CN106896409A - A kind of varying depth cable ghost ripple drawing method based on wave equation boundary values inverting - Google Patents

Abstract

The present invention relates to a kind of varying depth cable ghost ripple drawing method based on wave equation boundary values inverting, comprise the following steps：1) geological data to the collection of varying depth cable extracts common-shot-gather；2) one-dimensional Fourier transform is carried out to the geological data of certain big gun in common-shot-gather and obtains the frequency spectrum containing there's something fishy rolling land shakes data；3) the corresponding frequency domain geological data U containing there's something fishy ripple of certain frequencies omega in frequency spectrum is calculated_AB；4) according to geophone station depthCalculate G₁And G₂；5) according to U_ABAnd G₁And G₂Calculate the frequency domain geological data F after the corresponding terrible wave pressure system of frequencies omega_CD；6) all frequencies omegas in the big gun intermediate frequency spectrum are obtained with the frequency domain geological data after terrible wave pressure system；7) the frequency domain geological data other big guns in common-shot-gather arrived after terrible wave pressure system；8) to the frequency domain geological data F after terrible wave pressure system_CDThe common-shot-gather after inverse Fourier transform obtains terrible wave pressure system is carried out, the present invention can be used in the processing procedure of marine varying depth cable collection geological data.

Description

A kind of varying depth cable ghost ripple drawing method based on wave equation boundary values inverting

Technical field

The present invention relates to a kind of energy development exploitation method, specifically on a kind of change based on wave equation boundary values inverting Depth cable ghost ripple drawing method.

Background technology

Seismic prospecting is the important means of oil-gas exploration, particularly exploratory engineering of off-shore petroleum/gas reservoir, because its drilling cost is high, survey Other data such as well, geology are few, make have prior effect in seismic prospecting oil-gas exploration at sea.Wide band earthquake number The basic data of mid-deep strata signal to noise ratio can be improved again according to that can be construed to improve resolution ratio, improve structure interpretation and storage The precision and reliability of layer prediction, are one of targets that offshore seismic exploration is pursued.Yet with the limitation of a variety of conditions, this Target does not have realization well.When offshore seismic exploration is carried out, generally require and focus and receiver are respectively placed in Hai Ping Certain depth below face, because the contact surface of extra large water and air is a good reflecting surface, therefore receiver is except receiving To outside the back wave from subsurface interface, the ghost related to the reflex on sea level will be also received, this ghost It is exactly terrible ripple.Terrible ripple can produce trap effect to the reflected signal from underground so that the frequency band of geological data narrows, and reduces ground Shake the resolution ratio of section.When the depth of cable is larger, terrible waveguide causes false lineups to occur.At sea in seismic prospecting, drag Cable is the conventional collecting operation mode in field, typically in once gathering, will receive cable and is placed on some depth fixed On, the depth for receiving all of wave detector in cable is all identical., should be placed on towing cable to the greatest extent by the seismic data higher to obtain frequency In the shallow depth of amount, but at this moment the noise of low-frequency range can be very strong, towing cable is placed on into deeper place and is acquired and can be subtracted A small number of noises in, but because the trap of terrible ripple is acted on so that geological data frequency band narrows.Past, due to oil-gas exploration Destination layer bury shallower, most of thinner thicknesses are, it is necessary to high-resolution seismic data just can recognize that relatively thin oily Generally towing cable is tried one's best in reservoir, therefore collection is placed in shallower depth, first trap wave point of terrible ripple is located at earthquake Outside frequency range required for imaging.With the development of oil-gas exploration, the probability for finding oil-gas reservoir in middle-shallow layer is less and less, exploration Destination layer be increasingly turned to mid-deep strata.But due to the reflection of upper formation, energy subtracts significantly when seismic signal reaches mid-deep strata It is weak, the signal to noise ratio reduction of seismic data.In order to improve the signal to noise ratio of mid-deep strata, when field seismic data is gathered, cable is placed It is acquired in deeper place.This mode causes the trap influence of terrible ripple while seismic data signal to noise ratio is improved, also Greatly increase.

In order to the trap for suppressing terrible ripple influences, people use various methods in earthquake data acquisition and indoor treatment, such as Upper and lower cable acquisition method is exactly one of which.In the 1950's, Haggerty is proposed using upper and lower cable acquisition method earliest The concept of marine streamer data quality is improved, upper and lower cable acquisition method is exactly that dragging two is placed on different depth to acquisition vessel simultaneously On cable be acquired, deeper towing cable mainly measures low-frequency information, and shallower towing cable fills up the trap wave point of deep towing cable, so And the complexity and field operation difficulty that this can increase collection.Double inspection acquisition methods are the field acquisitions of another ghost wave pressure Method, double inspection acquisition methods increased land inspection (velocity detector) outside water inspection (pressure detector), and two sets of wave detectors are integrated In the same position of cable, pressure wavefield and the change of speed wave field that seismic wave causes in seawater communication process are recorded respectively, Optimal proportion merging is carried out to two kinds of output signals of wave detector, you can the terrible ripple of compacting.3rd method of terrible wave pressure is to become Depth cable is gathered, and in this kind of acquisition method, cable is placed on the oblique line at non-zero inclination angle or on curved line, so that terrible ripple Trap wave point is decentralized.Used as a kind of new acquisition method, its purpose is by making different inspections in cable to varying depth towing cable collection The trap wave point dispersion of ripple device, so as to be conducive to suppressing terrible ripple, while the part on towing cable away from ship is placed trying one's best deeply so that low Frequency range obtains the data of high s/n ratio.Constant depth with tradition collection is different, and the depth of towing cable changes with offset distance, drags The placement depth of the wave detector of diverse location is different in cable, and the trap frequency of each wave detector is different, so that finally combining The result of different wave detectors does not have obvious trap wave point.Treatment varying depth gathered data committed step is the pressure of geophone station ghost ripple System.The geological data of varying depth cable collection further suppresses terrible ripple for us and provides an extraordinary data basis, but this Planting data will can be only achieved the purpose of the terrible ripple of compacting and the frequency band for widening geological data by specific processing method.2010, The processing method of the geological data that Soubaras et al. is gathered to varying depth cable re-starts research, proposes to pass through joint deconvolution Method suppresses ghosting, and the basic thought of the method is to enter line displacement and mirrored offset to varying depth cable data, at the two Joint deconvolution is carried out on the basis of offset data to suppress terrible ripple, achieves preferable effect.2012, Soubaras again will The method is generalized to pre stack data, and the advantage of this method is that the terrible ripple of receiving point is regarded as a kind of special ripple by it, but The method needs to complete to offset twice, increases amount of calculation, therefore researcher solves double skew meters using filter operator is optimized The problem of calculation, terrible wave pressure system is realized for pre stack data.Researcher proposes a kind of frequency domain for varying depth cable geological data Radon transform methods, based on the ray path of receiving point ghost ripple, provide a kind of Radon inverse transformations operator, the method can with compared with Accuracy prediction ghost ripple high, then subtracts the terrible ripple of prediction, and then reach terrible wave pressure from the actual geological data for receiving Purpose.The application of these methods substantially increases the pressing result of terrible ripple, but these methods are all to carry out letter to wave equation Put forward after change, be adapted to the better simply underground medium of subsurface structure.With the development of oil-gas exploration, the oil-containing of main exploration Gas stratum becomes increasingly complex, for this complicated underground medium, the precision reduction of the terrible ripple of above method compacting, it is difficult to ghost completely Wave pressure system.

The content of the invention

Regarding to the issue above, it is applied to complicated underground medium it is an object of the invention to provide one kind and terrible wave pressure can be improved Varying depth cable based on the wave equation boundary values inverting ghost ripple drawing method of precision processed.

To achieve the above object, the present invention takes following technical scheme：A kind of deepening based on wave equation boundary values inverting Degree cable ghost ripple drawing method, it is characterised in that comprise the following steps：1) geological data to the collection of marine field varying depth cable is taken out Take common-shot-gather；2) geological data to certain big gun in common-shot-gather carries out one-dimensional Fourier transform, obtains containing there's something fishy ripple The frequency spectrum of geological data；3) the corresponding frequency domain geological data U containing there's something fishy ripple of certain frequencies omega in frequency spectrum is calculated_AB；4) according to defeated The geophone station depth for enteringIt is calculated the GREEN functions G of seawater face lower section datum level₁With datum level relative to seawater face The GREEN functions G of line of symmetry₂；5) according to obtaining the frequency domain geological data U containing there's something fishy ripple_ABAnd the G being calculated₁With G₂, it is calculated the frequency domain geological data F after the corresponding terrible wave pressure system of frequencies omega_CD；6) in common-shot-gather intermediate frequency spectrum All frequencies omegas carry out step 3)~5) obtain the frequency domain geological data after terrible wave pressure system；7) in common-shot-gather other Big gun carries out step 2)~6) obtain the frequency domain geological data after terrible wave pressure system；8) to the frequency domain earthquake number after terrible wave pressure system According to F_CDInverse Fourier transform is carried out, the common-shot-gather after terrible wave pressure system is obtained.

Further, the corresponding frequency domain geological data U containing there's something fishy ripple of certain frequencies omega in frequency spectrum is calculated_ABDetailed process For：Definition datum face is CD, and seawater face is EF, and varying depth cable is AB, is observed at CD, EC and FD section, the earthquake for obtaining Record is respectively u_CD、u_ECAnd u_FD, the earthquake record of varying depth cable AB is u in the seawater_AB, it is theoretical according to wave equation, by u_CD To u_ABForward problem be written as the direct problem of scattering form：

u(x,z,t)|_{(x, z) ∈ EC}=u_EC (8)

u(x,z,t)|_(x,z)∈FD=u_FD (9)

The boundary condition of seawater face EF is taken for free boundary condition, i.e.,：

In time t=0, wave field not yet starts to propagate, and primary condition is taken as：

Wherein, u (x, z, t) is displacement wave field, and x, z is respectively coordinate both horizontally and vertically, and v (x, z) is in medium The speed of (x, z) point, f_CDIt is by u_CDThe scattering source function that integration is obtained, for practical problem, u_ECAnd u_FDCannot obtain, Therefore absorbing boundary condition is taken on EC and FD, because forward problem is the propagation problem of the ripple for considering in the seawater, thus speed Degree can take constant value, i.e.,：

Because water meter is negative reflection, reflectance factor is -1, therefore seismic wave is divided into two parts, and a part is to pass directly up The wave table broadcast is shown as u₁, another part is to be shown as u by the backward lower wave table propagated of seawater face EF reflections₂, total wave field is expressed as u =u₁+u₂, and u₁Meet：

u₂Meet：

Wherein, line of symmetries of the face CD relative to seawater face EF, f on the basis of C ' D '_C’D’It is f_CDMirror image function, and f_C’D’With f_CDEqual in magnitude, now, formula (13) and (14) are the equation in uniform infinite medium, equal to formula (13) and (14) both sides Fourier transformation is taken on the time to obtain：

Formula (15) and (16) are obtained by GREEN function representations and solution：

Wherein, G₁、G₂It is GREEN functions, the receiving point of formula (17) and (18) on varying depth cable AB is also set up, i.e.,：

Above-mentioned formula (19) and (20) is write as matrix form to obtain：

U_AB1=G₁F_CD (21)

U_AB2=-G₂F_CD (22)

Formula (21) and (22) are merged and obtains the frequency domain geological data U containing there's something fishy ripple_AB：

U_AB=G₁F_CD-G₂F_CD=(G₁-G₂)F_CD (23)

Further, according to the geophone station depth of inputIt is calculated the GREEN functions of seawater face lower section datum level G₁The GREEN functions G of the line of symmetry with datum level relative to seawater face₂Detailed process is：In equal medium, the meter of GREEN functions Calculating formula is：

Wherein, parameter k=ω/v；Parameter

According to the geophone station depth of inputAnd formula (24) and (25) are calculated G respectively₁And G₂：

Further, according to the frequency domain geological data U containing there's something fishy ripple_ABAnd the G being calculated₁And G₂, it is calculated Frequency domain geological data F after frequencies omega ghost wave pressure system_CDDetailed process is：In formula (23), G₁-G₂It is a matrix, according to Formula (25)~(27) are calculated G₁-G₂, the sinking depth profile of varying depth cable AB during according to marine field earthquake data acquisition Obtain geophone station depthF_CDThe frequency domain geological data of terrible ripple is free from, is amount to be asked；U_ABObtained when being field earthquake-capturing The frequency domain geological data containing there's something fishy ripple for arriving, is known quantity, and the frequency without there's something fishy ripple is obtained by the solution of formula (23) Domain geological data F_CD。

Due to taking above technical scheme, it has advantages below to the present invention：1st, the present invention is described using wave equation The generation process of terrible ripple, thus with precision higher, propagation and ghost of the seismic wave in underground medium can well be described The generation process of ripple.2nd, the present invention is based on wave equation boundary values inverting, and the compacting problem of terrible ripple is attributed into the side of wave equation Value inversion problem, terrible wave pressure system is solved the problems, such as using wave equation inversion method, and terrible ripple pressing result is good.3rd, the present invention is directed to Common-shot-gather carries out terrible wave pressure system, can preferably keep the prestack feature of initial data, and the present invention to be carried out in frequency domain, Each frequency can be processed independently, thus with preferable concurrency and parallel efficiency is higher, can be with after the terrible ripple of compacting Seismic signal frequency spectrum is widened, the resolution ratio of seismic data is improved, marine varying depth cable collection earthquake is present invention can be widely used to In the processing procedure of data.

Brief description of the drawings

Fig. 1 is principle schematic of the invention, wherein,It is the round of terrible ripple,It is have The round of effect ripple (not comprising terrible ripple)；

Fig. 2 is implementing procedure figure of the invention；

Fig. 3 is the Numerical Experiment without terrible ripple of the Numerical Experiment result after ghost wave pressure system of the invention and synthesis Comparative result figure, wherein, Fig. 3 (a) is the single-shot road collection simulated seismogram without terrible ripple of synthesis, and Fig. 3 (b) is synthesis containing ghost The single-shot road collection simulated seismogram of ripple, Fig. 3 (c) is the single-shot road collection simulated seismogram after ghost wave pressure system of the invention；

Fig. 4 is the Numerical Experiment without terrible ripple of the Numerical Experiment frequency spectrum after ghost wave pressure system of the invention and synthesis Spectral contrast figure, wherein, Fig. 4 (a) is the single-shot road collection amplitude spectrum without terrible ripple of synthesis, and Fig. 4 (b) is the list containing terrible ripple of synthesis Big gun road collection amplitude spectrum, Fig. 4 (c) is the single-shot road collection amplitude spectrum after ghost wave pressure system of the invention；

Fig. 5 is the result after the actual terrible ripple of varying depth cable geological data compacting of the invention and the knot before terrible wave pressure system Fruit comparison diagram, wherein, Fig. 5 (a) is an earthquake single-shot road collection data of varying depth cable collection, and Fig. 5 (b) is present invention compacting ghost Earthquake single-shot road collection data after ripple.

Specific embodiment

Detailed description is carried out to the present invention below in conjunction with accompanying drawing.It should be appreciated, however, that accompanying drawing has been provided only more Understand the present invention well, they should not be interpreted as limitation of the present invention.

As shown in figure 1, seismic wave excites backward underground propagation from O points, reflected after running into each subsurface reflective boundary Upwardly propagate, first pass around datum level CD, seismic wave now is free from that there's something fishy ripple, seismic wave continues up propagation, one Divide and be propagate directly to varying depth cable AB, another part propagates down into varying depth after traveling to seawater face EF by the total reflection of seawater face Cable AB, this part seismic wave is exactly terrible ripple.Therefore, both contained by datum level CD in the seismic wave that varying depth cable AB is received It is propagate directly to the seismic wave field of varying depth cable AB upwards afterwards, also contains the seismic wave propagated downwards by the total reflection of seawater face , i.e., terrible ripple.So from from the point of view of wave field propagation, terrible wave pressure system is exactly the earthquake record that known varying depth cable AB is received, such as What asks for the earthquake record of the datum level CD without there's something fishy ripple by inverting.

Terrible wave pressure system is illustrated above by physical angle, terrible wave pressure system is said below by mathematical angle It is bright, the available following wave equation description of propagation of the seismic wave in two-dimensional medium：

Wherein u (x, z, t) is displacement wave field, and x, z is respectively coordinate both horizontally and vertically, and v (x, z) is in medium The speed of (x, z) point, δ () is Dirac δ-function, and g (t) is source function.Assuming that in O point earthquake-wave-excitings, in CD, EC and FD sections is observed, the earthquake record for obtaining respectively u_CD、u_ECAnd u_FD.Consider ground in the CDFE of region by earthquake record The propagation problem of seismic wave, control equation is formula (1), by u_CD、u_ECAnd u_FDRespectively as the boundary condition of CD, EC, FD, i.e.,：

u(x,z,t)|_(x,z)∈CD=u_CD (2)

u(x,z,t)|_(x,z)∈EC=u_EC (3)

u(x,z,t)|_(x,z)∈FD=u_FD (4)

In view of the actual conditions of seismic prospecting, the boundary condition of seawater face EF is taken for free boundary condition, i.e.,：

Primary condition is taken as：

Sea can be obtained by the numerical solution of wave equation formula (1) and its border and primary condition formula (2)~(6) Earthquake record u in water on varying depth cable AB_AB, while defining one by u_CDTo u_ABWave field forward-propagating process just drilling Problem.And the compacting of terrible ripple is then by u_ABSolve u_CD, this is the anti-of the i.e. wave equation formula (1) of back-propagation process of wave field Problem is drilled, when inversion problem is solved, unknown is the boundary values of wave equation.In art of mathematics, wave equation formula (1) is inclined Differential form, is properly termed as partial differential equation or the differential equation, solves the inversion problem of the equation, can be described as indirect problem.It is above-mentioned Terrible wave pressure system is by u_ABSolve u_CDProcess, be mathematically the indirect problem for solving the differential equation, also referred to as boundary values indirect problem, ground It is referred to as wave equation boundary values inverting in seismic exploration.

As shown in Fig. 2 the analysis based on above-mentioned physical angle and mathematical angle, of the invention anti-based on wave equation boundary values The varying depth cable ghost ripple drawing method drilled, specifically includes following steps：

1) geological data to the collection of marine field varying depth cable extracts common-shot-gather, comprising terrible wave number in the road collection According to.

2) geological data to certain big gun in common-shot-gather carries out one-dimensional Fourier transform, obtains the earthquake number containing there's something fishy ripple According to frequency spectrum.

3) the corresponding frequency domain geological data U containing there's something fishy ripple of certain frequencies omega in frequency spectrum is calculated_AB。

It is theoretical according to wave equation, it is above-mentioned by u_CDTo u_ABForward problem can be written as the direct problem of scattering form：

u(x,z,t)|_(x,z)∈EC=u_EC (8)

u(x,z,t)|_(x,z)∈FD=u_FD (9)

The boundary condition of seawater face EF is taken for free boundary condition, i.e.,：

In time t=0, wave field not yet starts to propagate, and primary condition is taken as：

Wherein, f_CDIt is by u_CDThe scattering source function that integration is obtained.For practical problem, u_ECAnd u_FDCannot obtain, because This takes absorbing boundary condition on EC and FD.Due to above-mentioned forward problem be in water consider ripple propagation problem, thus speed Spending can take constant value, v (x, z)=v in formula (7), i.e.,：

Further, because water meter is negative reflection, usual reflectance factor is -1, therefore seismic wave is segmented into two parts, one Part is that the wave table propagated directly up is shown as u₁, another part is shown as by the backward lower wave table propagated of seawater face EF reflections u₂, total wave field is expressed as u=u₁+u₂, and u₁Meet：

u₂Meet：

Wherein, line of symmetries of the face CD relative to seawater face EF, f on the basis of C ' D '_C’D’It is f_CDMirror image function, and f_C’D’With f_CDIt is equal in magnitude.Now, formula (13) and (14) are the equation in uniform infinite medium, equal to formula (13) and (14) both sides Fourier transformation is taken on the time to obtain：

Formula (15) and (16) are obtained by GREEN function representations and solution：

Wherein, G₁、G₂It is GREEN functions, concrete form is forth below.Formula (17) and (18) are on varying depth cable AB Receiving point is also set up, i.e.,：

Above-mentioned formula (19) and (20) is write as matrix form to obtain：

U_AB1=G₁F_CD (21)

U_AB2=-G₂F_CD (22)

Formula (21) and (22) are merged and obtains the frequency domain geological data U containing there's something fishy ripple_AB：

U_AB=G₁F_CD-G₂F_CD=(G₁-G₂)F_CD (23)

4) according to the geophone station depth of inputIt is calculated the GREEN functions G of datum level CD below the EF of seawater face₁With The GREEN functions G of line of symmetry C ' Ds ' of the datum level CD relative to seawater face EF₂。

In equal medium, the computing formula of GREEN functions is：

Wherein, parameter k=ω/v；Parameter

According to the geophone station depth of inputAnd formula (24) and (25) are calculated G respectively₁And G₂：

5) according to obtaining the frequency domain geological data U containing there's something fishy ripple_ABAnd the G being calculated₁And G₂, it is calculated frequency Frequency domain geological data F after the corresponding terrible wave pressure systems of rate ω_CD。

In formula (23), G₁-G₂It is a matrix, G can be calculated according to formula (25)~(27)₁-G₂, according to sea Outside u'eno during earthquake data acquisition varying depth cable AB sinking depth profile, geophone station depth can be obtainedF_CDIt is free from The frequency domain geological data of terrible ripple, is amount to be asked；U_ABThe ground of the frequency domain containing there's something fishy ripple obtained when being marine field earthquake-capturing Shake data, are known quantity；Frequency domain geological data F without there's something fishy ripple can be obtained by the solution of formula (23)_CD, so as to reach To the purpose of the terrible ripple of compacting.

6) step 3 is carried out to all frequencies omegas in common-shot-gather intermediate frequency spectrum)~5) obtain the frequency after terrible wave pressure system Rate domain geological data.

7) step 2 is carried out to other big guns in common-shot-gather)~6) obtain the frequency domain geological data after terrible wave pressure system.

8) to the frequency domain geological data F after terrible wave pressure system_CDInverse Fourier transform is carried out, the common big gun after terrible wave pressure system is obtained Point road collection.

As shown in figure 3, the present invention analyzes the forward and backward Numerical Experiment result of terrible wave pressure system, Fig. 3 (a) is synthesis Single-shot road collection simulated seismogram without terrible ripple, Fig. 3 (b) is the single-shot road collection simulated seismogram containing terrible ripple of synthesis, by Fig. 3 B using Fig. 3 (c) is obtained after the terrible ripple of present invention compacting, comparison diagram 3 (c) and Fig. 3 (a) can be seen that two to the simulated seismogram of () Width figure is completely the same, and the terrible ripple in explanatory diagram 3 (b) has been pressed, and useful signal is effectively maintained.

As shown in figure 4, Fig. 4 is the spectrogram corresponding to each figure in Fig. 3, Fig. 4 (a) is the single-shot road without terrible ripple of synthesis Collection amplitude spectrum, Fig. 4 (b) is the single-shot road collection amplitude spectrum containing terrible ripple of synthesis, can be clearly seen that the terrible ripple in Fig. 4 (b) Trap is acted on, and Fig. 4 (c) is the single-shot road collection amplitude spectrum after ghost wave pressure system of the invention, and trap band is can see from Fig. 4 (c) Frequency spectrum is recovered.

As shown in figure 5, Fig. 5 is to carry out the forward and backward place of terrible wave pressure system to actual varying depth cable geological data using the present invention Reason Comparative result, Fig. 5 (a) is an earthquake single-shot road collection data of varying depth cable collection, can clearly be seen in the diagram To terrible ripple, Fig. 5 (b) is to suppress the earthquake single-shot road collection data after terrible ripple with the present invention, and contrasting this two width figure can clearly see Arrive, suppressed well by the terrible ripple in the original earthquake single-shot data after present invention treatment, while original earthquake single-shot Significant wave in data is kept well.

The various embodiments described above are merely to illustrate the present invention, and wherein each step of method etc. all can be what is be varied from, all The equivalents and improvement carried out on the basis of technical solution of the present invention, should not exclude protection scope of the present invention it Outward.

Claims (4)

1. a kind of varying depth cable ghost ripple drawing method based on wave equation boundary values inverting, it is characterised in that comprise the following steps：

1) geological data to the collection of marine field varying depth cable extracts common-shot-gather；

2) geological data to certain big gun in common-shot-gather carries out one-dimensional Fourier transform, obtains the geological data containing there's something fishy ripple Frequency spectrum；

3) the corresponding frequency domain geological data U containing there's something fishy ripple of certain frequencies omega in frequency spectrum is calculated_AB；

4) according to the geophone station depth of inputIt is calculated the GREEN functions G of seawater face lower section datum level₁With datum level phase For the GREEN functions G of the line of symmetry in seawater face₂；

5) according to obtaining the frequency domain geological data U containing there's something fishy ripple_ABAnd the G being calculated₁And G₂, it is calculated frequencies omega Frequency domain geological data F after corresponding terrible wave pressure system_CD；

6) step 3 is carried out to all frequencies omegas in common-shot-gather intermediate frequency spectrum)~5) obtain the frequency domain after terrible wave pressure system Geological data；

7) step 2 is carried out to other big guns in common-shot-gather)~6) obtain the frequency domain geological data after terrible wave pressure system；

8) to the frequency domain geological data F after terrible wave pressure system_CDInverse Fourier transform is carried out, the common-source point road after terrible wave pressure system is obtained Collection.

2. a kind of varying depth cable ghost ripple drawing method based on wave equation boundary values inverting as claimed in claim 1, its feature It is to calculate the corresponding frequency domain geological data U containing there's something fishy ripple of certain frequencies omega in frequency spectrum_ABDetailed process be：

Definition datum face is CD, and seawater face is EF, and varying depth cable is AB, is observed at CD, EC and FD section, the earthquake for obtaining Record is respectively u_CD、u_ECAnd u_FD, the earthquake record of varying depth cable AB is u in the seawater_AB, it is theoretical according to wave equation, by u_CD To u_ABForward problem be written as the direct problem of scattering form：

$\frac{{\∂}^{2}u(x,z,t)}{\∂x^2}+\frac{{\∂}^{2}u(x,z,t)}{\∂z^2}-\frac{1}{v^2(x,z)}\frac{{\∂}^{2}u(x,z,t)}{\∂t^2}=f_{CD}---\left(7\right)$

u(x,z,t)|_(x,z)∈EC=u_EC (8)

u(x,z,t)|_(x,z)∈FD=u_FD (9)

The boundary condition of seawater face EF is taken for free boundary condition, i.e.,：

$\frac{\∂u(x,z)}{\∂z}{|}_{(x,z)\∈EF}=0---\left(10\right)$

In time t=0, wave field not yet starts to propagate, and primary condition is taken as：

$u(x,z,0)=\frac{\∂u(x,z,0)}{\∂t}=0---\left(11\right)$

Wherein, u (x, z, t) is displacement wave field, and x, z is respectively coordinate both horizontally and vertically, and v (x, z) is in medium (x, z) The speed of point, f_CDIt is by u_CDThe scattering source function that integration is obtained, for practical problem, u_ECAnd u_FDCannot obtain, therefore Absorbing boundary condition is taken on EC and FD, because forward problem is the propagation problem of the ripple for considering in the seawater, thus speed can be with Constant value is taken, i.e.,：

$\frac{{\∂}^{2}u}{\∂x^2}+\frac{{\∂}^{2}u}{\∂z^2}-\frac{1}{v^2}\frac{{\∂}^{2}u}{\∂t^2}=f_{CD}---\left(12\right)$

Because water meter is negative reflection, reflectance factor is -1, therefore seismic wave is divided into two parts, and a part is propagated directly up Wave table is shown as u₁, another part is to be shown as u by the backward lower wave table propagated of seawater face EF reflections₂, total wave field is expressed as u=u₁+ u₂, and u₁Meet：

$\frac{{\∂}^2{u}_1}{\∂x^2}+\frac{{\∂}^2{u}_1}{\∂z^2}-\frac{1}{v^2(x,z)}\frac{{\∂}^2{u}_1}{\∂t^2}=f_{CD}---\left(13\right)$

u₂Meet：

$\frac{{\∂}^2{u}_2}{\∂x^2}+\frac{{\∂}^2{u}_2}{\∂z^2}-\frac{1}{v^2(x,z)}\frac{{\∂}^2{u}_2}{\∂t^2}=-f_{C^{,}{D}^{,}}---\left(14\right)$

Wherein, line of symmetries of the face CD relative to seawater face EF, f on the basis of C ' D '_C’D’It is f_CDMirror image function, and f_C’D’With f_CDGreatly Small equal, now, formula (13) and (14) are the equation in uniform infinite medium, to formula (13) and (14) both sides on Time takes Fourier transformation and obtains：

$\frac{{\∂}^2{u}_1}{\∂x^2}+\frac{{\∂}^2{u}_1}{\∂z^2}-\frac{{\mathrm{\ω}}^2}{v^2}{u}_1=f_{CD}---\left(15\right)$

$\frac{{\∂}^2{u}_2}{\∂x^2}+\frac{{\∂}^2{u}_2}{\∂z^2}-\frac{{\mathrm{\ω}}^2}{v^2}{u}_2=-f_{C^{,}{D}^{,}}---\left(16\right)$

Formula (15) and (16) are obtained by GREEN function representations and solution：

$u_1(x,z,\mathrm{\ω})=\underset{CD}{\∫}{G}_1(x,z,\mathrm{\ω}|x^{\′},z^{\′})f_{CD}(x^{\′},z^{\′},\mathrm{\ω}){\mathrm{dx}}^{\′}{\mathrm{dz}}^{\′}---\left(17\right)$

$u_2(x,z,\mathrm{\ω})=-\underset{C^{\′}{D}^{\′}}{\∫}{G}_2(x,z,\mathrm{\ω}|x^{\′},z^{\′})f_{C^{,}{D}^{,}}(x^{\′},z^{\′},\mathrm{\ω}){\mathrm{dx}}^{\′}{\mathrm{dz}}^{\′}---\left(18\right)$

Wherein, G₁、G₂It is GREEN functions, the receiving point of formula (17) and (18) on varying depth cable AB is also set up, i.e.,：

$u_1(x,z,\mathrm{\ω}){|}_{(x,z)\∈AB}=\underset{CD}{\∫}{G}_1(x,z,\mathrm{\ω}|x^{\′},z^{\′})f_{CD}(x^{\′},z^{\′},\mathrm{\ω}){\mathrm{dx}}^{\′}{\mathrm{dz}}^{\′}---\left(19\right)$

$u_2(x,z,\mathrm{\ω}){|}_{(x,z)\∈AB}=-\underset{C^{\′}{D}^{\′}}{\∫}{G}_2(x,z,\mathrm{\ω}|x^{\′},z^{\′})f_{C^{,}{D}^{,}}(x^{\′},z^{\′},\mathrm{\ω}){\mathrm{dx}}^{\′}{\mathrm{dz}}^{\′}---\left(20\right)$

Above-mentioned formula (19) and (20) is write as matrix form to obtain：

U_AB1=G₁F_CD (21)

U_AB2=-G₂F_CD (22)

Formula (21) and (22) are merged and obtains the frequency domain geological data U containing there's something fishy ripple_AB：

U_AB=G₁F_CD-G₂F_CD=(G₁-G₂)F_CD (23)

3. a kind of varying depth cable ghost ripple drawing method based on wave equation boundary values inverting as claimed in claim 2, its feature It is, according to the geophone station depth of inputIt is calculated the GREEN functions G of seawater face lower section datum level₁With datum level phase For the GREEN functions G of the line of symmetry in seawater face₂Detailed process is：

In equal medium, the computing formula of GREEN functions is：

$G\left(x,z,\mathrm{\ω}|x^{\′},z^{\′}\right)=-\frac{i}{4}{H}_0^{\left(2\right)}\left(kr\right)---\left(24\right)$

Wherein, parameter k=ω/v；Parameter

$H_0^{\left(2\right)}\left(kr\right)=\sqrt{\frac{2}{\mathrm{\π}}}\frac{1}{kr}{e}^{-i(kr-\frac{\mathrm{\π}}{4})}---\left(25\right)$

According to the geophone station depth of inputAnd formula (24) and (25) are calculated G respectively₁And G₂：

$G_1(x,z,\mathrm{\ω}|x^{\′},z^{\′}){|}_{(x^{\′},z^{\′})\∈CD}=-\frac{i}{4}{H}_0^{\left(2\right)}\left(kr\right)---\left(26\right)$

$G_2(x,z,\mathrm{\ω}|x^{\′},z^{\′}){|}_{(x^{\′},z^{\′})\∈C^{\′}{D}^{\′}}=-\frac{i}{4}{H}_0^{\left(2\right)}\left(kr\right)---\left(27\right)$

4. a kind of varying depth cable ghost ripple drawing method based on wave equation boundary values inverting as claimed in claim 3, its feature It is, according to the frequency domain geological data U containing there's something fishy ripple_ABAnd the G being calculated₁And G₂, it is calculated frequencies omega ghost wave pressure Frequency domain geological data F after system_CDDetailed process is：

In formula (23), G₁-G₂It is a matrix, G is calculated according to formula (25)~(27)₁-G₂, according to marine field earthquake The sinking depth profile of varying depth cable AB obtains geophone station depth during data acquisitionF_CDIt is free from the frequency domain earthquake of terrible ripple Data, are amount to be asked；U_ABThe frequency domain geological data containing there's something fishy ripple obtained when being field earthquake-capturing, is known quantity, is passed through The solution of formula (23) obtains the frequency domain geological data F without there's something fishy ripple_CD。