Produção Científica
Artigo em Revista
3D reverse time migration using a wavefield domain dynamic approach 3D Reversetime migration (RTM) is a powerful technique for imaging complex geologic structures. This approach requires a significant computational effort, demanding a high amount of memory for storing the source's wavefields, consequently leading to a high cost to perform the imaging condition. Thus, this work aims to reduce these problems by introducing a dynamic approach (DA) that considers the sparsity of the wavefield in the first periods of propagation. The RTM combined with the DA (RTMDA) approximates the computational domain to the propagation domain, which is the region delimited by the wavefront. In practical terms, the computational domain expands together with the wavefront, reflecting in a very significant economy of memory and reduction of processing time when compared to the conventional RTM, which we denominate as a static approach (RTMSA). To reduce the sparsity of the wavefields in the first periods of propagation, we have built an empirical 3D filter that maps each timestep of the wavefield and gives the coordinates to approximate the computational domain to the propagation domain. We compare both approaches using the 3D SEG/EAGE Salt model and demonstrate that the RTMDA is more efficient than the RTMSA in terms of memory consumption and computational time, preserving the quality of the seismic image. 

Artigo em Revista
Influence of Bubblepoint Pressure on the Gas Formation in an Oil Reservoir Under Water Injection To evaluate the oil recovering in a reservoir producing at the bubblepoint pressure, we performed numerical simulations using a sandbox model and a black oil approach for the reservoir, and the toolkit CFD software OpenFOAM. A new solver treats the threephase dynamics of the oil watergas in the reservoir. The calculation includes four cases with different pressures of the injection and production wells to explore the free gas formation. Our results show that even keeping constant the pressure unbalance between the injection and production wells, we observe different dynamics. There is no gas formation and a typical production profile results if the bottomhole pressure is just above the bubblepoint in the injection and production wells. In case only the production well bottomhole pressure is just below the bubblepoint, we see no gas formation near the injection well and oscillatory gas formation around the production well. We see a triphasic flow along with the whole domain if both bottom hole pressures are just below the bubblepoint. However, if the bottomhole pressure in both wells goes further below, the gas flow rate no more oscillates and the gas formation becomes continuous. We have also treated a special case to analyze the influence of gravity on the triphasic flow. Here we observed the gravity segregation to be not significant. 

Artigo em Revista
Interferometric redatuming by deconvolution and correlationbased focusing Seismic interferometry is a method used to calculate wavefields for sources and receivers that are located where only sources or only receivers are available. There are correlation or deconvolutionbased interferometric methods that can be used to reposition the seismic array from the earthâ€™s surface to an arbitrary datum at depth. Based on the oneway reciprocity theorems of convolution and correlation type, we have determined that interferometric redatuming can be achieved in a deconvolutiononly procedure in three steps. The first two steps consist of separately retrieving, for sources at the earthâ€™s surface, the downward and upwardpropagating Greenâ€™s functions at receivers at the datum, which are then used in the third step to reposition the sources to the datum. For the involved deconvolutions, transmitted and backscattered wavefields need to be modeled with a velocity model between the acquisition and datum levels. Our numerical experiments demonstrate that the method can help to reduce nonphysical events and other artifacts that commonly arise in purely correlationbased procedures. If a highquality overburdenvelocity model is available, it correctly accounts for inhomogeneities in the overburden medium. Because the methodâ€™s sensitivity to the velocity model is mainly introduced by backscattering at overburden heterogeneities, a smooth model is sufficient when overburden scattering is weak. 
Artigo em Revista
Porosity, specific surface area and permeability in porous media In the present work,we obtained explicit formulas that relate permeability to porosity and specific surface area of pores and cracks.We showthat Darcy's law is not an obligatory condition for the determination of fluid flow velocity; this empirical law may be true for some geometry of grains and pores, and maybe not valid for another geometry with flowing conditions. The role of permeability is played by the ratio of porosity (to the third power) to the specific surface area (to the second power) of pores or cracks. Fluid flow velocity depends on porosity, specific surface area, viscosity, and borehole radius. The analog of Darcy's law can be calculated using integral geometry parameters and boundary conditions; i. e., it does not have to be only empirical, but it is also an analytical law. The dependence of permeability on porosity differs significantly from enough big to small porous media. The fluid flow can be calculated using the elastic equilibrium equations and the incompressibility of viscous fluid without any phenomenological parameters. 
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Representation of discontinuous seismic velocity fields by sigmoidal functions for ray tracing and travel time modelling Wavemodelling methods based on asymptotic ray theory have a lower computational cost than full waveequation methods but require a smooth velocity field, though discontinuities may be handled by imposing interface conditions between adjacent blocks. We propose to approximate discontinuous velocity fields with model parametrizations based on smooth, rapidly varying functions known as sigmoidal functions. We have implemented the proposed technique on Cartesian grids using the wavelet theory formalism. Numerical experiments with 2D and 3D initialvalue and twopoint ray tracing in heterogeneous media show that the ray paths and traveltimes produced with the sigmoidal representation are consistent with the results produced by conventional ray tracing in block structures, broadening the scope of classical algorithms based on smooth velocity fields. 
Artigo em Revista
Oil Spill Detection and Mapping: A 50Year Bibliometric Analysis Oil spill detection and mapping (OSPM) is an extremely relevant issue from a scientific point of view due to the environmental impact on coastal and marine ecosystems. In this study, we present a new approach to assess scientific literature for the past 50 years. In this sense, our study aims to perform a bibliometric and network analysis using a literature review on the application of OSPM to assess researchers and trends in this field of science. In methodological terms we used the Scopus base to search for articles in the literature, then we used bibliometric tools to access information and reveal quantifying patterns in this field of literature. Our results suggest that the detection of oil in the sea has undergone a great evolution in the last decades and there is a strong relationship between the technological evolution aimed at detection with the improvement of remote sensing data acquisition methods. The most relevant contributions in this field of science involved countries such as China, the United States, and Canada. We revealed aspects of great importance and interest in OSPM literature using a bibliometric and network approach to give a clear overview of this fieldâ€™s research trends. 
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, reversetime migration (RTM), and fullwaveform 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 socalled 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 randomaccess 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 orientationdependent tensor decomposition Multidimensional seismic data reconstruction and denoising can be achieved by assuming noiseless and complete data as lowrank matrices or tensors in the frequencyspace domain. We propose a simple and effective approach to interpolate prestack seismic data that explores the lowrank property of multidimensional signals. The orientationdependent tensor decomposition represents an alternative to multilinear algebraic schemes. Our method does not need to perform any explicit matricization, only requiring to calculate the socalled covariance matrix for one of the spatial dimensions. The elements of such a matrix are the inner products between the lowerdimensional tensors in a convenient direction. The eigenvalue decomposition of the covariance matrix provides the eigenvectors for the reducedrank 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 (nondestructive 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 finitedifference methods, pseudospectral methods, finitevolume methods, Galerkin continuous and discontinuous finiteelement methods (classical or based on spectral interpolation), and still others such as physicscompatible, 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. 
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Multiphase flow mobility impact on oil reservoir recovery: An opensource simulation This work uses Computational Fluid Dynamics (CFD) to simulate the twophase 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 opensource CFD OpenFOAM platform. In this solver, the blackoil model represented the oil. The results show that the Buckleyâ€“Leverett waterflood equation is a good approach for the threedimensional 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. 