CN109633737B - Marine broadband air gun source based on the combination of virtual and real depth - Google Patents
Marine broadband air gun source based on the combination of virtual and real depth Download PDFInfo
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- G01V1/02—Generating seismic energy
- G01V1/133—Generating seismic energy using fluidic driving means, e.g. highly pressurised fluids; using implosion
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- G—PHYSICS
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- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
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- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/02—Generating seismic energy
- G01V1/133—Generating seismic energy using fluidic driving means, e.g. highly pressurised fluids; using implosion
- G01V1/137—Generating seismic energy using fluidic driving means, e.g. highly pressurised fluids; using implosion which fluid escapes from the generator in a pulsating manner, e.g. for generating bursts, airguns
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Abstract
The invention discloses a kind of marine broadband air gun source based on the combination of virtual and real depth, including principal earthquake source and N grades of auxiliary focus, the Mintrop wave of first order auxiliary focus and the ghost reflection in principal earthquake source in the N grades of auxiliary focus are completely counterbalanced by far field end；The Mintrop wave of next stage auxiliary focus and the ghost reflection of its upper level auxiliary focus are completely counterbalanced by far field end；Auxiliary focus is equivalent to the air gun source for being set in specific virtual depth；Principal earthquake source and N grades of auxiliary focus itself are designed as the air-gun array that there is real depth to combine simultaneously；The Mintrop wave in-phase stacking of air gun at different depth in principal earthquake source may be implemented by the way of delay excitation.The present invention effectively improves low frequency response, while compensating for the frequency domain trap introduced by virtual and real depth ghost reflection；Realize the purpose of design of broadband source wavelet.
Description
Technical field
The invention belongs to air gun source design field, in particular a kind of marine wideband based on the combination of virtual and real depth
Band air gun source.
Background technique
Common air gun source marine at present is to be composed of the different air gun of more bar capacity in same depth.Using
The mode that multiple gun excites simultaneously realizes Mintrop wave in-phase stacking, simultaneously because utilizing the difference of bubble oscillation period caused by capacity volume variance
Offset residual bubble.Polarity occurs when Mintrop wave travels to sea to invert to form ghost reflection.The presence of focus ghost reflection, causes frequency
The missing of some specific frequencies in domain reduces the resolution ratio of seismic data, referred to as trap effect.In order to eliminate trap effect,
It has been proposed that air gun submatrix or single rifle are placed at different depth, are excited using delay and guarantee Mintrop wave in-phase stacking, and swashed
The delay of hair time causes ghost reflection no longer in-phase stacking, to realize the compensation of trap.However theoretical and actual observation all shows
This three-dimensional combination can't improve the response of ultralow frequency end (mainly 7Hz or less), this is mainly by ghost reflection trap and bubble
Caused by shaking dominant frequency leading " neutralizing effect " (Hopperstad, et al., 2012).Citation information is as follows:
Hopperstad, J.F.,Laws,R.,and Kragh,E.2012.Hypercluster of airguns–more low
frequencies for the same quantity of air.74th Annual International Meeting,
EAGE,Expanded Abstracts,Z011.
" neutralizing effect " for causing low frequency to lack can understand in terms of two: 1) high pressure gas is after being discharged into water, meeting
Rectilinear oscillation is generated, the dominant frequency of oscillation increases as air gun shooting depth increases, and becomes strong to the compacting of low frequency energy, such as Fig. 1
It is shown；2) ghost reflection weakens in the trap effect that frequency domain introduces with the increase of depth, weakens to the compacting of low frequency energy, such as
Shown in Fig. 2.Two kinds of effects interact in far field, the change of low frequency energy will not be caused change in depth, such as Fig. 3 institute
Show.It is also found that ghost reflection trap causes some specific frequencies missing of medium-high frequency from Fig. 3, the complete of frequency spectrum is affected
Property.Trap frequency changes with depth simultaneously, and diversity feature is presented.
Nietal. (2017) propose to utilize auxiliary focus (such as 1/3 main seismic source energy) counteracting portion smaller than principal earthquake source capacity
Divide principal earthquake source ghost reflection, enhances low frequency energy to a certain extent.But due to being partial offset, low frequency improves to be had very much
Limit, does not all compensate simultaneously for the low frequency trap and original medium-high frequency trap thus introduced.Citation information
It is as follows: Ni, Y., Shen, H., and Elboth, T.2017.Method and device for boosting low-
The present invention is based on auxiliary focus by frequencies for a marine seismic survey.US2017/0276774A1.
It realizes that ghost reflection is completely counterbalanced by and significantly enhances low frequency response, in combination with the trap diversity of real depth combination, realize
The purpose of design of broadband air gun source.
Summary of the invention
It is an object of the invention to overcome the deficiencies in the prior art, the present invention intends on the basis that more depth solids combine
Principal earthquake source ghost reflection is offset by introducing auxiliary focus, to break neutralizing effect, improves low frequency response, while compensating medium-high frequency
Trap realizes the design of broadband air gun source truly.
Technical scheme is as follows:
Marine broadband air gun source based on the combination of virtual and real depth includes: principal earthquake source and N grades of auxiliary focus, N
≥1；Principal earthquake source is for obtaining main excitation signal；
In the N grades of auxiliary focus, first order auxiliary focus obtains the first auxiliary spark excitation signal for exciting；Described first
Auxiliary spark excitation signal is identical as the ghost reflection that main excitation signal is formed, but polarity is on the contrary, the excitation instant of first order auxiliary focus is
When the ghost reflection in principal earthquake source reaches first order auxiliary focus, the Mintrop wave of first order auxiliary focus and the ghost reflection in principal earthquake source are in far field
It is completely counterbalanced by；
The ghost reflection that next stage assists the excitation signal of focus to be formed with the excitation signal of its upper level auxiliary focus is identical, but
Polarity on the contrary, next stage auxiliary focus excitation instant be its upper level assist focus ghost reflection reach this grade assist focus when
It waits, the ghost reflection of the Mintrop wave and its upper level auxiliary focus of next stage auxiliary focus is completely counterbalanced by far field.
Preferably, the principal earthquake source and N grades of auxiliary focus are more depth solid focus.
Preferably, the principal earthquake source and N grades of auxiliary focus are made of the multistage air gun unit for being located at different depth；Often
Grade air gun unit is including one or more air gun, and principal earthquake source assists the air gun unit series of focus identical with N grades.
Preferably, between the air gun type of the principal earthquake source and N grades of auxiliary focus, combined capacity, depth of placement and depth
Every all the same.
The invention also discloses a kind of depth of marine broadband air gun source to combine exciting method, including walks as follows
It is rapid:
1) according to exploration demand, it is designed and arranged principal earthquake source, wherein principal earthquake source is more depth solid focus, and according to principal earthquake
Source is designed and arranged N grades of auxiliary focus, keeps the first auxiliary spark excitation signal identical as the ghost reflection that main excitation signal is formed, but polarity phase
Instead, the excitation signal of next stage auxiliary focus is identical as the ghost reflection that the excitation signal of its upper level auxiliary focus is formed, but polarity
On the contrary；
2) principal earthquake source is excited, keeps principal earthquake source each by the way of delay excitation according to the depth of placement interval of three-dimensional focus
Form the Mintrop wave in-phase stacking of air gun；
3) when the ghost reflection in principal earthquake source reaches first order auxiliary focus, it is same excited using delay by the way of excite the
Level-one assists focus, and the ghost reflection of the Mintrop wave and principal earthquake source that make first order auxiliary focus is completely counterbalanced by far field；When upper level assists
When the ghost reflection of focus reaches next stage auxiliary focus, excites next stage to assist focus in an identical manner, keep next stage auxiliary
The Mintrop wave of focus is helped to assist the ghost reflection of focus to be completely counterbalanced by far field with its upper level, until N grades of auxiliary focus are excited and finished.
In the above-mentioned methods, auxiliary focus is not necessarily identical as principal earthquake source (integrated mode and placement depth etc.),
When the two depth difference, auxiliary focus can be changed, be obtained by adjusting capacity, pressure and multiple gun assembly mode
With the approximate wave field of principal earthquake source ghost reflection, the counteracting of principal earthquake source ghost reflection also may be implemented.As preferred embodiment, the N
Grade auxiliary focus is more depth solid focus.
More further, the N grade auxiliary focus and principal earthquake source are by the multistage air gun unit for being located at different depth
Composition；Every grade of air gun unit is including one or more air gun, and principal earthquake source assists the air gun unit series of focus identical with N grades.This
When, the delay mode of excitation of step 3) the auxiliary focus specifically:
The ghost reflection in principal earthquake source is composed of the ghost reflection of principal earthquake source air gun unit excitations at different levels, the ghost reflection of air gun units at different levels
The time for reaching first order auxiliary focus is different；Air gun units at different levels in first order auxiliary focus are respectively used to completely eliminate master
The ghost reflection that the air gun unit of series generates is corresponded in focus；The firing time of air gun units at different levels in first order auxiliary focus is
Ghost reflection that the air gun unit of series generates is corresponded in principal earthquake source at the time of reach this grade of air gun unit；
Air gun units at different levels in next stage auxiliary focus are respectively used to completely eliminate respective stages in upper level auxiliary focus
The ghost reflection that several air gun units generates；Its firing time is the ghost that upper level assists the air gun unit for corresponding to series in focus to generate
At the time of wave reaches this grade of air gun unit.
More further, the principal earthquake source is identical with the depth of placement of N grades of auxiliary focus, air gun type is identical, holds
Amount combination is identical with depth interval, in this case, the air gun in the principal earthquake source or N grades of auxiliary focus at different depth
Using delay mode of excitation, different firing time t is set according to depthi:
Wherein, t0、hsIt corresponds respectively in principal earthquake source place depth most shallow air gun depth and firing time, hi、tiFor
The placement depth of i-th air gun and corresponding firing time in same focus, c are sound wave speed in water, and N is auxiliary focus grade
Not, Sp, Sa respectively indicate principal earthquake source and auxiliary focus.
Compared with prior art, the present invention has the beneficial effects that
The present invention introduces auxiliary focus Sa on the basis that conventional focus Sp (principal earthquake source) is designed, when the ghost reflection of Sp reaches
Where Sa when depth, excite Sa, the Mintrop wave that Sa is excited at this time because with Sp ghost reflection polarity on the contrary, when reaching far field two
Person realizes and cancels out each other that far-field wavelet finally obtained in this way is exactly the Mintrop wave in principal earthquake source and the superposition for assisting focus ghost reflection.
Depth h when Mintrop wave corresponds to principal earthquake source excitation at this time, and ghost reflection is for Mintrop wave, arrival time is further delayed,
Be similar to air gun be placed at virtual depth 2h excite as a result, thus having broken the neutralizing effect dominated by same depth.
The present invention proposes to introduce more depth solid focus among the design of virtual depth focus, by different air guns or son
Battle array is placed at different depth, and the Mintrop wave in-phase stacking of different air guns may be implemented by the way of delay excitation, utilize simultaneously
Diversity of the trap frequency with change in depth, therefore effectively trap compensation can be carried out.
Of the invention effectively improves low frequency response based on virtual and real depth combination focus, while compensating for level
The trap of focus；Realize the purpose of design of broadband source wavelet.
Detailed description of the invention
Fig. 1 is near-field wavelet analog result when the mono- rifle of 250cu.in excites at different depth, and Fig. 1 (a) is time-domain
Wave morphology；Fig. 1 (b) is corresponding spectrum curve.
Fig. 2 is impulse response comparing result of the ghost reflection trap effect under different depth shooting condition, and Fig. 2 (a) is pulse
Source wavelet form；Fig. 2 (b) is corresponding frequency spectrum, wherein assuming that the reflection coefficient of sea surface is -1.
Fig. 3 is that the mono- rifle of 250cu.in excites obtained far-field wavelet analog result at different depth, when Fig. 3 (a) is
Between domain wavelet form；Fig. 3 (b) is corresponding spectrum curve.
Fig. 4 is virtual depth building process.Fig. 4 (a) is observation system schematic diagram；Figure, 4 (b) be main focus and auxiliary shake
Source excitation time and corresponding ghost reflection time relationship schematic diagram.
Fig. 5 is virtual depth focus operation principle schematic diagram.Fig. 5 (a) is time-domain pulse wavelet, it is assumed that principal earthquake source and auxiliary
Helping the depth of focus is 6m；Fig. 5 (b) is corresponding amplitude spectrum.
Fig. 6 amplitude regulatory factor Scalar is with auxiliary focus quantity and frequency variation curve.Calculated result is based on depth
6m and water speed 1500m/s are obtained.N=0 corresponds to the case where only principal earthquake source, all exists for selected frequency signal and suppresses
It influences.
Virtual depth focus schematic diagram of the Fig. 7 based on inclination air gun mode.Principal earthquake source and auxiliary focus are multiple in figure
Air gun oblique arrangement is composed.
The virtual depth focus far-field wavelet arrival time schematic diagram that Fig. 8 is combined based on two layers of depth.
Fig. 9 is based on horizontal (Fig. 9 (a)) and tilts the virtual depth focus amplitude regulatory factor pair of (Fig. 9 (b)) integrated mode
Compare result.It is 6m that horizontal focus, which places depth, and tilts depth of focus group and be combined into 6-7-8-9-10-11m.Two kinds of focus are all adopted
It is combined with 6 rifles, amplitude regulatory factor Scalar=1 corresponds to Fidelity signal.
Figure 10 is that conventional levels tune rifle battle array and assist the inclination combine analog virtual depth focus pair of focus comprising one
Than.Figure 10 (a) is time-domain wavelet form, and Figure 10 (b) is corresponding spectrum curve.
Specific embodiment
Invention is described further with reference to the accompanying drawing.
In order to break neutralizing effect, the marine broadband air gun source packet of the invention based on the combination of virtual and real depth
It includes: principal earthquake source and N grades of auxiliary focus, N >=1；In the N grades of auxiliary focus, first order auxiliary focus obtains first for exciting
Auxiliary spark excitation signal；The first auxiliary spark excitation signal is identical as main excitation signal, and the excitation instant of first order auxiliary focus is
When the ghost reflection in principal earthquake source reaches first order auxiliary focus, the Mintrop wave of first order auxiliary focus and the ghost reflection in principal earthquake source are supported completely
Disappear；Next stage assists the excitation signal of focus identical as its upper level auxiliary excitation signal of focus, and next stage assists focus
Excitation instant be its upper level assist focus ghost reflection reach this grade assist focus when, next stage assist focus Mintrop wave with
The ghost reflection of its upper level auxiliary focus is completely counterbalanced by.
It is described with reference to the drawings as follows: introducing auxiliary focus Sa on the basis of conventional focus Sp (principal earthquake source) design, such as
Shown in Fig. 4 (a).Where the ghost reflection of Sp reaches Sa when depth, Sa is excited, the Mintrop wave that Sa is excited at this time is because terrible with Sp
Wave polarity is cancelled out each other on the contrary, realizing both when reaching far field, and far-field wavelet finally obtained in this way is exactly the head in principal earthquake source
Wave and the superposition for assisting focus ghost reflection, as shown in Fig. 4 (b).Depth h when Mintrop wave is corresponding to principal earthquake source excitation at this time, and it is terrible
Wave for Mintrop wave, further delayed by arrival time, be similar to air gun be placed at virtual depth 2h excite as a result,
Thus the neutralizing effect dominated by same depth has been broken.In order to realize being completely counterbalanced by for Sp ghost reflection, method the simplest
Exactly auxiliary focus is designed as forming with principal earthquake source and placement depth is identical.
Fig. 5 gives the virtual depth focus by taking pulse wavelet as an example, and principal earthquake source and auxiliary focus are all placed on 6m at this time
Depth corresponds at 12m virtual depth by Fig. 5 (a) as can be seen that final ghost reflection has twice of time delay.Phase
Answer in frequency domain, low frequency energy will be compensated, as shown in Fig. 5 (b).But it can introduce fall at about 60Hz accordingly
Wave.
When for only one auxiliary focus as shown in Figure 4 and Figure 5, final far-field wavelet P (t) be may be expressed as:
P (t)=Pp(t)-Pp(t+4h/c) (1)
Wherein PpIt (t) is the Mintrop wave of main pulse, h is main focus and the placement depth for assisting focus, and c is that underwater acoustic wave is fast
Degree.
In order to further increase low frequency response, it is not auxiliary for offsetting upper level that more auxiliary focus can be introduced accordingly
The ghost reflection of focus is helped, far-field wavelet P (t) final in this way is exactly that principal earthquake source Mintrop wave is superimposed with the ghost reflection of the last one auxiliary focus
As a result:
P (t)=Pp(t)-Pp(t+2(n+1)h/c) (2)
Wherein n is the number for assisting focus.Through formula (2) as can be seen that compared with Mintrop wave, ghost reflection is considered as being right
The excitation result of Ying Yu (n+1) * h depth.
Formula (2) is done into Fourier transform to frequency domain, and seeks amplitude spectrum and obtains:
P (f) |=Scalar | Pp(f)| (3)
Wherein P (f) and PpIt (f) is respectively P (t) and Pp(t) amplitude spectrum.Assist change of the introducing of focus for Mintrop wave
It can be described by product term amplitude regulatory factor Scalar.
Fig. 6 gives Scalar with the rule of auxiliary focus quantity n and frequency f variation.It is indicated as Scalar > 1
Head wave energy is enhanced, and is then compressed on the contrary.And ideally the regulatory factor numerical value of all frequencies is all 1, meaning
Signal fidelity it is high.From fig. 6, it can be seen that, when Sa is less than 5, energy increases with Sa for 7Hz or less low frequency part
More approximately linear enhancings, need sufficient amount of Sa (in such as this particularly with ultra low frequency signal such as 2Hz signal in figure
10) it can just be completely counterbalanced by the pressing result of ghost reflection.For 7Hz frequencies above, excessive Sa makes since virtual depth is excessive
It is lower at trap frequency, therefore presents first to increase and subtract feature afterwards, such as 15Hz frequency signal, suppressed strongly in n=7, frequency is rung
The phenomenon that the case where only principal earthquake source should be even lower than, the introducing of virtual depth causes trap frequency to reduce, is consistent with Fig. 5.It is right
In full waveform inversion, since mainly based on low frequency signal, the medium-high frequency trap that this auxiliary focus introduces not will cause very
It is big to influence, but for high-resolution seismic survey, due to needing broadband focus to guarantee frequency spectrum integrity degree, it is therefore desirable to centering
High frequency trap compensates.
In order to overcome the problems, such as this, more depth solid focus are introduced into virtual depth focus and design it by present invention proposition
In.Trap frequency f caused by ghost reflectionnIt is related with depth, it can indicate are as follows:
Wherein θ is wavelet incident angle, θ=90 ° when below vertical air gun.
Different air guns or submatrix are placed at different depth, different air guns may be implemented by the way of delay excitation
Mintrop wave in-phase stacking, while trap frequency is utilized with the diversity of change in depth, therefore effectively trap benefit can be carried out
It repays.Fig. 7 gives the virtual depth focus schematic diagram based on inclination air gun array mode.Fig. 7 left half is conventional inclination
Air gun source, figure right half are auxiliary focus.The firing time t of air guniIt may be expressed as:
Wherein, hsAnd t0Respectively most shallowly locate principal earthquake source air gun depth and firing time, hiFor the placement depth of air gun i.It is auxiliary
The each single rifle firing time helped in focus delays 2h than being placed in the principal earthquake source list rifle at same depths/c。
Fig. 8 illustrates each air gun firing time schematic diagram in the virtual depth focus combined by two layers of depth.It can be seen that
It is combined using real depth, the in-phase stacking of ghost reflection can be destroyed, while the ghost reflection arrival time of differentiation has broken by same
The leading neutralizing effect of one depth.
Similarly, for there is the case where n grades of auxiliary focus (using canted arrays as unit), final far-field wavelet P (t) can
It indicates are as follows:
Wherein, Pi(t) wavelet for being air gun i, m are main focus air gun number.It is assumed that principal earthquake source and auxiliary focus
Wave morphology is consistent, only there is temporal delay.It can be realized being laid in a manner of relevant rifle in same depth
(principal earthquake source and auxiliary focus air gun each one, at this time d~=1m in Fig. 7).
Using with formula (3) and (4) identical thinking, Fourier transform is done to formula (7) while seeking its amplitude spectrum, can
To obtain the amplitude regulatory factor Scalar under inclination air gun array mode:
Result as shown in Figure 9 is obtained for assisting the influence of focus quantity to be simulated based on formula (8).Here false
If tilting combined principal earthquake source to be composed of 6 rifles, and depth groups are combined into 6-7-8-9-10-11m.Left figure is based on horizontal air gun
The virtual depth focus of integrated mode (depth 6m) is as a result, it is apparent that increasing with auxiliary focus quantity, low frequency
Energy is enhanced, and sinking degree is eased, but simultaneously, in same frequency range, assists the increase of focus quantity
Improve the frequency of trap appearance.And the virtual depth focus for tilting air gun array, low frequency improvement and horizontal pattern
Quite, while having benefited from the trap diversity of more depth, the number that medium-high frequency trap occurs is significantly lower than conventional levels mode.?
In the dominant frequency band frequency range of air gun excitation (such as 10-150Hz), secondary trap can just go out when introducing 4 groups of auxiliary focus
It is existing.
Figure 10 compared horizontal focus (250-150-100-80-60-40cu.in tunes rifle battle array), 12 rifles of 6 rifles combination
The horizontal focus (2 group of 6 rifle tunes rifle battle array) of combination and the virtual depth focus based on 6-11m tilt mode comprising one layer of Sa
(combination of 250-150-100-80-60-40cu.in order, depth interval 1m) far-field wavelet form and spectrum curve.With 6 rifle groups
It closes focus to compare, it can be clearly seen that virtual depth focus effectively improves low frequency response, while compensating for horizontal focus position
In the trap of 125Hz.Realize the purpose of design of broadband source wavelet.It is combined with 12 rifles compared to (air gun used in the two always holds
Measure identical), virtual focus slightly has advantage for low frequency enhancing ability, while can to avoid conventional capacity it is directly cumulative caused by
Destruction of the high impulse (long dotted line in Figure 10 (a)) for marine environment.
It should be pointed out that auxiliary focus is not necessarily identical as principal earthquake source (integrated mode and placement depth etc.),
When the two depth difference, needs to be changed auxiliary focus, be obtained by adjusting capacity, pressure and multiple gun assembly mode
With the approximate wave field of principal earthquake source ghost reflection, the counteracting of principal earthquake source ghost reflection also may be implemented.
Claims (10)
1. a kind of marine broadband air gun source based on the combination of virtual and real depth, characterized by comprising:
Principal earthquake source, for obtaining main excitation signal；
N grades of auxiliary focus, N >=1；
In the N grades of auxiliary focus, first order auxiliary focus obtains the first auxiliary spark excitation signal for exciting；First auxiliary
Excitation signal is identical as the ghost reflection that main excitation signal is formed, but polarity is on the contrary, the excitation instant of first order auxiliary focus is principal earthquake
When the ghost reflection in source reaches first order auxiliary focus, the first order assists the Mintrop wave of focus and the ghost reflection in principal earthquake source complete in far field
It offsets；
The ghost reflection that next stage assists the excitation signal of focus to be formed with the excitation signal of its upper level auxiliary focus is identical, but polarity
On the contrary, when the excitation instant of next stage auxiliary focus is that its upper level assists the ghost reflection of focus to reach this grade auxiliary focus,
The Mintrop wave of next stage auxiliary focus and the ghost reflection of its upper level auxiliary focus are completely counterbalanced by far field.
2. the marine broadband air gun source according to claim 1 based on the combination of virtual and real depth, feature exist
In the principal earthquake source and N grades of auxiliary focus be more depth solid focus.
3. the marine broadband air gun source according to claim 1 or 2 based on the combination of virtual and real depth, feature
It is that the principal earthquake source and N grades of auxiliary focus are made of the multistage air gun unit for being located at different depth；Every grade of air gun unit
Including one or more air gun, principal earthquake source assists the air gun unit series of focus identical with N grades.
4. the marine broadband air gun source according to claim 1 or 2 based on the combination of virtual and real depth, feature
It is that air gun type, combined capacity, depth of placement and the depth interval in the principal earthquake source and N grades of auxiliary focus are all the same.
5. a kind of depth based on broadband air gun source in sea described in claim 1 combines exciting method, it is characterised in that packet
Include following steps:
1) according to exploration demand, it is designed and arranged principal earthquake source, wherein principal earthquake source is more depth solid focus, and is set according to principal earthquake source
Meter and arrangement N grades of auxiliary focus, keep the first auxiliary spark excitation signal identical as the ghost reflection that main excitation signal is formed, but polarity on the contrary,
The ghost reflection that next stage assists the excitation signal of focus to be formed with the excitation signal of its upper level auxiliary focus is identical, but polarity phase
Instead；
2) principal earthquake source is excited, forms principal earthquake source respectively by the way of delay excitation according to the depth of placement interval of three-dimensional focus
The Mintrop wave in-phase stacking of air gun；
3) same to excite the first order by the way of delay excitation when the ghost reflection in principal earthquake source reaches first order auxiliary focus
Focus is assisted, the ghost reflection of the Mintrop wave and principal earthquake source that make first order auxiliary focus is completely counterbalanced by far field；When upper level assists focus
Ghost reflection reach next stage auxiliary focus when, in an identical manner excite next stage assist focus, make next stage auxiliary shake
The Mintrop wave in source and the ghost reflection of its upper level auxiliary focus are completely counterbalanced by far field, until N grades of auxiliary focus are excited and finished.
6. according to the method described in claim 5, it is characterized in that the N grade auxiliary focus is more depth solid focus.
7. according to the method described in claim 6, it is characterized in that the N grade auxiliary focus and principal earthquake source is different by being located at
The multistage air gun unit of depth forms；Every grade of air gun unit is including one or more air gun, the gas in principal earthquake source and N grades of auxiliary focus
Rifle unit series is identical.
8. according to the method described in claim 7, it is characterized in that the delay mode of excitation tool of step 3) the auxiliary focus
Body are as follows:
The ghost reflection in principal earthquake source is composed of the ghost reflection of principal earthquake source air gun unit excitations at different levels, and the ghost reflection of air gun units at different levels reaches
The first order assists the time of focus different；Air gun units at different levels in first order auxiliary focus are respectively used to completely eliminate principal earthquake source
The ghost reflection that the air gun unit of middle corresponding series generates；It is principal earthquake that the first order, which assists the firing time of the air gun units at different levels in focus,
Ghost reflection that the air gun unit of series generates is corresponded in source at the time of reach this grade of air gun unit；
Air gun units at different levels in next stage auxiliary focus, which are respectively used to completely eliminate in upper level auxiliary focus, corresponds to series
The ghost reflection that air gun unit generates；Its firing time is that the ghost reflection that upper level assists the air gun unit for corresponding to series in focus to generate arrives
At the time of up to this grade of air gun unit.
9. according to the method described in claim 5, it is characterized in that the depth of placement phase in the principal earthquake source and N grades of auxiliary focus
, combined capacity identical with, air gun type and depth interval are identical.
10. according to the method described in claim 9, it is characterized by: different depth in the principal earthquake source or N grades of auxiliary focus
The air gun at place sets different firing time t according to depth using delay mode of excitationi:
Wherein, t0To place the most shallow air gun firing time of depth, h in main focussTo place the most shallow air gun of depth in main focus
Depth, hi、tiPlacement depth and corresponding firing time for the i-th air gun in same focus, c are that speed, N are sound wave in water
Focus rank is assisted, Sp, Sa respectively indicate principal earthquake source and auxiliary focus.
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| CN110568479B (en) * | 2019-08-26 | 2021-04-06 | 广州海洋地质调查局 | Method for determining far-field wavelet of marine air gun seismic source |
| CN110579791B (en) * | 2019-09-09 | 2020-08-14 | 自然资源部第二海洋研究所 | Method for reducing air gun seismic source wavelet directivity by optimizing air gun spatial distribution |
| CN114779317A (en) * | 2022-04-23 | 2022-07-22 | 中国海洋大学 | Ocean controllable coding air gun seismic source and design method |
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