Papers by João Carlos Ribeiro Cruz
Proceedings of the 5 Simpósio Brasileiro de Geofísica, 2012
Simulação de reflexões primárias e múltiplas usando aproximação paraxial de tempos de trânsito CR... more Simulação de reflexões primárias e múltiplas usando aproximação paraxial de tempos de trânsito CRS de 4ª ordem.
9th International Congress of the Brazilian Geophysical Society & EXPOGEF, Salvador, Bahia, Brazil, 11-14 September 2005, 2005
The Gaussian Beam concept has been of great importance for works on modeling and migration, durin... more The Gaussian Beam concept has been of great importance for works on modeling and migration, during the last two decades. This work then joins the flexibility of the true amplitude (diffraction stack) Kirchhoff migration procedure with the regularity description of the wavefield represented by the Gaussian Beam. We apply our final operator in some simple numerical examples of geophysical exploration interest. Our process can be named as Kirchhoff Gaussian Beam Prestack Depth Migration (KGB-PSDM) in a true amplitude sense.
71st EAGE Conference and Exhibition - Workshops and Fieldtrips, 2009
The common reflecting element (CRE) method is an interesting alternative to the familiar methods ... more The common reflecting element (CRE) method is an interesting alternative to the familiar methods of com-mon midpoint (CMP) stack or migration to zero offset (MZO). Like these two methods, the CRE method aims at constructing a stacked zero-offset section from a set of constant-offset sections. However, it requires no more knowledge about the generally laterally inhomogeneous subsurface model than the near-surface values of the ve-locity field. In addition to being a tool to construct a stacked zero-offset section, the CRE method simultane-ously obtains information about the laterally inhomoge-neous macrovelocity model. An important feature of the CRE method is that it does not suffer from pulse stretch. Moreover, it gives an alternative solution for conflicting dip problems. In the 1-D case, CRE is closely related to the optical stack. For the price of having to search for two data-derived parameters instead of one, the CRE method provides important advantages over the con-ventional ...
The multiple reflections include in the seismograms important informations about the reflectors i... more The multiple reflections include in the seismograms important informations about the reflectors in subsurface and can become completely invisible. In marine data acquisition the water layer behaves as a wave trap, where the waves are repeatedly reflected at the sea surface and sea bottom without significant amplitude loss. In order to identify and locate target reflectors, these multiples must be eliminated or, at least, attenuated. In this work, interbed symmetric multiple reflections were identified in synthetic dataset. We compare the parameters of hypothetical wavefronts Normal-Incidence-Point (NIP) and Normal (N) obtained by forward modeling and Kirchhoff migration. This comparison was extended to consider the Normal-Moveout (NMO) velocity. These comparisons led us to identify and differentiate between multiple and primary reflections. INTRODUCTION Seismograms include multiple reflections that can be so strong that the desired primary reflections become completely invisible. In...
The simulation of a zero-offset (ZO) seismic section from multi-coverage seismic data is a standa... more The simulation of a zero-offset (ZO) seismic section from multi-coverage seismic data is a standard imaging method widely used in seismic processing that allows to reduces the amount of data and increases the signal-to-noise ratio. The CRS stacking method simulates ZO sections and does not dependent on a macro-velocity model. It is based on a second-order traveltime approximation parametrized with three kinematic wavefield attributes. In this work, we tested the Taylor expansion of the second-order CRS conventional operator, so-called the fourth-order CRS stacking operator, to simulate ZO seismic sections. This formula depends on the same three parameters as the secondorder CRS operator. Synthetic examples have shown a good performance of the proposed expression compared to the CRS conventional operator. INTRODUCTION The seismic stacking is performed along traveltime moveout expressions (curves or surfaces) that depend on one or more parameters. As result of the stacking process, on...
By considering arbitrary source-receiver configurations the compressional primary reflections can... more By considering arbitrary source-receiver configurations the compressional primary reflections can be imaged into time or depth-migrated reflections so that the migrated wavefield amplitudes are a measured of angle-dependent reflection coeffients. In order to do this various migration algorithms were proposed in the recent past years based on Born or Kirchhoff approach. Both of them treats of a weighted diffraction stack integral operator that is applied to the input seismic data. As result we have a migrated seismic section where at each reflector point there is the source wavelet with the amplitude proportinal to the reflection coefficient at that point. Based on Kirchhoff approach, in this paper we derive the weight function and the diffraction stack integral operator for the two and one half (2.5-D) seimic model and apply it to a set of synthetic seismic data in noise enviroment. The result shows the accuracy and stability of the 2.5-D migration method as a tool for obtaining imp...
In this work we extend the KGB-PSDM algorithm to the special case of a constant gradient velocity... more In this work we extend the KGB-PSDM algorithm to the special case of a constant gradient velocity media. Following the same lines as for the homogeneous media, se have teste our operator in some synthetic important geological models and we have observed an increase in the resolution of the seismic images, as well as a great reduction of migration artifacts and noise. INTRODUCTION Kirchhoff-type migration has been used as workhorse by the oil industry since the pioneering work of Hagedoorn (1954), whose “maximum convexity surfaces” were later related to the acoustic wave equation and have since then become familiar in the geophysics literature as Kirchhoff migration (Schneider, 1978; Hertweck et al., 2003). However, in the last two decades Kirhhoff migration has evolved from a single imaging operator to an operator that embraces, among others, the structure of an inversion operator. This allowed the development of several others techniques (Tygel et al., 1993; Tygel et al., 1998), su...
The recently introduced Common-Reflection-Surface (CRS) method is a natural generalization of the... more The recently introduced Common-Reflection-Surface (CRS) method is a natural generalization of the well-established Normal Moveout (NMO) method, designed to simulate a zero-offset (ZO) section by a stacking procedure applied to multicoverage data. As opposed to NMO, the stacking procedure in the CRS is not restricted to common-midpoint (CMP) gathers, but uses much more general supergathers of non-symmetrical sources and receivers. Moreover, no selection of interpreted events is required. For the 2D situation considered in this paper, the CRS stacking curve is the general hyperbolic traveltime moveout, that depends on three kinematic wavefield attributes. The crucial step of the CRS method is the estimation of the wavefield attributes at each point of the simulated ZO section to be constructed. This is carried out by means of optimization procedures using as objective function the coherence (semblance) of the seismic traces along the stacking curve. Although a few strategies are alrea...
Proceedings of the VIII Simpósio Brasileiro e Geofísica
Revista Brasileira de Geofísica
13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013, 2013
Contents of this paper were reviewed by the T echnic al Commit tee of the 13 th International Con... more Contents of this paper were reviewed by the T echnic al Commit tee of the 13 th International Congress of the Brazilian G eophysical Soci et y and do not nec essaril y represent any position of the SBG f, its officers or members. Electronic reproduction or storage of any part of this paper f or commercial purpos es without the written consent of the Brazilian G eophysical Soci et y is pr ohibit ed.
74th EAGE Conference and Exhibition incorporating EUROPEC 2012, 2012
The Gaussian Beam (GB) is an asymptotic solution of the elastodynamic equation in the paraxial vi... more The Gaussian Beam (GB) is an asymptotic solution of the elastodynamic equation in the paraxial vicinity of a central ray, which approaches better the wave field than the standard zero-order ray theory. The GB regularity in the description of the wave field, as well as its high accuracy in some singular regions of the propagation medium, provide us with a strong alternative to solve seismic modeling and imaging problems. In this paper, we use the concept of the projected Fresnel zone to limit the superposition integral of Gaussian beams, in order to obtain a more stable Gaussian beam propagation. This result is used to calculate synthetic seismograms with more effectiveness.
60th EAGE Conference and Exhibition, 1998
11th International Congress of the Brazilian Geophysical Society & EXPOGEF 2009, Salvador, Bahia, Brazil, 24-28 August 2009, 2009
After eight years of the first distribution of the user's manual of the Seismic Unix (SU) package... more After eight years of the first distribution of the user's manual of the Seismic Unix (SU) package, it is yet a challenge to execute some seismic processing SU scripts, especially for inexperienced users. Up to now there are few friendly Graphical User Interfaces (GUI) for the SU package, namely Tksu, iSU and GêBR. In order to obtain a more robust and flexible way to work with the SU package, we present a new graphical user interface written in the Java programming language, which can be used under any operating system, the so-called BOTOSEIS. It is adequate to be used both as a production or as interactive development environment, by creating and managing projects, lines and flowcharts of seismic data processing. It is also possible to add SU based softwares, interactively, without knowledge about any programming language. The BOTOSEIS platform is structured by modules, which can be a single application or a combination of SU programs to produce a more complex result, e.g., iVIEW, iVELAN and iNIP-PICKING. The first is a GUI used for data visualization, the second is an important interactive tool for velocity analysis fitted for production environments, and the last is a software for data picking in the zero-offset seismic section that is fundamental for traveltime inversion methods.
60th EAGE Conference and Exhibition, 1998
In this paper the reflection coefficient map is obtained applying a geometrical spreading correct... more In this paper the reflection coefficient map is obtained applying a geometrical spreading correction factor to the principal component of the primary reflection wavefields, corresponding to seismic traces into zero-offset configuration data.
Seg Technical Program Expanded Abstracts, 2006
The Common-Reflection-Surface (CRS) stack method produces zerooffset (ZO) sections with high sign... more The Common-Reflection-Surface (CRS) stack method produces zerooffset (ZO) sections with high signal-to-noise ratio and three useful kinematic wavefield attributes from multi-coverage seismic data. With the knowledge of the near surface velocity only, the CRS stack is based on the determination of these attributes by means of automatic search processes based on coherency analysis. These kinematic CRS wavefield attributes can be used for several seismic applications. In this work we propose a procedure for mapping the stacked amplitudes along the CRS operator in the ZO section to depth domain. Then, for the ZO plane, the kinematic attributes are used to calculate the stacking operator and to determine the projected first Fresnel zone to be used to restrict the size of the CRS stacking operator. Similar to preor post-stack depth migrations, this mapping procedure also requires the a priori unknown velocity model. This mapping procedure is illustrated by means of applying it to a synthetic data of a simple model example.
Journal of Applied Geophysics, 2000
By considering arbitrary source-receiver configurations, compressional primary reflections can be... more By considering arbitrary source-receiver configurations, compressional primary reflections can be imaged into time or depth-migrated seismic sections so that the migrated wavefield amplitudes are a measure of angle-dependent reflection coefficients. Several migration algorithms were proposed in the recent past based on the Born or Kirchhoff approach. All of them are given in form of a weighted diffraction-stack integral operator that is applied to the input seismic data. The result is a migrated seismic section where at each reflection point the source wavelet is reconstructed with an amplitude proportional to the reflection coefficient at that point. Based on the Kirchhoff approach, we derive the weight function and the diffraction Ž. stack integral operator for a two and one-half 2.5-D seismic model and apply it to a set of synthetic seismic data in noisy environment. The result shows the accuracy and stability of the 2.5-D migration method as a tool for obtaining important information about the reflectivity properties of the earth's subsurface, which is of great interest for amplitude vs. offset Ž. Ž. angle analysis. We also present a new application of the Double Diffraction Stack DDS inversion method to determine three important parameters along the normal ray path, i.e., the angle and point of emergence at the earth surface, and also the Ž. radius of curvature of the hypothetical Normal Incidence Point NIP wave.
Revista Brasileira de Geofísica
O trabalho em pauta tem como objetivo o modelamento da crosta, atraves da inversao de dados de re... more O trabalho em pauta tem como objetivo o modelamento da crosta, atraves da inversao de dados de refracao sismica profunda, segundo camadas planas horizontais lateralmente homogeneas, sobre um semi-espaco. O modelo direto e dado pela expressao analitica da curva tempo-distância como uma funcao que depende da distância fonte estacao e do vetor de parâmetros velocidades e espessuras de cada camada, calculado segundo as trajetorias do raio sismico, regidas pela Lei de Snell. O calculo dos tempos de chegada por este procedimento exige a utilizacao de um modelo cujas velocidades sejam crescente com a profundidade, de modo que a ocorrencia da camada de baixa velocidade (CBV) e contornada pela reparametrizacao do modelo, levando-se em conta o fato de que o topo da CBV funciona apenas como um refletor do raio sismico, e nao como refrator. A metodologia de inversao utilizada tem em vista nao so a determinacao das solucoes possiveis, mas tambem a realizacao de uma analise sobre as causas responsaveis pela ambiguidade do problema. A regiao de pesquisa das provaveis solucoes e vinculada segundo limites superiores e inferiores para cada parâmetro procurado e pelo estabelecimento de limites superiores para os valores de distâncias criticas, calculadas a partir do vetor de parâmetros. O processo de inversao e feito utilizando-se uma tecnica de otimizacao do ajuste de curvas atraves da busca direta no espaco dos parâmetros, denominado COMPLEX. Esta tecnica apresenta a vantagem de poder ser utiliada com qualquer funcao objeto e ser bastante pratica na obtencao de multiplas solucoes do problema. Devido a curva tempo-distância corresponder ao caso de uma multi-funcao, o algoritmo foi adaptado de modo a minimizar simultaneamente varias funcoes objeto, com vinculos nos parâmetros. A inversao e feita de modo a se obter um conjunto de solucoes representativas do universo existente. Por sua vez, a analise da ambiguidade e realizada pela analise fatorial modo-Q, atraves da qual e possivel se caracterizar as propriedades comuns existentes no elenco das solucoes analisadas. Os testes com dados sinteticos e reais foram feitos tendo como aproximacao inicial ao processo de inversao, os valores de velocidades e espessuras calculados diretamente da interpretacao visual do sismograma. Para a realizacao dos primeiros, utilizou-se sismogramas calculados pelo metodo da refletividade, segundo diferentes modelos. Por sua vez, os testes com dados reais foram realizados utilizando-se dados extraidos de um dos sismogramas coletados pelo projeto Lithospheric Seismic Profile in Britain (LISPB), na regiao norte da Gra-Bretanha. Em todos os testes foi verificado que a geometria do modelo possui um maior peso na ambiguidade do problema, enquanto os parâmetros fisicos apresentam apenas suaves variacoes, no conjunto das solucoes obtidas. ABSTRACT Inversion of deep seismic refraction data through time-distance curve ¾ The aim of this thesis is to obtain crustal model through the inversion of deep seismic refraction data considering lateraly homogeneous horizontal plain layers over a half-space. The direct model is given by analytic expression for the travel-time curve, as a function that depends on the source-station distance and on the array of parameters, formed by velocity and thickness of each layer. The expression is obtained from the trajectory of the seismic ray by Snell's Law. The calculation of the arrival time for seismic refraction by this method takes into account a model with velocities increasing with depth. The occurrence of low velocity layers (LVL) are solved as a model reparametrization, taking into account the fact that top boundary of the low velocity layer is only a reflector, and not a refractor of seismic waves. The inversion method is used to solve for the possible solutions, and also to perform an analysis about the ambiguity of the problem. The search region of probable solutions is constrained by high and lower limits of each parameter considered, and by high limits of each critical distance, calculated using the array of parameters. The inversion process used is an optimization technique for curve fitting corresponding to a direct search in the parameter space, called COMPLEX. This technique presents the advantage of using any objective function, and as being practical in obtaining different solutions for the problem. As the travel-time curve is a multi-function, the algorithm was adapted to minimize several objective functions simultaneously, with constraints. The inversion process is formulated to obtain a representative group of solutions of the problem. Afterwards, the analysis of ambiguity is made by Q-mode factor analysis, through which is possible to find the common properties of the group of solutions. Tests with synthetic and real data were made having as initial approximation to the inversion process the velocity and thickness values calculated by the straightforward visual interpretation of the seismograms. For the…
6th International Congress of the Brazilian Geophysical Society
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Papers by João Carlos Ribeiro Cruz