Produção Científica
Artigo em Revista
| Potencial de exploração de não-convencionais - Bahia. A Bahia, com seu pioneirismo e história de sucesso na produção comercial de petróleo na Bacia do Recôncavo, possui significativo potencial exploratório. Embora as atividades de exploração e produção estejam em declÃnio, devido ao baixo fator de recuperação de poços em campos produtores e ao desinvestimento da Petrobras na exploração em áreas terrestre, desperta interesse o potencial de gás associado aos folhelhos da Formação Candeias, que são rochas geradora+reservatório de gás, pois possuem valores elevados de carbono orgânico total e maturação térmica adequada. A localização privilegiada da Bacia do Recôncavo, em relação aos centros consumidores, aumenta a importância dos reservatórios de baixa permeabilidade no cenário de E&P do estado. Neste capÃtulo, será apresentado o contexto geológico das áreas terrestres potenciais para exploração em reservatórios não convencionais, com maior ênfase na Bacia do Recôncavo. Será dado destaque, ainda, à importância e ao potencial dos dados geofÃsicos disponÃveis no BDEP/ ANP20, à s contribuições da UFBA na formação de recursos humanos para a E&P e à importância do reprocessamento de dados sÃsmicos e da interpretação sismoestratigráfica na investigação do potencial de shale gas do Estado da Bahia. |
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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 have adopted 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 calculation of 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. Synthetic and field data examples illustrate the method’s effectiveness for denoising and interpolating 4D and 5D seismic data with randomly missing traces. |
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Artigo em Revista
| Time evolution of the first-order linear acoustic/elastic wave equation using Lie product formula and Taylor expansion We propose a new numerical solution to the first-order linear acoustic/elastic wave equation. This numerical solution is based on the analytic solution of the linear acoustic/elastic wave equation and uses the Lie product formula, where the time evolution operator of the analytic solution is written as a product of exponential matrices where each exponential matrix term is then approximated by Taylor series expansion. Initially, we check the proposed approach numerically and then demonstrate that it is more accurate to apply a Taylor expansion for the exponential function identity rather than the exponential function itself. The numerical solution formulated employs a recursive procedure and also incorporates the split perfectly matched layer boundary condition. Thus, our scheme can be used to extrapolate wavefields in a stable manner with even larger time-steps than traditional finite-difference schemes. This new numerical solution is examined through the comparison of the solution of full acoustic wave equation using the Chebyshev expansion approach for the matrix exponential term. Moreover, to demonstrate the efficiency and applicability of our proposed solution, seismic modelling results of three geological models are presented and the processing time for each model is compared with the computing time taking by the Chebyshev expansion method. We also present the result of seismic modelling using the scheme based in Lie product formula and Taylor series expansion for the firstorder linear elastic wave equation in vertical transversely isotropic and tilted transversely isotropic media as well. Finally, a post-stack migration results are also shown using the proposed method. |
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Artigo em Revista
| Potencial gerador e maturidade térmica dos folhelhos da Formação Barreirinha, borda sul da Bacia do Amazonas, Brasil Este trabalho tem como objetivo avaliar o potencial gerador e o efeito da intrusiva Ãgnea básica na maturidade térmica das amostras com base no estudo de geoquÃmica orgânica e palinologia. Foram estudadas 15 amostras de rocha coletadas em um afloramento da Formação Barreirinha, borda sul da Bacia do Amazonas. Nesse afloramento foi observada uma soleira de basalto que pode ter influenciado os dados geoquÃmicos das amostras localizadas no topo do perfil. Os teores de Carbono orgânico total (COT; 0,04–2,06%) e os resultados da pirólise Rock-Eval indicam a presença de querogênio predominantemente dos tipos II e III, potencial gerador de hidrocarbonetos (S2; 0,04–3,00 mg HC/g rocha) variando de pobre a médio, baixa concentração de hidrocarbonetos livres (S1; 0,01–0,25 mg HC/g rocha) e uma variação na maturidade termal (Tmáx: 359–605°C). A razão aquático-terrestre (RAT; 0,08–1,16) indica a predominância de deposição de matéria orgânica algálica, e as razões dos biomarcadores saturados [Hopanos/esteranos; gamacerano/(gamacerano + C30 hopano); TTP/(TTP + DIA); e esteranos C27-C28-C29] indicam um paleoambiente marinho com contribuição variável de componentes terrestres, devido as oscilações do nÃvel do mar ocorridas durante o Devoniano Superior. A razão entre os isoprenóides Pristano e Fitano (P/F: 1,6–7,1) apontam ambiente sub-óxico. Os resultados da cromatografia gasosa e das razões de biomarcadores saturados dos extratos orgânicos [Ts/(Ts + Tm); C29 αββ/(αββ + ααα); C29 S/(C29 S + C29R)] indicam a variação na maturidade térmica ao longo do afloramento, e sugerem a geração e migração de óleo e gás, e/ou a degradação termal de alguns biomarcadores saturados. |
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Artigo em Revista
| Some problems related to nonlinear 3Dmagnetoelasticity We consider some direct and inverse problems associated with the vibration of an elastic conductive body governed by the Lamé and Maxwell equations coupled through the nonlinear magnetoelastic effect. First, we prove the existence and uniqueness result for a mixed initial-boundary value problem. Uniqueness is proved under additional assumptions on the smoothness of the solution. Second, we prove the solvability of an inverse problem, which consists of identifying the unknown scalar function α(t) in the elastic force α(t)β(x, t) acting on the body when some additional measurement is available. |
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Artigo em Revista
| AN ANALYTICAL SOLUTION OF THE SATURATED AND INCOMPRESSIBLE POROELASTIC MODEL FOR TRANSIENT WAVE PROPAGATION A transient wave propagation model is provided as a consequence of a new theory of porous media and wave propagation in saturated poroelastic media. This theory, in the linear case, becomes to be equivalent to the theory proposed by de Boer, R., Ehlers, W. & Liu, Z. in 1993. It leads to a model for the 1-D porous saturated column problem, which after the appropriate establishment of boundary and initial conditions, can be solved analytically with the aid of the Laplace transform concerning time. Numerical experiments are performed to illustrate the behavior of constituents displacement fields. The theory results in having an inertial effect on the motion of solid constituents as commonly expected. However, in contrast to Biot’s theory, is not introduced by the present theory the relative acceleration as an interactive force between solid and fluid constituents to account for the apparent inertial effect. |
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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 pre-salt 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. |
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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 Ursin’s form in a plane-layered 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 algorithm’s reliability, identifying the main wave events in both low-frequency and high-frequency 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. |
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Artigo em Revista
| An application of the Marchenko internal multiple elimination scheme formulated as a least-squares 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 source-receiver 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 data-driven, can remove or attenuate most of these internal multiples, and was originally based on the Neumann series solution of Marchenko’s projected equations. However, the Neumann series approximate solution is conditioned to a convergence criterion. We reformulate the MME as a least-squares 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 in-depth 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. |
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Artigo em Revista
| 3D reverse time migration using a wavefield domain dynamic approach 3D Reverse-time 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 (RTM-DA) 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 (RTM-SA). 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 RTM-DA is more efficient than the RTM-SA in terms of memory consumption and computational time, preserving the quality of the seismic image. |
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