Dip-angle Decomposition in Relation with Subsurface Offset Extended Wave-equation Migration

2016 ◽  
Author(s):  
R. Dafni ◽  
W.W. Symes
Keyword(s):  
Wave Equation ◽  
Dip Angle

Imaging diffractors using wave-equation migration

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. S459-S468 ◽  
Author(s):  
Lu Liu ◽  
Etienne Vincent ◽  
Xu Ji ◽  
Fuhao Qin ◽  
Yi Luo
Keyword(s):  
Wave Equation ◽  
Field Data ◽  
Recursive Algorithm ◽  
Median Filter ◽  
Random Noise ◽  
Plane Waves ◽  
Computationally Efficient ◽  
Imaging Point ◽  
Local Plane ◽  
Dip Angle

We have developed a fast and practical wave-equation-based migration method to image subsurface diffractors. The method is composed of three steps in our implementation. First, it decomposes extrapolated receiver wavefields at every imaging point into local plane waves by a linear Radon transform; the transform is realized by a novel computationally efficient recursive algorithm. Second, the decomposed plane waves are zero lag-correlated with the incident source wavefields, where the incident angles are computed via the structure tensor approach. The resulting prestack images are binned into dip-angle gathers according to the directions of the decomposed plane waves and the calculated incident angles. Third, a windowed median filter is applied to the dip-angle gathers to suppress the focused reflection energy, and it produces the desired diffraction images. This method is tested on synthetic and field data. The results demonstrate that it is resistant to random noise, computationally efficient, and applicable to field data in practice. The results also indicate that the diffraction images are able to provide important discontinuous geologic features, such as scattering and faulting zones, and thus are helpful for seismic interpretation.

Kinematic artifacts in the subsurface-offset extended image and their elimination by a dip-domain specularity filter

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. S477-S495 ◽  
Author(s):  
Raanan Dafni ◽  
William W. Symes
Keyword(s):  
Wave Equation ◽  
Field Data ◽  
Seismic Inversion ◽  
Scattering Angle ◽  
Specular Reflections ◽  
Dip Angle ◽  
Seismic Reflections ◽  
Angle Of Reflection ◽  
Inversion Techniques

Common-image gathers in the dip-angle domain may be computed in relation to wave-equation migration methods, extended by the subsurface offset. They involve the application of a postmigration local Radon transform on the subsurface-offset extended image. In the dip-angle domain, seismic reflections are focused around the specular dip angle of reflection. This focusing distinguishes them from any other event in the image space. We have incorporated the dip-angle information about the presence of specular reflections into the computation of the conventional scattering-angle-dependent reflection coefficient. We have designed a specularity filter in the dip-angle domain based on a local semblance formula that recognizes and passes events associated with specular reflections, while suppressing other sorts of nonspecular signal. The filter is remarkably effective at eliminating either random or coherent noises that contaminates the prestack image. In particular, our dip-angle filter provides a method for the suppression of kinematic artifacts, commonly generated by migration in the subsurface-offset domain. These artifacts are due to an abrupt truncation of the data acquisition geometry on the recording surface. We have studied their appearance and devised an appropriate formation mechanism in the subsurface-offset and scattering-angle domains. The prominent presence of the kinematic artifacts in image gathers usually impairs the quality of the postmigration analysis and decelerates the convergence of wave-equation inversion techniques. We have determined from testing on synthetic and field data that using the proposed dip-angle-domain specularity filter efficiently eliminates the kinematic artifacts in the delivered gathers. We expect involvement of the specularity filter to increase the reliability and quality of the seismic processing chain and provide a faster convergence of iterative methods for seismic inversion.

scholarly journals Scattering and dip angle decomposition based on subsurface offset extended wave-equation migration

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. S119-S138 ◽  
Author(s):  
Raanan Dafni ◽  
William W. Symes
Keyword(s):  
Wave Equation ◽  
Reflection Coefficient ◽  
Field Data ◽  
Scattering Angle ◽  
Seismic Migration ◽  
Imaging Condition ◽  
Inversion Methods ◽  
Dip Angle ◽  
Seismic Reflections ◽  
Seismic Images

An angle-dependent reflection coefficient is recovered by seismic migration in the angle domain. We have developed a postmigration technique for computing scattering and dip angle common-image gathers (CIGs) from seismic images, extended by the subsurface offset, based on wave-equation migration methods. Our methodology suggests a system of Radon transform operators by introducing local transform relations between the subsurface offset image and the angle-domain components. In addition to the commonly used decomposition of the scattering angle, the methodology associates the wave-equation migration with dip-domain images as well. The same postmigration subsurface offset image is used to decompose scattering and dip angle CIGs individually or to decompose a multiangle CIG by showing simultaneously both angles on the gather’s axis. We show that the dip-angle response of seismic reflections is a spot-like signature, focused at the specular dip of the subsurface reflector. It differs from the well-studied smile-like response usually associated with reflections in the dip domain. The contradiction is clarified by the nature of the subsurface offset extension, and by emphasizing that the angles are decomposed from the subsurface offset image after the imaging condition, without directly involving the propagating incident and scattered wavefields. Several synthetic and field data tests proved the robustness of our decomposition technique, by handling various subsurface models, including seismic diffractions. It is our belief that dip-angle information, decomposed by wave-equation migration, would have a great impact in making the scattering-angle reflection coefficient more reliable and noise free, in addition to the acceleration of wave-equation inversion methods.

Wave-equation diffraction imaging using pseudo dip-angle gather

Geophysics ◽  
2022 ◽  
pp. 1-45
Author(s):  
Lu Liu ◽  
Yue Ma ◽  
Yang Zhao ◽  
Yi Luo
Keyword(s):  
Wave Equation ◽  
Plane Wave ◽  
Incident Angle ◽  
Median Filter ◽  
Computational Cost ◽  
Scattered Wave ◽  
Vertical Axis ◽  
Wave Source ◽  
Dip Angle ◽  
Angle Gather

Diffraction images can directly indicate local heterogeneities such as faults, fracture zones, and erosional surfaces that are of high interest in seismic interpretation and unconventional reservoir development. We propose a new tool called pseudo dip-angle gather (PDAG) for imaging diffractors using the wave equation. PDAG has significantly lower computational cost compared with the classical dip-angle gather (DAG) due to using plane-wave gathers, a fast local Radon transform algorithm, and one-side decomposition assumption. Pseudo dip angle is measured from the vertical axis to the bisector of the plane-wave surface incident angle and scattered wave-propagation angle. PDAG is generated by choosing the zero lag of the correlation of the plane-wave source wavefields and the decomposed receiver wavefields. It reveals similar diffraction and reflection patterns to DAG, i.e. diffractions spreading as a flat event and reflections focused at a spectacular angle, while they may have dissimilar coverage for diffraction and different focused locations for reflection compared with that of DAG. A windowed median filter is then applied to each PDAG for extracting the diffraction energy and suppressing the focused reflection energy. Besides, the stacked PDAG can be used to evaluate the migration accuracy by measuring the flatness of the image gathers. Numerical tests on both synthetic and field data sets demonstrate that our method can efficiently produce accurate results for diffraction images.

Dip angle-compensated one-way wave equation migration

2010 ◽  
Vol 41 (2) ◽  
pp. 137-145 ◽  
Author(s):  
Weijia Sun ◽  
Binzhong Zhou ◽  
Li-Yun Fu
Keyword(s):  
Wave Equation ◽  
Dip Angle

Failure Analysis Of Buried Gas Pipelines Crossing Seismic Faults

2020 ◽  
Vol 3 (2) ◽  
pp. 781-790
Author(s):  
M. Rizwan Akram ◽  
Ali Yesilyurt ◽  
A.Can. Zulfikar ◽  
F. Göktepe
Keyword(s):  
Ground Deformation ◽  
Warning System ◽  
Strike Slip ◽  
Gas Pipelines ◽  
Steel Pipes ◽  
Seismic Fault ◽  
Fault Parameters ◽  
Dip Angle ◽  
Permanent Ground Deformation ◽  
Recent Earthquakes

Research on buried gas pipelines (BGPs) has taken an important consideration due to their failures in recent earthquakes. In permanent ground deformation (PGD) hazards, seismic faults are considered as one of the major causes of BGPs failure due to accumulation of impermissible tensile strains. In current research, four steel pipes such as X-42, X-52, X-60, and X-70 grades crossing through strike-slip, normal and reverse seismic faults have been investigated. Firstly, failure of BGPs due to change in soil-pipe parameters have been analyzed. Later, effects of seismic fault parameters such as change in dip angle and angle between pipe and fault plane are evaluated. Additionally, effects due to changing pipe class levels are also examined. The results of current study reveal that BGPs can resist until earthquake moment magnitude of 7.0 but fails above this limit under the assumed geotechnical properties of current study. In addition, strike-slip fault can trigger early damage in BGPs than normal and reverse faults. In the last stage, an early warning system is proposed based on the current procedure. 

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