Jürgen Mann

Common‐reflection‐surface stack: Image and attributes

The common‐reflection‐surface stack provides a zero‐offset simulation from seismic multicoverage reflection data. Whereas conventional reflection imaging methods (e.g. the NMO/dip moveout/stack or prestack migration) require a sufficiently accurate macrovelocity model to yield appropriate results, the common‐reflection‐surface (CRS) stack does not depend on a macrovelocity model. We apply the CRS stack to a 2-D synthetic seismic multicoverage dataset. We show that it not only provides a high‐quality simulated zero‐offset section but also three important kinematic wavefield attribute sections, which can be used to derive the 2-D macrovelocity model. We compare the multicoverage‐data‐derived attributes with the model‐derived attributes computed by forward modeling. We thus confirm the validity of the theory and of the data‐derived attributes. For 2-D acquisition, the CRS stack leads to a stacking surface depending on three search parameters. The optimum stacking surface needs to be determined for each point...

Common-reflection-surface stack — a real data example

Abstract The simulation of a zero-offset (ZO) stack section from multi-coverage reflection data is a standard imaging method in seismic processing. It significantly reduces the amount of data and increases the signal-to-noise ratio due to constructive interference of correlated events. Conventional imaging methods, e.g., normal moveout (NMO)/dip moveout (DMO)/stack or pre-stack migration, require a sufficiently accurate macro-velocity model to yield appropriate results, whereas the recently introduced common-reflection-surface stack does not depend on a macro-velocity model. For two-dimensional seismic acquisition, its stacking operator depends on three wavefield attributes and approximates the kinematic multi-coverage reflection response of curved interfaces in laterally inhomogeneous media. The common-reflection-surface stack moveout formula defines a stacking surface for each particular sample in the ZO section to be simulated. The stacking surfaces that fit best to actual events in the multi-coverage data set are determined by means of coherency analysis. In this way, we obtain a coherency section and a section of each of the three wavefield attributes defining the stacking operator. These wavefield attributes characterize the curved interfaces and, thus, can be used for a subsequent inversion. In this paper, we focus on an application to a real land data set acquired over a salt dome. We propose three separate one-parametric search and coherency analyses to determine initial common-reflection-surface stack parameters. Optionally, a subsequent optimization algorithm can be performed to refine these initial parameters. The simulated ZO section obtained by the common-reflection-surface stack is compared to the result of a conventional NMO/DMO/stack processing sequence. We observe an increased signal-to-noise ratio and an improved continuity along the events for our proposed method — without loss of lateral resolution.

Data stacking beyond CMP

Stacking has been used in seismic data processing for a long time. In fact, stacked sections (or volumes in 3D) are standard deliverables in the industry, and the concepts of common-midpoint (CMP) gathers and normal moveout (NMO) correction are mentioned in almost every textbook on seismic processing. Although the general trend is toward prestack imaging (either in time or in depth), the construction of stacked sections remains an important step within the seismic processing flow, since they are almost always the first available interpretable images of the subsurface.

Common-Reflection-Surface Stack And Conflicting Dips

Summary. The recently introduced common-reflection-surf ace (CRS) stack simulates a zero-offset (ZO) section from multi-coverage seismic reflection data for 2-D media in a data-driven way, i. e., without explicit knowledge of the macro-velocity model. The “best” stacking operators are determined by an optimization of the coherency along different test stacking operators in the multi-coverage data. Previous implementations determine only one optimum stacking operator for each ZO sample to be simulated. Consequently, conflicting dips are not taken into account but only the most prominent event contributes to a particular stack sample. In this work, I show how this limitation can be overcome. The pragmatic search strategy of the original CRS stack implementation consists of three one-parametric search steps to determine the stacking operators. In the first step, an automatic CMP stack, conflicting dips can hardly be considered because the respective stacking velocities might be quite similar. However, I observe that conflicting dips can still be detected and separated in the subsequent search steps that are applied to the result of the automatic CMP stack. I propose an extension of the pragmatic approach to account for conflicting dips. For ZO samples where conflicting dips are detected, an additional one-parametric search is required. This provides a set of three kinematic wavefield attributes for each of the conflicting events and allows to simulate their interference in the simulated ZO section.

Event‐consistent smoothing in generalized high‐density velocity analysis

High-density velocity analysis provides more detailed information about the seismic reflection data compared to the conventional approach with smooth stacking velocity models based on selected CMP locations and reflection events. However, the high-density stacking velocity is subject to fluctuations and outliers complicating its interpretation and further use. The Common-Reflection-Surface stack, a generalized multiparameter multi-dimensional high-density stacking velocity analysis tool, provides an entire set of stacking parameters instead of stacking velocity, only. These stacking parameters easily allow an event-consistent smoothing based on a combination of median filtering and averaging that removes fluctuations and outliers without loss of information about the parameterized reflection events, even in case of conflicting dip situations. The smoothed stacking parameters not only improve the stack result but also provide a superior basis for subsequent applications like the determination of an interval velocity model.

A seismic reflection imaging workflow based on the Common-Reflection-Surface (CRS) stack: theoretical background and case study

In recent years, many case studies have demonstrated that the Common-Reflection-Surface (CRS) stack produces reliable stack sections with an excellent signal-to-noise ratio. In addition, an entire set of physically interpretable stacking parameters, so-called kinematic wavefield or CRS attributes, is determined. These attributes can be applied in further processing in such a way that a complete and consistent seismic reflection imaging workflow can be established which leads from the preprocessed multicoverage data in the time domain to migrated sections in the depth domain. The basic steps of this CRS-stack-based seismic reflection imaging workflow are the CRS stack itself, the determination of a smooth macrovelocity model by means of CRS attributes, and limited-aperture preand poststack Kirchhoff-type depth migration where the aperture is possibly optimized by means of the determined attributes. Our workflow approach has been applied to a recently acquired seismic dataset and revealed superior results compared to standard processing based on NMO/DMO/stack with a subsequent time migration and depth conversion.

True‐amplitude CRS‐based Kirchhoff time migration for AVO analysis

The achievable image quality and the reliability of amplitudes in Kirchhoff migration strongly depend on the selection of the migration aperture. Our aim is to use CRS-based minimum apertures in Kirchhoff prestack time migration to obtain the best possible input for AVO/AVA analyses. The basic idea is demonstrated for a synthetic data set which contains events from a common sequence of gas/water/oil contacts. We discuss the determination and extrapolation of stationary points and projected Fresnel zones based on CRS wavefield attributes, as well as a simple and efficient way to set up a migration velocity model. The first results show a significant reduction of amplitude dispersion in common-image gathers as well as in the zero-offset section, thus providing superior input to AVO/AVA analyses.

The finite‐offset CRS stack: An alternative stacking tool for subsalt imaging

The Finite-Offset Common-Reflection-Surface stack has been developed in the last two years as an extension to the established Common-Reflection-Surface stack. It can provide any finite-offset section from multi-coverage data in a data-driven way. In this paper, we show that this new imaging tool can be an alternative in case of complicated subsurface structures. This is demonstrated by means of a complex synthetic data example which has especially been designed to investigate the difficulties that occur in subsalt imaging.

CRS‐based minimum‐aperture time migration — A 2D land‐data case study

The Common-Reflection-Surface stack provides a set of kinematic wavefield attributes that characterize the reflection events in seismic prestack data. One of their applications is the determination of minimum migration apertures in Kirchhoff migration. So far, CRS-based minimum-aperture migration in the time domain was mainly used to provide more reliable and less noisy amplitudes in the migrated image. In this contribution, we demonstrate the potential of the minimumaperture approach to improve the overall image quality. The theoretical as well as the practical aspects of the application to real data are discussed. We show the improved imaging of fault structures on a 2D land dataset compared to the results of conventional Kirchhoff migration.

Applications of the common‐reflection‐surface stack

The simulation of a zero-offset stack section from multicoverage seismic reflection data for 2-D media is a widely used seismic reflection imaging method that reduces the amount of data and enhances the signal-to-noise ratio. The aim of the common-reflection-surface stack is not only to provide a well-simulated zero-offset stack section but also to determine certain attributes of hypothetical wavefronts at the surface useful for a subsequent inversion.