CN102636809B - Method for generating spreading angle domain common image point gathers - Google Patents

Abstract

The invention relates to a method for generating spreading angle domain common image point gathers. The method comprises the following steps that: 1) longitudinally partitioning a complex inhomogeneous medium to be prospected into different depth layers from the earth surface utilized as the beginning point; 2) arousing seismic waves in a successive blasting manner at the earth surface, spreading the seismic waves aroused each time downwards in a mode of spherical waves, when the seismic waves reach the different depth layers, respectively calculating an ordinary seismic offset wave field and a seismic offset wave field with spreading angle correction on each depth layer by using a wave equation; 3) generating angle information of the wave field at an imaging point on each depth layer; 4) obtaining ware field angle information on each imaging point in the depth layers to be prospected, selecting an angle adoption interval and an angle scope so as to perform data overlapping on an offset imaging result falling in one sampling interval until the offset data overlapping within all the angle scopes is completed, and transforming common-source imaging point gathers are into common angle domain imaging point gathers. The method can be used in the generation process of the angle domain common imaging point gathers in petroleum seismic prospecting widely.

Description

A kind of propagation angle territory is the generation method of image gather altogether

Technical field

The present invention relates to a kind of generation method of image gather altogether, particularly about a kind of propagation angle territory generation method of image gather being altogether useful in petroleum prospecting complex structure.

Background technology

Prestack depth migration has become the powerful tool that solves complex structure exploration problem, because its Dependent Layer rate pattern causes it to be restricted in actual applications.Uncertain and the insecure problem of rate pattern for the depth shift result existing in seismic imaging, prior art adopts the Full wave shape method of inversion, tomographic inversion method and residue curvature method to process conventionally, wherein adopt the Full wave shape method of inversion can obtain rate pattern comparatively reliably, but calculated amount is very huge, therefore the method is mainly suitable in low frequency (conventionally≤10Hz) scope; Adopt tomographic inversion method also can obtain rate pattern comparatively reliably, its calculated amount is large but be less than the Full wave shape method of inversion, but the method is mainly suitable within the scope of medium and low frequency.In order to reduce calculated amount, above-mentioned two kinds of methods adopt ray casting to carry out inverting conventionally, but ray casting is because the problem such as high-frequency approximation and multipath is inapplicable in complex structure area.Along with China's oil-gas exploration deepen continuously and degree of prospecting improves constantly, the target of petroleum prospecting progressively turns to complicated hidden reservoir, reservoir under these complicated sedimentary environments has thin thickness, lithology height heterogeneous body, Effective Reservoirs distributes and disperses, the features such as rock physics relation complexity and reservoir lithology contrast are weak, therefore remaining curvature method is current more conventional method, it is mainly progressively to revise initiation layer rate pattern by the relation between the bending curvature of common image gather lineups and slowness (inverse of speed) disturbance, the relatively above-mentioned two kinds of methods of the calculated amount of the method are less.

The core of residue curvature method is to generate image gather altogether, utilizes the continuous iteration renewal speed of relation between bending curvature and the velocity error that is total to image gather, the final interval velocity model obtaining for pre-stack depth migration.Image gather mainly contains common reflection point (CRP) road collection, big gun territory image gather, offset domain common image gathers and angle domain common image gathers altogether altogether, in above-mentioned image gather altogether, angle domain common image gathers is subject to being offset the interference minimum of noise or skew illusion, especially under complex structure condition, angle domain common image gathers can not produce the road collection of any " illusion " (false lineups), all there is skew illusion in other, is unfavorable for analysis and the inverting research of migration velocity.Existing angle domain common image gathers technology is completed by the Radon mathematic(al) manipulation of standard by offset domain common image gathers conventionally, but its calculated amount and memory data output are all very huge, if calculate three-dimensional perspective territory image gather altogether, these class methods need to be stored the data volume of five dimensions, have been subject in actual applications certain restriction.

Summary of the invention

For the problems referred to above, the object of this invention is to provide a kind of calculated amount and memory space all smaller, not only effectively avoid skew " false picture " phenomenon to occur, and can suppress the propagation angle territory generation method of image gather altogether of migration noise.

For achieving the above object, the present invention takes following technical scheme: a kind of propagation angle territory is the generation method of image gather altogether, comprises the following steps: be 1) starting point take earth's surface, complex heterogeneous medium to be explored is longitudinally divided into different depth layer; 2) at earth's surface place by successively putting the mode earthquake-wave-exciting of big gun, the seismic event exciting is each time propagated downwards in the mode of spherical wave, in the time that seismic event arrives different depth layer, the seismic migration wave field that utilizes wave equation to calculate respectively the common seismic skew wave field in each depth layer and proofread and correct with propagation angle; 3) angle information that generates wave field on the imaging point of each depth layer is:

$\mathrm{\θ}(x,z)={\cos }^{-1}\mathrm{real}\left[\frac{\underset{\mathrm{\ω}}{\mathrm{\Σ}}\left[I_{\mathrm{cmplx}}(x,z,\mathrm{\ω})\right]}{\underset{\mathrm{\ω}}{\mathrm{\Σ}}\left[I_{\mathrm{cmplx}}^{\′}(x,z,\mathrm{\ω})\right]}\right]$

In formula, x, z represent respectively the value of the corresponding level in rectangular coordinate system and the direction of directly hanging down, and ω is the frequency of seismic wave propagation, and real represents to get real number;

4) obtain treating the wave field angle information on each imaging point in depth of exploration layer, choose angle and adopt interval and angular range, the migration imaging result dropping in some sampling interval is carried out to data stack, until complete the offset data stack in all angular ranges, will be total to big gun image gather and be transformed into corner-sharing degree domain imaging point road collection.

Step 2) with the seismic migration wave field of propagation angle correction be:

${\tilde{u}}_s(K_T,z;\mathrm{\ω})=\frac{k_0}{k_z\left(z\right)}{u}_s(K_T,z;\mathrm{\ω})$

In formula, u _sfor conventional source wavefield, K _t=(k _x, k _y) be horizontal wave number, k _zfor the vertical wave number at depth z place and meet following relational expression: k _z=k ₀cos θ,

ω is the frequency of seismic wave propagation, the speed that v is seismic wave propagation, and θ is propagation angle, i.e. the angle of seismic wave propagation direction and depth z direction.

Described step 3) in

u in formula _gfor seismic detection point wave field,

earthquake source wave field u _sconjugation.

Described step 3) in

in formula, θ is propagation angle, i.e. the angle of seismic wave propagation direction and depth z direction, u _gfor seismic detection point wave field,

for earthquake source wave field u _sconjugation.

The present invention is owing to taking above technical scheme, it has the following advantages: 1, the present invention from earth's surface by successively putting the mode earthquake-wave-exciting of big gun, seismic event is propagated along exploration principal direction (being generally depth direction), utilize the skew of big gun territory to obtain big gun territory image gather and angle information altogether, generate propagation angle territory image gather altogether, the method numerical evaluation in complex structure situation is stable, and result of calculation is reliable, and compared with traditional offset method, make computation amount.2, by big gun territory, altogether image gather and the angle information that obtains generate the requirement of the realistic application of data volume that angle domain common image gathers relates in the present invention, for calculating three-dimensional perspective territory image gather altogether, only need to store two 3-D data volume (space X, Y, Z three-dimensional), be two 3-D data volumes of migration imaging result and angle information, therefore data volume is much smaller than other class methods.3, the present invention adopts plural number but not real number calculating when angle information, does not therefore have computational stability problem in complex area extremely.4, the present invention is based on the big gun territory offset method generation angle domain common image gathers of wave equation, effectively overcome the problem that the defect such as " multipath " and high-frequency approximation of existing ray class methods causes, thereby made the present invention effectively avoid the generation of skew " false picture " phenomenon.5, the present invention utilizes the angle information of acquisition first to choose rational angle and adopts interval (conventionally choosing 2 °～5 °) and rational angular range (common 0 °～50 °), the migration imaging result that drops on (in the sampling interval of 5 °～10 °) in some sampling interval is carried out to data stack, until complete the offset data stack in all angular ranges, because stack can effectively strengthen useful signal, therefore the present invention can effectively suppress migration noise.The present invention can be widely used in the angle domain common image gathers generative process of oil seismic exploration.

Accompanying drawing explanation

Fig. 1 is that the present invention calculates used rate pattern schematic diagram, has four layers of medium and a sphenoid in figure, and dotted line represents the position of the common image gather that the present invention extracts;

Fig. 2 (a) is the migration before stack result of calculation schematic diagram that the present invention calculates by one-way wave equation;

Fig. 2 (b) is the present invention big gun territory that (being the degree of depth corresponding to Fig. 1 dotted line place) generates at horizontal level x=4000m place image gather schematic diagram altogether;

Fig. 3 (a) is the prestack migration profile schematic diagram that angle domain common image gathers superposition calculation of the present invention obtains;

Fig. 3 (b) be the present invention at horizontal level x=4000m place the angle domain common image gathers of (being the degree of depth corresponding to Fig. 1 dotted line place).

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in detail.

The propagation angle of the present invention territory altogether generation method of image gather comprises the following steps:

1) take earth's surface as starting point is towards direction to be explored, complex heterogeneous medium to be explored is longitudinally divided into different depth layer, be about to medium to be explored and divide different depth layer according to the depth interval of setting, for the different depth layer of more vivid expression, each depth interval can be arranged to a horizontal thin plate, can think and form a series of horizontal thin plate along the depth direction of exploration.

2) artificial at earth's surface place by successively putting the mode earthquake-wave-exciting of big gun, the seismic event exciting is each time propagated downwards in the mode of spherical wave, in the time that seismic event arrives different depth layer, calculate respectively the common seismic skew wave field in each depth layer, and be offset by common seismic the seismic migration wave field that wave field derivation is proofreaied and correct with propagation angle, concrete computation process is as follows:

The round trip wave equation of seismic event under spherical coordinate system is:

$(\frac{{\mathrm{\ω}}^2}{v^2}-\frac{{\∂}^2}{\∂r^2}+\frac{2}{r}\frac{\∂}{\∂r})u(r,\mathrm{\ω})=0---\left(1\right)$

In formula,

for radial distance, radially true origin to any distance of space, the frequency that ω is seismic wave propagation, the speed that v is seismic wave propagation, u is seismic wave field.For convenience of calculation and theoretical derivation simply, introduce new wave field p=ru, p is the seismic wave field of proofreading and correct through geometrical attenuation, formula (1) can be write as the form of the standard under spherical coordinate system:

$(\frac{{\∂}^2}{\∂r^2}+\frac{{\mathrm{\ω}}^2}{v^2})p=0---\left(2\right)$

Formula (2) is carried out to factorization, obtains following formula:

$(\frac{\∂}{\∂r}-{\mathrm{ik}}_0)(\frac{\∂}{\∂r}+{\mathrm{ik}}_0)p=0---\left(3\right)$

Ask the represented solution of equations of above-mentioned formula (3), resolve into two one-way wave equations by formula (3), these two one-way wave equations are described respectively the seismic event ripple that radially r inwardly and outwards propagates.Making two in equation (3) to be at 1 o'clock, is now the one solution of equation (3), as following formula table shows:

$\left\{\begin{array}{c}(\frac{\∂}{\∂r}-{\mathrm{ik}}_0)p=0\\ (\frac{\∂}{\∂r}+{\mathrm{ik}}_0)p=0\end{array}\right.---\left(4\right)$

In formula,

refer to the reference wave number along seismic wave propagation direction.

In actual petroleum prospecting, normally in rectangular coordinate system, calculate.Therefore, two one-way wave equations under spherical coordinate system need to be transformed in rectangular coordinate system, shown in the following formula of transfer process:

In formula, θ is propagation angle, i.e. the angle of seismic wave propagation direction and depth z direction,

for horizontal azimuth, i.e. the angle of seismic wave propagation direction and horizontal direction x, wherein earthquake wave frequency and phase velocity (phase place of seismic event is propagated in space) relation is that dispersion relation is:

k _z＝k ₀cosθ

Formula (6) is updated to and in formula (5), can obtains following formula:

$(\frac{\∂}{\∂x}\±{\mathrm{ik}}_x)p_x+(\frac{\∂}{\∂y}\±{\mathrm{ik}}_y)p_y+(\frac{\∂}{\∂z}\±{\mathrm{ik}}_z)p_z=0---\left(7\right)$

In formula, k _x, k _yand k _zbe respectively along three axle x of rectangular coordinate system, the axial wave number of y and z,

p _z=pcos θ.P _x, p _yand p _zbe respectively geometrical attenuation proofread and correct after seismic wave field p along three axle x of rectangular coordinate system, the axial component of y and z.

Equation (7) is carried out to solving equation, even three in equation (7) are zero, this kind of mode is the one solution of equation (7), can be split into following three one-way wave equations:

$(\frac{\∂}{\∂x}\±{\mathrm{ik}}_x)p_x=0---\left(8\right)$

$(\frac{\∂}{\∂y}\±{\mathrm{ik}}_y)p_y=0---\left(9\right)$

With

$(\frac{\∂}{\∂z}\±{\mathrm{ik}}_z)p_z=0---\left(10\right)$

Above-mentioned three one-way wave equations have been described respectively along rectangular coordinate system x-, y-, the seismic event that z-direction of principal axis is propagated.The one-way wave equation of proofreading and correct by the classical non-angular calculating is:

$(\frac{\∂}{\∂z}\±{\mathrm{ik}}_z)u=0---\left(11\right)$

Relatively formula (10) and formula (11), obtains the computing formula with the seismic migration wave field of propagation angle correction:

$p=\frac{1}{\cos \mathrm{\θ}}u=\frac{k_0}{k_z}u---\left(12\right)$

The form that above-mentioned formula (12) is written as to standard is:

${\tilde{u}}_s(K_T,z;\mathrm{\ω})=\frac{k_0}{k_z\left(z\right)}{u}_s(K_T,z;\mathrm{\ω})---\left(13\right)$

In formula,

for the source wavefield of angularity correction, u _sfor conventional source wavefield, K _t=(k _x, k _y) be horizontal wave number, k _zfor the vertical wave number at depth z place and meet following relational expression: k _z=k ₀cos θ.

3) generate the angle information of wave field on the imaging point of each depth layer, wherein imaging point can be regarded each point for the treatment of in exploration geology as.

The dependent imaging condition of pre-stack depth migration is:

$I(x,z)=\mathrm{real}\left[\underset{\mathrm{\ω}}{\mathrm{\Σ}}{u}_g(x,z,\mathrm{\ω})u_s^{*}(x,z,\mathrm{\ω})\right]---\left(14\right)$

In formula, seismic detection point wave field u _gwith conventional source wavefield u _sfor plural number, earthquake source wave field u _sconjugation, after last frequency summation, it is got to real number.For a frequency, the plural form of formula (14) can be write:

$I_{\mathrm{cmplx}}(x,z,\mathrm{\ω})=u_g(x,z,\mathrm{\ω})u_s^{*}(x,z,\mathrm{\ω})---\left(15\right)$

To in above-mentioned formula (13) substitution formula (15), obtain following formula:

$I_{\mathrm{cmplx}}^{\′}(x,z,\mathrm{\ω})=\frac{1}{\cos \mathrm{\θ}}{u}_g(x,z,\mathrm{\ω})u_s^{*}(x,z,\mathrm{\ω})---\left(16\right)$

Formula (15) is divided by respectively and can obtains the angle information of wave field on each imaging point with the right and left of formula (16):

$\mathrm{\θ}(x,z)={\cos }^{-1}\mathrm{real}\left[\frac{\underset{\mathrm{\ω}}{\mathrm{\Σ}}\left[I_{\mathrm{cmplx}}(x,z,\mathrm{\ω})\right]}{\underset{\mathrm{\ω}}{\mathrm{\Σ}}\left[I_{\mathrm{cmplx}}^{\′}(x,z,\mathrm{\ω})\right]}\right]---\left(17\right)$

4) obtain after the wave field angle information on each imaging point in depth of exploration layer, choose rational angle and adopt interval (conventionally choosing 2 °～5 °) and rational angular range (common 0 °～50 °), the migration imaging result that drops on (in the sampling interval of 5 °～10 °) in some sampling interval is carried out to data stack, until complete the offset data stack in all angular ranges, will be total to big gun image gather and be transformed into corner-sharing degree domain imaging point road collection.

For effect of the present invention is described, embodiments of the invention have been chosen a multilayered model that contains sphenoid, and as shown in Figure 1, in figure, dotted line only represents the position of common image gather.As shown in Fig. 2 (a)～Fig. 2 (b), complete the angle information that can obtain the common image gather in big gun territory and aerial image point after the seismic migration of all big guns, as shown in Fig. 3 (a)～Fig. 3 (b), utilize the angle information at spatial point place to superpose and can obtain propagation angle territory image gather altogether the common image gather in big gun territory.

The various embodiments described above are only for illustrating the present invention, and the step that wherein method is implemented etc. all can change to some extent, and every equivalents of carrying out on the basis of technical solution of the present invention and improvement, all should not get rid of outside protection scope of the present invention.

Claims (5)

1. a propagation angle territory generation method for image gather altogether, comprises the following steps:

1) be starting point take earth's surface, complex heterogeneous medium to be explored is longitudinally divided into different depth layer;

2) at earth's surface place by successively putting the mode earthquake-wave-exciting of big gun, the seismic event exciting is each time propagated downwards in the mode of spherical wave, in the time that seismic event arrives different depth layer, the seismic migration wave field that utilizes wave equation to calculate respectively the common seismic skew wave field in each depth layer and proofread and correct with propagation angle;

3) angle information that generates wave field on the imaging point of each depth layer is:

$\mathrm{\θ}(x,z)={\cos }^{-1}\mathrm{real}\left[\frac{\underset{\mathrm{\ω}}{\mathrm{\Σ}}\left[I_{\mathrm{cmplx}}(x,z,\mathrm{\ω})\right]}{\underset{\mathrm{\ω}}{\mathrm{\Σ}}\left[I_{\mathrm{cmplx}}^{\′}(x,z,\mathrm{\ω})\right]}\right]$

In formula, x, z represent respectively the value of the corresponding level in rectangular coordinate system and the direction of directly hanging down, and ω is the frequency of seismic wave propagation, and real represents to get real number;

4) obtain treating the wave field angle information on each imaging point in depth of exploration layer, choose angle and adopt interval and angular range, the migration imaging result dropping in some sampling interval is carried out to data stack, until complete the offset data stack in all angular ranges, will be total to big gun image gather and be transformed into corner-sharing degree domain imaging point road collection.

2. a kind of propagation angle as claimed in claim 1 territory generation method of image gather altogether, is characterized in that: step 2) with the seismic migration wave field of propagation angle correction be:

${\tilde{u}}_s(K_T,z;\mathrm{\ω})=\frac{k_0}{k_z\left(z\right)}{u}_s(K_T,z;\mathrm{\ω})$

In formula, u _sfor conventional source wavefield, K _t=(k _x, k _y) be horizontal wave number, k _zfor the vertical wave number at depth z place and meet following relational expression: k _z=k ₀cos θ,

ω is the frequency of seismic wave propagation, the speed that v is seismic wave propagation, and θ is propagation angle, i.e. the angle of seismic wave propagation direction and depth z direction.

3. a kind of propagation angle as claimed in claim 1 territory generation method of image gather altogether, is characterized in that: described step 3) in

u in formula _gfor seismic detection point wave field,

earthquake source wave field u _sconjugation.

4. a kind of propagation angle as claimed in claim 2 territory generation method of image gather altogether, is characterized in that: described step 3) in

u in formula _gfor seismic detection point wave field,

earthquake source wave field u _sconjugation.

5. a kind of propagation angle territory as claimed in claim 1 or 2 or 3 or 4 generation method of image gather altogether, is characterized in that: described step 3) in

in formula, θ is propagation angle, i.e. the angle of seismic wave propagation direction and depth z direction, u _gfor seismic detection point wave field,

for earthquake source wave field u _sconjugation.

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