Produção Científica
Artigo em Revista
Computation of Acoustic Velocity of Natural Gases With an Alternative Heat Capacity Ratio Equation and Application to Seismic Modeling We investigate three formulations for computing acoustic velocity of natural gas and derive an equation for the heat capacity ratio, which plays a central role in these formulations. The first formulation is a compilation of fundamental equations available in the engineering literature, referred to as the DASH formulation. The second formulation is a development from the first, in which we use the derived equation for the heat capacity ratio (modified DASH). The third formulation is a mainstream method implemented in Geoscience (BW formulation). All three formulations stem from virial Equations of State that take preponderance in the exploration stage, when the detailed fluid composition is unknown and compositional methods are frequently inapplicable. We test the formulations on an extensive experimental data set of acoustic velocity of natural gases and compare the resulting accuracies. Both DASH and modified DASH formulations provide significantly higher accuracy when compared to the BW formulation. Additionally, the modified DASH, as we derive in this work, has the highest accuracy at pressures above 7000 psi, a condition typically encountered in the Brazilian presalt reservoirs. In a final step, we investigate how these different formulations and corresponding accuracies in velocity computation may affect seismic modeling, using a single interface model between a dense gas reservoir and a sealing rock. A direct comparison of amplitude versus offset modeling using our modified DASH formulation and the BW formulation shows up to 50% difference in amplitude calculation in a sensitivity exercise, especially at the longer offsets and higher pressures. 

Artigo em Revista
NUMERICAL SIMULATION OF SEISMIC WAVES IN POROUS MEDIA This work presents a mathematical algorithm for modeling the propagation of poroelastic waves. We have shown how the classical Biot equations can be put into Ursinâ€™s form in a planelayered 3D porous medium. Using this form, we have derived explicit formulas that can be used as the basis of an efficient computational algorithm. To validate the algorithm, numerical simulations were performed using both the poroelastic and equivalent elastic models. The results obtained confirmed the proposed algorithmâ€™s reliability, identifying the main wave events in both lowfrequency and highfrequency regimes in the reservoir and laboratory scales, respectively. We have also illustrated the influence of some physical parameters on the attenuation and dispersion of the slow wave. 

Artigo em Revista
An application of the Marchenko internal multiple elimination scheme formulated as a leastsquares problem Images produced by migration of seismic data related to complex geology are often contaminated by artifacts due to the presence of internal multiple reflections. These reflections are created when the seismic wave is reflected more than once in a sourcereceiver path and can be interpreted as the main coherent noise in seismic data. Several schemes have been developed to predict and subtract internal multiple reflections from measured data, such as the Marchenko multiple elimination (MME) scheme that eliminates the referred events without requiring a subsurface model or an adaptive subtraction approach. The MME scheme is datadriven, can remove or attenuate most of these internal multiples, and was originally based on the Neumann series solution of Marchenkoâ€™s projected equations. However, the Neumann series approximate solution is conditioned to a convergence criterion. We reformulate the MME as a leastsquares problem (LSMME) in such a way that it can provide an alternative that avoids a convergence condition as required in the Neumann series approach. To demonstrate the LSMME scheme performance, we apply it to 2D numerical examples and compare the results with those obtained by the conventional MME scheme. In addition, we evaluate the successful application of our method through the generation of indepth seismic images, by applying reverse time migration (RTM) to the original data set and to those obtained through MME and LSMME schemes. From the RTM results, we found that the application of both schemes on seismic data allows the construction of seismic images free of artifacts related to internal multiple events. 

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. 
Artigo em Revista
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. 