CN110703327A - Full-band imaging method - Google Patents
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- 238000003384 imaging method Methods 0.000 title claims abstract description 95
- 230000005012 migration Effects 0.000 claims abstract description 12
- 238000013508 migration Methods 0.000 claims abstract description 12
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- 230000001629 suppression Effects 0.000 claims description 10
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- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
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- G01V1/301—Analysis for determining seismic cross-sections or geostructures
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- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
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Abstract
The invention relates to a full-band imaging method, which is an imaging method capable of carrying out full-band frequency expansion processing on seismic data before migration through pulse deconvolution and improving the signal-to-noise ratio of a seismic imaging section through a self-adaptive aperture; secondly, generating an inclination angle gather corresponding to the sample CDP, and determining an inclination angle imaging area on the inclination angle gather; and thirdly, carrying out pre-stack time migration imaging by using the inclination angle imaging area to obtain a final imaging result. The invention can broaden effective seismic signals in a full frequency band, fully excavate available information in seismic data, determine an accurate imaging area by utilizing the dip angle gather, realize self-adaptive aperture imaging, and achieve the purposes of suppressing migration noise and improving the signal-to-noise ratio of a seismic stack section.
Description
The technical field is as follows:
the invention relates to the technical field of reflection seismic data processing in seismic exploration, in particular to a full-band imaging method.
Background art:
in the conventional imaging processing process of the reflection seismic data, only the seismic data in a frequency band range with a higher signal-to-noise ratio is generally extracted and imaged, and low-frequency and high-frequency data which are in a frequency suppression band and have a relatively lower signal-to-noise ratio are not processed, so that effective signals of seismic original data are not fully mined and utilized, the effective bandwidth of the seismic imaging data is reduced, and the precision and the accuracy of subsequent seismic exploration work are influenced. Full frequency band imaging can bring the problem that the noise is violently enlargied at the in-process of fully excavating the effective signal of earthquake, generally adopts the mode of the post-stack data body filtering and denoising to improve the SNR of seismic section, but can lose, harm the effective signal of earthquake, has violated the original intention of full frequency processing, has weakened the effect of full frequency processing.
In summary, the conventional imaging method often has the disadvantage that data in a frequency suppression band and with a low signal-to-noise ratio cannot be effectively utilized, and the adopted post-stack filtering denoising can bring adverse effects on effective seismic signals aiming at the problem of severe noise amplification caused by full-frequency processing. In view of the above problems, no effective solution has been proposed.
The invention content is as follows:
the invention aims to provide a full-band imaging method, which is used for solving the problems that the conventional imaging method cannot effectively utilize data which are positioned in a frequency suppression band and have a low signal-to-noise ratio and the problem of severe noise amplification caused by full-band processing.
The technical scheme adopted by the invention for solving the technical problems is as follows: this full band imaging method:
step one, performing conventional noise suppression processing on seismic data before stacking;
carrying out full-band frequency extension processing on the seismic data subjected to noise suppression by using a single-channel pulse deconvolution technology, wherein a pulse function is used as expected output of pulse deconvolution;
step three, aiming at a plurality of common center point positions on the seismic imaging section, extracting common center point gathers, recording the gathers as sample CDP, carrying out conventional dynamic correction speed pickup on the gathers, and carrying out interpolation smoothing on the obtained result to be used as an initial migration speed field;
step four, performing offset impulse response calculation on each channel of input data by using an initial offset velocity field, classifying and partially overlapping the offset impulse response according to the offset distance of the input data to form a common reflection point offset distance gather for each common center point position, and determining a final offset velocity field according to whether the in-phase axis in the common reflection point gather is straight or not;
step five, calculating the seismic wave travel time, the migration amplitude and the dip angle of each imaging point of the pre-stack data at the sample CDP position by using the final migration velocity field, arranging according to the dip angle, and partially overlapping to obtain a dip angle gather of the sample CDP position;
the calculation of the travel time, the offset amplitude and the dip angle of the seismic wave is realized as follows: starting from a one-way wave equation and a phase-stabilizing point principle, defining the horizontal coordinate of an excitation point as xsHorizontal coordinate of receiving point is xgPhi is the azimuth angle, the coordinates of the imaging point are (x, T), and the offset velocity of the imaging point is vrmsAnd seismic wave travel time from the excitation point to the imaging point and then to the receiving point:
defining integers
Wherein delta t is the sampling interval of the seismic data, the amplitude values of four points i-1, i, i +1 and i +2 on the seismic data are used for quadratic curve interpolation, the seismic amplitude value delta at the travel time tau is solved, and the dimensionless imaging weight coefficient is calculated
The magnitude of the shift at the imaging point (x, T) is then
And (3) obtaining the inclination angle: the following variables, x1＝xs-x,x2＝xs+xg-2 x; calculating the distance variable a ═ x1cosφ；b＝x1x2+2(vrmsT)2；c＝x2cosφ；Then k is equal to (ad)2-bc)/(c2-d2) The tilt angle theta is arctan [ (x)1+kcosφ)/(vrmsT)]；
Determining dip angle imaging areas aiming at the dip angle gather corresponding to the CDP positions of the sample, and determining the dip angle imaging areas corresponding to the rest CDP positions by utilizing the determined dip angle imaging areas in an interpolation continuation mode;
step seven, utilizing the final offset velocity field to calculate the dip angle of each imaging point on all CDP positions of the data before the stack, if the dip angle is positioned in the dip angle imaging area, continuously calculating the travel time and the amplitude of the imaging point to finish imaging, and if the dip angle is positioned outside the dip angle imaging area, repeating the operation of the step on the next imaging point;
and step eight, finishing the calculation of all CDP position imaging points to obtain a final seismic imaging section.
In the scheme, the step three is realized by the following steps of extracting a common-center-point gather from a plurality of common-center-point positions on the seismic imaging section: and selecting the position of the common center point at equal intervals on the conventional section according to the change condition of the structure, and distributing the offset distances at equal intervals from small to large when extracting the common center point gather.
In the scheme, the method for determining the dip angle imaging area for the dip angle gather corresponding to the CDP position of the sample in the step six comprises the following steps: a decision condition is introduced to the system that,
psi (t, x) is an imaging value corresponding to an angle x of an imaging point at a time depth t position in a dip gather，
Angle of imaging point at time depth t position of dip trace concentration from theta-eta1To theta + eta2The imaging superposition value in the range, theta is the true formation dip of the dip gather time depth t position, gamma is the threshold value, and is set as
AmaxWhen the condition is satisfied, the imaging result at the time depth t position tends to be stable and presents a phase-stable state [ theta-eta ] for the maximum absolute amplitude of the dip gather1,θ+η2]Is the dip imaging area to be determined at the time depth t position of the dip gather.
The invention has the following beneficial effects:
1. the invention carries out full-band frequency extension processing on the seismic data before migration, so that the data with low signal-to-noise ratio in the frequency suppression band of the seismic data is fully mined and effectively utilized.
2. The invention utilizes the dip angle channel set to determine the accurate imaging area, suppresses signal noise in the imaging process and solves the problem of severe noise amplification caused by full frequency processing.
Drawings
FIG. 1 is a conventional deconvolution stack cross-section.
FIG. 2 is a pulse deconvolution stack cross section.
FIG. 3 compares conventional deconvolution to pulse deconvolution spectra.
Fig. 4 is a full-frequency imaging method using a conventional post-stack denoising profile.
Fig. 5 is a cross-section of full-frequency imaging using the method of the present invention.
FIG. 6 shows a comparison of the cross-section spectrum obtained by the method of the present invention and the conventional post-stack denoising method used in full-frequency imaging.
Detailed Description
The invention is further illustrated below:
the full-band imaging method takes a certain seismic data of No. 1 block of the Jidong oilfield, and specifically comprises the following steps:
1. the pre-stack seismic data is subjected to conventional noise suppression processing, the data sampling interval is 2ms, the recording duration of the seismic signals is 5000ms, the CDP interval is 25m, the minimum offset is 100m, the maximum offset is 5400m, and the offset interval is 50 m.
(2) And carrying out full-band frequency broadening processing on the seismic data after the noise suppression by utilizing a single-channel pulse deconvolution technology, wherein a pulse function is taken as expected output of the pulse deconvolution.
(3) And (3) extracting a common-center offset gather aiming at a plurality of common-center positions on the section, recording the common-center offset gather as a sample CDP, performing conventional dynamic correction speed pickup on the gathers, and performing interpolation smoothing on the obtained result to be used as an initial offset speed field.
(4) And (3) performing offset impulse response calculation on each channel of data by using an initial offset velocity field, classifying and partially superposing impulse responses according to the offset distance of the data at the position of each common center point to form a common reflection point offset distance gather.
(5) And (3) calculating the seismic wave travel time, the migration amplitude and the dip angle of each imaging point of the pre-stack data at the sample CDP position by using the final migration velocity field, arranging according to the dip angle, and partially stacking to obtain the dip angle gather of the sample CDP position.
(6) And determining dip angle imaging areas aiming at the dip angle gather corresponding to the sample CDP, and determining the dip angle imaging areas corresponding to the rest CDP positions by utilizing the determined plurality of dip angle imaging areas in an interpolation continuation mode.
(7) And calculating the dip angle of each imaging point on all CDP positions of the data before the stacking by using the final offset velocity field, continuously calculating the travel time and amplitude of the imaging point if the dip angle is positioned in the dip angle imaging area, finishing imaging, and repeating the operation of the step for the next imaging point if the dip angle is positioned outside the dip angle imaging area.
(8) And finishing the calculation of all CDP position imaging points to obtain a final seismic imaging section.
Fig. 1 is a conventional deconvolution cross section, fig. 2 is a pulse deconvolution cross section obtained after the use, it can be seen that the signal-to-noise ratio of the deep layer in fig. 2 is significantly low, and high-frequency noise is developed violently, fig. 3 is a comparison of conventional deconvolution and pulse deconvolution spectra, the dotted line on the graph represents the conventional deconvolution spectrum, the solid line represents the pulse deconvolution spectrum, and it can be seen that the high-frequency part of the spectrum is significantly broadened after the pulse deconvolution processing. Fig. 4 is a cross section of full-frequency imaging after conventional post-stack denoising, fig. 5 is a cross section obtained by full-frequency imaging after the method of the present invention is adopted, it can be seen that interlayer information is richer in fig. 5, details are depicted more clearly, fig. 6 is a cross section frequency spectrum obtained by full-frequency imaging after conventional post-stack denoising and the method of the present invention, a dotted line on the graph represents a frequency spectrum of the conventional post-stack denoising method, a solid line represents a frequency spectrum processed by the method of the present invention, it can be seen that the frequency spectrum obtained by the method of the present invention is obviously superior to the conventional post-stack denoising method in terms of bandwidth, although the conventional post-stack denoising suppresses high-frequency noise, improves the signal-to-noise ratio, but damages the high-frequency effective signal, and the method of the present invention does not damage the high-frequency effective.
Claims (3)
1. A full band imaging method, comprising the steps of:
step one, performing conventional noise suppression processing on seismic data before stacking;
carrying out full-band frequency extension processing on the seismic data subjected to noise suppression by using a single-channel pulse deconvolution technology, wherein a pulse function is used as expected output of pulse deconvolution;
step three, aiming at a plurality of common center point positions on the seismic imaging section, extracting common center point gathers, recording the gathers as sample CDP, carrying out conventional dynamic correction speed pickup on the gathers, and carrying out interpolation smoothing on the obtained result to be used as an initial migration speed field;
step four, performing offset impulse response calculation on each channel of input data by using an initial offset velocity field, classifying and partially overlapping the offset impulse response according to the offset distance of the input data to form a common reflection point offset distance gather for each common center point position, and determining a final offset velocity field according to whether the in-phase axis in the common reflection point gather is straight or not;
step five, calculating the seismic wave travel time, the migration amplitude and the dip angle of each imaging point of the pre-stack data at the sample CDP position by using the final migration velocity field, arranging according to the dip angle, and partially overlapping to obtain a dip angle gather of the sample CDP position;
the calculation of the travel time, the offset amplitude and the dip angle of the seismic wave is realized as follows: starting from a one-way wave equation and a phase-stabilizing point principle, defining the horizontal coordinate of an excitation point as xsHorizontal coordinate of receiving point is xgPhi is the azimuth angle, the coordinates of the imaging point are (x, T), and the offset velocity of the imaging point is vrmsAnd seismic wave travel time from the excitation point to the imaging point and then to the receiving point:
defining integers
Wherein delta t is the sampling interval of the seismic data, the amplitude values of four points i-1, i, i +1 and i +2 on the seismic data are used for quadratic curve interpolation, the seismic amplitude value delta at the travel time tau is solved, and the dimensionless imaging weight coefficient is calculated
The magnitude of the shift at the imaging point (x, T) is then
And (3) obtaining the inclination angle: the following variables, x1＝xs-x,x2＝xs+xg-2 x; calculating the distance variable a ═ x1cosφ；b＝x1x2+2(vrmsT)2；c＝x2cosφ；
Then k is equal to (ad)2-bc)/(c2-d2) The inclination angle theta is arctan[(x1+kcosφ)/(vrmsT)]；
Determining dip angle imaging areas aiming at the dip angle gather corresponding to the CDP positions of the sample, and determining the dip angle imaging areas corresponding to the rest CDP positions by utilizing the determined dip angle imaging areas in an interpolation continuation mode;
step seven, utilizing the final offset velocity field to calculate the dip angle of each imaging point on all CDP positions of the data before the stack, if the dip angle is positioned in the dip angle imaging area, continuously calculating the travel time and the amplitude of the imaging point to finish imaging, and if the dip angle is positioned outside the dip angle imaging area, repeating the operation of the step on the next imaging point;
and step eight, finishing the calculation of all CDP position imaging points to obtain a final seismic imaging section.
2. The full band imaging method of claim 1, wherein: the step three is realized by that a plurality of common center point positions on the seismic imaging section are extracted, and the common center point gather is extracted: and selecting the position of the common center point at equal intervals on the conventional section according to the change condition of the structure, and distributing the offset distances at equal intervals from small to large when extracting the common center point gather.
3. The full band imaging method of claim 1, wherein: the sixth step is a method for determining the dip angle imaging area for the dip angle gather corresponding to the sample CDP position:
a decision condition is introduced to the system that,
psi (t, x) is an imaging value corresponding to an angle of an imaging point x at a time depth t position in the dip gather,angle of imaging point at time depth t position of dip trace concentration from theta-eta1To theta + eta2Imaging stack value in the range, θ is tiltThe true formation dip angle at the time depth t position of the angle trace concentration, gamma is a threshold value and is set as
AmaxWhen the condition is satisfied, the imaging result at the time depth t position tends to be stable and presents a phase-stable state [ theta-eta ] for the maximum absolute amplitude of the dip gather1,θ+η2]Is the dip imaging area to be determined at the time depth t position of the dip gather.
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| CN111538077A (en) * | 2020-05-07 | 2020-08-14 | 中国石油天然气集团有限公司 | Pre-stack depth migration method and device based on dip angle constraint |
| CN115857007A (en) * | 2022-11-15 | 2023-03-28 | 东北石油大学 | Full-signal imaging method and device |
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