CN103984012B - Diffracted wave field separation method based on prestack Gaussian beam depth migration - Google Patents

Abstract

The present invention proposes a kind of diffracted wave field separation method based on prestack Gaussian beam depth migration, using high-quality Prestack seismic data as input, the angle gathers that inclines is exported by prestack Gaussian beam depth migration, utilize echo and diffracted wave in the difference in territory, inclination angle, similar analysis of spectrum is adopted to remove pole energy, extract diffracted wave energy, individually carry out imaging, in order to better identify hole seam reservoir.The present invention is directed under complex geological structure, the fine description of speleothem calcite hole type reservoir, by the combination with Gaussian beam seismic migration technology, effectively suppress the influence of noise of engineering construction system, improve the imaging precision of diffraction target, thus high accuracy carbonate rock cranny and cave reservoir is explained when serving complex dielectrics, improve and developed the technical know-how that diffracted wave field separates.

Description

Diffracted wave field separation method based on prestack Gaussian beam depth migration

Technical field

The invention belongs to petroleum exploration field, relate to a kind of hole based on prestack Gaussian beam depth migration and stitch imaging technique, particularly relate to a kind of diffracted wave field separation method based on prestack Gaussian beam depth migration.

Background technology

The response of underground medium is known by inference subsurface information by seismic wave by seismic prospecting, and when underground exists medium sudden change, often response is diffracted wave.Carbonate rock area at western part of China, for instance Tarim Basin, main hydrocarbon pore volume is secondary corrosion hole and crack, therefore, in oil-gas exploration, the identification of this secondary pore is just particularly important, and the area that hole is grown is often good reservoir.But the distribution that corrosion hole is in underground is very irregular, size is little compared with the wavelength of seismic wave, and its seismic response is based on irregular diffraction.It is therefore desirable to study these diffracted waves, but in common skew, diffracted wave can converge to a point on section, thus being submerged between numerous lineups, can not differentiate.Concentrating in common CRP road, Diffraction Point and pip all show as evening up of lineups, and causing that Diffraction Point is concentrated in CRP road can not be identified.

The diffracted wave field isolation technics in territory, inclination angle can effectively solve the problems referred to above, it is achieved diffracted wave separates with echo, the effective information extracting hole seam reservoir.One of core of territory, inclination angle wave field separation is the extraction of angle gathers of inclining, and is first offset data-bias to territory, inclination angle by territory, inclination angle, is realized separation and the imaging of diffracted wave field by the bigger difference of diffraction lineups and reflection line-ups form in territory, inclination angle.By seismic data through territory, inclination angle offset outputting high quality the angle gathers that inclines be diffracted wave field separate key one step.

Another branch as ray class offset method, Gaussian beam skew is the Kirchhoff offset method of a kind of improvement, it it is a kind of Depth Domain formation method accurate, flexible, efficient, it not only has the imaging precision close to wave equation migration, also retains Kirchhoff and offset feature flexible, efficient and the adaptability that complex near surface conditions is good, can to many subwaves to carrying out imaging, often than Kirchhoff skew, there is higher imaging precision, and also there is high efficiency and the motility of Kirchhoff skew.

Summary of the invention

The present invention proposes a kind of diffracted wave field separation method based on prestack Gaussian beam depth migration, using high-quality Prestack seismic data as input, the angle gathers that inclines is exported by prestack Gaussian beam depth migration, utilize echo and diffracted wave in the difference in territory, inclination angle, extract diffracted wave energy, individually carry out imaging, in order to better identify hole seam reservoir.

The concrete scheme that the present invention realizes above-mentioned purpose is as follows:

A kind of diffracted wave field separation method based on prestack Gaussian beam depth migration, it is characterized in that, using high-quality Prestack seismic data as input, the angle gathers that inclines is exported by prestack Gaussian beam depth migration, utilize echo and diffracted wave in the difference in territory, inclination angle, adopt similar analysis of spectrum to remove pole energy, extract diffracted wave energy, individually carry out imaging, in order to better identify fracture cave reservoir；

Described method comprises the steps:

Step 1: seismic data is carried out relative amplitude preserved processing, and seismic data is rearranged into big gun collection record；

Step 2: prestack Gaussian beam depth migration extracts the angle gathers that inclines；

Step 3: after the angle gathers that obtains inclining, utilizes echo and diffracted wave to concentrate from difference in road, inclination angle, adopts similar Zymography to remove pole energy here and is removed by reflected energy；

Step 4: the angle gathers superposition of inclining of reflected energy will be removed, it is possible to obtain the stacked section of the independent imaging of diffracted wave.

The incline method of angle gathers of output in described step 2 is:

A. read in an earthquake big gun record, source wavefield is carried out Gaussian beam decomposition；

B. big gun record Gaussian beam decomposed and carry out the big gun record plane wave after local dip superposition is decomposed；

C. according to up and down four when walking of coarse grid in Gaussian beam beam center and corresponding Gaussian beam thereof, it is possible to ask for the ray parameter that Gaussian beam is propagated, and then ask for the propagation angle of Gaussian beam；

D. the propagation angle of the Gaussian beam of coarse net lattice point is utilized, it is possible to ask for the propagation angle of the Gaussian beam of imaging point place focus and reception point, and then ask for the inclination angle that this imaging point position goes out；

E. cross-correlation image-forming condition is utilized to ask for imaging value and carry out mapping projections according to incident angle, it is possible to obtain single big gun and offset the angle gathers that inclines obtained；

F. all single big gun migration result correspondence superpositions obtained can be obtained the final angle gathers that inclines.

Similar analysis of spectrum in described step 3 removes the method for pole energy:

A. the angle gathers that inclines is read in；

B. it is scanned obtaining the similarity information at each angle points place of corresponding each degree of depth along territory, inclination angle reflection line-ups curve point by point, obtains similar spectrum；

C. the angle-determining pole position corresponding to the maximum similarity at this each depth location place of similar spectrum automatic Picking；

D. the pole position according to each depth location place, removes the reflection line-ups near pole along reflection line-ups curve linear relationship, it is achieved reflected energy is suppressed.

Compared with the prior art the present invention reaches to provide the benefit that:

For under complex geological structure, the fine description of speleothem calcite hole type reservoir, by the combination with Gaussian beam seismic migration technology, effectively suppress the influence of noise of engineering construction system, improve the imaging precision of diffraction target, thus high accuracy carbonate rock cranny and cave reservoir is explained when serving complex dielectrics, improve and developed the technical know-how that diffracted wave field separates.

Accompanying drawing illustrates:

Fig. 1 is based on the diffracted wave field separation method flow chart of prestack Gaussian beam depth migration；

Fig. 2 a is one and comprises two different angle reflecting interfaces, the model schematic of a Diffraction Point；

Fig. 2 b is the angle gathers response schematic diagram that inclines in the observation of x=0 place；

Fig. 2 c is the angle gathers response schematic diagram that inclines in the observation of x=-100m place；

Fig. 2 d is the angle gathers response schematic diagram that inclines in the observation of x=100m place；

Fig. 3 is Gaussian beam pre-stack depth migration schematic diagram；

Fig. 4 is sigsbee2a rate pattern schematic diagram；

Fig. 5 a is the angle gathers schematic diagram that inclines at CDP400 place；

Fig. 5 b is the similar spectral obtained by the angle gathers that inclines of CDP400；

Fig. 5 c is the angle gathers figure that inclines at the CDP400 place after reflected energy compacting；

Fig. 6 a is the stacked profile map after sigsbee2a model offset；

Fig. 6 b is the diffracted wave field stacked section after sigsbee2a model separation.

Detailed description of the invention

In conjunction with Sigsbee2a numerical model and accompanying drawing, the specific embodiment of the present invention is described.

See Fig. 1, based on the diffracted wave field separation method flow chart of prestack Gaussian beam depth migration.

A kind of diffracted wave field separation method based on prestack Gaussian beam depth migration, using high-quality Prestack seismic data as input, the angle gathers that inclines is exported by prestack Gaussian beam depth migration, utilize echo and diffracted wave in the difference (Fig. 2) in territory, inclination angle, similar analysis of spectrum is adopted to remove pole energy, extract diffracted wave energy, individually carry out imaging, in order to better identify fracture cave reservoir；

It is as follows that the present invention is embodied as step:

Step 1: seismic data is carried out relative amplitude preserved processing, and seismic data is rearranged into big gun collection record.

Step 2: prestack Gaussian beam depth migration extracts the angle gathers that inclines

A. first read in an earthquake big gun record, represented by focal point to the Green's function calculating point by source wavefield, then obtaining the Gaussian beam representation of source wavefield in Gaussian beam skew is:

$G(x_s,x;\mathrm{\ω})=\frac{i}{4\mathrm{\π}}\∫\frac{{\mathrm{dp}}_x}{p_z}{B}_{\mathrm{GB}}(x_s,x;p,\mathrm{\ω})---\left(1\right)$

$U_{\mathrm{GB}}(x_s,x;p,\mathrm{\ω})=\sqrt{\frac{V\left(s\right)Q\left(s_0\right)}{V\left(s_0\right)Q\left(s\right)}}\exp \{\mathrm{i\ω\τ}\left(s\right)+\frac{\mathrm{i\ω}}{2}\frac{P\left(s\right)}{Q\left(s\right)}{n}^2\}---\left(2\right)$

Wherein, V (s) is the current interval velocity calculating some s arc length positions place, and s is the reference arc length that focal point currently calculates a little to ray, p_xAnd p_zThe kinetics ray-tracing parameter that respectively the horizontal and vertical component of central ray initial slowness, P (s) and Q (s) are s position, τ (s) is when walking of s position, U_GB(x_s, x;P, ω) for dimensional Gaussian wave beam, represent wave equation near central ray high-frequency asymptote solution.

B. secondly big gun record Gaussian beam decomposed and carry out the big gun record decomposition of plane wave formula after local dip superposition is decomposed:

$u(x,x_s,\mathrm{\ω})\≈-\frac{\sqrt{3}}{4\mathrm{\π}}{\left(\frac{{\mathrm{\ω}}_r\mathrm{\ΔL}}{w_0}\right)}^2\underset{L}{\mathrm{\Σ}}\∫\∫d{p}_{\mathrm{Lx}}{U}_{\mathrm{GB}}^{*}(x,L,P_L,\mathrm{\ω})D_s(L,p_{\mathrm{Lx}},\mathrm{\ω})---\left(3\right)$

$D_S(L,p_{\mathrm{Lx}},\mathrm{\ω})={\left|\frac{\mathrm{\ω}}{{\mathrm{\ω}}_r}\right|}^{3/2}\∫d{x}_{r}u(x_r,x_s,\mathrm{\ω})\exp [\mathrm{i\ω}{p}_{\mathrm{Lx}}(x_r-L)-|\frac{\mathrm{\ω}}{{\mathrm{\ω}}_r}\left|\frac{{(x_r-L)}^2}{2w_0^2}\right]---\left(4\right)$

Wherein, L is beam center position, w₀For the original width of Gaussian beam, Δ L is beam center spacing, ω_rFor reference frequency；D_S(L,p_Lx, ω) and it is the part plan wave component synthesized, p_LxAnd p_LzThe respectively horizontal and vertical component of beam center slowness, u (x_r,x_s, ω) and for the earthquake record wave field in Gaussian window.

C. then up and down four coarse grids in a given Gaussian beam beam center and corresponding Gaussian beam thereof, if corresponding to four mesh points real-valued walk time respectively t_u, t_d, t_l, t_r；Beam center position real-valued walk time be t_m；The respectively Δ g of mesh spacing both horizontally and vertically_xWith Δ g_z, can obtain:

$\left\{\begin{array}{c}{p}_x=\frac{t_r^2-t_l^2}{4t_m\mathrm{\Δ}{g}_x}\\ p_z=\frac{t_d^2-t_u^2}{4t_m\mathrm{\Δ}{g}_z}\end{array}\right.---\left(5\right)$

Thus obtaining the propagation angle (ray is with the angle between z-axis forward) of mesh point Gaussian beam

$\mathrm{\&beta;}=\left\{\begin{array}{cc}\arctan \left(\frac{p_x}{p_z}\right)-\mathrm{\&pi;}& p_x<0,p_z<0\\ \arctan \left(\frac{p_x}{p_z}\right)+\mathrm{\&pi;}& p_x>0,p_z<0\\ \arctan \left(\frac{p_x}{p_z}\right)& \mathrm{other}\end{array}\right.---\left(6\right)$

D. by the Gaussian beam propagation angle interpolation of coarse net lattice point can be obtained the propagation angle on imaging mesh point, the propagation angle of imaging point position focus and reception point Gaussian beam is utilized can to derive this inclination angle, imaging point position:

$\mathrm{\&alpha;}=\left\{\begin{array}{cc}\frac{{\mathrm{\&beta;}}_s+{\mathrm{\&beta;}}_r-\mathrm{\&pi;}}{2}& {\mathrm{\&beta;}}_r>0\\ \frac{{\mathrm{\&beta;}}_s+{\mathrm{\&beta;}}_r+\mathrm{\&pi;}}{2}& {\mathrm{\&beta;}}_r\&le;0\end{array}\right.---\left(7\right)$

By Gaussian beam migration imaging value

$\left\{\begin{array}{c}I(x,x_s)=\frac{\mathrm{\&Delta;L}{\mathrm{\&omega;}}_r}{4{\mathrm{\&pi;}}^2{w}_0}\underset{L}{\mathrm{\&Sigma;}}\&Integral;\mathrm{d\&omega;}\sqrt{\mathrm{i\&omega;}}\&Integral;d{p}_{\mathrm{mx}}\\ \&times;\frac{A_s^{*}{A}_L^{*}}{\sqrt{T^{*\&prime;\&prime;}\left(p_{\mathrm{hx}}^0\right)}}\exp [-\mathrm{i\&omega;}(T_s^{*}+T_L^{*})]D_s(L,p_{\mathrm{Lx}}^0,\mathrm{\&omega;})\end{array}\right.---\left(8\right)$

E. according to incident angle (x, x_s, α) carry out mapping projections and can obtain the angle gathers that inclines that single shot record obtains,

F. finally all single big gun migration result correspondence superpositions are then obtained the final angle gathers that inclines.

Step 3: after the angle gathers that obtains inclining, utilizes echo and diffracted wave to concentrate from difference in road, inclination angle, adopts similar Zymography to remove pole energy here and is removed by reflected energy.Can carry out according to following operation:

A. first, the angle gathers that inclines is read in.

B. secondly, it is scanned obtaining the similarity information at each angle points place of corresponding each degree of depth along territory, inclination angle reflection line-ups curve (formula 9) pointwise, obtains similar spectrum.

$z=\frac{Z_0\cos {\mathrm{\&alpha;}}_0\cos \mathrm{\&alpha;}}{1-\sin {\mathrm{\&alpha;}}_0\sin \mathrm{\&alpha;}}---\left(9\right)$

Wherein Z₀For the degree of depth of reflecting interface current location, α₀Inclination angle for reflecting interface.

C. again, the angle-determining pole position corresponding to the maximum similarity at this each depth location place of similar spectrum automatic Picking.

D. last, the pole position according to each depth location place, remove the reflection line-ups near pole along reflection line-ups curve linear relationship, it is achieved reflected energy is suppressed.

Step 4: the angle gathers superposition of inclining of reflected energy will be removed, it is possible to obtain the stacked section of the independent imaging of diffracted wave.

Fig. 4 is Sigsbee2a interval velocity model, and model meshes is 1201 × 2133, and lateral separation is 37.5ft (foot), and longitudinal separation is 25ft (foot).Forward record has 500 big guns, and max number of channels is 348 roads, and shot interval is 75ft, and road is spaced apart 75ft.Being 17000ft and there are two row's high speed diffractors at 25000 feet of places in the degree of depth, have a high speed salt dome, also comprise a large amount of tomography in model in the middle part of model, diffraction is horn of plenty relatively.

By step 2(Fig. 3) generate the angle gathers (such as Fig. 5 a) that inclines.Concentrate in road, inclination angle diffracted wave lineups well to be evened up, and the response curve of echo is the curve of upward opening.

Respectively obtain the similar spectrum (Fig. 5 b) of counter-bevel road collection by step 3 and remove the angle gathers (Fig. 5 c) that inclines of pole energy.

Obtain diffracted wave stacked section (Fig. 6 b) by step 4, and contrast with the stacked section (Fig. 6 a) before separating, it can be seen that on stacked section after isolation, reflective information is removed preferably, and the diffraction information such as diffractor and tomography obtains reservation.

Claims (2)

1. the diffracted wave field separation method based on prestack Gaussian beam depth migration, it is characterized in that, using high-quality Prestack seismic data as input, the angle gathers that inclines is exported by prestack Gaussian beam depth migration, utilize echo and diffracted wave in the difference in territory, inclination angle, adopt similar analysis of spectrum to remove pole energy, extract diffracted wave energy, individually carry out imaging, in order to better identify fracture cave reservoir；

Described method comprises the steps:

Step 1: seismic data is carried out relative amplitude preserved processing, and seismic data is rearranged into big gun collection record；

Step 2: prestack Gaussian beam depth migration extracts the angle gathers that inclines；

Step 3: after the angle gathers that obtains inclining, the difference utilizing echo and diffracted wave to concentrate in road, inclination angle, adopt similar Zymography to remove pole energy；

Step 4: the angle gathers superposition of inclining of reflected energy will be removed, it is possible to obtain the stacked section of the independent imaging of diffracted wave；

The incline method of angle gathers of output in described step 2 is:

A. read in an earthquake big gun record, source wavefield is carried out Gaussian beam decomposition；

B. big gun record Gaussian beam decomposed and carry out the big gun record plane wave after local dip superposition is decomposed；

C. according to up and down four when walking of coarse grid in Gaussian beam beam center and corresponding Gaussian beam thereof, it is possible to ask for the ray parameter that Gaussian beam is propagated, and then ask for the propagation angle of Gaussian beam；

D. the propagation angle of the Gaussian beam of coarse net lattice point is utilized, it is possible to ask for the propagation angle of the Gaussian beam of imaging point place focus and reception point, and then ask for the inclination angle that this imaging point position goes out；

E. cross-correlation image-forming condition is utilized to ask for imaging value and carry out mapping projections according to incident angle, it is possible to obtain single big gun and offset the angle gathers that inclines obtained；

F. all single big gun migration result correspondence superpositions obtained are obtained the final angle gathers that inclines.

2. the diffracted wave field separation method based on prestack Gaussian beam depth migration according to claim 1, it is characterised in that the similar analysis of spectrum in described step 3 is removed the method for pole energy and is:

A. the angle gathers that inclines is read in；

B. it is scanned obtaining the similarity information at each angle points place of corresponding each degree of depth along territory, inclination angle reflection line-ups curve point by point, obtains similar spectrum；

C. the angle-determining pole position corresponding to the maximum similarity at this each depth location place of similar spectrum automatic Picking；

D. the pole position according to each depth location place, removes the reflection line-ups near pole along reflection line-ups curve linear relationship, it is achieved reflected energy is suppressed.