Produção Científica
Apresentação
| Iterative SSA method to filtering of the land seismic data Normally the singular value decomposition (SVD) filtering is applied in the time × distance domain, exploring the spatial correlation between a set of seismic traces. In the present work we explore the Singular Spectrum Analysis (SSA) method in the time direction using a iterative algorithm. The SSA method extract the correlation between reflected events along the time variable and decompose seismic traces in the low (first eigenimage only) and high frequency parts (sum the rest of the eigenimages). We illustrate the effectiveness of this new approach to the prediction and subtraction of the ground roll and improve velocity analisys and stacking of the seismic data. |
Apresentação
| Stabilized unidimensional deconvolution-based imaging conditions in Marchenko imaging Multiple reflections are typically not accounted for in seismic migration processes, which can lead to the emergence of artifacts. In Marchenko imaging, we retrieve the complete up- and downgoing wavefields in the subsurface to construct an image without such artifacts. The quality of this image depends on the type of imaging condition that is applied. In this work, we introduce an imaging condition that is based on stabilized unidimensional deconvolution (SUD). Two specific approaches are considered. In the first approach, we use the full up- and downgoing wavefields for deconvolution. Although this leads to balanced and relatively accurate amplitudes, the crosstalk is not completely removed. The second one is to incorporate the initial focusing function in the deconvolution process, in such a way that the retrieval of crosstalk is avoided. We compare images with the results of the classical cross-correlation imaging condition, which we apply to reverse-time migrated wavefields and to the up- and downgoing wavefields that are retrieved by the Marchenko method. |
Apresentação
| Conventional seismic processing flow analysis: 2D line of the Rio Grande Chain region Southeastern Brazil Seismic reflection is one of the most important tools for the oil and gas industry, both in the exploratory and in the production phase. It is divided into three components: acquisition, processing and interpretation. This work is inserted in the context of seismic data processing. For this, the processing of a real 2-D line acquired in 1979, located in the region of the Rio Grande Chain, southeast of Brazil, was made using the software ProMAX/SeisSpace. In order to generate a representative image of the geological framework of the area, a conventional processing flow that includes two different procedures was applied: procedure 1 and procedure 2, which are respectively related to the application of post and pre-stack migrations. The steps of the processing flow were submitted to different parameterizations, and the inputs and outputs were compared aiming to evaluate how they work to improve the seismic data. Based on the processing flow used, the best result obtained for the final seismic section was the one corresponding to the Kirchhoff pre-stack time migration, due to its better seismic aspect. |
Apresentação
| Estimation of P-wave dispersion and attenuation under pore-texture complexities in carbonates Biot's theory of poroelasticity provides a theoretical basis for phenomena understanding of low-frequency seismic P-wave dispersion and attenuation due to the wave-induced fluid flow. An important mechanism to explain the P-wave attenuation in saturated porous media is the fluid flow induced by the wave on the mesoscopic scale, i.e., a scale larger than the pore size and smaller than the wavelength. Carbonates exhibit complex pore structure and texture that hinder the understanding about P-wave dispersion and attenuation at dry and fluid-saturated conditions. Therefore, this work treats the influence of petrophysical, depositional texture and geometrical parameters in P-wave dispersion and attenuation in clean limestones. Data set is composed by 6 samples of oolitic and cemented grainstones – Albian age from Campos basin, Brazil, with textural characterization and laboratory measurements that allowed us applied Gassmann’s and Geertsma and Smith (1961) approaches to estimate P-wave dispersion, Dvorkin and Mavko (2006) model to predict the P-wave attenuation based on characteristic frequency determination at mesoscopic scale by interlayer flow White et al. (1975) model. |
Apresentação
| Mercury intrusion porosimetry and 2D DIA applied to the estimation of pore-structure parameters and permeability Reservoir characterization requires an understanding of rock’s textural and mineralogical characteristics as well as geometric properties of the porous space. Pore geometry also control key petrophysical properties that determine reservoir quality of reservoir with respect to the productibility. In this study were quantified pore structure parameters and their influence on absolute permeability in a set of carbonate samples, using the integration of Mercury Intrusion Porosimetry (MIP) and 2D Digital Image Analysis (DIA) Methods. The man aim was to verify the interdependence between geometric properties and porosity to estimate the absolute permeability, using a multiple linear regression methodology (MLR). |
Apresentação
| Effects of the dip angle in the induction anisotropy logs This paper performs an analysis of the effects of the well’s deviated angle on the tensor triaxial induction tool signals within a thinly sand-shale laminated reservoirs and their equivalent intrinsic anisotropic models. The responses from coaxial and coplanar coil arrays in inclined wells are studied in detail, including the analysis of their apparent anisotropy logs, as well as their estimation of sand conductivity in the environments with a structural anisotropy.The dip angle effects are modeled in simple geometries as one-dimensional (1D) models, neglecting the presence of the borehole and the invasion zones, since they provide basic insight for understanding tool responses in more complex models. The results show a strong sensitivity of both the coaxial and coplanar signals to the deviated angle. It is verified that the anisotropy values are significantly reduced when the well is inclined as compared to what is found for the true vertical case, even for inclinations small enough for the wells to be classified as technically vertical (30 degrees or less). Therefore, the angle effects must be carefully considered, even for technically vertical wells. Otherwise, potential finely laminated reservoirs can be underestimated or even ignored. |
Apresentação
| Pore System Characterization of Carbonate Outcrops from Oman Using X-Ray Tomography Images and Permeability Relationship Carbonates 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 Fluids In the early 90’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 Data The 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. |
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