scholarly journals Research on the Improved Least Squares Reverse Time Migration Imaging Method

2021 ◽  
Vol 236 ◽  
pp. 04017
Author(s):  
Xiaodan Zhang ◽  
Dongxiao Liu ◽  
Guizhong Liu ◽  
Haiyang Gou ◽  
Rui Li ◽  
...  
Keyword(s):  
Least Squares ◽  
Iteration Process ◽  
Convergence Speed ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Migration Imaging ◽  
And Performance ◽  
Key Techniques

An improved Least Squares Reverse Time Migration (LSRTM) method is proposed in the paper, which can effectively improve convergence speed and imaging accuracy. Firstly, the key techniques in the implementation of LSRTM are discussed. Secondly, a condition factor is introduced in the iteration process of conjugate gradient method. Finally, the imaging effect and performance of the algorithm are analyzed. The experiment results indicate that it can speed up the convergence speed and improve the convergence accuracy, so as to improve the imaging effect. Compared with the conventional LSRTM, the data residual of improved LSRTM can be reduced by about 5%.

Diffraction imaging for fault-karst structure by least-squares reverse time migration

2020 ◽  
pp. 1-40
Author(s):  
Xinru Mu ◽  
Jianping Huang ◽  
Liyun Fu ◽  
Shikai Jian ◽  
Bing Hu ◽  
...  
Keyword(s):  
Least Squares ◽  
Western China ◽  
Small Scale ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Imaging Results ◽  
Heterogeneous Structures ◽  
Karst Reservoir

The fault-karst reservoir, which evolved from the deformation and karstification of carbonate rock, is one of the most important reservoir types in western China. Along the deep-seated fault zones, there are a lot widely spread and densely distributed fractures and vugs. The energy of the diffractions generated by heterogeneous structures, such as faults, fractures and vugs, are much weaker than that of the reflections produced by continuous formation interface. When using conventional full wavefield imaging method, the imaging results of continuous layers usually cover small-scale heterogeneities. Given that, we use plane-wave destruction (PWD) filter to separate the diffractions from the full data and image the separated diffractions using least-squares reverse time migration (LSRTM) method. We use several numerical examples to demonstrate that the newly developed diffractions LSRTM (D-LSRTM) can improve the definition of the heterogeneous structures, characterize the configuration and internal structure of the fault-karst structure well and enhance the interpretation accuracy for fault-karst reservoir.

Multi-Cross-hole 3-D reverse time migration imaging

2020 ◽  
Author(s):  
Fei Cheng ◽  
Jiangping Liu
Keyword(s):  
Dimensional Space ◽  
Three Dimensional ◽  
Geological Structure ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Migration Imaging ◽  
The Cross ◽  
Three Dimensional Space

<p>Cross-well 2-D seismic CT imaging method has been widely used in many fields such as oil-gas exploration and engineering geological exploration, but for the real three-dimensional space, this traditional method can only obtain the two-dimensional velocity profile between the two wells, cannot obtain the lateral geological structure outside the profile; Besides, the seismic signal received from cross-well exploration is the response of geologic body in three-dimensional space, which may be influenced by the geologic body outside the two-well profile, and that will give a result of image distortion and having an effect on geological interpretation. Based on the theory of three-dimensional acoustic wave equation, this paper implements a three-dimensional cross-well reverse-time migration imaging method to obtain the cross-well 3-D geological structure with the observed value from multiple wells by using the first-order velocity-stress acoustic wave equation and firing time imaging conditions. Calculation results of the typical theoretical models show that: The multi-well three-dimensional imaging method adopted in this paper can accurately and effectively realize the cross-well 3-D geological imaging with high resolution and reliable results. Multi-well three-dimensional imaging method can effectively obtain the cross-well three-dimensional structure distribution, which can solve the issue of hard to obtain the transverse structure change by 2-D imaging. It also can solve the imaging problems of big dip angle interface in CT imaging and obtains the true cross-well 3-D geological structure with the multiple well data, which can provide the basis for cross-well 3-D seismic exploration.</p>

Viscoacoustic least-squares reverse time migration using a time-domain complex-valued wave equation

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. S479-S499 ◽  
Author(s):  
Jidong Yang ◽  
Hejun Zhu
Keyword(s):  
Wave Equation ◽  
Least Squares ◽  
Time Domain ◽  
Inverse Operator ◽  
Total Variation Regularization ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Complex Valued

With limited recording apertures, finite-frequency source functions, and irregular subsurface illuminations, traditional imaging methods have been insufficient to produce satisfactory reflectivity images with high resolution and amplitude fidelity. This is because most traditional imaging approaches are commonly formulated as the adjoint instead of the inverse operator with respect to the forward-modeling operator. In addition, intrinsic attenuation introduces amplitude loss and phase dispersion during wave propagation. Without considering these effects, migrated images might be kinematically and dynamically incorrect. We have developed a viscoacoustic least-squares reverse time migration (LSRTM) method based on a time-domain complex-valued wave equation. According to the Born approximation, we first linearized the viscoacoustic wave equation and derived a demigration operator. Then, using the complex-valued Lagrange multiplier method, we derived the adjoint viscoacoustic wave equation and corresponding sensitivity kernel. With the forward and adjoint operators, a linear inverse problem is formulated to estimate the subsurface reflectivity model. A total-variation regularization scheme is introduced to enhance the robustness of our viscoacoustic LSRTM, and a diagonal Hessian is used as the preconditioner to accelerate the convergence. Three synthetic examples are used to demonstrate that our approach enables us to compensate attenuation effects, improve imaging resolution, and enhance amplitude fidelity in comparison with the adjoint imaging method.

Sparsity-promoting multi-parameter pseudoinverse Born inversion in acoustic media

Geophysics ◽  
2021 ◽  
pp. 1-62
Author(s):  
Milad Farshad ◽  
Hervé Chauris
Keyword(s):  
Least Squares ◽  
Cross Talk ◽  
Radon Transform ◽  
Weighted Least Squares ◽  
Variable Density ◽  
Imaging Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Acoustic Media

Least-squares reverse-time migration has become the method of choice for quantitative seismic imaging. The main drawback of such scheme is that it requires many migration/modeling cycles. The convergence of least-squares reverse-time migration can be accelerated by using a suitable preconditioner. In the context of extended domain in a variable density acoustic media, the pseudoinverse Born operator is the recommended preconditioner, providing quantitative results within a single iteration. This method consists of two steps: application of the pseudoinverse Born operator, and inversion of two parameters using an efficient weighted least-squares approach based on the Radon transform. As expected, cross-talk artifacts are generated in the second step due to limited acquisition. We present a variable density pseudoinverse Born operator constrained with the ℓ1-norm for each model parameter to suppress the artifacts. The fast iterative shrinkage-thresholding algorithm is used to carry out the optimization problem. In classical iterative least-squares migration, the ℓ1-norm constraints would affect the whole imaging process. As the imaging method is split into two steps, only the Radon transform part is modified, where no wave-based operators are involved. Through numerical experiments, we verify the robustness of the proposed method against different migration artifacts including the parameter cross-talk, interfaces with abrupt truncations, sparse shot acquisition geometry, noisy data and high contrast complex structures.

Decoupled elastic least-squares reverse time migration and its application in tunnel geological forward-prospecting

Geophysics ◽  
2021 ◽  
pp. 1-136
Author(s):  
Bin Liu ◽  
Jiansen Wang ◽  
Yuxiao Ren ◽  
Xu Guo ◽  
Lei Chen ◽  
...  
Keyword(s):  
Least Squares ◽  
Tunnel Construction ◽  
Stable Convergence ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Migration Imaging ◽  
Imaging Results ◽  
Geological Conditions ◽  
Migration Method

Accurate seismic imaging can ensure safe and efficient tunnel construction under complex geological conditions. As a high-precision migration method, reverse time migration (RTM) has been introduced into tunnel seismic forward-prospecting. However, the resolution of traditional RTM imaging results may not meet the requirements in a complex tunnel environment, which affects the interpretation of tunnel seismic forward-prospecting results. In this study, we propose a least-squares RTM method based on the decoupled elastic wave equation in tunnels. The Born forward modeling operator and its exact adjoint migration imaging operator are derived to ensure a stable convergence of the conjugate gradient method. Moreover, a pseudo-Hessian based preconditioning operator is adopted to accelerate the convergence. Numerical examples are provided to verify the efficiency of the proposed scheme. A field test in a traffic tunnel construction site is performed to show the good application effect of the decoupled elastic least-squares RTM in practical situations.

From acoustic to elastic inverse extended Born modeling: a first insight in the marine environment

Geophysics ◽  
2021 ◽  
pp. 1-73
Author(s):  
Milad Farshad ◽  
Hervé Chauris
Keyword(s):  
Least Squares ◽  
Marine Environment ◽  
Computational Cost ◽  
Physical Parameters ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
S Wave ◽  
Time Migration ◽  
Physical Density ◽  
Acoustic Approximation

Elastic least-squares reverse time migration is the state-of-the-art linear imaging technique to retrieve high-resolution quantitative subsurface images. A successful application requires many migration/modeling cycles. To accelerate the convergence rate, various pseudoinverse Born operators have been proposed, providing quantitative results within a single iteration, while having roughly the same computational cost as reverse time migration. However, these are based on the acoustic approximation, leading to possible inaccurate amplitude predictions as well as the ignorance of S-wave effects. To solve this problem, we extend the pseudoinverse Born operator from acoustic to elastic media to account for the elastic amplitudes of PP reflections and provide an estimate of physical density, P- and S-wave impedance models. We restrict the extension to marine environment, with the recording of pressure waves at the receiver positions. Firstly, we replace the acoustic Green's functions by their elastic version, without modifying the structure of the original pseudoinverse Born operator. We then apply a Radon transform to the results of the first step to calculate the angle-dependent response. Finally, we simultaneously invert for the physical parameters using a weighted least-squares method. Through numerical experiments, we first illustrate the consequences of acoustic approximation on elastic data, leading to inaccurate parameter inversion as well as to artificial reflector inclusion. Then we demonstrate that our method can simultaneously invert for elastic parameters in the presence of complex uncorrelated structures, inaccurate background models, and Gaussian noisy data.

Sign in / Sign up

Export Citation Format

Share Document