Produção Científica
Apresentação
| Reverse time migration as the transpose of forward operator by rapid expansion method (REM) This paper presents a reverse time migration (RTM) method formulated as the transpose of the forward operator. For modeling, the wave equation solution is expressed by the rapid expansion method (REM). The REM is a wave equation solution method that is based on the Chebyshev expansion and can be used to stably extrapolate wavefields even for larger time steps. The forward operator is commonly reused in RTM for back-propagation and achieves satisfactory results, but, in order to correctly apply the reverse time migration, it requires the adjoint wave-equation solution. Here, we show that the adjoint operator using the REM as the forward modeling operator can be obtained by transposing the forward operator. The new adjoint operator based on the REM is easily implemented with little changes in the existing RTM code. During the imaging condition procedure, we choose the causal imaging condition which is employed to avoid low-frequency noise and false events produced by the conventional cross-correlation imaging condition. A numerical example is used to compare the results produced by the traditional RTM and the proposed reverse adjoint time method and also to show the benefits of the adjoint method versus the conventional RTM. |
Apresentação
| Linking permeability and elastic properties in carbonate rocks Permeability is the ability of a rock to allow the movement of fluids through its pore system. It is one the most important petrophysical properties of a reservoir and is tightly linked to production estimates and reservoir management. Nevertheless, it is one of the most difficult parameters to be described in a reservoir study, as it cannot be measured directly by geophysical methods. The use of permeability variation maps along the reservoir can aid to identify flow barriers, guide the location of wells and optimize production. This work studied the relationship between the absolute permeability, porosity and elastic properties of dry and brine-saturated carbonate rocks. The main goal was to derive a relationship between these properties that best estimates the absolute permeability using a multiple linear regression methodology. |
Apresentação
| Seismostratigraphic interpretation and reservoir mapping using inverse Q filtering and impedance inversion: A Campos Basin — Brazil example, Pampo field A comprehensive analysis of the stratigraphic record and a reliable construction of geological conceptual model are key steps towards understanding reservoir genesis, leading to a guided mapping of reservoir distribution and characterization. In this work we develop an interpretation workflow based on inverse Q filtering and impedance inversion, respectively to improve seismic vertical resolution and to represent the seismic expression of geological features. By improving resolution of seismic data, we obtain clearer images of the reflector terminations and stratal relations. These features in connection to latest software technology allow for detailed seismoestratigraphic analysis. At the reservoir level, impedance inversion gives relative impedance, a basic volumetric attribute that can be used to generate multiple attributes, representing different views of geological bodies. This provides ideal information for the construction of the conceptual model for the reservoir. We present an application of our workflow to the seismic data interpretation of Pampo field in the Campos Basin, Brazil, highlighting the main points leading to improved interpretation results. |
Apresentação
| Automatic first-breaks picking using linear moveout correction and complex seismic traces A correção estática corresponde a um deslocamento em tempo, aplicado ao traço sísmico, para eliminar a variação no tempo das reflexões causada pela variação da topografia e da camada de intemperismo. Essa correção depende da determinação precisa dos tempos das primeiras quebras, processo este denominado de picking. De um modo geral, a primeira quebra está relacionada com as condições próximas a superfície, como o tipo de fonte e a relação sinal/ruído. Tradicionalmente, a determinação do sinal que corresponde à primeira quebra foi realizada através de uma inspeção visual das amplitudes, e os picking feitos manualmente. Além de ser muito demorada, essa estratégia pode levar a escolhas tendenciosas e inconsistentes, pois, depende da subjetividade de cada profissional. Com o desenvolvimento de computadores modernos, foram criados softwares de picking automáticos, ainda assim, todo o procedimento ainda é muito demorado e subjetivo. Nesse contexto, é proposto um método de picking capaz de determinar, de forma automática e confiável as primeiras quebras do sismograma de reflexão para cálculo das correções estáticas. Os resultados obtidos, sobre dados sintéticos e reais, mostram que o método proposto é robusto, computacionalmente eficiente e fácil de aplicar. |
Apresentação
| Obtaining interval velocities using an adaptive hybrid inversion multiscale approach The understanding of the interior of the planet through the seismic method requires the mapping of the velocities with which the elastic waves propagate. The main objective of this work is the development of improved techniques to obtain interval velocities in time, by inversion of RMS velocities. In this article, the data inversion is performed with a combination of local and global optimization methods. In order to reduce the problems related to the large number of inversion parameters, a multiscale approach will be presented in the parameter domain. The proposed method is tested in subdetermined problems and with addition of noise. The results shown in the M3 model simulate how this methodology it can be applied applied to real data, which raises the relevance of this research. |
Apresentação
| Influence of Topography and Low Velocity Layer on Seismic Image This work analyzes the effects of static field corrections and residual correction, and when this can be neglected, by comparing the results of modeling and processing of synthetic seismic data. Both direct modeling and processing were done using ProMAX/SeisSpace software. During processing, the following steps were applied: geometry, editing, static corrections, velocity analysis, stacking and residual static corrections. In the modeling phase, models were created in different situations to analyze the influence of static corrections, a very important step for the processing of land seismic data. The results show how impaired the seismic section is in terms of different degrees of variation of the topography and the thickness of the weathered layer. |
Apresentação
| Full-waveform inversion using alternative objective functions in the presence of noise and uncertainties of source signature Full-waveform inversion (FWI) is a method able to estimate model parameters in subsurface from seismic data. The algorithm consists on the minimization of an objective function that relates observed seismic data and synthetic data for the estimated model. Thus, the successful application of FWI depends on the accurate correspondence between modeled and field data. Some problems that appear in the application of FWI to field data are dealt by using alternative functionals for objective function. The results, obtained by using synthetic data, show that the definition based on the least absolute value norm and the cross-correlation error measure have advantages over least squares norm, turning the method more robust when facing noisy data and uncertainties in source signature used for inversion. The quasi-Newton formulation of L-BFGS method is applied to non-quadratic objective functions without affecting, in practice, the convergence of inversion scheme. |
Apresentação
| Otimização automática do custo de processamento de programas SPITS na AWS Plataformas de serviço de computação em nuvem oferecem uma ampla variedade de recursos computacionais que possuem características de desempenho com custos diferenciados. Neste trabalho, investigamos como as instancias Spot e as zonas de disponibilidade da Amazon Web Services (AWS) podem ser utilizadas para a redução do custo de processamento. Em adição propomos um algoritmo de gerenciamento automático de instâncias na AWS para otimizar custo na execução de programas implementados sobre o modelo de programação Scalable Partially Idempotent Task System (SPITS). Os resultados obtidos indicam que o método proposto é capaz de identificar para ajustar dinamicamente os tipos de máquinas virtuais que oferecem o melhor custo-benefício. |
Apresentação
| Denoising of the groundroll using Wavelets Thresholding In this work the method is based on the spectral decomposition of the seismic data using Wavelet Transforms (WT) to attenuate the groundroll. The WT is used to represent a signal at different resolutions and various time and frequency contents. The filtering method separates the signal by frequency range and the band of coefficients related to the noise, then signal-to-noise ratio of the seismic data is improved by attenuating the groundroll. The signal filtering is done by estimating a cutoff, threshold (l), for signal amplitudes which are related to noise. The determination of l takes into account the standard deviation and the size of the signal sample. In order to test the efficiency of the method in question, the land seismic line (RL5090) of the Tacutu basin was processed and good results were obtained. |
Apresentação
| Inversão cinemática em meios TI usando uma nova aproximação do tempo de reflexão One of the challenges of traveltime inversion in anisotropic media is the fact that the equations are nonlinear. We present a simple approach to estimate the model parameters in a medium with TI - transverse isotropy. The proposed approach uses the Levenberg-Marquardt (LM) inversion method and shows a better performance in the inversion and in the nmo correction of the seismic section. It was observed that the precision in the estimation of the anisotropy parameter with the proposed approximation depends not only on the correct extraction of the transit times of the data, but also on the value of () and the layer inclination angle of inclination. |
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