Produção Científica
Artigo em Revista
| Can Full-Waveform Inversion Compensate for the Lack of Illumination in Crosswell Tomography? Seismic illumination can be defined as the maximum angle between rays that pass through a point. Only interfaces completely contained in the angular apertures can be correctly imaged with first arrival traveltime tomography (FATTT). We investigate if 2D acoustic full-waveform inversion (FWI) can compensate for the lack of illumination of a crosshole tomography experiment. We use synthetic data generated with Ricker wavelets with peak frequencies at 100 or 500 Hz, resulting in small overlapping in the frequency bandwidths, allowing the use of a multiscale FWI approach. We investigate two FWI cases: in the first case (FWI T), just the waves recorded at the opposite borehole are used whilst, in the second case (FWI T+R), the waves recorded at the two boreholes are used. For a single interface, the shape of the transmitted waveform only varies significantly when it is contained in the angular apertures. Accordingly, shot gathers for layered models with interfaces outside the angular apertures can be roughly reproduced with equivalent homogeneous media. Thus, in comparison with FATTT, both FWI cases give mild improvements for models with interfaces inside the angular coverage, and cannot compensate for the lack of illumination of the experiment. However, in the mixed condition where layers with interfaces inside the angular coverage are cut by a fault, FWI offers substantial improvements over FATTT, even if the fault plane is outside the angular coverage. In this mixed situation, resolution increases when FWI T+R is used. However, for the studied cases, no significant improvements were obtained in the FWI stage where the 500 Hz peak frequency was used. |
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Artigo em Revista
| Correlation analysis: application of DFA and DCCA in well log profiles Detrended fluctuation analysis and detrended cross correlation analysis are used in this work to identify and characterize correlated well log data. This is performed by first separating the different fluctuations due to external trends, and evaluating the autocorrelation and cross-correlation exponents to determine whether scale properties persist as the size of the series changes. Two new methodologies were developed to identify optimal values of the cross-correlation coefficients and graphically display them, which we call the automatic search procedure and correlation map. The methodologies were applied to well logs from the Jequitinhonha Basin, Brazil, to verify the existence of scale property in these data. For practical purposes, our goal is to use a local analysis framework to detect all points of high cross-correlation among different physical parameters in the same well, and among one same physical parameter in different wells. The correlated events suggested the continuity of geological features, including the vertical displacements of rock layers. In particular, it was possible to identify layers of calcilutites in a specific depth range. These rocks are of particular importance to the study of stratigraphic correlations due to their great regional extent and regular layering. |
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Artigo em Revista
| Controls of fracturing on porosity in pre-salt carbonate reservoirs This work aims to improve the understanding of how fracture zones affect carbonate reservoir properties based on observations of a pre-salt well located in the Santos Basin, Brazil. The identification of fracture zones allowed for the observation of a relationship between the occurrence of rock fractures and the silicification, as the latter plays an important role in determining porosity (higher silica content may increase brittleness of the rocks therefore increasing the likelihood of creating fractures zones and fractures may be filled up reducing the total porosity). To support the proposed observation, an inte-grated study was conducted using borehole imaging, spectroscopy logs, and sidewall core samples. The porosities were defined using nuclear magnetic resonance log analysis, alongside sidewall core samples, and thin sections. The integration of rock samples and well data with seismic analysis was performed to analyze the presence of a regional fault system that could explain high fracture densities as well as observed silica content characteristics. The results show how different types of cement filling up the formation pores affect fracture densities and total porosity. Furthermore, it was possible to infer that the amount of silica content observed in well logs and thin sections relates to hydrothermal fluids reaching out the reservoir through regional fault systems detected in the seismic section. Therefore, this paper supports the comprehension of how diagenetic processes can significantly affect the properties of pre-salt reservoirs. |
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Artigo em Revista
| Compartmentalization and stratigraphic-structural trapping in pre-salt carbonate reservoirs of the Santos Basin: A case study in the Iara complex The reservoir characterization of the Brazilian Santos Basinâs pre-salt carbonates is a major challenge due to the faciological and depositional complexity, providing high lateral and vertical heterogeneities, and consequently, the formation of static/dynamic intraformational seals. Regarding this context, there is a massive pre-salt accumulation known as the Iara Cluster. During the early development stage, this cluster was split into three distinct accumulations named BerbigĂŁo, Sururu, and Atapu. This study aims to characterize the geological and hydrodynamic factors that affect the Iara Cluster reservoir compartmentalization. To achieve this objective, we applied an integrated analysis based on 3D seismic interpretation, well logs, pressure formation and fluid geochemistry analysis. The spatial distribution of the reservoir rangeâs five main seismic patterns indicates potential stratigraphic-structural barrier zones. The well log analysis correlated with formation pressure data enabled the identification of several irregular oil-water contacts and free water levels. Small relative variations are associated with the perched-water phenomenon, while large variations are related to compartmentalization. The formation pressure analysis shows the hydraulic compartmentalization of the reservoirs in the Berbigao Ë Field. Sururu and Atapu fieldsâ oil zones are possibly connected by a dynamic sealing zone or a common aquifer, which provides a pressure balance on a geological time scale, since their oil gradients are similar. Our analyzes identified stratigraphic components in reservoir trapping associated with reservoir quality lateral obliteration. Dissimilarities in the oil sample composition and properties indicate different petroleum charge histories along with the distinct CO2 contamination timing. The Berbigao Ë oil-associated gas formed in earlier stages of maturation than the Sururu and Atapu samples. The results integration through a risk matrix revealed areas with a greater chance of compartmentalization and perched-water phenomenon. Our study highlights the importance of multidisciplinary analysis to comprehend complex carbonate reservoirs connectivity, and offers input to de-risk new venturesâ pre-salt reservoir quality. |
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Artigo em Revista
| Bibliometric analysis of surface water detection and mapping using remote sensing in South America The detection and mapping of surface water resources for South America (DMSWSA) in Remote sensing context is a highly relevant issue from a scientific point of view due to the impact on the understanding of changes in the hydrological cycle, water availability, and climate in global terms since 45% of all water resources available on the globe are present on this continent. This study presents a new approach to evaluating the scientific literature of the last 21 years focused on DMSWSA in a Remote sensing scientific literature. Our study aims to carry out a bibliometric analysis on the application of the DMSWSA in a Remote sensing dominium to assess researchers, countries, and trends. We used the Scopus database for the literature search. Then we used bibliometric tools to access information and reveal quantification patterns of literature. Our results show that the most relevant contributions involved Brazil and Argentina. DMSWSA has only shown an expansion in recent years regarding the number of articles published and citations. It was possible to show that the DMSWSA in a Remote sensing scientific area needs further collaboration expansion between countries within South America and beyond this continental border. We reveal aspects of great importance and interest in the literature using bibliometric approaches to give a clear view of research trends for DMSWSA. |
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Artigo em Revista
| On the estimation of reflectivity in reverse time migration: Implementational forms of the inverse-scattering imaging condition The inverse-scattering imaging condition (ISIC) for reverse time migration (RTM) aims at recovering amplitudes proportional to seismic reflectivity. It has been derived as the high-frequency asymptotic inverse of Born modeling, which justifies its being called a true-amplitude imaging condition. It involves the temporal and spatial derivatives of the up- and downgoing wavefields, in this way generalizing the conventional crosscorrelation imaging condition. The temporal derivations can be redistributed between different wavefield contributions, in this way deriving a set of different implementational forms of the ISIC. By making use of the wave equation for the up- and downgoing wavefields, one can substitute the time derivatives by the Laplacian operator. This provides a theoretical foundation for a popular filter for reducing the backscattering artifacts in RTM. Using Born data from a simple three-layer model and the Marmousi II model as well as the Sigsbee2b data, we have determined that the theoretical equivalence of the equations leads to similar but not identical images. Our numerical tests indicate that the ISIC versions using spatial derivatives are the most economical approach, and that the images obtained with the second time derivative of the source wavefield indicate slightly improved resolution over the other implementations, making the combination of these two characteristics the best choice. |
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Artigo em Revista
| Controls of fracturing on porosity in pre-salt carbonate reservoirs This work aims to improve the understanding of how fracture zones affect carbonate reservoir properties based on observations of a pre-salt well located in the Santos Basin, Brazil. The identification of fracture zones allowed for the observation of a relationship between the occurrence of rock fractures and the silicification, as the latter plays an important role in determining porosity (higher silica content may increase brittleness of the rocks therefore increasing the likelihood of creating fractures zones and fractures may be filled up reducing the total porosity). To support the proposed observation, an inte-grated study was conducted using borehole imaging, spectroscopy logs, and sidewall core samples. The porosities were defined using nuclear magnetic resonance log analysis, alongside sidewall core samples, and thin sections. The integration of rock samples and well data with seismic analysis was performed to analyze the presence of a regional fault system that could explain high fracture densities as well as observed silica content characteristics. The results show how different types of cement filling up the formation pores affect fracture densities and total porosity. Furthermore, it was possible to infer that the amount of silica content observed in well logs and thin sections relates to hydrothermal fluids reaching out the reservoir through regional fault systems detected in the seismic section. Therefore, this paper supports the comprehension of how diagenetic processes can significantly affect the properties of pre-salt reservoirs. |
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Material Didático
| MANUAL DE MODELAGEM DE DADOS DE GPR NO DOMĂNIO DO TEMPO (GPRMAX) APLICANDO EFEITOS DA DISPERSĂO ATRAVĂS DE UMA ABORDAGEM LINEAR PARA SIMULAR UM MODELO DE Q CONSTANTE USANDO VĂRIOS POLOS DEBYE. |
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Artigo em Revista
| Viscoelastic and viscoacoustic modelling using the Lie product formula We present efficient and accurate modelling of seismic wavefields in anelastic media.We use a first-order viscoelastic wave equation based on the generalized Robertssonâsformulation. In our work, viscoacoustic and viscoelastic wave equations use the stan-dard linear solid mechanism. To numerically solve the first-order wave equation, weemployed a scheme derived from the Lie product formula, where the time evolutionoperator of the analytic solution is written as a product of exponential matrices, andeach exponential matrix term is approximated by the Taylor series expansion. Theaccuracy of the proposed scheme is evaluated by comparison with the analytical so-lution for a homogeneous medium. We also present simulations of some geologicalmodels with different structural complexities, whose results confirm the accuracy ofthe proposed scheme and illustrate the attenuation effect on the seismic energy duringits propagation in the medium. Our results demonstrate that the numerical schemeemployed can be used to extrapolate wavefields stably for even larger time steps thanthose usually used by traditional finite-difference schemes. |
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Artigo em Revista
| Multiparameter vector-acoustic least-squares reverse time migration The use of dual-sensor acquisitions enabled different studies using the so-calledvector-acoustic equations, which admit particle velocity (displacement or accel-eration) information instead of solely the pressure wavefield. With cost far fromelastic formulations but comparable with the usually used second-order acousticequation, previous works involving the use of vector-acoustic equations along withmulticomponent data have been applied to conventional reverse time migration andfull-waveform inversion, always emphasizing the benefits of using wavefields con-taining directivity information, which make the receiver ghosts interact constructivelywith the backpropagated reflected wavefield. Thus, generated results are superior tothose of conventional single-component data imaging techniques, particularly withspatial subsampling of marine seismic data. To assess whether the effects of applyingthe vector-acoustic equations persist in a linearized inversion, we developed a multi-parameter vector-acoustic least-squares reverse time migration, inverting reflectivitiesassociated with velocity and density. To demonstrate the methodâs performance, weapply it to two-dimensional numerical examples and compare the results with thoseobtained by the conventional acoustic least-squares reverse time migration. Theresults obtained by the vector-acoustic least-squares reverse time migration methodare accurate for all inverted parameters and also deliver better convergence whencompared with the conventional least-squares reverse time migration. |
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