayleigh wave dispersion curve.

5. A method of multi-component seismic surface wave exploration, as claimed in claim 1, wherein: the step four pairs of extracted Z component frequency dispersion curves f-v_RZijPerforming a damped least squares inversion comprising: the initial iteration number T is recorded as 1, and the inversion iteration formula is as follows:

where I is the identity matrix, x₀The method is characterized in that the method is an inversion initial model parameter, mu is a damping factor, the initial value of the method is set to be 1, and A is a Jacobian matrix.

6. A method of multi-component seismic surface wave exploration, as claimed in claim 5, wherein: the fourth step further comprises: based on the obtained parameter correction quantity delta x, a parameter optimal correction step length lambda is obtained by using the steepest descent method, and the obtaining formula is as follows:

in the formula, g_i＝(A^TA+μI)Δx_i

The inverse model parameters are corrected to x ═ x₀+ lambda delta X, making T ═ T +1, inverting by using the above-mentioned iterative formula until reaching the preset iteration number, recording inversion result X_z(v_S，h)。

7. The multi-component seismic surface wave survey of claim 1The method is characterized in that: fifthly, extracting an H component frequency dispersion curve f-v_RHijExtracting Z component dispersion curve f-v_RZijFurther comprising: h component dispersion curve f-v_RHijThe resolution of the fundamental dispersion in some frequency bands becomes worse, but the corresponding higher order dispersion shows higher resolution; and Z component dispersion curve f-v_RZijThe fundamental dispersion shows better resolution over the entire frequency band. Therefore, the H component is dispersed in the curve f-v_RhijAnd Z component dispersion curve f-v_RZijThe two are combined with each other and applied, so that the accuracy and the resolution of the inversion formation result can be improved.

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