CN1797038A - Method for shifting depth before superposition in seismic data process of undulating the earth's surface - Google Patents

Abstract

The invention is a prestack depth migration method for seismic data processing of a relief land surface, determining an imaging reference plane according to the highest point of a collection region, and projecting the relief land surface to a regular grid to fill a constant speed approaching to the near land surface in the relief land surface; using Fourier finite extrapolation operators of one-way wave equation to make wave field extrapolation on shot seismic source wave fields and detector received wave fields along the depth axis, and keeping the wave field between input and output datum equal to zero; imaging the extrapolated shot and detector wave field record by conjugate related imaging conditions, and stacking the related results of each frequency and processing the imaging result into a section image by routine display software, and the invention has an obvious imaging effect of complex construction on the condition of relief land surface.

Description

The prestack depth migration method that a kind of relief surface geological data is handled

Technical field

The present invention relates to the migration before stack imaging technique category in the reflection wave geological data processing procedure, is the prestack depth migration method that a kind of relief surface geological data is handled.

Background technology

Carry out in the process of seismic prospecting in surface conditions more complicated area, the collection of data is to carry out on the face of land that rises and falls, and the geodetic level that obtains the data place is a curved surface, rather than a plane.This geological data is when handling, need adopt wave equation migration before stack imaging technique for improving image quality, at this moment can face two problems: the first, conventional wave equation pre stack depth migration is based on the precondition on the horizontal face of land, is not inconsistent with the condition of actual relief surface; The second, carry out imaging if use based on the wave equation pre stack depth migration method on the horizontal face of land, it will twist the actual form of underground structure.Carry out wave equation migration before stack imaging if use based on the method on the horizontal face of land, acquisition will be the interface of a bending, its crooked rule is the enantiomorphism of relief surface.If subsurface interface was exactly bending change originally, obtain the image of actual configuration form that has been exactly more complicated disengaging so, be interpreted into figure can for follow-up subterranean strata construction solution and drilling well causes misleading.

For the structure imaging under the relief surface condition, one of way in the past is to move to data on the reference field of a level by static correction earlier, between the face of land of the reference field of level and fluctuating, adopt a replacement velocity, use then based on the wave equation pre stack depth migration on the horizontal face of land and realize structure imaging.The problem of this method is that the amount of moving of static correction is excessive so if level reference is placed on the relief surface peak; If be placed on the center line of relief surface, the velocity contrast between replacement velocity and the actual underground medium is bigger so.Static shift has just been considered moving of ray vertical direction simultaneously, does not consider that there is error in the actual propagation path mobile and ripple of radiation levels component.Another way in the past is to use kirchhoff integral method pre-stack depth migration technology; advantage is that condition and the irregular observation station that can handle relief surface neatly distribute; but because that this method is based on high-frequency ray is approximate; some wave phenomenon is difficult to realize, and is therefore lower for the imaging precision of complex structure.

Summary of the invention

The present invention will provide a kind of big gun territory wave equation pre stack depth migration method based on relief surface, and it not only can adapt to the surface conditions of fluctuating, solves vertical time shift static correction error, and can improve the imaging precision of complex structure effectively.

Big gun territory wave equation pre stack depth migration technology based on relief surface of the present invention, concrete steps comprise:

(1) input prestack big gun collection geological data.

(2) peak according to relief surface is specified to the reference field that picture is exported, and relief surface is projected on the regular grid, fills a velocity amplitude approaching with the constant speed of near surface on the relief surface.

(3) utilize the Fourier finite difference continuation operator of one-way wave equation respectively the source wavefield of shot point and the reception wave field of geophone station to be carried out wave field extrapolation along degree of depth axle, and the wave field between maintenance input reference face and the output reference face is zero.

(4) conjugation dependent imaging condition used in the wave field record of shot point after the continuation and geophone station and carry out imaging.

(5) software for display by routine is treated to the stratigraphic section image with imaging results.

Big gun territory wave equation pre stack depth migration method based on relief surface of the present invention; keeping a numerical value between input reference face and output reference face is that zero wave field layer solves the relief surface problem in the wave equation pre stack depth migration, has drawn the advantage of handling relief surface in the kirchhoff integration pre-stack depth migration flexibly.

Big gun territory wave equation pre stack depth migration method based on relief surface of the present invention; pre stack data is set in the big gun territory; it can adapt to irregular recording geometry and distribute; especially land recording geometry and subsea cable recording geometry have been drawn the advantage of handling irregular recording geometry in the kirchhoff integration pre-stack depth migration flexibly.

Big gun territory wave equation pre stack depth migration method based on relief surface of the present invention; utilize Fourier finite difference continuation operator to come the continuation wave field; to improve the complex structure imaging precision, improved kirchhoff integration pre-stack depth migration for the low shortcoming of complex structure imaging precision.

Specific implementation principle of the present invention is as follows:

The reference field of selected pre-stack depth migration imaging output is a level, and is positioned on the peak of relief surface, and the mesh generation of rule is carried out in the space under the level reference, so the surface configuration that rises and falls becomes the part of regularization grid after by discretize.

For any one the prestack big gun collection of on relief surface, gathering record R (x, y, z (x, y), t), the employing Fourier transform is R (x after it is transformed to frequency field, y, and z (x, y), ω), it is carried out downward continuation, be recorded as U (x after the continuation with up-going wave equation, y, z, ω), this process can be expressed as: U (x, y, z, ω)=Wz[R (x, y, z (x, y), ω)], x wherein, y is respectively the coordinate of two horizontal directions in the rectangular coordinate system in space, z is the coordinate of depth direction, and ω is a circular frequency, W _zIt is continuation operator.Source wavefield for shot point is S (x ₀, y ₀, z (x ₀, y ₀), t), it is transformed to be S (x after the frequency field ₀, y ₀, z (x ₀, y ₀), ω), can adopt downgoing wave equation that it is propagated downwards, after the propagation be recorded as D (x, y, z, ω), this process can be written as: $D(x,y,z,\mathrm{\ω})=W_z^{*}\left[R(x_0,y_0,z(x_0,y_0),\mathrm{\ω})\right],$ W wherein _z ^*It is the conjugation continuation operator.The wave field of the next degree of depth is the stack in this position of the continuation result of a last degree of depth wave field and original wave field in the continuation process, participates in normal wave field and propagates and the continuation process by one zero wave field layer is set between output reference face and the input reference face simultaneously.

Wave field after the continuation is carried out the conjugation dependent imaging, and, just obtains the result of pre-stack depth migration under the relief surface condition all frequency summations: $I(x,y,z)={\∫}_{{\mathrm{\ω}}_{\min }}^{{\mathrm{\ω}}_{\max }}U(x,z,\mathrm{\ω})D^{*}(x,z,\mathrm{\ω})\mathrm{d\ω}.$ Then

Software for display by routine is treated to the stratigraphic section image with imaging results.

Above-mentioned continuation operator obtains by approaching according to one way wave equation, adopts stable Fourier finite difference operator to realize that this operator can be divided into: W=W ₁+ W ₂+ W ₃, wherein:

$w_1=\sqrt{\frac{{\mathrm{\ω}}^2}{v_r^2}+\frac{{\∂}^2}{{\∂x}^2}},w_2=\frac{\mathrm{\ω}}{v}-\frac{\mathrm{\ω}}{v_r},w_3=\frac{\mathrm{\ω}}{v_r}\frac{a\frac{\∂}{\∂x}\left(r\frac{\∂}{\∂x}\right)}{1+b{\left(\stackrel{\‾}{v}\frac{\∂}{\∂x}\right)}^2}$

Wherein v is the actual speed field, and Vr is the reference velocity field, r=v/v _r-1.0, be a constant that speed is relevant, v is a comprehensive speed $\stackrel{\‾}{v}=\sqrt{v^2+{\mathrm{vv}}_r+{v_r}^2},$ Parameter a, the value of b has influence on the inclination maximum of skew:

The present invention adopts the big gun territory wave equation pre stack depth migration method that is adapted to relief surface, has following characteristics, mainly shows as:

(1) can correctly handle relief surface condition in the migration imaging.

(2) relief surface, big gun territory and the continuation of Fourier finite difference operator wave equation are organically combined.

(3) has tangible imaging effect for the complex structure under the relief surface condition.

Description of drawings

Fig. 1 is a two-dimentional relief surface model that has only two stratum, and the maximum fluctuating discrepancy in elevation on the face of land is 250 meters.

Fig. 2 is that exciting of theogram receives the raypath synoptic diagram, has only excited 8 big guns.

Fig. 3 is the theogram of preceding 4 big guns, and as can be seen, although subsurface reflective boundary is a level, serious bending has taken place the reflection line-ups form of big gun record.

Fig. 4 moves to big gun record landform center line on big gun record by relief surface through vertical static time shift, and the big gun record becomes comparison near the hyperbolic curve form as can be seen.

Fig. 5 is to the result who carries out pre-stack depth migration imaging based on the method on the horizontal face of land of the record after the time shift, as can be seen horizontal reflection interface discontinuous seismic event and existence distortion.

Fig. 6 carries out result behind the pre-stack depth migration imaging with present technique, and the reflecting interface of imaging is straight and continuous.

Fig. 7 is the result who the complex structure model of a relief surface is used the integral method pre-stack depth migration, exists significant imaging noise as can be seen on the imaging section, and simultaneously, many little tiltedinterfaces do not have imaging.

Fig. 8 carries out the result of pre-stack depth migration to relief surface complex structure model with this method, and as can be seen, noise level significantly reduces, and the imaging background is clear, and many little imaging interface imagings are clear, and imaging effect has tangible improvement than integral method.

Fig. 9 is the integral method pre-stack depth migration result of real data, and structural feature is not obvious.

To be this real data carry out the result of pre-stack depth migration with this method to Figure 10, and one obviously is out to oblique structure.

Embodiment

The prestack depth migration method that a kind of relief surface geological data is handled is specially following steps:

1) prestack big gun collection geological data is read in collection;

2) peak according to the pickup area relief surface is specified to the picture reference field, and relief surface is projected on the regular grid, makes and fills a velocity amplitude approaching with the constant speed of near surface on the relief surface;

3) utilize the Fourier finite difference continuation operator of one-way wave equation respectively the source wavefield of shot point and the reception wave field of geophone station to be carried out wave field extrapolation along degree of depth axle, and the wave field between maintenance input reference face and the output reference face is zero;

Specifically: the shot point source wavelet is arranged on the corresponding regularization grid position of shot point, and it is transformed to frequency field; The geological data wave field that acceptance point is received is arranged on the respective rule grid position and transforms to frequency field; Geological data is carried out Fourier analysis; With primary wave with stop frequency range f1 and the f2 that ripple is determined wave field extrapolation, f1 is 5 hertz, and getting f2 is 60 hertz, determines continuation operator W=W ₁+ W ₂+ W ₃, wherein:

$W_1=\sqrt{\frac{{\mathrm{\ω}}^2}{v_r^2}+\frac{{\∂}^2}{{\∂x}^2}},W_2=\frac{\mathrm{\ω}}{v}-\frac{\mathrm{\ω}}{v_r},W_3=\frac{\mathrm{\ω}}{v_r}\frac{a\frac{\∂}{\∂x}\left(\frac{\∂}{\∂x}\right)}{1+b{\left(\stackrel{\‾}{v}\frac{\∂}{\∂x}\right)}^2}$

Wherein v is the actual speed field, and Vr is the reference velocity field, r=v/v _r-1.0, be a constant relevant with speed, v is a comprehensive speed $\stackrel{\‾}{v}=\sqrt{v^2+{\mathrm{vv}}_r+{v_r}^2};$

Parameter a, the value of b and the inclination maximum of skew are:

To the source wavefield and the acceptance point wave field of each frequency between f1 and the f2, all adopt the stable Fourier finite difference operator of narrating previously respectively to the source wavefield downward continuation;

Wave field in the continuation process on the next degree of depth is wave field and the stack of original wave field on this position after the last degree of depth continuation, and the step size of use is identical with the grid of velocity field;

Participating in normal wave field by one zero data Layer between output reference face and the input reference face simultaneously propagates and the continuation process.

4) conjugation dependent imaging condition used in the wave field record of shot point after the continuation and geophone station and carry out imaging, and result's stack with each frequency simple crosscorrelation, this has just finished imaging process, and the result of output pre-stack depth migration has promptly finished whole pre-stack depth migration.

Fig. 7 and Fig. 8 are the test examples of complex structure generated data under the relief surface condition.

1) input prestack big gun collection geological data.

2) peak according to relief surface is specified to the reference field that picture is exported, and relief surface is projected on the regular grid, determines that according to track pitch mesh spacing is 20m, fills the constant speed 4000m/s near near surface on the relief surface.

3) utilize the Fourier finite difference continuation operator of one-way wave equation respectively the source wavefield of shot point and the reception wave field of geophone station to be carried out wave field extrapolation along degree of depth axle, and the wave field between maintenance input reference face and the output reference face is zero.Specifically, the shot point source wavelet is arranged on the corresponding regularization grid position of shot point, and it is transformed to frequency field, the geological data wave field that acceptance point is received is arranged on the respective rule grid position and transforms to frequency field, by geological data is carried out Fourier analysis, set the frequency range f1 and the f2 of wave field extrapolation, generally it is set at the effective band of geological data, usually, getting f1 is 5 hertz, getting f2 is 60 hertz, can satisfy most requirements according to imaging.Parameter a, b gets 65 ° of inclination angles and can satisfy actual requirement, i.e. a=0.4761, b=0.3767.To the source wavefield and the acceptance point wave field of each frequency between f1 and the f2, all adopt the stable Fourier finite difference operator of narrating previously respectively to the source wavefield downward continuation; Wave field in the continuation process on the next degree of depth is wave field and the stack of original wave field on this position after the last degree of depth continuation, and the step size of use is identical with the grid of velocity field; Participating in normal wave field by one zero data Layer between output reference face and the input reference face simultaneously propagates and the continuation process.

4) conjugation dependent imaging condition used in the wave field record of shot point after the continuation and geophone station and carry out imaging, and result's stack with each frequency simple crosscorrelation, this has just finished imaging process, and the result of output pre-stack depth migration has promptly finished whole pre-stack depth migration.

5) software for display by routine is treated to the stratigraphic section image as shown in Figure 8 with imaging results, and Fig. 7 is that the result of integral method skew is used for comparison.

Fig. 9 and Figure 10 are the test examples of the real data of complex structure under the relief surface condition.

1) input prestack big gun collection geological data.

2) peak according to relief surface is specified to the reference field that picture is exported, and relief surface is projected on the regular grid, determines that according to track pitch mesh spacing is 25m, fills the constant speed 2500m/s near near surface on the relief surface.

3) utilize the Fourier finite difference continuation operator of one-way wave equation respectively the source wavefield of shot point and the reception wave field of geophone station to be carried out wave field extrapolation along degree of depth axle, and the wave field between maintenance input reference face and the output reference face is zero.Specifically, the shot point source wavelet is arranged on the corresponding regularization grid position of shot point, and it is transformed to frequency field, the geological data wave field that acceptance point is received is arranged on the respective rule grid position and transforms to frequency field, by geological data is carried out Fourier analysis, set the frequency range f1 and the f2 of wave field extrapolation, generally it is set at the effective band of geological data, usually, getting f1 is 5 hertz, getting f2 is 50 hertz, can satisfy most requirements according to imaging.Parameter a, b gets 65 ° of inclination angles and can satisfy actual requirement, i.e. a=0.4761, b=0.3767.To the source wavefield and the acceptance point wave field of each frequency between f1 and the f2, all adopt the stable Fourier finite difference operator of narrating previously respectively to the source wavefield downward continuation; Wave field in the continuation process on the next degree of depth is wave field and the stack of original wave field on this position after the last degree of depth continuation, and the step size of use is identical with the grid of velocity field; Participating in normal wave field by one zero data Layer between output reference face and the input reference face simultaneously propagates and the continuation process.

4) conjugation dependent imaging condition used in the wave field record of shot point after the continuation and geophone station and carry out imaging, and result's stack with each frequency simple crosscorrelation, this has just finished imaging process, and the result of output pre-stack depth migration has promptly finished whole pre-stack depth migration.

5) software for display by routine is treated to the stratigraphic section image as shown in figure 10 with imaging results, and Fig. 9 is the result of integral method skew.

Claims (4)

1, a kind of prestack depth migration method of relief surface geological data processing is characterized in that adopting following steps:

1) with conventional means collection and read prestack big gun collection geological data;

2) be specified to the reference field of picture according to the peak of pickup area relief surface, relief surface is projected on the regular grid, make and fill a velocity amplitude approaching on the relief surface with the constant speed of near surface;

3) utilize the Fourier finite difference continuation operator of one-way wave equation respectively the source wavefield of shot point and the reception wave field of geophone station to be carried out wave field extrapolation along degree of depth axle, and the wave field between maintenance input reference face and the output reference face is zero;

4) conjugation dependent imaging condition used in the wave field of shot point after the continuation and geophone station record and carry out imaging, and with result's stack of each frequency simple crosscorrelation, the software for display by routine is treated to profile image with imaging results.

2, the prestack depth migration method of a kind of relief surface geological data processing according to claim 1, it is characterized in that: following steps are adopted in wave field extrapolation:

The shot point source wavelet is arranged on the corresponding regularization grid position of shot point, and it is transformed to frequency field;

Be arranged on the seismic wave field data that receive on the respective rule grid position and transform to frequency field;

Geological data is carried out Fourier analysis;

Determine the frequency range of wave field extrapolation with primary wave and termination ripple;

To the source wavefield and the acceptance point wave field of each frequency in the frequency range, adopt stable Fourier finite difference operator respectively to the source wavefield downward continuation;

The wave field of the next degree of depth is the stack in this position of result after the last degree of depth wave field extrapolation and original wave field in the continuation process, and the step size of use is identical with the grid of velocity field;

Participating in normal wave field by one zero data Layer simultaneously between reference field propagates and the continuation process.

3, the prestack depth migration method of a kind of relief surface geological data processing according to claim 1 and 2, it is characterized in that: original frequency is 5 hertz, stopping frequency wave is 60 hertz.

4, the prestack depth migration method of a kind of relief surface geological data processing according to claim 1 and 2 is characterized in that: continuation operator W=W ₁+ W ₂+ W ₃,

$W_1=\sqrt{\frac{{\mathrm{\ω}}^2}{v_r^2}+\frac{{\∂}^2}{\∂x^2}},$ $W_2=\frac{\mathrm{\ω}}{v}-\frac{\mathrm{\ω}}{v_r},$ $W_3=\frac{\mathrm{\ω}}{v_r}\frac{a\frac{\∂}{\∂x}\left(r\frac{\∂}{\∂x}\right)}{1+b{\left(\stackrel{\‾}{v}\frac{\∂}{\∂x}\right)}^2}$

Wherein v is the actual speed field, and Vr is the reference velocity field, r=v/v _r-1.0, be a constant relevant with speed, v is a comprehensive speed $\stackrel{\‾}{v}=\sqrt{v^2+v{v}_r+{v_r}^2},$ A, the value of b and the inclination maximum of skew are:

Images