Produção Científica

Artigo em Revista

A wavefield domain dynamic approach: Application in reverse time migration
This paper proposes a novel technique to handle the wavefield domain involved in the procedures of seismic modeling, reverse-time migration (RTM), and full-waveform inversion (FWI). This method considers that the size of the wavefield domain varies with time, in other words, that it expands concomitantly to the propagation. However, in the geophysical literature, this dynamism has always been neglected as the wavefield domain is constantly considered to be fixed, thus, representing what we call a static approach (SA). This assumption may incur unnecessary use of available computational resources, thereby compromising application performance. Herein, we create a so-called dynamic approach (DA), capable of obtaining truly significant gains in terms of memory consumption and computational time. This new methodology is based on the application of an empirical filter that delimits the wavefront. This filter functions as a window and it is applied at each timestep until the wavefront reaches the model's boundaries, selecting the area where the seismic wavefield exists. This approach tries to approximate the computational domain to the propagation domain in order to obtain valuable computational gains, by eliminating unnecessary work, thus reducing the amount of work needed to perform forward and backward propagation. We compare both approaches using the Pluto model. The seismic data generated from the Pluto model is very large and it was not possible to use the static approach with it relying only on the random-access memory (RAM) of the used hardware. In order to perform the conventional RTM, we implement and compare the effective boundary technique for wavefield reconstruction with the RTM using the proposed dynamic approach. With the dynamic approach, it was possible to perform RTM of a 2D seismic data obtained from the Pluto model using only the RAM of the computational nodes and without the need of reconstruction techniques.
Artigo em Revista

Prestack seismic data reconstruction and denoising by orientation-dependent tensor decomposition
Multidimensional seismic data reconstruction and denoising can be achieved by assuming noiseless and complete data as low-rank matrices or tensors in the frequency-space domain. We propose a simple and effective approach to interpolate prestack seismic data that explores the low-rank property of multidimensional signals. The orientation-dependent tensor decomposition represents an alternative to multilinear algebraic schemes. Our method does not need to perform any explicit matricization, only requiring to calculate the so-called covariance matrix for one of the spatial dimensions. The elements of such a matrix are the inner products between the lower-dimensional tensors in a convenient direction. The eigenvalue decomposition of the covariance matrix provides the eigenvectors for the reduced-rank approximation of the data tensor. This approximation is used for recovery and denoising, iteratively replacing the missing values. We present synthetic and field data examples to illustrate the method's effectiveness for denoising and interpolating 4D and 5D seismic data with randomly missing traces.
Artigo em Revista

Modelling of mechanical wave propagation
The numerical modeling of mechanical waves is currently a fundamental tool for the study and investigation of their propagation in media with heterogeneous physical properties and/or complex geometry, as, in these cases, analytical methods are usually not applicable. These techniques are used in geophysics (geophysical interpretation, subsoil imaging, development of new methods of exploration), seismology (study of earthquakes, regional and global seismology, accurate calculation of synthetic seismograms), in the development of new methods for ultrasonic diagnostics in materials science (non-destructive methods) and medicine (acoustic tomography). In this paper we present a review of numerical
methods that have been developed and are currently used. In particular we review the key concepts and pioneering ideas behind finite-difference methods, pseudospectral methods, finite-volume methods, Galerkin continuous and discontinuous finite-element methods (classical or based on spectral interpolation), and still others such as physics-compatible, and multiscale methods. We focus on their formulations in time domain along with the main temporal discretization schemes. We present the theory and implementation for some of these methods. Moreover, their computational characteristics are evaluated in order to aid the choice of the method for each practical situation.
Artigo em Revista

Multiphase flow mobility impact on oil reservoir recovery: An open-source simulation
This work uses Computational Fluid Dynamics (CFD) to simulate the two-phase flow (oil and water) through a reservoir represented by a sandbox model. We investigated the influence in the flows of water having higher and lower mobilities than oil. To accomplish this, we also developed a dedicated solver, with the appropriated equations and representative models implemented in the open-source CFD OpenFOAM platform. In this solver, the black-oil model represented the oil. The results show that the Buckley‚ÄďLeverett water-flood equation is a good approach for the three-dimensional flow. We observe that the water wall front is mixed to some extent with the oil and evolves obeying an exponential law. Water with mobility lower than oil is not common. However, in this case, the oil recovery is improved and the amount of injected water is reduced. The results comparing different mobilities show that a careful economic assessment should be performed before the field development. We have shown that the low water mobility can increase, as in this studied example, the water front saturation from 0.57 to 0.73, giving a substantial improvement in the oil recovery. The reservoir simulation can provide all process information needed to perform an economical assessment in an oil field exploration.
Artigo em Revista

Geometrical influence of the source/drains configuration on the flow interactions in a sandbox model: A three-dimensional OpenFOAM simulation
This paper explores the interaction of di¬ģerent ¬įow paths in a porous medium by observing the e¬ģect of having more than one drain in a simple model domain with a single source. The work is based on three-dimensional numerical simulations of the ¬įow of injected water in a sandbox domain with porous volume completely ¬Įlled by water and oil. The calculation uses the OpenFOAM library to solve Darcy's equations for the dynamics of a two-phase ¬įow: water as the wetting, oil as the nonwetting ¬įuid. We observe the interactions of ¬įows in di¬ģerent paths under changes of number of drains and their relative positions.
Material Didático

Dynamics of Underground Rocks Containing Fluids
This is the fourth book partially supported by the National Institute of Science and Technology of Petroleum Geophysics (INCT-GP). The INCT-GP started in July, 2008, and it is one of 122 projects created by CNPq, as part of the National Institutes of Science and Technology (INCT) Program, with nancial support from CNPq/MCT, PETROBRAS and the Coordination for Development of Higher Level Personnel (CAPES/MEC). The INCT-GP joins together professors and researchers from 5 Brazilian universities (UFBA, UFPA, UFRN, UNICAMP and UENF) that work in the research and training of human resources in the areas of geophysics, geology and engineering applied to oil and gas exploration and reservoir studies.
The book is intended for students, teachers and researchers in the areas of geophysics, that apply seismic methods in exploration, mainly for oil and gas exploration. It comprises of 4 chapters and an extraordinary bibliography. The book presents theoretical and practical aspects of the physics of wave propagation in porous and crack media. At the end of each chapter, there is a summary of the theory and applications. The text and illustrations reect
the academic experience of the authors in a bene cial international cooperation centered at the Federal University of Para, Belem, and the Russian Academy of Sciences, Siberian Branch, Novosibirsk.
We would like to acknowledge to those people that have direct or indirect helped for the accomplishment of this book.
Prof. Dr. Milton José Porsani
Coordinator of INCT-GP
Salvador, Bahia, Brazil. March, 2020

Artigo em Revista

Can euler deconvolution outline three‚Äźdimensional magnetic sources?
Severe limitations of the standard Euler deconvolution (ED) to outline source shapes have been pointed out. However, ED has been widely employed on field data to outline interfaces, as faults and thrust zones. We investigate the limitations of the 3D ED‚Äźderived estimates of source dip and volume with the use of reduced‚Äźto‚Äźthe‚Äźpole synthetic and field anomalies. The synthetic anomalies are generated by two types of source bodies: 1) uniformly magnetized prisms, presenting either smooth or rough interfaces, and 2) bodies presenting smooth delimiting interfaces but strong internal variation of magnetization intensity. The dip of the first type of body might be estimated from the ED solution cluster if the ratio between the depth to the top and vertical extent is relatively high (>1/4). For the second type of body, besides dip, the source volume can be approximately delimited from the solution cluster envelope, regardless of the referred ratio. We apply ED to two field anomalies which are caused by a curved‚Äźshape thrust zone and by a banded iron formation. These anomalies are chosen because they share characteristics with the two types of synthetic bodies. For the thrust zone, the obtained ED solutions show spatial distribution allowing to estimate a source dip that is consistent with the surface geology data, even if the above mentioned ratio is much less than 1/4. Thus, there are other factors, like a heterogeneous magnetization, which might be controlling the vertical spreading of the ED solutions in the thrust zone. On the other hand, for the iron‚Äźore formation, the solution cluster spreads out occupying a volume, in accordance with the results obtained with the synthetic sources having internal variation of magnetization intensity. As conclusion, although ED‚Äźderived solutions cannot offer accurate estimates of source shapes, they might provide a sufficient degree of reliability in the initial estimates of the source dip and volume, which may be useful in a later phase of more accurate modeling.
Artigo em Revista

Enhancing stratigraphic, structural and dissolution features in GPR images of carbonate karst through data processing
Obtaining high‚Äźquality ground penetrating radar (GPR) images in karst is difficult because materials resulting from the weathering of carbonate rocks might be electrically conductive. As a consequence, penetration depth and signal resolution might be greatly reduced due to attenuation. In addition, fractures and faults might cause a significant amount of electromagnetic wave scattering. We present a 2D data processing flow which allows improving the quality of GPR images in carbonate karst. The processing flow is composed of the following steps: obtaining a zero‚Äźoffset section by removing the direct wave, low‚Äźfrequency noise removal, geometrical spreading and exponential gain compensation, spectral balancing, Kirchhoff migration, bandpass filtering, amplitude‚Äźvolume enhancement, and topographic correction. For a 200‚ÄźMHz dataset, we present in detail each step of the processing flow, exemplifying how to parameterize every step. Spectral balancing is of key importance because it can approximately replenish the high‚Äźfrequency content lost due to propagation effects. In this step, we recommend to shift the centroid frequency as much as possible to high‚Äźfrequency values, even exceeding the nominal value of the antenna center frequency, but still looking for a band‚Äźlimited spectrum as the goal. Despite the difficulty of migrating GPR data, we show that migration (even assuming a constant velocity) might enhance the lateral continuity of the reflection events and allows identification of discontinuities such as faults and fractures. If imaged in a better way, these structures can have special importance as they are often the boundaries of dissolution features. Obtaining images based on amplitude‚Äźvolume enhancement techniques allows to better visualize karst voids and deep‚Äźrooted discontinuities because these features are often associated with low‚Äźamplitude zones, which are highlighted in such images. Due to this processing flow, stratigraphic, structural and dissolution features can be enhanced, allowing the interpreter to establish spatial and genetic associations among these elements to obtain a better understanding of the karst formation process.
Artigo em Revista

Estimation of the seismic wavelet through homomorphic deconvolution and well log data: application on well-to-seismic tie procedure
Wavelet estimation and well-tie procedures are important tasks in seismic processing and interpretation. Deconvolutional statistical methods to estimate the proper wavelet, in general, are based on the assumptions of the classical convolutional model, which implies a random process reflectivity and a minimum-phase wavelet. The homomorphic deconvolution, however, does not take these premises into account. In this work, we propose an approach to estimate the seismic wavelet using the advantages of the homomorphic deconvolution and the deterministic estimation of the wavelet, which uses both seismic and well log data. The feasibility of this approach is
verified on well-to-seismic tie from a real data set from Viking Graben Field, North Sea, Norway. The results show that the wavelet estimated through this methodology produced a higher quality well tie when compared to methods of estimation of the wavelet that consider the classical assumptions of the convolutional model.
Artigo em Revista

Fast estimation of prestack Common Reflection Surface parameters.
We present a method for fast estimation of finite offset common reflection surface parameters. Firstly, the derivatives with respect to offset are derived from the velocity guide. Secondly, we apply structure tensors to extract the derivatives with respect to midpoint from stacked common offset sections. Finally, the mixed derivative is estimated using a one‚Äźparametric semblance search. The proposed method is compared to the global five‚Äźparametric semblance search and the pragmatic sequential two‚Äźparametric semblance search on one synthetic and one real data set. The experiments show that the proposed method is more robust against noise than the pragmatic search and have comparable robustness with the global search. The proposed method smoothes parameter estimates in a local window, and the window size is set to give the best trade‚Äźoff between detail and robustness. Since the proposed method is dependent on a velocity guide, the quality of the other parameter estimates may be influenced by any inaccuracies in the guide. The main advantage of the proposed method is the computational efficiency. When compared with a gridded implementation of the semblance search, the proposed method is 10 and 400 times faster than the pragmatic and global search. Alternative search strategies significantly reduce the computational cost of the global search. However, since more than 99% of the computational cost of the proposed method comes from the semblance search to estimate the mixed derivative, it is expected that such techniques also reduce the computational cost for the proposed method.
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A Semana de Inverno de Geofísica é um evento regular do Instituto Nacional de Ciência e Tecnologia de Geofísica do Petróleo (INCT-GP/CNPq), organizado pelo Grupo de Geofísica Computacional (GGC) do IMECC/UNICAMP.O evento é direcionado a estudantes em fim de graduação e início de pós-graduação interessados na área de Geofísica Aplicada, principalmente nos temas ligados à exploração de petróleo. A Semana presta-se a divulgar a carreira de Geofísica, franqueando aos alunos de pós-graduação o acesso a temas atuais de pesquisa em Geofísica, por meio de especialistas renomados na área.

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