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Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the SEG International Exposition and Annual Meeting, September 15–20, 2019

Paper Number: SEG-2019-3215272

... couldn t describe the mis-tie time information caused by azimuthal anisotropy. Thus, the anisotropic model building must

**use**the full-azimuth**reflection**angle**gathers**. (a) (b) Figure 2: Comparison of the full-azimuth**reflection**angle**gathers**(a) and the traditional offset domain**common****reflection****point**...
Abstract

ABSTRACT Precise anisotropic parameter estimation and modeling is crucial for anisotropic imaging in transversely isotropic (TI) media. Anisotropy must be considered in seismic imaging with the rapidly development of computer hardware and wide-azimuth acquisition. A set of single directional fractures with high dip angle shows remarkable anisotropic characteristics. Conventional common-offset gathers were constructed by sorting the image gathers using offset vectors of surface attribute data, and they didn’t accurately contain all the reflection angle and azimuth information of seismic data. At the same time, uncertainty occurs in the anisotropic depth model building by only using the common-offset gathers. This is mainly caused by the multiplicity of anisotropic parameters. However, by introducing the well data to constrict the model building, anisotropic multiplicity can be reduced greatly. Thus, a set of joint model building method based on well data and full-azimuth angle gathers were proposed in this paper. Firstly, local anisotropic parameters were extracted from every well using Walk-away vertical seismic profile (VSP) and well-logging data. Then, azimuthal-dependent anisotropic time mis-tie information can be acquired using full-azimuth reflection angle gathers. Finally, precise anisotropic velocity model was built through anisotropic iterative inversion of anisotropic velocity and parameters Epsilon () and Delta () using full-azimuth angle domain tomography technique. The proposed solution was tested on field seismic data and the results showed favorable effect in fracture detection and seismic imaging which proved the applicability and effectiveness of the proposed method. Presentation Date: Wednesday, September 18, 2019 Session Start Time: 8:30 AM Presentation Time: 10:35 AM Location: 221C Presentation Type: Oral

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2005 SEG Annual Meeting, November 6–11, 2005

Paper Number: SEG-2005-2261

... of ZTD

**gathers**. A**common**-receiver style ZTD**gathers**calculated**using****reflection**ray tracing and the scattering ray tracing are given in Figure 6 and Figure 7 respectively. In addition, since the ZTD data set is corresponding to a portion of reflector rather than a single imaging**point**, we may take...
Abstract

ABSTRACT Not giving mathematical details but the simple principles, we present two types of techniques for both depth and time prestack migration velocity analysis. The first type of the techniques is based on the migration velocity spectrum, and the second is based on the migration velocity scanning. The accuracy of the picked/selected velocities can be tested by the common image gathers with a common-shot style. An alternate approach, based on the so-called zero-timedifference gathers computed by reflection or scattering ray tracing regarding to the migrated horizon(s), is proposed to be used as an additional way for migration velocity testing in complex areas.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2005 SEG Annual Meeting, November 6–11, 2005

Paper Number: SEG-2005-2542

...

**common****reflection**-**point**based tomographic seismic migration**velocity****analysis**Weihong Fei, and George A. McMechan, the University of Texas at Dallas Summary 3-D prestack depth migration and residual picking in**common**image**gathers**(CIGs) are the most time- consuming part in 3-D migration**velocity**...
Abstract

ABSTRACT 3-D prestack depth migration and residual picking in common image gathers (CIGs) are the most timeconsuming part in 3-D migration velocity analysis. We propose a new algorithm that provides 3-D velocity analysis quickly and accurately. Spatial coordinates and orientations of reflection points are provided by 3-D poststack or prestack parsimonious migration; the migration involves only time samples that are picked from the salient reflection events on a poststack volume or on one common-offset volume. Ray tracing from the reflection points to the surface provides a common-reflection point (CRP) gather for each reflection point. Predicted moveouts for local velocity perturbations, based on the maximizing stacked amplitude, gives the estimated velocity updates for each CRP gather. The traveltime picking is limited to only a stacked or common-offset volume, and it needs to be done only once; there is no need to do intensive 3-D prestack depth migration. Hence, the computation is much faster than other migration-based velocity analyses. 3-D synthetic data tests show the algorithm works effectively and efficiently.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the SEG International Exposition and Annual Meeting, October 11–16, 2020

Paper Number: SEG-2020-3427456

... built by

**using**ray-based**reflection**tomography. Unlike conventional beam migration algorithms, CRAM enables to extract specular energy via bottom-up ray tracing from each image**point**, and directly calculate angle domain**common**image**gather**(ADCIG). The resulted stacked section of CRAM showed higher SNR...
Abstract

Using common reflection angle migration (CRAM) which is an advanced beam migration, we successfully improved signal-to-noise ratio (SNR) and image continuity in the volcanic reservoir, offshore Myanmar. In this field, seismic imaging is challenging because high impedance contrast at the top of the reservoir attenuates seismic energy, and various kinds of volcanic facies cause complex velocity field. Kirchhoff PSTM was initially applied in this field, but it failed to obtain satisfactory image in the volcanic reservoir. To address these challenges, we applied CRAM with the anisotropic velocity model built by using ray-based reflection tomography. Unlike conventional beam migration algorithms, CRAM enables to extract specular energy via bottom-up ray tracing from each image point, and directly calculate angle domain common image gather (ADCIG). The resulted stacked section of CRAM showed higher SNR and lateral continuity by weighting specular events. The seismic traces of CRAM were better correlated with the synthetic seismogram at wells. The obtained ADCIGs showed more stable behavior and less noise than the conventional offset domain common image gathers (ODCIGs). These improvements are valuable for the following seismic facies analysis and AVO analysis and inversion to characterize complicated volcanic facies. Presentation Date: Tuesday, October 13, 2020 Session Start Time: 9:20 AM Presentation Time: 11:25 AM Location: Poster Station 6 Presentation Type: Poster

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2010 SEG Annual Meeting, October 17–22, 2010

Paper Number: SEG-2010-3375

...

**velocity****reflection****velocity**model upstream oil & gas automatic cr stack apex cmp**gather**csp**gather**levantine basin reservoir characterization migration**velocity**An automatic time imaging**using****Common**Scatter**Point****gathers**Sergius Dell , Dirk Gajewski, and Claudia Vanelle, University...
Abstract

SUMMARY Prestack time migration (PreSTM) still represents the majority of seismic imaging activities in the industry. The reason for this is the speed and robustness of time imaging and its ability to focus seismic events for most geological settings. However, well defined migration velocities are necessary. When we speak about migration velocities and migration operators we implicitly assume time migration velocities and time migration operators. Usually, the migration velocities are not known and, therefore, approximated by stacking velocities. The stacking velocity is attached to the stationary point of the migration operator, however the migration velocity is defined at the apex of the migration operator. Due to this discrepancy, the stacking velocity may deviate from the migration velocity, e.g., in the case of dipping reflectors, and the final time image may be unfocused. In order to correct for the velocity difference and to enhance the time imaging, the velocity model needs to be refined. There are several techniques to provide an updated velocity model. However, all the techniques are based on an iterative approach requiring a strong manual interaction. We propose a new workflow for the time imaging which includes an automatic update of time migration velocities. The workflow is based on an automatic Common-Reflection-Surface (CRS) stack of Common Scatter Point (CSP) gathers and provides an improved time migration velocity model and, hence, a highly focused time image. INTRODUCTION The migrated image strongly depends on how well the migration velocities are defined. Usually the migration velocities are determined from root mean square (RMS) velocities. However, the RMS velocities are not known and are assumed to coincide with the stacking velocities. The stacking velocity is attached to the stationary point of the migration operator in contrast to the migration velocity which is defined at the apex of the migration operator. The migration velocity is not a physical property and can be interpreted as a best fit parameter which fits the migration operator to the reflection events in the data. In case of a complex structure of the overburden, the stacking velocities may significantly deviate from the migration velocities. The difference between the migration velocities and the stacking velocities leads to an unfocused time image. In order to correct for this difference, the velocity model needs to be refined. Conventionally, residual moveout (RMO) analysis is carried out to refine time migration velocities (Yilmaz, 2001). The RMO routine is an iterative approach and is based on the Deregowski loop (Deregowski, 1990). The RMO analysis starts with PreSTM which is performed with an initial velocity model. After the PreSTM Common Image Point (CIP) gathers are constructed which may show residual moveout. For the selected CIP gathers an inverse NMO correction is applied using the initial velocities. The inverse NMO correction forms Common Scatter Point gathers from the CIP gathers. However, the RMO routine suffers on the fact that the presence of residual moveout in the migrated gathers indicates that the event being picked is located at the wrong spatial position.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2001 SEG Annual Meeting, September 9–14, 2001

Paper Number: SEG-2001-0885

... in the

**reflection**angle domain. Such angle-domain**common**image**gathers**can be obtained from either wave equation- based or Kirchhoff integral-based prestack depth migration methods. RMS residual**velocity**associated with each subsurface image**point**is determined from semblance scan of**common**image**gathers**followed...
Abstract

Summary We present a migration velocity analysis system for updating velocities based on common image gathers in the reflection angle domain. Such angle-domain common image gathers can be obtained from either wave equationbased or Kirchhoff integral-based prestack depth migration. Residual velocity associated with each subsurface image point is determined from semblance scans of common image gathers over a plausible range of values followed by automated picking. The extracted residuals can be tied to and smoothed along geologic horizons to improve an initial velocity model through vertical, normal-ray, or tomographic update. A marine data set and two synthetic examples are given to illustrate residual velocity analysis of common image gathers in the reflection angle domain. Introduction There is an increasing demand for advanced imaging techniques capable of providing improved knowledge of the subsurface detail in areas with complex geologic structure.

Proceedings Papers

Publisher: Offshore Technology Conference

Paper presented at the Offshore Technology Conference Asia, March 22–25, 2016

Paper Number: OTC-26412-MS

... the divide between turnkey on-time turnaround depth imaging processing and respect of the geology.

**reflection****point**upstream oil & gas cig time**gather**imaging process**velocity**model salt dome migration reservoir characterization time domain geophysicist algorithm synthetic seismogram...
Abstract

Subsalt imaging is an important process for exploration of offshore basins. These salt basins present a technical challenge for present day imaging methods. Strong lateral velocity variations, irregular salt bodies, and subsalt structure imaging require quality control during the image processing phase. Methodologies and techniques are available for interpreting geophysicists to quality control prestack common image gathers (CIGs) and the velocity model (VM) in depth. The three dimensional (3D) SEG/EAGE Salt Model ( Ober et al.,1996 ) is an ideal dataset to demonstrate the process because it was designed to contain major complex features common to offshore basins. The SEG/EAGE C3 Narrow Angle Subset Salt Model is used to demonstrate the methodology employed for quality control, CIGs, and the interval velocities in depth used in imaging the data. The methodology involves residual move-out semblance panels based on RHO/percentage (RHO - Greek typography representing percent error) move-out trajectories. Velocity percentages are generated in the image domain to measure the curvature of reflection events on migrated offset image gathers. The curvature of offset image gathers depends strongly on the velocity used in the migration. If the velocity is correct, the reflection events on offset image gathers are horizontally aligned. If the velocity is incorrect, then the reflection events will show depth residual move-out. Techniques are available for depth imaging that allows the interpreting geophysicist to respect the geologic concepts by controlling the quality control of the CIGs and the VM during the depth imaging processing phase. This includes salt dome basins where the depth imaging technology is most challenged. Interpreting geophysicists are searching for solutions that balance the divide between turnkey on-time turnaround depth imaging processing and respect of the geology.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2016 SEG International Exposition and Annual Meeting, October 16–21, 2016

Paper Number: SEG-2016-13712816

...-out

**analysis**precision beam migration annual meeting**velocity**field vertical**velocity**function lad**gather**information upstream oil & gas**velocity****analysis****velocity**model angle division imaging angle resolution Gray , S. H. , 2005 , Gaussian beam migration of**common**-shot...
Abstract

ABSTRACT We propose a Gaussian beam pre-stack depth imaging method that makes better use of the propagation directions for the purpose of velocity analysis. When dealing with complex velocity structures, this method can lead to more accurate velocity models for imaging. Precision Beam Migration (or PBM for short) presented here directly results in two complementary, full-azimuths, common-image angle gather systems: directional and reflection, which lends naturally to tomography. Observing the fact that the maximum available reflection angle varies with depth, we change the angle division with depth to optimally extend deep events, which helps residual move-out analysis. Presentation Date: Thursday, October 20, 2016 Start Time: 11:25:00 AM Location: 171/173 Presentation Type: ORAL

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2012 SEG Annual Meeting, November 4–9, 2012

Paper Number: SEG-2012-0402

... are correct, the RMO = 0 and the angle

**gathers**are flat. zo is the**reflection****point**in depth of the RMO. Wave path construction from P-wave polarization MVA based on RMO and it does not**use**matching the er- ror of traveltime on the whole ray path to do the inversion. RMO MVA is based on the**common**image**point**...
Abstract

SUMMARY A new algorithm for wave-equation migration velocity analysis is proposed. Wavefield extrapolation is done with a two-way wave-equation in reverse-time migration, and the angles in the angle-domain common gathers (ADCIGs) are extracted by a polarization method without ray tracing. In the ADCIGs, the residual moveout in depth is used to build a linear system for velocity updating. Wavepaths (which are similar to the raypaths in ray tomography) are constructed from the source-only wavefield polarizations (without ray tracing). In the linear equations, the wavepaths in depth and the residual moveouts, are connected at the reflection point; by solving a linear system, the velocity model can be updated. The convergence condition is flattening of the ADCIGs. A layered synthetic model with a fault successfully illustrates the procedure.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2016 SEG International Exposition and Annual Meeting, October 16–21, 2016

Paper Number: SEG-2016-13778639

... and minimizes the deviation in the

**Common**Image**Gathers**(CIG) from a flat event. In our implementation, we select special image**points**based on dip and event coherency called back- projection**points**, from which the tomography traces rays back to the surface in order to distribute the**velocity**residual values...
Abstract

ABSTRACT We present a novel high resolution, wide azimuth (BT) based on the Fast Beam Migration (FBM) algorithm. The Beam Tomography uses Fast Beam Migration to directly output a set of image points (x,y,z) with velocity update values, which bypasses the time consuming steps required for traditional tomography, including preparing the gathers for semblance analysis, semblance picking and back-projection picks QC. The method enables a very rapid estimation of the depth or time delays along each ray that can be used to produce a high quality alignment of the common-image angle or offset gathers. Presentation Date: Wednesday, October 19, 2016 Start Time: 4:25:00 PM Location: 143/149 Presentation Type: ORAL

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2003 SEG Annual Meeting, October 26–31, 2003

Paper Number: SEG-2003-2164

... of the reservoir geometry can be obtained. The

**Common**Focus**Point**(CFP) tomographic inversion**uses**one-way focusing operators in order to obtain a global**velocity**model (Berkhout, 1997a,b; Cox and Verschuur, 2001, 2003). All focusing operators (corresponding to the**reflection****points**related to all reflectors...
Abstract

Summary For a North Sea data set global tomographic velocity inversion is combined with a local, target-oriented tau-p interval velocity analysis. The goal is to derive an optimal velocity-depth model, thus to improve the imaging result, especially near the target. Hence, a better estimate of the reservoir geometry can be obtained. The Common Focus Point (CFP) tomographic inversion uses one-way focusing operators in order to obtain a global velocity model (Berkhout, 1997a,b; Cox and Verschuur, 2001, 2003). All focusing operators (corresponding to the reflection points related to all reflectors) are inverted at the same time. Moreover, the reflection points are positioned in depth. Also based on the CFP technology is the local, tau-p interval velocity analysis method.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2003 SEG Annual Meeting, October 26–31, 2003

Paper Number: SEG-2003-2096

...) showed the application of the intercept time ray parameter p)

**velocity****analysis**to**common**source, receiver and midpoint**gathers**. In general, the proposed**velocity****analysis**method can be applied to offset versus travel time data. The**common**midpoint**gathers**are related to one**reflection****point**...
Abstract

Summary Presented is a local interval velocity analysis method using pre-stack, offset-travel time gathers related to a reflection point in the subsurface. This data – obtained after velocity-independent redatuming – is transformed to the t-p domain for a better event definition. The method assumes that the interfaces around the target horizon are locally homogeneous, such that events around the reflection point response in the t-p domain are mapped as half-ellipses, and that complex overburden effects have been taken care of by the redatuming. Accumulation of interval velocity errors in a traditional layer-stripping velocity estimation procedures is thus avoided. The method is especially suitable for applying below complex zones, in time lapse applications with special emphasis on the target, and also for multi-component data.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2009 SEG Annual Meeting, October 25–30, 2009

Paper Number: SEG-2009-2914

... versa. The practical

**uses**of the method are for**velocity****analysis**or AVO studies**using**existing commercial toolkits. Introduction The need for an accurate**gather**conversion method from**common**-offset-**gathers**(COG) to**common**-image-**gathers**(CAG), and vice versa, stems from the manifold...
Abstract

Summary Most migration methods produce either common-offset- gathers (COG) or common-angle-gathers (CAG) gathers. But none produce both, that is until now. We have developed an accurate and efficient method that converts common offset image gathers to common angle image gathers, or vice versa. The practical uses of the method are for velocity analysis or AVO studies using existing commercial toolkits. Introduction The need for an accurate gather conversion method from common-offset-gathers (COG) to common-image- gathers (CAG), and vice versa, stems from the manifold applications of COGs and CAGs. Uses of COGs of depth migrated data include updating the subsurface velocity from residual moveouts, and inversion for rock properties from amplitude variations with offset. CAGs, on the other hand, are partitioned according to opening angles at the subsurface rather than the source-receiver offset at the surface, as is the case with COGs. Hence CAGs have advantages over COGs in that they allow tomography programs to use specular ray pairs more naturally and provide amplitude versus angle information more readily. Sometimes individual angle volumes are more interpretable than either stacked volumes or individual offset volumes. A typical case illustrating this is found in sub-horizontal strata underneath a salt wedge (Helsing and Berman, 2006). A gather conversion method is developed based on the diplet decomposition technology (Peng, 2006). A 3D seismic volume can be expressed as the superposition of components that we call “diplets”. Each “diplet” carries distinct information about its spatial location (x, y, z), orientation (inline dip and crossline dip), amplitude, wavelet, acquisition configuration (acquisition offset and acquisition azimuth), coherency, and derived attributes such as reflection angle, reflection azimuth, wavelet stretch, beam spread, wavefront curvature etc. The diplet’s special and unique structure allows for the simultaneous storage of surface acquisition and subsurface reflection information. It makes demigration and remigration more convenient and efficient through the process of transformation of diplets between the unmigrated time-domain and migrated depth-domain using dynamic ray tracing. It also simplifies the gather conversion task: binning and sorting the migrated diplets according to acquisition offsets or local reflection angles is all that is required. The process is not only accurate but also extremely efficient. Method Let’s assume COGs are available and they are already decomposed into diplets. As shown in Fig. 1, one such decomposed diplet will have its focal point X coordinates, normal direction ñ of the reflector and acquisition offset and azimuth on the surface. The reflection angle ? can be calculated by searching for two rays (XS and XR, from image point X to acquisition surface S and R, respectively), and by minimizing the difference between the vector SR and the vector determined by a given acquisition distance and azimuth. Next, let’s assume CAGs are available and they are already decomposed into diplets. Similarly, a decomposed diplet for a given CAG will have the reflection angle as well as its focal point X coordinates and normal direction of the reflector. The offset can be estimated by searching two rays XS and XR which satisfy Snell’s law at the image point and that make the same reflection angle; the distance of SR provides the approximation of the acquisition offset.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2017 SEG International Exposition and Annual Meeting, September 24–29, 2017

Paper Number: SEG-2017-17723539

...

**analysis**for**common**scatter**point****gather**for equivalent offset migration technique Tomoaki Tanaka*, Hitoshi Mikada, Junichi Takekawa, Kyoto University Summary We noticed that an equivalent offset migration (EOM) technique could be applied to horizontal components of acquired**reflection**seismic data...
Abstract

ABSTRACT We noticed that an equivalent offset migration (EOM) technique could be applied to horizontal components of acquired reflection seismic data with the advantages in the extraction of S-wave events and in the estimation of S-wave velocities. EOM attracts a lot of attention in geophysical processing for its simplicity in the computation and in the accuracy as a dynamic move-out technique, but the current practice of EOM has been mainly limited to the vertical component of received waveforms. We gathered horizontal component data with respect to common scatter points (CSP) and found out amplitude reversal clearly due to S-wave AVO effects for an earth model of horizontally stratified layers. After the application of least square error minimization, we confirmed the possibility of our approach to estimate the contrast of S-waves at a reflector in our model. Presentation Date: Monday, September 25, 2017 Start Time: 1:50 PM Location: Exhibit Hall C, E-P Station 3 Presentation Type: EPOSTER

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 1997 SEG Annual Meeting, November 2–7, 1997

Paper Number: SEG-1997-1822

... they are not correct. It will be argued that

**velocity****analysis**in the CFP domain brings improvement to these two crucial elements. The essence of the MVA tomography is to**use**the postmigrated domain, a**common**image**gather**(CIG) or**common****reflection****point**(CRP)**gather**, to analyse the consistency (i.e., the alignment...
Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2007 SEG Annual Meeting, September 23–28, 2007

Paper Number: SEG-2007-2210

... imaging algorithms. The quantitative

**analysis**of the amplitude, re- lies on**common**-image**gathers**being flat (or equivalently, at the same depth). But the waves with different incident angles will have differ- ent apparent**velocities**, resulting in different depths for the same image**point**at different...
Abstract

SUMMARY In AVO (Amplitude Variation with Offset) analysis, the amplitudes of reflected waves with different incident angles are studied to deduce lithology information beyond the structure map obtained by seismic imaging algorithms. The quantitative analysis of the amplitude, relies on common-image gathers being flat (or equivalently, at the same depth). But the waves with different incident angles will have different apparent velocities, resulting in different depths for the same image point at different angles, or non-flat common image gathers. In many scenarios, non-flat common-image gather was flattened by trim means at the cost of compromising zero-crossing and polarity-reversal information. This work presents a solution based on the seismic imaging subseries of the inverse scattering series (ISS) that flattens the common image gather without knowing or determining the subsurface velocity, and without any harmful amplitude consequencies. INTRODUCTION Inverse scattering series (ISS) is a comprehensive theory for processing primaries and multiples without the traditional need for a subsurface velocity. Several task-specific subseries of ISS (Weglein et al., 2003) had been identified. These subseries correspond to classical objectives of seismic data processing: (1) eliminating free-surface multiple (Carvalho et al., 1991; Carvalho, 1992), (2) eliminating the internal multiples, (3) imaging reflectors at depth (Weglein et al., 2000, 2002; Shaw et al., 2003; Innanen, 2003; Shaw, 2005; Liu, 2006), (4) determining the parameter changes across the reflectors (Zhang, 2006). This article is specific to task (3): the image of the same reflector in the same lateral coordinate, flattened and migrated to the same (actual) depth without knowing or determining the subsurface reflector. Description of the problem For simplicity, consider an exploration problem in 2D where z s (the elevation of the source) and z g (the elevation of the receiver) are fixed. In this case, the seismic data is considered a function of three variables: x s (the horizontal coordinate of the source), x g (the horizaontal coordinates of the receivers), and t (time). Physical properties at points in the subsurface, including reflector location in space, are not in any way dependent on the surface reflection data, or any subset of the data, used to determine or estimate those properties. That criteria is in used current leading-edge imaging as a necessary condition that an imaging algorithm with a correct velocity would satisfy. For example, images from different offset components of the data ought to locate at the same point in space if the velocity is correct. That concept is simple but in practice often not easy to realize. Methods to force or “iron” the common-image gather data flat and horizontal can have very serious and harmful consequences on subsequent analysis with lost polarity reversals and difficulty identifying class I and class II AVO anomalies. In this paper we demonstrate that the higher-order velocity-independent imaging subseries automatically produces the flat common-image gather, as you would expect from an imaging algorithm that produces the image at the correct depth. Not only is there no velocity, but the flatness is achieved without damaging the offset dependent amplitude information in imaged the data.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2008 SEG Annual Meeting, November 9–14, 2008

Paper Number: SEG-2008-3003

..., the relations to form the

**common**scattering angle**gathers**are derived by**using**the connection between the local slowness vectors and the incidence and dip angles (Sava and Fomel, 2005, 2006). The geometry of the local slowness vectors are at the central**point**of the directional**analysis**in wave-equation imaging...
Abstract

SUMMARY Angle domain common image gathers display the image points depth location with respect to the incidence angle. The possibility of image gathers as a function of both the scattering angle and the dip angle of the reflector has recently been considered for Kirchhoff prestack migration to detect diffraction events and use the dip information to provide a new tool for migration velocity analysis. The theory has not been completed yet for wave equation prestack migration. We have found two different methods to construct the dip angle gather, the first from prestack wave equation migration, the second from zero offset/poststack migration. INTRODUCTION In seismic imaging, common image gathers (CIG) constitute a tool of primary importance for amplitude versus offset (AVO), amplitude versus angle (AVA) and migration velocity analysis. The velocity analysis is conventionally performed by flattening the common offset or common incidence angle gathers (Brandsberg-Dahl et al., 1999). The display of common image gather as a function of scattering angle, rather than offset, offers numerous advantages (Xu et al., 1998). Prucha et al. (1999) set the method to perform the transformation from the offset domain to the scattering angle domain. The full extension to create incidence angle gathers from waveequation prestack migration (Sava and Fomel, 2003) uses the local offset in the image space and performs a Radon transform to display the common image gather as a function of the local scattering angle at the image point. During this process, the dip angles are implicitly stacked. Meanwhile, selecting only the dip in the vicinity of the geological dip improves the image by suppressing artifacts created for example by multipathing (Brandsberg-Dahl et al., 2003). In wave-equation prestack depth migration, the dip of reflectors influences both the quality of common incidence angle gathers and the velocity analysis (Biondi and Symes, 2004). The concept of Kirchhoff migration in the scattering angle domain (Audebert et al., 2002) clarified the influence and contribution of different illumination dip angles to the result of the Kirchhoff integral. Steep dips, structural conflicting dips, and the presence of diffractor points in faulted sedimentary layers can create spurious artificial events and compromise the interval velocity analysis by generating image points dispersal. A way to detect the geological dip before stacking, in Kirchhoff prestack depth migration, was proposed by generating illumination dip gathers and panels (Qin et al., 2005). This dip selection procedure has been demonstrated to enhance both the coherency of the reflectors image on noisy 3D seismic land prestack data (Gulunay et al., 2007) and the quality of the AVA analysis on a real 2D dataset (Bernasconi and Re, 2005). Another application of interest is migration velocity analysis (Reshef and Rüger, 2005) using in particular the detection of diffraction events (Fomel et al., 2007). In wave-equation prestack migration, the relations to form the common scattering angle gathers are derived by using the connection between the local slowness vectors and the incidence and dip angles (Sava and Fomel, 2005, 2006). The geometry of the local slowness vectors are at the central point of the directional analysis in wave-equation imaging.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 1999 SEG Annual Meeting, October 31–November 5, 1999

Paper Number: SEG-1999-0824

... to multipathing and why angle domain

**common**image**gathers**will not. Then we will demonstrate the construction of angle-domain**common**image**gathers**from wave equation downward continued data for**use**in**velocity****analysis**and amplitude-versus-**reflection**angle**analysis**. KINEMATICS OF MULTIARRIVALS IN THE SHOT...
Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2016 SEG International Exposition and Annual Meeting, October 16–21, 2016

Paper Number: SEG-2016-13957039

... ABSTRACT High resolution true-amplitude RTM Angle-Domain

**Common**Image**Gathers**(ADCIGs), indexed by subsurface**reflection**and azimuth angles, can be**used**for: In practice, the coarsely-sampled or irregularly-sampled shot and receiver locations on the surface leads to severe under-sampling...
Abstract

ABSTRACT High resolution true-amplitude RTM Angle-Domain Common Image Gathers (ADCIGs), indexed by subsurface reflection and azimuth angles, can be used for: In practice, the coarsely-sampled or irregularly-sampled shot and receiver locations on the surface leads to severe under-sampling artifacts in ADCIGs with small angle binning size. These under-sampling artifacts are worse for the shallow reflectors and small reflection angle in the case of 3D data. In this paper, we first derive that the theoretical number of hitcount for each angle bin is given by the determinant of the Jacobian matrix of transforming subsurface angle to surface shot coordinates. Then we illustrate that the under-sampling artifacts are linearly proportional to the percentage deviation of actual hitcount number with respect to the theoretical hitcount number. At last, we propose using relative hitcount compensation to reduce the under-sampling artifacts for RTM 3D ADCIGs, and demonstrate its effectiveness on 3D synthetic. Presentation Date: Monday, October 17, 2016 Start Time: 4:10:00 PM Location: Lobby D/C Presentation Type: POSTER

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2013 SEG Annual Meeting, September 22–27, 2013

Paper Number: SEG-2013-1149

...) proposed the concept of CIP (

**common**image**point**). Instead of computing CIGs at every image**point**, or even in vertical columns, they are computed only at selected positions where, it is thought, they will yield**useful**information for**velocity****analysis**. Calculating angle**gathers**from CIGs with only time lags...
Abstract

Summary Common-image gathers (CIGs) in the angle domain contain important information for velocity analysis and subsurface attribute analysis; and they may also be used to improve stacked migration images. In this paper we propose a new approach to compute the angle-domain CIGs for RTM based on an inverse-scattering imaging condition, in which the reflection angle presents itself implicitly as weighting of the wave fields. Two images are generated with and without the implicit reflection angle factor. The reflection angle is computed by dividing one pre-stack image by the other. Then pre-stack images from all the shots are mapped and binned into angle domain to form CIGs. Since the angle gathers are extracted in a post-migration step, it adds little memory requirement to RTM; and the computation is very efficient, especially for isotropic media. We demonstrate the method with several synthetic examples.

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