Beam Prestack Depth Migration Research Articles

Adaptive Focused Beam Prestack Depth Migration Under the Condition of Rugged Topography

The complex topography is a challenging issue in onshore seismic exploration. The rugged terrain and lateral change of near-surface velocity pose a significant obstacle to the accurate imaging of seismic data. The adaptive focused beam migration method retains the good applicability of the ray methods for calculating the seismic wavefield under complex surface conditions. It can effectively solve the contradiction between the imaging accuracy of deep and shallow strata in traditional Gaussian beam migration. We extend the adaptive focused beam migration approach to the deep domain imaging of seismic data under complex surface conditions. Firstly, the basic principles of the adaptive focused beam are reviewed. Then, Green’s functions of the seismic source and the receiving point of rugged topography are characterized by the adaptive focused beam, and an adaptive focused beam prestack depth migration method based on cross-correlation imaging is proposed. The full-wave-arrival imaging strategy is applied to image all wave arrivals of subsurface imaging points. A single input seismic trace is adopted for imaging, which can directly emit the focused beam from the receiving point of rugged topography for wave field continuation, thus avoiding multiple focusing. As a result, the applicability of the migration approach to complex surface conditions was improved, and the imaging accuracy of the migration method was also effectively enhanced. The numerical model migration test of different rugged topography conditions and tectonic forms verified that the proposed method was an effective prestack depth migration applicable to accurately imaging seismic data under the rugged topography condition.

Gaussian Beam Migration for Free-Surface Multiples in VSP

The vertical seismic profiling (VSP) Gaussian beam migration is a seismic imaging method with both computational efficiency and imaging precision. It can get high-resolution structural features near the well. However, the VSP migration based on primary reflection imaging is limited by the observation system, which makes it unable to image for the shallow structure at far offset. The free-surface multiples in VSP can expand the illumination range for far offset effectively. Therefore, Gaussian beam migration (GBM) for free-surface multiples imaging in VSP is proposed. Firstly, based on the ground Gaussian beam pre-stack depth migration, the method for decomposing the plane wave is improved and adapted into VSP geometry. We decompose the seismic records received by the well into plane waves in different directions according to different window centers and image the plane wave of each direction independently. Secondly, through the mirror image of both the velocity model and VSP receivers, the VSP free-surface multiples are converted into VSP primary reflections which are involved in the VSP Gaussian beam migration method, and thus, the method of the primaries is used to image the free-surface multiples. Finally, the effectiveness and robustness of the proposed method are verified by the theoretical model and practical data.

A method of directly extracting multiwave angle-domain common-image gathers

Angle-domain common-image gathers (ADCIGs) can provide an effective way for migration velocity analysis and amplitude versus angle analysis in oil–gas seismic exploration. On the basis of multi-component Gaussian beam prestack depth migration (GB-PSDM), an alternative method of directly extracting multiwave ADCIGs is presented in this paper. We first introduce multi-component GB-PSDM, where a wavefield separation is proceeded to obtain the separated PP- and PS-wave seismic records before migration imaging for multiwave seismic data. Then, the principle of extracting PP- and PS-ADCIGs using GB-PSDM is presented. The propagation angle can be obtained using the real-value travel time of Gaussian beam in the course of GB-PSDM, which can be used to calculate the incidence and reflection angles. Two kinds of ADCIGs can be extracted for the PS-wave, one of which is P-wave incidence ADCIGs and the other one is S-wave reflection ADCIGs. In this paper, we use the incident angle to plot the ADCIGs for both PP- and PS-waves. Finally, tests of synthetic examples show that the method introduced here is accurate and effective.

Angle-domain common-image gathers from anisotropic Gaussian beam migration and its application to anisotropy-induced imaging errors analysis

An approach for extracting angle-domain common-image gathers (ADCIGs) from anisotropic Gaussian beam prestack depth migration (GB-PSDM) is presented in this paper. The propagation angle is calculated in the process of migration using the real-value traveltime information of Gaussian beam. Based on the above, we further investigate the effects of anisotropy on GB-PSDM, where the corresponding ADCIGs are extracted to assess the quality of migration images. The test results of the VTI syncline model and the TTI thrust sheet model show that anisotropic parameters ε, δ, and tilt angle 𝜃, have a great influence on the accuracy of the migrated image in anisotropic media, and ignoring any one of them will cause obvious imaging errors. The anisotropic GB-PSDM with the true anisotropic parameters can obtain more accurate seismic images of subsurface structures in anisotropic media.

Implementing the CRS beam prestack depth migration with double-smearing operator within the unified Kichhoff imaging theory

The unified Kirchhoff imaging theory provides an essential theoretical foundation for understanding any Kirchhoff-type imaging methods. The local kinematic attributes are important information regarding a local coherently event in seismic dataset. We develop a double-smearing operator based common-reflection-surface (CRS) beam prestack depth migration (PSDM) based on the unified Kirchhoff imaging theory and the local kinematic attributes. Differing from the previous works based on the Hugens-curve-stacking scheme, the double-smearing operator employed in this paper is derived on the basis of the isochrones-smearing scheme defined in the unified Kirchhoff imaging theory. It provides a parallel approach to implement the CRS beam PSDM. The synthetic and real data examples demonstrate the effectiveness and robustness of the double-smearing CRS beam PSDM operator.

Multiwave Gaussian beam prestack depth migration of exploration‐scale seismic data with complex near‐surface effects

ABSTRACTThe direct prestack depth migration methods of nonplanar data provide effective ways to address the complex near‐surface problem. Based on the study of local slant stacks considering the elevation and dip angle information of an irregular surface, an alternative method for multiwave Gaussian beam prestack depth migration of exploration‐scale seismic data with complex near‐surface effects is presented here. We first derive the downward‐continued wavefield for an irregular surface in terms of Gaussian beams, where we directly decompose the seismic records within a Gaussian window into a local plane‐wave component. The PP‐ and PS‐wave Gaussian beam prestack depth migration methods under complex near‐surface conditions are then presented, after the wavefield separation is performed with an affine coordinate‐system transform. Tests with numerical examples demonstrate the accuracy and effectiveness of the method.

Attenuation compensation in multicomponent Gaussian beam prestack depth migration

Gaussian beam prestack depth migration is an accurate imaging method of subsurface media. Prestack depth migration of multicomponent seismic data improves the accuracy of imaging subsurface complex geological structures. Viscoelastic prestack depth migration is of practical significance because it considers the viscosity of the subsurface media. We use Gaussian beam migration to compensate for the attenuation in multicomponent seismic data. First, we use the Gaussian beam method to simulate the wave propagation in a viscoelastic medium and introduce the complex velocity Q-related and exact viscoelastic Zoeppritz equation. Second, we discuss PP- and PS-wave Gaussian beam prestack depth migration algorithms for common-shot gathers to derive expressions for the attenuation and compensation. The algorithms correct the amplitude attenuation and phase distortion caused by Q, and realize multicomponent Gaussian beam prestack depth migration based on the attenuation compensation and account for the effect of inaccurate Q on migration. Numerical modeling suggests that the imaging resolution of viscoelastic Gaussian beam prestack depth migration is high when the viscosity of the subsurface is considered.

Gaussian beam prestack depth migration in heterogeneous transversely isotropic media

The transversely isotropic (TI) media approximation is commonly applied to assist in the processing of seismic data acquired in sedimentary environments. Based on anisotropic kinematic and dynamic ray tracing systems, a P-wave Gaussian beam prestack depth migration (GB-PSDM) method for TI media is introduced in this paper. The imaging principle of anisotropic GB-PSDM and the corresponding migration parameters are presented on the basis of the GB-PSDM method in isotropic media. Tests of synthetic and field seismic data show that the method is an accurate and efficient anisotropic prestack depth migration method in TI media.

Gaussian beam prestack depth migration of converted wave in TI media

Abstract Increasing amounts of multi-component seismic data are being acquired on land and offshore because more complete seismic wavefield information is beneficial for structural imaging, fluid detection, and reservoir monitoring. S-waves are typically influenced more by anisotropy in a medium than are P-waves; as a result, the anisotropy cannot be ignored during the converted PS-wave imaging. Gaussian beam migration, an elegant and efficient depth migration method, is becoming a new topic in the study of PS-wave migration; its accuracy is comparable to that of wave-equation migration, and its flexibility is comparable to that of Kirchhoff migration. In this paper, we introduce an anisotropic Gaussian beam prestack depth migration (GB-PSDM) method for the converted PS-wave, in which the anisotropic media can be a transversely isotropic (TI) medium with a vertical or tilted symmetry axis. We present the PS-wave common shot gathers GB-PSDM imaging condition and derive the ray tracing of P- and SV-waves in two-dimensional TI media. The migration impulse responses of P- and SV-propagation modes in TI media with both vertical and tilted symmetry axes are presented. The results of numerical examples indicate that the method introduced here offers significant improvements in the quality of converted PS-wave imaging compared with an isotropic algorithm.

Multiwave velocity analysis based on Gaussian beam prestack depth migration

Prestack depth migration of multicomponent seismic data improves the imaging accuracy of subsurface complex geological structures. An accurate velocity field is critical to accurate imaging. Gaussian beam migration was used to perform multicomponent migration velocity analysis of PP- and PS-waves. First, PP- and PS-wave Gaussian beam prestack depth migration algorithms that operate on common-offset gathers are presented to extract offset-domain common-image gathers of PP- and PS-waves. Second, based on the residual moveout equation, the migration velocity fields of P- and S-waves are updated. Depth matching is used to ensure that the depth of the target layers in the PP- and PS-wave migration profiles are consistent, and high-precision P- and S-wave velocities are obtained. Finally, synthetic and field seismic data suggest that the method can be used effectively in multiwave migration velocity analysis.

Multi-component Gaussian beam prestack depth migration

As the depth migration of multi-component seismic data can obtain better images of the subsurface structures with multi-wave information in seismic records, an effective multi-component Gaussian beam migration method is presented in this paper. Firstly, a detailed numerical analysis on the local slant stack is carried out, which demonstrates that the Gaussian beam migration method has good directionality and computational efficiency through decomposing seismic records into different outgoing directional local plane waves. Then two different Gaussian beam prestack depth migration algorithms are presented, corresponding to the PP- and PS-waves, after a wavefield separation is effected with an affine coordinate system transform. Finally, tests of synthetic and field seismic data show that the method introduced above would be an accurate and efficient prestack depth migration alternative for multi-component seismic data.

Beam migration for imaging of complex geology

Beam Migration provides an effective alternative to Kirchhoff or wave equation migration. Beam Migration relaxes the single arrival limitation of Kirchhoff while retaining its steep dip capability. There are a number of different types of Beam Migration implementations such as Hill?s Gaussian Beam Migration. Our implementation of Beam Migration is unique in the industry and involves a decomposition of the data into dip components using the Radon transform and a back-propagation of the dip components into the earth. The dip components can be enhanced based on various criteria before the back-propagation, thereby giving a more coherent image. The methodology inherently allows the attenuation of multiple energy, and coherent as well as non coherent noise. Our implementation of Beam Migration (which we refer to as BPSDM for Beam Pre-Stack Depth Migration) has merits of simplicity, economy, flexibility, and future development possibilities. Migrated images have excellent accuracy and quality, especially in areas of poor signal to noise ratio and steep dip. The relative economy makes it an excellent velocity estimation tool to use prior to other, more computation intensive, depth migration methods.

3D beam prestack depth migration with examples from around the world

In 1999, we specialized in 2D seismic depth processing. It was necessary to progress into 3D depth migration, but it seemed unrealistic to utilize Kirchhoff or wave-equation methods and be able to compete with large companies, their compute resources, and their economies of scale. Consequently, it was decided to attempt the commercial development of an alternative approach that would hopefully provide similar or improved technical quality, but with capital outlay and economics that were more appropriate to a small company. A very straightforward approach referred to as beam prestack depth migration (BPSDM) was adopted; its origins dated to work performed in the 1930s by Frank Rieber. The anticipated merits of BPSDM were overall simplicity, economy, flexibility, and future development possibilities. The unknowns were the migration accuracy and quality achievable. BPSDM was essentially developed independently, but aspects of it obviously are related to much recently published work on other beam migrations a...