CN104375173B - A kind of spatial sampling meeting migration before stack determines method - Google Patents

Abstract

The present invention is that a kind of spatial sampling meeting migration before stack of geophysical exploration determines method.Seismic data according to conventional earthquake obtains root mean sequare velocity, the highest frequency of zoning is obtained from conventional earthquake known seismic data process data, known geologic information or seismic interpretation data according to measuring in the past obtain inclined reflection stratigraphic dip, root mean sequare velocity according to inclination angle, desired highest frequency and superstratum determines the spatial sampling interval of tilted stratum, calculate the diffraction fluctuation school time difference, the anti-ripple time after the dynamic(al) correction differential to spatial sampling interval, determines spatial sampling interval according to spatial sampling theorem.The present invention in conjunction with the desirable highest frequency of need useful signal to be protected by the inclination angle of tilted stratum and root mean sequare velocity, can be determined spatial sampling interval, meet the needs of prestack migration image.

Description

A kind of spatial sampling meeting migration before stack determines method

Technical field

The present invention relates to geophysical exploration technology, be a kind of spatial sampling side of determination meeting migration before stack Method.

Background technology

In Seismic acquisition designs, spatial sampling is selected primarily based upon two kinds of theories: one is based on folded Add theory, i.e. require that spatial sampling meets without aliasing alias；Two is that skew based on Diffraction Point is theoretical, i.e. Require that spatial sampling meets without skew alias.Two kinds of theoretical calculating formula forms derived are:

$\mathrm{dx}=\frac{v}{4f_m\sin \mathrm{\θ}}$

Wherein: the dx representation space sampling interval；V represents the above root mean sequare velocity of target zone；f_maxExpression can Desired highest frequency；θ represents stratigraphic dip or skew inclination angle.Skew inclination angle typically takes 30 °, if ground Layer is very steep, and when such as larger than 30 °, in formula, θ means that stratigraphic dip.

Obviously θ is meant that and obscures in above formula: for Diffraction Point on horizontal interface and tilted interface Migration imaging for, skew inclination angle be the same；For steep stratum (more than 30 °) migration imaging and Speech, spatial sampling is the most relevant with stratigraphic dip, requires unrelated with migration imaging.These problems show in the past Spatial sampling computing formula be not suitable for the migration imaging requirement of tilted stratum.

Spatial sampling computing formula was to meet sampling theorem according to diffracted wave to derive, so only fitting in the past Playback for diffracted wave.

It practice, the essence of migration imaging is the non-in-phase stacking of echo, and diffracted wave is made to playback, from The diffracted wave field distribution characteristics of tilted stratum is set out, and wants diffracted wave field protection according to prestack migration image Ask, select to meet the spatial sampling interval of aerial image needs and be the medium-term and long-term hope in this area and do not solve Problem.Up to the present in the case of also nobody is given at tilted stratum, the space towards migration imaging is adopted Sample computational methods.

Summary of the invention

Present invention is primarily intended to propose in order in earthquake data acquisition in the wild, according to prestack migration image Select spatial sampling, it is ensured that the spatial sampling of inclined reflection layer can meet the requirement of prestack migration image A kind of spatial sampling meeting migration before stack determines method.

Concrete implementation step of the present invention is as follows:

1) seismic data collected according to conventional earthquake obtains root mean sequare velocity, from conventional earthquake-capturing The known seismic data process data obtained obtains the highest frequency of zoning；According to measured in the past Known geologic information or seismic interpretation data obtain inclined reflection stratigraphic dip；

2) according to the inclination angle of inclined reflection layer, desirable highest frequency and the root mean sequare velocity of superstratum Determine the spatial sampling interval of tilted stratum；

Step 2) determine that the spatial sampling interval of tilted stratum is from superposition theory, calculate diffraction fluctuation The school time difference, the differential to spatial sampling interval of the anti-ripple time after dynamic(al) correction, true according to spatial sampling theorem Determine spatial sampling interval；

Determine spatial sampling interval dx use following formula:

$\mathrm{dx}=\frac{v}{4f_{\max }(\sin \mathrm{\α}+\sin \mathrm{\θ})}$

In formula: dx is spatial sampling interval；V represents the above root mean sequare velocity of target zone；f_maxExpression can the phase The highest frequency hoped；θ is skew inclination angle, usually meets the convergence of diffraction information energy and takes 30 °；α is ground Inclination layer.

The present invention can be by the inclination angle of tilted stratum and root mean sequare velocity, in conjunction with needing effective letter to be protected Number desirable highest frequency, determine spatial sampling interval, meet the needs of prestack migration image.

Accompanying drawing explanation

Fig. 1 is the theory relation deduction schematic diagram of tilted stratum reflected wave field and diffracted wave field.

In figure, p is a Diffraction Point；S is a shot point on earth's surface；R is a reception point on earth's surface；H is Geophone offset half；X is offset distance；θ is skew inclination angle；Z₁For the Diffraction Point degree of depth；Z₂At zero The degree of depth of tilted interface；α is stratigraphic dip；t₁Represent that shot point arrives the propagation time receiving point again to Diffraction Point； t₂Represent the self excitation and self receiving time of tilted interface at offset distance x.

Fig. 2 spatial sampling is with the change of pitch angle graph of a relation of inclined reflection layer.

Vertical coordinate is spatial sampling interval size, and unit is m, and abscissa is the inclination angle of inclined reflection layer, Unit is degree, represents with " ° ", and blue line is the spatial sampling change of pitch angle curve with inclined reflection layer, The peak frequency needing tilted stratum to be protected during calculating is 50Hz, and superstratum root mean sequare velocity is 2000m/s, skew inclination angle is 30 °.

Fig. 3 spatial sampling is with the variation relation figure of frequency.

Vertical coordinate is spatial sampling interval size, and unit is m, and abscissa is the inclination angle of inclined reflection layer, Unit is degree, represents with " ° ", and blue line is the spatial sampling change of pitch angle curve with inclined reflection layer, During calculating, the inclination angle of tilted stratum is 30 °, and superstratum root mean sequare velocity is 2000m/s, and skew inclination angle is 30°。

Detailed description of the invention

The present invention determines the spatial sampling of inclined reflection layer based on prestack migration image, by inclined reflection The spatial sampling quantitative analysis of layer, is met migration before stack and processes the spatial sampling interval size required, Implement situation as follows:

1) seismic data collected according to conventional earthquake obtains root mean sequare velocity, from conventional earthquake-capturing The known seismic data process data obtained obtains the highest frequency of zoning；According to measured in the past Known geologic information or seismic interpretation data obtain inclined reflection stratigraphic dip.

Taking 30 ° of inclination angle of skew in this example, the root mean sequare velocity of superstratum, reflecting layer is 2000m/s, with It is 50Hz toward the getable highest frequency of seismic data.

2) according to the inclination angle of inclined reflection layer, desirable highest frequency and the root mean sequare velocity of superstratum Determine that tilted stratum determines spatial sampling interval.

Step 2) determine that the spatial sampling interval of tilted stratum is from superposition theory, calculate diffraction fluctuation The school time difference, seek the differential to spatial sampling of the echo time after dynamic(al) correction, true according to spatial sampling theorem Determine spatial sampling interval；

Determine that the formula of spatial sampling is as follows:

$\mathrm{dx}=\frac{v}{4f_{\max }(\sin \mathrm{\α}+\sin \mathrm{\θ})}$

In formula: dx is spatial sampling interval；V represents the above root mean sequare velocity of target zone；f_maxExpression can the phase The highest frequency hoped；θ is skew inclination angle, usually meets the convergence of diffraction information energy and takes 30 °；α is ground Inclination layer.

If it is 50Hz that zoning target zone can obtain the highest frequency of reflected signal, space can be obtained Sampling is with the change of pitch angle graph of a relation (Fig. 2) of inclined reflection layer, when the stratigraphic dip of zoning is less than 20 ° time, spatial sampling interval should select maybe can meet the requirement of migration before stack at about 12m.

If when the stratigraphic dip of zoning target zone is less than 30 °, can obtain being that spatial sampling is with frequency The variation relation figure (Fig. 3) of rate, the significant wave signal of 40Hz to be protected, spatial sampling interval should select About 11m can meet the requirement of migration before stack.

Claims (1)

1. meet the spatial sampling of migration before stack and determine that a method, feature are that to realize step as follows:

1) seismic data collected according to conventional earthquake obtains root mean sequare velocity, from conventional earthquake collect known Seismic data process data obtains the highest frequency of zoning；According to the known geologic information measured or earthquake in the past Interpretation data obtains the inclination angle of inclined reflection layer；

2) determine obliquely according to the root mean sequare velocity of the inclination angle of inclined reflection layer, desirable highest frequency and superstratum The spatial sampling interval of layer；

Step 2) determine that the spatial sampling interval of tilted stratum is from superposition theory, calculate the diffraction fluctuation school time difference, dynamic The echo time after the correction differential to spatial sampling interval, determines spatial sampling interval according to spatial sampling theorem；

Determine spatial sampling interval dx use following formula:

$dx=\frac{v}{4f_{max}(sin\mathrm{\α}+\sin \mathrm{\θ})}$

In formula: dx is spatial sampling interval；V represents the above root mean sequare velocity of target zone；Fmax represents desirable the highest Frequency；θ is skew inclination angle, meets the convergence of diffraction information energy and takes 30 °；α is stratigraphic dip.