Produção Científica

**Apresentação**

Pore System Characterization of Carbonate Outcrops from Oman Using X-Ray Tomography Images and Permeability RelationshipCarbonates can exhibit a complex mineralogy and complicated pore system, and petrophysical properties of carbonate reservoir rocks can vary significantly because of the reactive nature of minerals during the diagenesis. In this way, carbonate outcrop rocks can be employed as analogous to reservoir modelling and understanding of the pore system properties as porosity and permeability. This study employs carbonate outcrop samples of limestone, dolomitic limestone, and dolostone from Sultanate of Oman, inserted in two distinct geological contexts at Huqf and Dhofar. X-ray micro-tomography images were correlated with mineralogical and petrophysical measurements to characterize the pore system properties of interest as porosity and permeability at different lithology. Mineralogy was affected by the dolomitization that may have caused changes in texture and pore system. However, density analysis showed that the dolomite occurrence cannot be considered as an isolated parameter for permeability evaluation. The computed pore size diameter, pore throat diameter, and medium pore chord were applied for pore system characterization and have a direct relationship with permeability, expressing best permeability for simple texture structure samples. PoA and DOMsize results allowed a good analysis of the pore complexities and effects on permeability, suggesting a great potential for rock evaluation. |

**Apresentação**

Evaluation of an Alternative Formulation for Computing Seismic Properties of Hydrocarbon FluidsIn the early 90â€™s, Batzle and Wang (1992) proposed an important formulation for the calculation of seismic properties of pore fluids, which has been extensively used by the Geoscience community. Meanwhile, the Engineering community has developed different formulations, rendering special attention to the equations proposed by Dranchuk and Abou-Kassem (1975). We analyze and compile a set of equations mainly based on Dranchuk and Abou-Kassem (1975) with variations as prescribed by Sutton and Hamman (2009) for modeling seismic properties of natural gas fluids, therefore referred as DASH formulation. We also evaluate this alternative formulation, testing it on data collected from literature. In total, 949 data points are used as reference data to evaluate DASH formulation, using Batzle and Wang (1992) equations, referred as BW formulation, for comparison. The results show that the alternative formulation outperforms the traditional Batzle and Wang formulation (BW), yielding superior data fitting and error reduction. |

**Apresentação**

Time-migration Tomography based on Reflection Slopes in Pre-stack Time-migrated Seismic DataThe accuracy of migration velocity estimation is critical for seismic imaging. Historically, ray-theory based approaches to migration-velocity estimation have been widely used in the industry. However, these approaches may be quite time consuming for a variety of reasons, e.g., event picking, extensive computation of ray-tracing results, total iteration turn-around time, etc. We present an efficient approach to estimation of a velocity model for time migration. As input, we use reflection slopes belonging to a pre-stack time-migrated seismic data set, which has been migrated using a preliminary (initial) velocity model. The slopes are derived using the gradient structure tensor method. We apply a fast migration velocity estimation loop, which combines kinematic de-migration, kinematic migration and linearized inversion for the parameters of the migration velocity model. The iteration scheme is based on minimizing the offset slope in the time-migration domain. The approach can be generalized for use in the depth domain, if supplemented by appropriate time-to-depth mapping techniques. |

**Apresentação**

A cycle-skipping analysis in transformed domains for full waveform inversion using particle swarm optimization (PSO)Full waveform inversion (FWI) is a state-of-the-art method used to estimate subsurface parameters, such as the seismic velocity. FWI is an iterative method that requires an adequate starting velocity (SV) model as input, to converge to the correct solution. A SV model is considered adequate for the FWI when its low frequencies are correctly estimated or cycle-skipping events are not present. Currently, some strategies have been used to build SV models such as analytical methods, reflection tomography, and global optimization methods. In this work, we focus on the use of particle swarm optimization (PSO), which estimates a SV model by minimizing the number of cycle-skipping events can be measured in three different domains: time, frequency and complex trace domain. The computational cost of the proposed PSO method for SV estimation is reduced through the use of graphical processor units (GPUs). We show that, among the analyzed metrics and domains, the least square error metric of the cycle-skipping in the complex trace domain outperforms the others domains in the estimation of adequate SVMs. |

**Apresentação**

Decomposition and adaptive filtering using binomial filter bank for ground-roll attenuationThe ground-roll is a type of noise associated with land seismic data. It strongly harms the signal-to-noise ratio, and interferes in various stages of the seismic data processing, affecting the final quality of the obtained seismic images. In this paper we propose a method of adaptive filters using binomial filters built from the convolution of pairs of dipoles (1,c) e (c, âˆ’1) for the attenuation of the ground-roll, where c is the first coefficient prediction error calculated by Burg algorithm. It allows for the decomposition of signals in frequency bands from the lowest to the highest adapting to frequency content of the data. Its implementation and use in the processing of seismic data is relatively simple and computationally efficient. |

**Artigo em Revista**

Seismic processing applied to shale-gas reservoir characterization in Reconcavo basinThis paper is intended to present all the steps used in the seismic processing to characterize and interpret the 2D seismic line 0026-RL-1624, located between Dom JoÃ£o and Candeias fields, from the perspective of nonconventional reservoirs. It includes a new SVD (Singular Value Decomposition) method used to attenuate the ground-roll and direct wave, which had a very dispersive form in the shot domain, causing several problems in the visualization of reflections and, consequently, in the raw stacked data as well. It was later applied seismic attributes in order to have a better precision in mapping geological structures of interest and also interpret the main horizons present in the log well data. During the development of this work, the processing step were entirely performed by both Seismic Unix and SeisSpace/Promax, software developed by Landmark/Halliburton. |

**Apresentação**

Empirical Mode Decomposition and Spectral Balance to attenuate the Ground rollThis paper presents techniques to reduce this noise, based on the empirical modes decomposition and spectral balancing. The breakdown in empirical ways is to decompose the seismic trace in Intrinsic Mode Functions, which are symmetric functions with local mean zero and the same number of zeros and extreme. But the spectral balancing propose the equalization of data of the frequency bands which generates balanced trace by adding the trace decomposed into each frequency band. Therefore, the attenuation of the ground roll increases, consequently the signal to noise ratio of the line. The numerical results obtained from the seismic line Takutu Basin illustrate the performance of the proposed methodology. When considering the results, we have the guarantee of the value of the proposed method, which increases the signal/noise given since attenuates effectively the ground roll. |

**Apresentação**

An efficient fully spectral method for constant-Q seismic-wave propagationWe present a new modeling approach for wave propagation in anelastic media, based on a fractional spatial differential operator. The problem is solved with the Fourier pseudo-spectral method in the spatial domain and the REM (rapid expansion method) in the time domain, which, unlike the finite-difference scheme, does not require an intermediate storage of the solution and is more accurate. To show the accuracy of the scheme, an analytical solution in a homogeneous anelastic medium is computed and compared with the numerical solution. We present an example of propagation at a reservoir scale and show the efficiency of the algorithm against the conventional finite-difference scheme. The new method, being spectral in time and space simultaneously, offers a highly accurate and efficient solution for wave propagation in attenuating media. |

**Apresentação**

Subsalt structure prediction based on the fast 3d salt tectogenesis modelingThere are presented some results of testing a computational program developed for prediction of the geological structures and the stress-strain state in exploration and characterization of the hydrocarbon deposits in the areas of salt tectonics. |

**Apresentação**

An Improved Method to Calculate the Analytical Wavefield for Causal Imaging ConditionIn this work the analytical wavefield is computed by just solving the wave equation once, differently of conventional methods that need to solve the wave equation twice: once for the source and another for the Hilbert transformed source. Our proposed method can improve the computation of wavefield separation and can bring the causal imaging condition into practice. For time extrapolation, we are using the rapid expansion method to compute the wavefield and its first order time derivative and then compute the analytical wavefield. This method is unconditionally stable and free of numerical noise. By computing the analytical wavefield, we can, therefore, separate the wavefield into down- and up-going components for each time step in an explicit way. For reverse time migration (RTM) applications, we can now employ the causal imaging condition and through a synthetic example, we could demonstrate the effectiveness of this new imaging condition. Moreover, our method has shown to be efficient in term of computation time in comparison with the conventional RTM method using the cross-correlation imaging condition. The RTM result also shows that it can successfully remove the low-frequency noise which is common in the typical cross-correlation imaging condition. |

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