US 11,892,578 B2 · Seismic imaging method, system, and device based on pre-stack high-angle fast Fourier transform

Abstract

This disclosure relates to geophysical exploration and seismic imaging, and more particularly to a seismic imaging method, system, and device based on pre-stack high-angle fast Fourier transform (FFT). The method includes: acquiring seismic data acquired during seismic exploration; extracting a common shot point gather from the seismic data followed by conversion into a frequency wavenumber domain common offset gather; calculating wave propagation angles; dividing an imaging region into a first region and a second region; solving constant coefficients of the first region and the second region; performing frequency-division layer-by-layer wavefield continuation on a frequency-wave number domain common offset gather to obtain imaging results at different depths and frequencies; subjecting the imaging results to integration followed by transformation to a spatial domain to obtain common offset imaging profiles; and subjecting the common offset imaging profiles to superposition obtain final imaging results. The disclosure achieves the highly-precise seismic imaging of high-steep structures and improves imaging efficiency.

A seismic imaging method, comprising:

(S100) collecting seismic data comprising seismic source type, seismic source dominant frequency, location of a shot point, maximum tectonic angle, a set temporal sampling interval, a size of a velocity model, and a spatial interval;
(S200) extracting a common shot point gather from the seismic data;
converting the common shot point gather to a time-space domain common offset gather according to the location of the shot point and a location of a receiver point;
and converting time-space domain common offset seismic data in the time-space domain common offset gather from time-space domain to frequency-wavenumber domain by using Fourier transform to obtain frequency-wavenumber domain common offset seismic data;
(S300) calculating a plurality of wave propagation angles of a plurality of grid points of the velocity model based on the frequency-wavenumber domain common offset seismic data through the following equation:
θ
=
arctan
⁡
(
|
∂
p
∂
x
|
/
|
∂
p
∂
z
|
)
,
wherein θ represents the wave propagation angles;
∂p/∂x represents a partial derivative of a seismic wavefield in x direction;
and ∂p/∂z represents a partial derivative of the seismic wavefield in z direction;
and
dividing an imaging region into a first region and a second region based on the plurality of wave propagation angles, wherein a wave propagation angle of the first region is smaller than a wave propagation angle of the second region;
(S400) calculating a plurality of optimized constant coefficients corresponding to the first region and the second region according to the following equation:
J
=
∫
0
1
∫
0
φ
(
1
-
k
x
¯
2
+
n
-
1
+
(
n
-
1
)
⁢
c
⁢
k
x
¯
2
a
+
b
⁢
k
x
¯
2
-
n
2
-
k
x
¯
2
)
2
⁢
d
⁢
θ
⁢
dn
;
wherein J is an objective function;
θ represents the wave propagation angle;
n is a medium refractive index;
a, b and c represent the plurality of optimized constant coefficients;
kx represents wavenumber in x direction;
kx represents normalized wavenumber in x direction, and kx=kx/k0;
k0 represents wavenumber based on background velocity;
and φ is a set maximum imaging angle;
(S500) constructing a rational function-approximation dispersion relation based on heterogeneity of a real underground medium;
and substituting the rational function-approximation dispersion relation into a frequency-wavenumber domain Fourier wavefield continuation fundamental equation to obtain a frequency-wavenumber domain wavefield continuation equation, expressed as:
P
⁡
(
k
x
,
z
+
Δ
⁢
z
)
=
{
(
1
-
α
)
⁢
exp
[
ik
0
⁢
Δ
⁢
z
⁡
(
n
-
1
)
]
+
α
⁢
exp
[
i
⁢
k
0
⁢
Δ
⁢
z
⁡
(
2
⁢
n
-
2
)
]
}
⁢
p
⁡
(
k
x
,
z
)
⁢
exp
⁡
(
i
⁢
k
z
⁢
Δ
⁢
z
)
;
wherein P(kx,z+Δz) represents wavefield information at a depth of z+Δz;
kz represents wavenumber in z direction;
p(kx,z) represents wavefield information at a depth of z;
α is an intermediate parameter variable, represented by
α
=
ck
x
2
_
a
+
bk
x
2
_
;
i represents an imaginary number;
and Δz represents a spatial sampling interval along a depth direction;
and
substituting the plurality of optimized constant coefficients obtained in step (S400) into the intermediate parameter variable α of the frequency-wavenumber domain wavefield continuation equation, and processing the frequency-wavenumber domain common offset seismic data by using the frequency-wavenumber domain wavefield continuation equation thereby obtaining a plurality of images at different depths and frequencies;
(S600) integrating the plurality of images to obtain a plurality of integrated images;
and transforming the plurality of integrated images to a spatial domain by using inverse Fourier transform to obtain a plurality of common offset imaging profiles;
and
(S700) superposing the plurality of common offset imaging profiles to obtain a seismic image.

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Seismic imaging method, system, and device based on pre-stack high-angle fast Fourier transform

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Seismic imaging method, system, and device based on pre-stack high-angle fast Fourier transform

Life of this patent

Abstract

Claims4