Produção Científica



Apresentação
07/11/2019

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.
Apresentação
07/11/2019

Poroelastic modeling in stratified media: Biot-JKD equations
We represent an exact mathematical procedure for the analysis of the elastic wave propagation in plane layered porous media taking into account the effect of high temporal frequencies. For the characterization of the effect we use the dynamic permeability expression proposed by Jonhson, Koplik and Dashen in 1987. The algorithm is based on a formalism introduced by Ursin in 1983.
Apresentação
07/11/2019

Microporosity analysis from petrographic thin-sections and elastic modulus estimative through DEM model in outcrop carbonate rocks
Carbonate reservoirs present a complex pore system characterized by their heterogeneity. It affects directly the rock's elastic properties. The external pressure's variation may cause pore volume reductions and affect the propagation velocity of elastics waves in sedimentary rocks. Thus, this paper aims to study the velocity variation of compressional and shear waves and the porosity in carbonate rock samples. By the data analysis from a number of samples, it intends to empirical models (Differential effective medium model – DEM) that relate variations in elastic velocity with changes in porosity.
Apresentação
07/11/2019

Synthesis and petrophysical characterization of an artificial mudstone analogous
Carbonate rocks are important for rock properties research because they are linked to significant oil and gas reserves around the world. The goal of synthesizing carbonate rocks in laboratory is to simulate the natural carbonate rock matrix regarding the main factors of lithification such as grain size and shape, concentration of cementing material and compaction pressure, and allowing the production of rock specimens that can be used for tests in extreme conditions in replacement of the high cost natural cores. The reproduction of rocks in laboratory also allows to access samples with predetermined characteristics enabling a better understanding of the relationship between their physical properties. In this work, samples of synthetic carbonate rocks were made by mixing a fixed amount of calcite and sand, and varying the amount of cement material (Portland cement and water). The behavior of the main petrophysical characteristics of these samples was investigated, such as porosity, permeability and P- and S-wave velocities versus the amount of cementing material. The results were compared with natural carbonate samples and showed a high similarity to the petrophysical behavior of natural mudstones rocks.
Apresentação
07/11/2019

Using the Benford's Law to analyze the sonic reflectivity
The caliper log can be sensitivity to borehole enlargement due drilling effect on different rock formations. The density of the lithology is affected by mud infiltration and the consequence is unrealistic values on the well-to-seismictie. In this work we use, in the first time, the statistical Benford's Law (BL) to analyze and check on the existence of errors or inconsistencies on the reflectivity log. The Benford's analysis is applied on the reflectivity series of two wells of the Viking Graben field. Effect of sonic and density logs despiking as well as the size of sample window to find the BL distribution were analyzed. The results on the real dataset analyzed shows that it is possible to find a optimum coefficient for the despiking process on the well logs according to the Benford's Law and that the segments of the reflectivity where the caliper log is stable the conformity with the Benford's Law is higher.
Apresentação
07/11/2019

Comparative Analysis of First Break Picking Methods in Noisy and Non-noisy P-wave Signal
The estimative of acoustic velocities is an important data that is extracted from data of exploration seismic, well logging (acoustic logging) and laboratory experiments. To realize this estimative a technique called first break picking is used, which consist in an analysis of time x Amplitude data to identify the wave arrival. The complexity of this analysis is in the fact of the data, generally is contaminated with noise and this one could be either inherent to the measuring equipment or other factors, that could make the simple visual analysis impossible. Considering this problem, the development of techniques which would be capable to identify the wave arrival automatic, accurate and faster, justify the study of advanced methods to accomplish this task.
Apresentação
07/11/2019

Differences between static and dynamic methods for pore compressibility in carbonates
The production of hydrocarbons from a reservoir occurs due to the variation of pore volume through a pressure differential. These variations are quantified by pore compressibility, an important parameter that interferes with the flow of fluids that saturate the porous medium, porosity and elastic properties of the rock. For many times pore compressibility was considered a constant, but the oil industry with the prospect and need to potentiate the reservoir's productive capacity has been attributed as an important factor in reserve calculations and decision-making related to well design in order to avoid unexpected interventions and loss of the reservoir by collapse. The compressibility of reservoir rock pores is determined through well profiles and seismic data, however for more accurate results, laboratory measurements are crucial. In this context, the objective of this work is to obtain pore compressibility through static and dynamic tests in samples of carbonates highlighting the influence of each method on the difference of the results. The static method was performed from uniaxial compression tests based on the technique of Unalmiser & Swalwell (1993). Dynamic tests were based on pore-elasticity theory through the propagation velocity of compression waves (P) and shear (S) and elastic constants of the rock when subjected to hydrostatic pressure variation. The correlation between the two methods is economically important for the industry as well as serving as the basis for the calibration process of the logging tools.
Apresentação
07/11/2019

Petrophysical-hysteresis analysis related to pore structure of sedimentary rocks
Reservoir rocks characterization consists of a critical stage on petroleum reserves evaluation, in which determining the relationships between petrophysical and mechanical rock properties is a required step to guarantee the accuracy of delivered data. Mechanical properties affect both drilling programs and hydrocarbon exploitation. Rock texture also plays a significant role on reservoir characterization, because porosity and permeability depend, mainly, on geometrical parameters, such as grain size, sorting, shape and diagenetic induced changes caused by cementation and dissolution. This work consists on an evaluation of the hysteretic characteristics of American outcrops samples when submitted pore system to induced loading and unloading, analyzing the influence of chemical composition, depositional texture, pore system structure and elastic mechanical properties on its hysteretic behavior. The hysteresis areas were mathematically estimated and petrophysical properties measured, as well as mineralogical composition. Elastic properties were estimated for the dry sample and also considering only the solid rock framework. Interesting correlations were observed among the analyzed properties and the expectation is that, in the future, hysteresis phenomena can be considered on reservoir deployment monitoring.
Apresentação
07/11/2019

Using SPITS to Optimize the Cost of High-Performance Geophysics Processing on the Cloud
Public cloud providers, such as the Microsoft Azure and the Amazon Web Services (AWS), offer a wide variety of virtual machines, with different specifications, and prices, that are enabling users to run high-performance programs without buying specialized and expensive hardware. Moreover, some providers, such as AWS, allow the user to bid for lower cost virtual machines, called Spot Instances. Nonetheless, these machines may be terminated within a few minutes of warning at the provider discretion. In this work, we leveraged the SPITS programming model to implement a high-performance and fault-tolerant seismic processing application that is proper for execution on Spot instances and analyzed how different virtual machines from the AWS may affect the performance and the price of the computation. Our experimental results indicate that Spot instances have similar performance to regular instances but are roughly three times less expensive. Finally, we show that AWS groups virtual machines in Availability Zones and that selecting virtual machines from different zones may also affect the total execution cost.
Apresentação
07/11/2019

Microporosity Aspect Ratio of Carbonate Rocks Under Pressure
Carbonate rocks usually present a complex porous system, especially regarding the differences in pore geometry. When those rocks are submitted to external pressure variation, that variations in pore geometry may affect the elastic velocities. In this work, we studied the behavior of compressional and shear wave velocities in a set of carbonate rocks at different pressure stages. Our approach is based in a supposition of a dual porosity scenario and consisted in determining the mean value of the aspect ratio of the macro-meso pores through the analysis of optical microscopy images and use the Differential Effective Medium (DEM) theory to estimate the microporosity aspect ratio. The results showed that such microporosity aspect ratio decreases exponentially as pressure increases.
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