Full-azimuth anisotropic prestack time migration in the local-angle domain and its applications on fracture detection

Geophysics ◽  
2015 ◽  
Vol 80 (2) ◽  
pp. C37-C47 ◽  
Author(s):  
Xuekai Sun ◽  
Sam Zandong Sun
Keyword(s):  
Signal To Noise Ratio ◽  
Carbonate Reservoir ◽  
Fracture Detection ◽  
Traveltime Inversion ◽  
Fracture Medium ◽  
Time Migration ◽  
Migration Method ◽  
Prestack Time Migration ◽  
Subsurface Fractures ◽  
Local Angle

Considering that geologic structures disturb prestack amplitude relationships, anisotropic migration is thus advocated not only for extracting azimuth-preserved common image gathers (CIGs), but also for preserving fracture-induced amplitude responses. However, most conventional anisotropic migration methods are hindered by their inefficiency in either modeling azimuthal traveltime variations at large offsets or characterizing subsurface reflections. Given that prestack time migration is widely applied for most practical purposes, we began with reformulations on a quartic traveltime formula, through which a new set of anisotropic parameters was developed. Then, an anisotropic migration method was established in the local-angle domain (LAD) for more reasonable uses of subsurface wavefield information. We also used a traveltime inversion scheme to estimate those anisotropic parameters required by anisotropic migration. Using this methodology on a physical model with a fracture medium, we derived better focused CIGs by thoroughly correcting the anisotropic effects of overburden. As a result, predicted properties of the fracture medium showed fewer interventions of geologic impacts. In a field example, a comprehensive study was performed on a deep carbonate reservoir to examine influences of different anisotropic migration algorithms on ultimate fracture prediction. Comparisons of the signal-to-noise ratio and agreements with formation microimage information reconfirmed the superiority of LAD anisotropic migration in recovering true properties of subsurface fractures, relative to routine methods (i.e., azimuth-sectored migration and anisotropic migration in the surface-offset domain).

scholarly journals Deabsorption prestack time migration from rugged topography

2021 ◽  
Vol 18 (2) ◽  
pp. 291-303
Author(s):  
Changshan Han ◽  
Linong Liu ◽  
Zelin Liu ◽  
Zhengwei Li
Keyword(s):  
Signal To Noise Ratio ◽  
Three Dimensional ◽  
Signal To Noise ◽  
Time Migration ◽  
Q Model ◽  
Rugged Topography ◽  
Migration Method ◽  
Prestack Time Migration ◽  
The Common ◽  
Quality Factor Q

Abstract We developed a modified topography prestack time migration (PSTM) scheme that can improve the imaging resolution by applying effective Q to topography migration. The computation of the traveltime at each imaging location in the migration is based on the floating datum smoothed by rugged topography. Unlike the common quality factor Q, the effective Q only determines the frequency-dependent amplitude and the traveltime at a single imaging location, which enables us to establish a Q model in an inhomogeneous medium. Hence, we can acquire the effective Q using a scanning technology according to the width of the frequency band and signal-to-noise ratio of the imaging gathers. The proposed migration method can be integrated into the conventional topography migration workflow. Synthetic and three-dimensional (3D) field datasets indicate that the proposed deabsorption PSTM from rugged topography is effective.

Prestack time migration from 3D irregular surfaces with near-surface-related deabsorption

Geophysics ◽  
2020 ◽  
Vol 85 (1) ◽  
pp. S21-S32
Author(s):  
Jincheng Xu ◽  
Jianfeng Zhang ◽  
Linong Liu ◽  
Wei Zhang ◽  
Hui Yang
Keyword(s):  
Fresnel Zone ◽  
Signal To Noise Ratio ◽  
Data Sets ◽  
Effective Parameters ◽  
Near Surface ◽  
Intrinsic Attenuation ◽  
Effective Velocity ◽  
Time Migration ◽  
Prestack Time Migration ◽  
Absorption And Dispersion

We have developed a 3D prestack time migration (PSTM) approach that can directly migrate nonplanar data with near-surface-related deabsorption using three effective parameters. The proposed scheme improves the so-called topography PSTM approach by adding a near-surface effective [Formula: see text] parameter that compensates for the absorption and dispersion of waves propagating through near-surface media. The two effective velocity parameters above and below the datum can be estimated by flattening events in imaging gathers, and the additional near-surface effective [Formula: see text] parameter can be obtained using scanning technology. Hence, no knowledge with respect to near-surface media is needed in advance for implementing the proposed scheme. The proposed topography-deabsorption PSTM method can be applied to seismic data recorded on a 3D irregular surface without statics corrections. Consequently, traveltimes are obtained with improved accuracy because the raypath bends away from the vertical in the presence of high near-surface velocities, and the absorption and dispersion caused by strong intrinsic attenuation in near-surface media are correctly compensated. Moreover, we attenuated the migrated noise by smearing each time sample only along the Fresnel zone rather than along the entire migration aperture. As a result, an image with a higher resolution and superior signal-to-noise ratio is achieved. The performance of the proposed topography-deabsorption PSTM scheme has been verified using synthetic and field data sets.

Prestack time migration by common-migrated-reflector-element stacking

Geophysics ◽  
2012 ◽  
Vol 77 (3) ◽  
pp. S73-S82 ◽  
Author(s):  
Sergius Dell ◽  
Dirk Gajewski ◽  
Claudia Vanelle
Keyword(s):  
Initial Time ◽  
Depth Migration ◽  
Time Migration ◽  
Migration Method ◽  
Prestack Time Migration ◽  
The Common ◽  
A New Technique ◽  
New Formulation ◽  
Time Image ◽  
Migration Velocities

Time migration is an attractive tool to produce a subsurface image because it is faster and less sensitive to velocities errors than depth migration. However, a highly focused time image is only achievable with well-determined time-migration velocities. Therefore, a refinement of the initial time-migration velocities often is required. We introduced a new technique for prestack time migration, based on the common-migrated-reflector-element stack of common scatterpoint gathers, including an automatic update of time-migration velocities. The common scatterpoint gathers are generated using a new formulation of the double-square-root equation that is parametrized with the common-offset apex time. The common-migrated-reflector-element stack is a multiparameter stacking technique based on the Taylor expansion of traveltimes of time-migrated reflections in the paraxial vicinity of the image ray. Our 2D synthetic and field data examples demonstrated that the proposed method provides updated time-migration velocities that are more robust and have higher resolution compared with the initial time-migration velocities. The prestack time migration method also showed a clear improvement of the focusing of reflections for such geologic features as faults and salt structures.

scholarly journals Shot-gather time migration of planar reflectors without velocity model

Geophysics ◽  
2011 ◽  
Vol 76 (2) ◽  
pp. S93-S101 ◽  
Author(s):  
Andrej Bóna
Keyword(s):  
Synthetic Data ◽  
Velocity Model ◽  
Migration Velocity ◽  
Time Migration ◽  
Second Derivatives ◽  
Migration Method ◽  
Prestack Time Migration ◽  
Zero Offset ◽  
2D And 3D ◽  
Homogeneous Media

Standard migration techniques require a velocity model. A new and fast prestack time migration method is presented that does not require a velocity model as an input. The only input is a shot gather, unlike other velocity-independent migrations that also require input of data in other gathers. The output of the presented migration is a time-migrated image and the migration velocity model. The method uses the first and second derivatives of the traveltimes with respect to the location of the receiver. These attributes are estimated by computing the gradient of the amplitude in a shot gather. The assumptions of the approach are a laterally slowly changing velocity and reflectors with small curvatures; the dip of the reflector can be arbitrary. The migration velocity corresponds to the root mean square (rms) velocity for laterally homogeneous media for near offsets. The migration expressions for 2D and 3D cases are derived from a simple geometrical construction considering the image of the source. The strengths and weaknesses of the methods are demonstrated on synthetic data. At last, the applicability of the method is discussed by interpreting the migration velocity in terms of the Taylor expansion of the traveltime around the zero offset.

Automatic waveform-based source-location imaging using deep learning extracted microseismic signals

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. KS171-KS183 ◽  
Author(s):  
Omar M. Saad ◽  
Yangkang Chen
Keyword(s):  
Clustering Algorithm ◽  
Signal To Noise Ratio ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Frequency ◽  
Time Migration ◽  
Frequency Representation ◽  
Convolutional Autoencoder ◽  
Migration Method

We have used an automatic unsupervised technique to extract waveform signals from continuous microseismic data. First, the time-frequency representation (scalogram) is obtained for the input microseismic trace. Second, the convolutional autoencoder (CAE) is used to extract the significant scalogram features related to the waveform signals and discard the rest. Third, the extracted features from the CAE encoder are considered as the input for the k-means clustering algorithm, in which the input samples are classified into waveform and nonwaveform components. The proposed algorithm is evaluated using several synthetic and field examples. We find that the proposed algorithm successfully extracts the waveform signals even in a noisy environment with a signal-to-noise-ratio as low as −10 dB. We compared the proposed algorithm to benchmark algorithms, for example, simple k-means and short-term and long-term average ratio methods, and find that the proposed algorithm performs best. We find that the detected waveform signals can enhance the resolution of microseismic imaging using a waveform-based reverse time migration method.

Azimuth-preserved local angle-domain prestack time migration in isotropic, vertical transversely isotropic and azimuthally anisotropic media

Geophysics ◽  
2012 ◽  
Vol 77 (2) ◽  
pp. S51-S64 ◽  
Author(s):  
Jiubing Cheng ◽  
Tengfei Wang ◽  
Chenlong Wang ◽  
Jianhua Geng
Keyword(s):  
Seismic Imaging ◽  
Transversely Isotropic ◽  
Anisotropic Media ◽  
Azimuthal Anisotropy ◽  
Velocity Estimation ◽  
Energy Propagation ◽  
Directional Information ◽  
Time Migration ◽  
Prestack Time Migration ◽  
Local Angle

Conventional prestack migration does not preserve local directional information of the seismic waves at the image points. New attempts such as sectored migration of azimuth-limited or common-offset-vector data only concern source-receiver azimuth and offset on the surface, which can be poor representation of subsurface wavepath direction. Moreover, they could result in inaccurate imaging because they do not account for the energy propagation between azimuths or offset-vectors. In the past decade, local angle-domain seismic imaging has been highly advocated to avoid migration artifacts and to improve velocity estimation in complex media. Considering prestack time migration (PSTM) is still widely used in seismic imaging and seismic data preconditioning for amplitude variations with offset or incident-angle (AVO/AVA) analysis, fracture detection, and reservoir characterization, we present an azimuth-preserved local angle-domain Kirchhoff PSTM approach for such purposes. We apply a seismic imaging condition in 3D local angle domain and use extended superposition of impulse responses retaining subsurface angular attributes, which are evaluated through the incident and scattering phase slowness vectors using classical-diffraction moveout equations in isotropic, vertical transversely isotropic (VTI) and azimuthally anisotropic media. Two-dimensional synthetic examples demonstrate what the migrated results look like in local angle domain. A wide-azimuth synthetic example with horizontal transversely isotropy (HTI) proves the necessity of azimuthal migration for reliable imaging and azimuthal analysis when azimuthal anisotropy exists in the overburden. Real data examples show the advantages of imaging in subsurface angle domain for properly focusing and revealing azimuth- and angle-dependent variations of residual moveout and migrated amplitudes.

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