CN108957551B - Vibroseis harmonic suppression method based on reconstructed ground force signal - Google Patents
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Abstract
The invention relates to a vibroseis harmonic suppression method based on a reconstructed ground force signal. Under the condition that the ground force signal cannot be estimated through a weighting sum method, by utilizing the characteristic that the direct wave is inconsistent with other seismic waves in time, the direct wave is effectively separated and extracted from the signals near the substrate through a reasonable matching filter to be used as a reconstructed ground force signal to replace an actual vibroseis lower transmission signal, and the seismic records are subjected to deconvolution processing to suppress harmonic waves. The method does not depend on the control mode and the specific coupling condition of the seismic source, not only well suppresses harmonic waves, but also greatly improves the data quality, has low requirements on the controllable seismic source control method and the control precision, has no strict limitation on the coupling of the seismic source and the earth surface, and allows the seismic source to adopt a low-cost open-loop control mode. The method has the advantages of wide application range and small target positioning error, and is suitable for hydraulic vibroseis harmonic suppression, and is also suitable for harmonic suppression of various vibroseiss with open-loop control or poor coupling conditions.
Description
The technical field is as follows:
the invention relates to a seismic exploration method, in particular to a vibroseis harmonic suppression method based on a reconstructed ground force signal.
Background art:
the controllable seismic source is favored in the exploration field because of the advantages of safety, environmental protection, low consumption, high efficiency, flexible mode and the like, the application in global land seismic exploration and acquisition occupies a great proportion, and the foreign controllable seismic source has the tendency of replacing destructive seismic sources such as explosive seismic sources and the like. However, the existence of harmonic interference is one of bottlenecks that restrict the rapid development of the vibroseis, and the existence of harmonic interference damages the quality of seismic data of the vibroseis and reduces the resolution of the data, so that the suppression of the harmonic interference becomes the research focus of the vibroseis technology, and the technology for suppressing the harmonic interference is continuously developed. Conventional methods for suppressing harmonics are mainly classified into two categories: one is to reduce the collection of harmonic interference components by improving the collection mode, adjusting the collection parameters and the like, which greatly simplifies the workload of the later data processing, but the method can not avoid the generation of harmonics, only can make the harmonic interference in the collected data smaller and delay the time of the harmonic interference; the other method is to suppress harmonic interference by carrying out relevant processing on the collected original seismic records and then carrying out processing modes such as phase shift filtering or adaptive filtering, or carrying out deconvolution processing on the original seismic records to obtain a stratum reflection coefficient. The second method has obvious harmonic suppression effect, but the method is mainly suitable for the conventional hydraulic controlled seismic sources, but is not suitable for various controlled seismic sources with open-loop control capability only, and the like, because the ground force signal cannot be effectively estimated by adopting a weighting sum method, the application range of the method is limited. Cao (2010) replaces correlation with deconvolution to suppress harmonic interference of a conventional hydraulic vibroseis with closed-loop control capability, the method can effectively suppress near-surface influence and harmonic components and improve data quality, but the method depends on vibroseis precision control and surface coupling conditions, is feasible for a hydraulic vibroseis working environment with good coupling conditions in an exploration area, but has poor suppression effect on harmonic interference and can generate phase shift and increase target positioning error for a hydraulic vibroseis working under poor coupling conditions and other vibroseiss with only open-loop control capability.
The invention content is as follows:
the invention aims to provide a vibroseis harmonic suppression method based on reconstructed ground force signals, aiming at the defects of the prior art.
The main idea of the invention is as follows: harmonic interference in vibroseis seismic exploration records greatly damages the quality of vibroseis seismic data and reduces the resolution of the data. The invention provides a vibroseis harmonic suppression method based on reconstructed ground force signals, which is used for vibroseiss only having open-loop control capacity, such as electromagnetic vibroseiss and the like, under the condition that the ground force signals cannot be estimated through a weighting sum method, the direct waves and other seismic waves are inconsistent in arrival time, through reasonably designing a matched filter, the direct waves are effectively separated and extracted from signals near a substrate to serve as reconstructed ground force signals to replace actual lower signals of the vibroseis, and seismic records are subjected to deconvolution processing, so that the effect of suppressing harmonics is achieved. The method does not depend on the control mode and the specific coupling condition of the seismic source, and the reconstructed ground force signal is adopted to replace the actual vibroseis downlink signal to perform deconvolution processing on the seismic record, so that harmonic interference is effectively suppressed. The method widens the application range of the vibroseis harmonic suppression technology, has low requirements on the vibroseis control method and control precision, has no strict limitation on the coupling condition of the vibroseis and the earth surface, allows the vibroseis to adopt a low-cost open-loop control mode, and has wider application range in the exploration field.
The purpose of the invention is realized by the following technical scheme:
the vibroseis harmonic interference suppression method based on the reconstructed ground force signal comprises the following steps:
a. collecting single shot point record and substrate nearby signal y without relevant processing by adopting conventional electromagnetic controlled seismic source seismic exploration method1(t)；
b. Let the vibroseis scanning signal s (t) be a Chirp signal, i.e.
Wherein a is1For scanning the amplitude of the signal, flAnd fhRespectively starting and ending scanning frequencies, T is scanning length, and a matched filter of a scanning signal s (T) is designed according to the maximum signal-to-noise ratio principle, wherein the unit impulse response of the matched filter is as follows:
h(t)＝s(-t+T) (1)
wherein T is more than or equal to 0 and less than or equal to T;
c. taking a signal y near the substrate1(t), let:
v1(t)＝y1(t)*h(t) (2)
wherein represents convolution, the convolution result v1(t) includes direct wave, reflected wave, refracted wave and other interference wave, etc., and window function is constructed to separate first arrival signal d1(t) as direct wave signals, wherein the window length is selected to completely separate the first arrival signals while simultaneously separating the first arrival signalsCoherent noise such as reflected waves and refracted waves is not included;
d. defining:
g(t)＝F-1{F[d1(t)]/F[h(t)]} (3)
wherein F represents Fourier transform and F-1Representing the inverse of the Fourier transform, d (t) being known1(t) has been isolated from the signal near the substrate using step c, and thus g (t), g (t) can be calculated from equation (3)
The reconstructed seismic source excitation signal is obtained;
e. vibroseis seismic recordings can be represented as convolution between the ground force signal and the earth formation response, and thus the convolution model of the composite seismic recording is
x(t,j)＝g(t)*r(t,j) (4)
Wherein x (t, j) is the j-th seismic signal, and r (t, j) is the stratum response corresponding to the j-th seismic signal;
f. from the formula (4), deconvolution is performed to obtain
r(t,j)＝F-1{F[x(t,j)]/F[g(t)]} (5)
g. Constructing an all-pass filter z (t), wherein the phase-frequency response of the all-pass filter z (t) is opposite to the phase-frequency characteristic of the deconvolution process, and realizing zero-phase filtering correction on r (t, j) to obtain r' (t, j);
h. and e, repeating the steps e to g for each trace of the current single-shot record until all seismic trace signal processing of the current common excitation point set is completed, and effectively suppressing harmonic interference of the single-shot seismic record.
Has the advantages that: through tests, the vibroseis harmonic suppression method based on the reconstructed ground force signal, provided by the invention, can well suppress harmonic waves, the data resolution is obviously improved after deconvolution processing is carried out on seismic records, the data quality is greatly improved, the method widens the application range of the vibroseis harmonic suppression technology, has lower requirements on the vibroseis control method and control precision, has no strict limitation on the coupling condition of the vibroseis and the ground surface, allows the vibroseis to adopt a low-cost open-loop control mode, and has wider application range in the exploration field and small target positioning error. The method is not only suitable for harmonic suppression of the conventional hydraulic controllable seismic source, but also suitable for harmonic suppression of various controllable seismic sources such as electromagnetic controllable seismic sources and the like which adopt open-loop control or work under bad coupling conditions.
Description of the drawings:
FIG. 1 comparison of deconvolution processing with conventional correlation processed single trace seismic records
(a) Single trace seismic signal after conventional correlation processing
(b) Deconvolution processed single-channel seismic signal
FIG. 2 comparison of deconvolution processing with conventional correlation processed single shot seismic records
(a) Conventional correlation post-processing single shot seismic record
(b) Single-shot seismic record after deconvolution processing
The specific implementation mode is as follows:
the following is a further detailed description with reference to the accompanying drawings:
in this example, a vibroseis single shot record excitation simulation was performed using a four-layer horizontal layered underground model, with a formation width of 2000m and a depth of 860 m. Depth h of first layer medium from surface to bottom1180m, formation velocity v11200 m/s; depth h of second layer medium2130m, formation velocity v21300 m/s; depth h of third layer medium3300m, formation velocity v32000 m/s; depth h of fourth layer medium4250m, formation velocity v42500 m/s. The scanning signal adopts a Chirp signal, the initial frequency is 10Hz, the cut-off frequency is 120Hz, the scanning length is 4s, the recording time is 6s, the sampling rate is 1000, the track interval is 20m, and the number of receiving tracks is 101.
a. Collecting single shot point record and substrate nearby signal y without relevant processing by adopting conventional electromagnetic controlled seismic source seismic exploration method1(t)；
b. Let the vibroseis scanning signal s (t) be a Chirp signal, i.e.
Wherein a is1For scanning the amplitude of the signal, flAnd fhRespectively starting and ending scanning frequencies, T is scanning length, and a matched filter of a scanning signal s (T) is designed according to the maximum signal-to-noise ratio principle, wherein the unit impulse response of the matched filter is as follows:
h(t)＝s(-t+T) (1)
wherein T is more than or equal to 0 and less than or equal to T;
c. taking a signal y near the substrate1(t), let:
v1(t)＝y1(t)*h(t) (2)
wherein represents convolution, the convolution result v1(t) includes direct wave, reflected wave, refracted wave and other interference wave, etc., and window function is constructed to separate first arrival signal d1(t) the direct wave signal is selected, wherein the window length is selected to completely separate the first arrival signal and not contain coherent noise such as reflected wave, refracted wave and the like;
d. defining:
g(t)＝F-1{F[d1(t)]/F[h(t)]} (3)
wherein F and F-1Representing the Fourier transform and its inverse, since h (t) is known, d1(t) has been separated from the signal near the substrate by step c, so that g (t) can be calculated from equation (3), which is reconstructed
A seismic source excitation signal;
e. vibroseis seismic recordings can be represented as a convolution between the ground force signal and the earth formation response, and thus the convolution model of the synthetic seismic recording is:
x(t,j)＝g(t)*r(t,j) (4)
wherein x (t, j) is the j-th seismic signal, and r (t, j) is the stratum response corresponding to the j-th seismic signal;
f. from equation (4), we perform deconvolution on the second seismic trace to obtain:
r(t,2)＝F-1{F[x(t,2)]/F[g(t)]} (5)
after the deconvolution filtering processing, the signal phase spectrum changes, and the arrival time can be found to be advanced;
g. constructing an all-pass filter z (t), wherein the phase-frequency response of the all-pass filter z (t) is opposite to the phase-frequency characteristic of the deconvolution process, and performing zero-phase filtering correction on r (t, j) to obtain r' (t, j);
FIG. 1(a) is the result of the second seismic signal after the conventional correlation processing, and the result after the deconvolution processing is shown in FIG. 1(b), and it can be seen by comparison that the harmonic interference is suppressed and the arrival time error is corrected after the deconvolution processing is performed on the signal in FIG. 1 (b);
h. and e, repeating the steps e to g for each signal of the current single-shot record until all the seismic channel signals of the current common excitation point set are processed, and effectively suppressing the harmonic interference of the single-shot seismic record. And (b) comparing the full shot seismic record after the deconvolution processing with the full shot seismic record after the conventional correlation processing, so that harmonic interference is suppressed, and the effect is obvious.
Claims (1)
1. A vibroseis harmonic suppression method based on reconstructed ground force signals is characterized by comprising the following steps:
a. collecting single shot point record and substrate nearby signal y without relevant processing by adopting conventional electromagnetic controlled seismic source seismic exploration method1(t)；
b. Let the vibroseis scanning signal s (t) be a Chirp signal, i.e.
h(t)＝s(-t+T) (1)
wherein the time variable T satisfies T is more than or equal to 0 and less than or equal to T;
c. taking a signal y near the substrate1(t) let
v1(t)＝y1(t)*h(t) (2)
Wherein represents convolution, the convolution result v1(t) containsDirect wave, reflected wave, refracted wave and other interference waves, etc. to construct window function and separate first arrival signal d1(t) the direct wave signal is selected, wherein the window length is selected to completely separate the first arrival signal and not contain coherent noise such as reflected wave, refracted wave and the like;
d. defining:
g(t)＝F-1{F[d1(t)]/F[h(t)]} (3)
wherein F represents the Fourier transform, F-1Representing the inverse Fourier transform, since h (t) is known, d1(t) the seismic source excitation signal is separated from the signal near the substrate by adopting the step c, so that g (t) can be calculated by formula (3), wherein g (t) is the reconstructed seismic source excitation signal;
e. vibroseis seismic recordings can be represented as a convolution between the ground force signal and the earth formation response, and thus the convolution model of the synthetic seismic recording is:
x(t,j)＝g(t)*r(t,j) (4)
wherein x (t, j) is the j-th seismic signal, and r (t, j) is the stratum response corresponding to the j-th seismic signal;
f. from equation (4), deconvolution results:
r(t,j)＝F-1{F[x(t,j)]/F[g(t)]} (5)
g. constructing an all-pass filter z (t), wherein the phase-frequency response of the all-pass filter z (t) is opposite to the phase-frequency characteristic of the deconvolution process, and performing zero-phase filtering correction on r (t, j) to obtain r' (t, j);
h. and e, repeating the steps from e to g for each signal recorded by the current single shot in sequence until all seismic channel signals of the current common excitation point set are processed, and effectively suppressing harmonic interference of the seismic record of the single shot.
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| CN113050166B (en) * | 2019-12-27 | 2023-04-07 | 中国石油天然气集团有限公司 | Seismic excitation signal correction method and device |
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| CN101136197A (en) * | 2007-10-16 | 2008-03-05 | 得理微电子（上海）有限公司 | Digital reverberation processor based on time-varying delay-line |
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