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首页改进的角域CIGs在差分似然优化方法中的应用
"差分似然优化方法在角度域CIGs中的应用" Differential Semblance Optimization (DSO) 方法是一种在地震反演领域中的创新策略,其主要目的是克服非线性最小二乘法可能导致的收敛问题。相比于传统的反演方法,DSO通过构建一个目标函数来度量地震资料与期望模型的偏差,强调全局凸性,从而减少陷入局部最小值的风险。这种方法对于提高地震成像和深度迁移的质量至关重要。 通常,在DSO的目标函数构建中,One-way Diffraction Cumulative Interferometric Gathers (ODCIGs) 被广泛采用。它们能够准确地捕捉到反射事件的传播路径和速度影响,有助于形成稳定的反演结果。然而,本研究在此基础上进一步探索,引入了Angle Domain CIGs (ADCIGs)。角度域CIGs的优势在于,它们能够直接评估速度模型的准确性,并且能够更精确地反映速度与深度之间的耦合关系。 Marmousi案例研究表明,角度域CIGs在速度校正方面表现出色,能够有效地减少图像噪声和伪影。这表明,利用ADCIGs在DSO框架下进行反演,不仅提高了速度模型的精度,还能确保迁移过程的稳定性,使得复杂迁移算法的优势在可靠性高的速度模型支持下得到充分展现。 总结来说,本文探讨了如何利用角度域CIGs改进Differential Semblance Optimization 方法,以提升地震数据处理中的速度模型重建效果,减少了迭代过程中的问题,为地震成像和解释提供了更为可靠的技术手段。这种方法对于提高地震勘探的整体质量和效率具有重要意义。
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Differential Semblance Optimization Method with Angle domain CIGs
Fang Ren*, ZhenChun Li, Min Zhang and FeiXu Chen, m China University of Petroleum
Summary
Differential semblance optimization (DSO) is an approach
to inverse the velocity which avoids the severe convergence
associated with nonlinear least-squares inversion. The DSO
objective function measures the deviation of image gathers
and expected to have much better global convexity property
and suffer less from the local minima. Generally, ODCIGs
are used in the construction of objective function. In this
paper, we also use ADCIGs to construct the function which
estimate the correctness of velocity model directly and
reflect the coupling relation between velocity and depth
accurately. The result of Marmousi shows that angle
domain CIGs correct the velocity effectively and almost
have no image artifacts.
Introduction
An accurate velocity model and exact migration algorithms
are both essential for the result of migration and imaging,
usually, velocity plays a more important role, as the
advantage of the sophisticated migration algorithms is
evident only when the velocity is reliable. Since first
proposed in exploration seismology in the 1970s (Gardner,
1974; Sattlegger,1975),migration velocity analysis has
become increasingly important in seismic imaging and
velocity modeling.
According to different theories, seismic velocity analysis
methods can be divided into two groups: One aims at
minimizing the misfit in data domain, such as waveform
inversion (WI) (Tarantola, 1984; Woodward, 1992; Pratt,
1999; Virieux and Operto, 2009), while the other aims at
improving the quality in image domain, such as migration
velocity analysis (MVA) (Symes and Carazzone,
1991;Biondi and Sava, 1999; Sava and Biondi, 2004a,b;
Shen and Symes, 2008; Guerra et al., 2009).Several
advantages drive us to use the image space method
(WEMVA) instead of data-space method (Waveform
Inversion): first, the migrated image is often much cleaner
than the recorded wave fields; second, the objective
function is directly related to the final image. However, as
only transmission information is used in the image domain
method, the vertical resolution of inverted velocity model is
limited.
Differential Semblance Optimization (Symes and
Carazzone, 1991; Shen and Symes, 2008) is one of the
wave-equation migration velocity analysis methods that
utilize the difference between image gathers to form
objective function, the function has better convexity and
the gradient is smooth, which avoids the local minimum
when there lacks low frequency or long offset information
in the data. Several authors have since developed inversion
algorithms based on the DSO concept (Shen et al, 2003,
Chauris and Noble, 2001, Plessix, et al, 2000). DSO-MVA
uses (one-way) wave equation migration as the engine to
calculate gathers and update the velocity model, with the
gradient of the objective function being calculated by the
adjoint state method.
Theory
DSO objective function: offset & angle
The concept of DSO method was proposed by Symes
(1991), it introduces a extend axis, usually is offset or angle,
when the velocity is correct, the normed difference between
neighboring traces along the “redundant” axis in a prestack
common image gather should be minimal.
First, we start with the imaging condition as following:
,,
( , ) ( , , ) ( , , ) ( , , )
sr
s r r s
xx
I x h G x h x G x h x d x x
(1)
where
I
is the image,
G
is the Green’s function,
d
is the
surface data,
h
is the subsurface offset,
s
x
and
r
x
are the
source and receiver coordinates respectively. Then we
construct the DSO objective function
2
1
|| ||
2
J PI
(2)
where
I
are the common image gathers,
P
is the DSO
operator that penalizes the singularity in common image
gathers when the velocity is accurate, and when the
velocity is inaccurate, the DSO operator can eliminate part
of the imaging errors. The image gathers
PI
is called
redundant images.
As to offset domain CIGs, the objective function can be
written as
22
11
|| || || ( , ) ||
22
hh
J P I hI x h
(3)
which
h
Ph
and
( , )I x h
are offset gathers which
effectively demonstrate the degree of focusing. In terms of
the image volume
( , , )I x z h
, the characteristic signature of
kinematically correct velocity is focusing or concentrating
at
0h
. If there exists some energy away from
0h
, then
( , , ) 0hI x z h
. So the DSO operator annihilates the energy
at
0h
and emphasizes the energy away from
0h
,
when the objective function verges to zero, the energy
mainly focuses at one point near
0h
, it thus provides a
Page 3698
© 2016 SEG
SEG International Exposition and 86th Annual Meeting
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