CN102636809A - 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 be total to the generation method of image gather about a kind of propagation angle territory that is useful in the petroleum prospecting complex structure.

Background technology

The pre-stack depth migration technology has become the strong instrument that solves complex structure exploration problem, causes it in practical application, to be restricted because it relies on interval velocity model.Uncertain and the insecure problem of rate pattern to the depth shift result who exists in the seismic imaging; Prior art adopts the all-wave shape method of inversion, tomographic inversion method and residue curvature method to handle usually; Wherein adopt the all-wave shape method of inversion can obtain comparatively reliable velocity model; But calculated amount is very huge, so this method mainly (is suitable in the scope at low frequency usually≤10Hz); Adopt the tomographic inversion method also can obtain comparatively reliable velocity model, its calculated amount is big but less than the all-wave shape method of inversion, but this method mainly is suitable in the medium and low frequency scope.In order to reduce calculated amount, above-mentioned two kinds of methods adopt ray casting to carry out inverting usually, but ray casting is because problems such as high-frequency approximation and multipath are inapplicable in the 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, effectively reservoir distribution is disperseed, rock physics concerns complicacy and reservoir lithology contrasts characteristics such as weak; Therefore remaining curvature method is method relatively more commonly used at present; It mainly is progressively to revise the initiation layer rate pattern through bending curvature that is total to the image gather lineups and the relation between slowness (inverse of the speed) disturbance, and the above-mentioned relatively two kinds of methods of the calculated amount of this method are less.

The core of residue curvature method is to generate image gather altogether, utilizes the bending curvature and the continuous iteration renewal speed of the relation between the velocity error of image gather altogether, the final interval velocity model that obtains to be used for pre-stack depth migration.Common image gather mainly contains common reflection point (CRP) road collection, big gun territory, and image gather, offset distance territory are total to image gather and the common image gather of angle domain altogether; In above-mentioned image gather altogether; Angle domain image gather altogether receives the skew noise or the interference minimum of the illusion that squints, and especially under the complex structure condition, angle domain is total to the road collection that image gather can not produce any " illusion " (false lineups); All there is the skew illusion in other, is unfavorable for the analysis and the inverting research of migration velocity.Existing angle domain is total to the image gather technology and is total to the Radon mathematic(al) manipulation completion of image gather through standard by the offset distance territory usually; 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 be stored the data volume of five dimensions, in practical application, have received certain restriction.

Summary of the invention

To the problems referred to above, it is all smaller to the purpose of this invention is to provide a kind of calculated amount and memory space, not only effectively avoids skew " false picture " phenomenon to take place, and the propagation angle territory that can the suppress migration noise generation method of image gather altogether.

For realizing above-mentioned purpose, the present invention takes following technical scheme: a kind of propagation angle territory is the generation method of image gather altogether, may further comprise the steps: 1) be starting point with the face of land, complex heterogeneous medium to be explored vertically is divided into different depth layer; 2) locate on the face of land through putting the mode earthquake-wave-exciting of big gun one by one; The seismic event that excites is each time propagated downwards with the mode of spherical wave; When seismic event arrives the different depth layer, utilize wave equation to calculate conventional earthquake off-set wave field and the seismic migration wave field that has the propagation angle correction on each depth layer respectively; 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 the formula, x, z represent the level of the correspondence in the rectangular coordinate system respectively and the value of the direction of directly hanging down, and ω is the frequency of seismic wave propagation, and real representes to get real number;

4) obtain treating the wave field angle information on each imaging point in the depth of exploration layer; Choosing angle adopts at interval and angular range; Migration imaging result to dropping in some SIs carries out the data stack; Offset data stack in accomplishing all angular ranges will be total to the big gun image gather and be transformed into common angle domain image gather.

Step 2) having the seismic migration wave field that propagation angle proofreaies and correct is:

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

In the formula, u _sBe the source wavefield of routine, K _T=(k _x, k _y) be horizontal wave number, k _zFor the vertical wave number at depth z place and satisfy following relational expression: k _z=k ₀Cos θ,

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

In the said step 3)

U in the formula _gBe earthquake geophone station wave field,

Earthquake source wave field u _sConjugation.

In the said step 3)

In the formula, θ is a propagation angle, i.e. the angle of seismic wave propagation direction and depth z direction, u _gBe earthquake geophone station wave field,

Be earthquake source wave field u _sConjugation.

The present invention is owing to take above technical scheme, and it has the following advantages: 1, through putting the mode earthquake-wave-exciting of big gun one by one, seismic event is propagated along exploration principal direction (being generally depth direction) from the face of land in the present invention; 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 under the complex structure situation is stable, and result of calculation is reliable; And compare with traditional offset method, make computation amount.2, the present invention by the big gun territory altogether image gather and the angle information that obtains generate angle domain altogether the data volume that relates to of image gather meet requirement of actual application; For calculating three-dimensional perspective territory image gather altogether; Only need store two 3-D data volumes (Z is three-dimensional for space X, Y); They be two 3-D data volumes of migration imaging result and angle information, so data volume is much smaller than other class methods.3, the present invention adopts plural number but not real number when calculating angle information, does not therefore have the computational stability problem at complex area extremely.4, the present invention is based on the common image gather of big gun territory offset method generation angle domain of wave equation; Effectively overcome the problem that the defectives such as " multipath " and high-frequency approximation of existing ray class methods cause, thereby made the present invention effectively avoid the generation of skew " false picture " phenomenon.5, the present invention utilizes the angle information of acquisition at first to choose angle with rational and adopts (choosing 2 °～5 ° usually) and angle with rational scope (common 0 °～50 °) at interval; The migration imaging result who drops on (in 5 °～10 ° SI) in some SIs is carried out the data stack; Offset data stack in accomplishing all angular ranges; Because stack can effectively strengthen useful signal, so the present invention can effectively suppress migration noise.The angle domain that the present invention can be widely used in oil seismic exploration is total in the image gather generative process.

Description of drawings

Fig. 1 is that the present invention calculates employed rate pattern synoptic diagram, has four layers of medium and a sphenoid among the figure, and dotted line is represented the position of the common image gather that the present invention extracts;

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

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

Fig. 3 (a) is that angle domain of the present invention is total to the prestack migration profile synoptic diagram that the image gather stack calculates;

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

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is carried out detailed description.

The propagation angle of the present invention territory generation method of image gather altogether may further comprise the steps:

1) be that starting point is towards direction to be explored with the face of land; Complex heterogeneous medium to be explored vertically is divided into different depth layer; Be about to medium to be explored and divide different depth layer according to the depth interval of setting; The different depth layer of expression for vivid more can be provided with a horizontal thin plate with each depth interval, then can think to form a series of horizontal thin plate along the depth direction of exploration.

2) artificial locating on the face of land through putting the mode earthquake-wave-exciting of big gun one by one; The seismic event that excites is each time propagated downwards with the mode of spherical wave; When seismic event arrives the different depth layer; Calculate the conventional earthquake off-set wave field on each depth layer respectively, and have the seismic migration wave field that propagation angle is proofreaied and correct through the derivation of conventional earthquake off-set wave field, concrete computation process is following:

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 the formula;

is radial distance; Promptly radially true origin to the space any distance; ω is the frequency of seismic wave propagation, and v is the speed of seismic wave propagation, and u is a seismic wave field.Simple for convenience of calculation and theoretical derivation, introduce new wave field p=ru, p is the seismic wave field through how much dispersion correction, formula (1) can be write as the form of the standard under the spherical coordinate system:

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

Formula (2) is carried out 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), be about to formula (3) and resolve into two one-way wave equations, these two one-way wave equations are described the radially inside and outside ripple of propagating of r of seismic event respectively.When making in the equation (3) two be zero, be a kind of the separating of equation (3) this moment, like following formulate:

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

In the formula,

is meant the reference wave number along the seismic wave propagation direction.

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

In the formula; θ is a propagation angle; It is the angle of seismic wave propagation direction and depth z direction;

is horizontal azimuth; Be 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 the space) relation is that dispersion relation is:

k _z＝k ₀cosθ

Formula (6) is updated in the formula (5) then 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 the 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 how much seismic wave field p after the dispersion correction along three axle x of rectangular coordinate system, the axial component of y and z.

Equation (7) is carried out solving equation, even three in the equation (7) are zero, this kind mode is a kind of the separating of equation (7), then 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 the z-direction of principal axis is propagated.The one-way wave equation of proofreading and correct through the non-angular of the classics that calculate is:

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

Relatively formula (10) and formula (11) obtain having the computing formula of 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 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 the formula, Be the source wavefield of angularity correction, u _sBe the source wavefield of routine, K _T=(k _x, k _y) be horizontal wave number, k _zFor the vertical wave number at depth z place and satisfy 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 of treating in the 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 the formula, earthquake geophone station wave field u _gSource wavefield u with routine _sBe plural number, Earthquake source wave field u _sConjugation, real number is got to it in last frequency summation back.For a frequency, the plural form of formula (14) can be write:

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

With obtaining formula in above-mentioned formula (13) the substitution formula (15):

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

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

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

4) obtain treating in the depth of exploration layer behind the wave field angle information on each imaging point; Choose angle with rational and adopt (choosing 2 °～5 ° usually) and angle with rational scope (common 0 °～50 °) at interval; The migration imaging result who drops on (in 5 °～10 ° SI) in some SIs is carried out the data stack; Offset data stack in accomplishing all angular ranges will be total to the big gun image gather and be transformed into common angle domain image gather.

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

Above-mentioned each embodiment only is used to explain the present invention, and wherein the step implemented of method etc. all can change to some extent, and every equivalents of on the basis of technical scheme of the present invention, carrying out and improvement all should not got rid of outside protection scope of the present invention.

Claims (5)

1. the propagation angle territory generation method of image gather altogether may further comprise the steps:

1) with the face of land is starting point, complex heterogeneous medium to be explored vertically is divided into different depth layer;

2) locate on the face of land through putting the mode earthquake-wave-exciting of big gun one by one; The seismic event that excites is each time propagated downwards with the mode of spherical wave; When seismic event arrives the different depth layer, utilize wave equation to calculate conventional earthquake off-set wave field and the seismic migration wave field that has the propagation angle correction on each depth layer respectively;

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

4) obtain treating the wave field angle information on each imaging point in the depth of exploration layer; Choosing angle adopts at interval and angular range; Migration imaging result to dropping in some SIs carries out the data stack; Offset data stack in accomplishing all angular ranges will be total to the big gun image gather and be transformed into common angle domain image gather.

2. a kind of propagation angle as claimed in claim 1 territory is the generation method of image gather altogether, it is characterized in that: step 2) have the seismic migration wave field that propagation angle proofreaies and correct and 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 the formula, u _sBe the source wavefield of routine, K _T=(k _x, k _y) be horizontal wave number, k _zFor the vertical wave number at depth z place and satisfy following relational expression: k _z=k ₀Cos θ,

ω is the frequency of seismic wave propagation, and v is the speed of seismic wave propagation, and θ is a 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 is the generation method of image gather altogether, it is characterized in that: in the said step 3)

U in the formula _gBe earthquake geophone station wave field,

Earthquake source wave field u _sConjugation.

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

U in the formula _gBe earthquake geophone station wave field,

Earthquake source wave field u _sConjugation.

5. like the generation method of the common image gather of claim 1 or 2 or 3 or 4 described a kind of propagation angle territories, it is characterized in that: in the said step 3)

In the formula, θ is a propagation angle, i.e. the angle of seismic wave propagation direction and depth z direction, u _gBe earthquake geophone station wave field, Be earthquake source wave field u _sConjugation.

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