Produção Científica



Apresentação
07/11/2019

On the problem of low-frequency static correction
This paper considers factor models used in the static and waveform correction. Such models lead to a system of linear equations, which allows us to perform a detailed analysis of the obtained solutions. In particular, it is possible to understand the low-frequency static correction problem and its connection with the structure of the system of seismic observations. At the same time, it is shown how this problem can be solved at the algorithmic level to optimize the use of a priori information. The latter is particularly important for the analysis of dynamic problems. In the study of linear systems two approaches are realized: an iterative process to estimate the parameters (factors) of the model, as well as analysis of heuristic conditions to guarantee uniqueness and stability of their determination.
Apresentação
07/11/2019

Basin Modeling: Pressure Prediction for the Marine Jequitinhonha
This paper aims at the composition of a seismicstratigraphical framework for part of Jequitinhonha basin (marine east part of the State of Bahia), for pressure prediction in gas and oil exploration in sedimentary basins. The knowledge of the velocity distributions can be based on seismic sections, petrophysical information and empirical model, and it is based on the knowledge of the compressional (vp) and shear (vs) velocities, and densities (ŌĀ). We presented details of the theoretical model, and an example to show how the pressure varies in the subsurface, where we highlight that pressure prediction does not necessarily increase linearly, but in a complex way that requires specific numerical formulas to be able to see important details. The model poses the vertical gravity load as pressure agent on the geological formations, and does not take into account the effects of curvatures, faulting and diagenesis, and lateral tectonic events. An accurate prediction needs a 3D model for a significantly complete practical application.
Apresentação
07/11/2019

Using a new approach of construction synthetic orthorhombic media: Application on the estimative of Thomsen's parameters
The goal of this work is to make artificial anisotropic synthetic samples with orthorhombic symmetry with different crack densities and relate these densities with Thomsen's parameters. For this purpose, we made four core samples with bedding planes and different number of parallel cracks. The first sample was made without fratcures and the others with 3, 4, and 6 fartcures, respectively. Based on the pulse transmission technique that propagates P- and S-waves through each sample to determine the waves' traveltimes and calculate their velocity in each direction for each sample. Those velocities were used to calculate Thomsen's parameters for orthorhombic media based on Tsvankin's notation.
Apresentação
07/11/2019

Verificação experimental do modelo efetivo de Hudson/Liu para meios fortemente fraturados
The knowledge about properties of subsurface, including cracking characteristics, are extremely important in the context of seismic exploration of anisotropic reservoir. One way of studying the waves behavior for different geological contexts is through the use of effective medium theories. A large number of effective theories have been proposed to study the influence of the geological medium by seismic wave investigation. These models, however, need a calibration in order to define their limitations. This process can be performed through physical modelling. This present work was done an attempt to calibrate a theoretical model (heavily fractured model from Hudson/Liu) simulating a medium containing crack planes. For this to be done, eight physical synthetic fractured sandstones were built. The anisotropic Thomsen parameter ő≥ were estimated through ultrasonic procedure. The results show that the theoretical model for low crack density has a good fit with experimental values of S-wave velocities as well as ő≥ parameter for crack densities up to 8%.
Apresentação
07/11/2019

A new and efficient way to construct synthetic porous fractured or heterogeneous medium
Fractures occur in the earth under wide range of scales and in different depths. Understand them from wave propagations, is a hard task, which has consumed plenty of research time both in the oil industry and academy. Many authors have been investigating the behaviour of seismic waves in fractured media through the use of physical modelling, which several methods for synthetic sample preparation has been used. We have developed a new, efficient and feasible methodology of fractured sample construction, based on: cement, sand, especial material (cuts holder) and solvent. The cuts holder (material A) (square piece or pennyshape) are leached out by using solvent B. The empty space created by this leaching can represent fractures or cracks in a porous background. The sample petrophysical parameters are controlled by pressure, temperature and clay content, or in this work by the cement content. To verify the feasibility of our methodology, P- and S-wave ultrasonic velocities and Thomsen anisotropy parameters (őĶ and ő≥) were estimated in four dry fractured samples and in a reference sample. Purposely, our reference sample has a background anisotropy induced by layer-by-layer material deposition. The results show a coherent behaviour of anisotropy parameter as function of number of dry fractures. This new methodology highlights the possibility of using less expensive materials and in a short time to construct anisotropic media made by fractured or cracked regions.
Apresentação
07/11/2019

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
07/11/2019

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
07/11/2019

Seismostratigraphic interpretation and reservoir mapping using inverse Q filtering and impedance inversion: A Campos Basin ‚ÄĒ 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
07/11/2019

Automatic first-breaks picking using linear moveout correction and complex seismic traces
A corre√ß√£o est√°tica corresponde a um deslocamento em tempo, aplicado ao tra√ßo s√≠smico, para eliminar a varia√ß√£o no tempo das reflex√Ķes causada pela varia√ß√£o da topografia e da camada de intemperismo. Essa corre√ß√£o depende da determina√ß√£o precisa dos tempos das primeiras quebras, processo este denominado de picking. De um modo geral, a primeira quebra est√° relacionada com as condi√ß√Ķes pr√≥ximas a superf√≠cie, como o tipo de fonte e a rela√ß√£o sinal/ru√≠do. Tradicionalmente, a determina√ß√£o do sinal que corresponde √† primeira quebra foi realizada atrav√©s de uma inspe√ß√£o visual das amplitudes, e os picking feitos manualmente. Al√©m de ser muito demorada, essa estrat√©gia 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 autom√°ticos, ainda assim, todo o procedimento ainda √© muito demorado e subjetivo. Nesse contexto, √© proposto um m√©todo de picking capaz de determinar, de forma autom√°tica e confi√°vel as primeiras quebras do sismograma de reflex√£o para c√°lculo das corre√ß√Ķes est√°ticas. Os resultados obtidos, sobre dados sint√©ticos e reais, mostram que o m√©todo proposto √© robusto, computacionalmente eficiente e f√°cil de aplicar.

Apresentação
07/11/2019

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.
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