Programa de Pós-Graduação em Geodinâmica e Geofísica
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Doctoral Thesis Análise probabilística da ameaça sísmica para o Nordeste do Brasil(Universidade Federal do Rio Grande do Norte, 2024-11-29) Fonsêca, José Augusto Silva da; Nascimento, Aderson Farias do; https://orcid.org/0000-0002-3961-5884; http://lattes.cnpq.br/8600906973888297; https://orcid.org/0000-0002-2756-686X; http://lattes.cnpq.br/8516129832322936; Bezerra, Francisco Hilário Rego; Ferreira, Joaquim Mendes; Assumpção, Marcelo Sousa de; Miranda, Paulo de Souza TavaresAlthough they exhibit lower seismicity compared to plate boundary regions, Stable Continental Regions (SCR) are not free from adverse seismic impacts. Assessing seismic hazard in these regions is essential, especially considering the presence of critical infrastructure and urban areas, where low-probability but significant-sized events can still pose substantial risks. In this context, Northeast Brazil stands out as one of the most seismically active areas in the SCR of South America, with events in recent decades causing significant damage to civil structures. This study conducted a Probabilistic Seismic Hazard Analysis for Northeast Brazil, focusing on critical locations, using an updated regional earthquake catalog and newly defined seismic source zones. For this, the application of more appropriate models for magnitude distribution was sought, revealing the rejection of the Gutenberg-Richter relation in one of the seismic sources. The results showed PGA values < 0.01 g for most of the study area, typically ranging between 0.01 g and 0.04 g for much of its northeastern portion, considering a 10% probability of exceedance over 50 years. In this region, under the same conditional probability, the highest PGA values were found in the range of 0.10 g to 0.20 g around the four most active seismic sources. The uniform hazard spectrum indicated values between 0.18 g and 0.08 g over a wide range of structural period for a critical location, reaching an average peak of 0.31 g. The findings suggest that, although most of the region complies with the current Brazilian seismic code, certain areas present significantly higher seismic hazard. In these areas, the respective seismic intensities can vary between VI and VIII, potentially causing damage ranging from minor in civil constructions to the collapse of older buildings.Doctoral Thesis Caracterização de efeitos dispersivos em dados de GPR causados por bandas de deformação em arenitos: petrofísica, modelagem numérica e análise multiatributo(Universidade Federal do Rio Grande do Norte, 2024-05-15) Cedraz, Victória Maria de Almeida Santos; Medeiros, Walter Eugênio de; https://orcid.org/0000-0002-6757-0572; http://lattes.cnpq.br/2170299963939072; http://lattes.cnpq.br/9706823103892668; Bruna, Vincenzo La; Costa, Jessé Carvalho; Strugale, Michael; Lupinacci, Wagner MoreiraWe evaluate the dispersive effect on Ground-Penetrating Radar (GPR) data caused by deformation bands (DBs) present in sandstones. To achieve this objective, we used a 200 MHz GPR cube surveyed on a sandstone outcrop, highly impacted by DBs, located in the Rio do Peixe Basin (Northeast Brazil). To interpret the GPR cube, we developed an integrated and multidisciplinary approach that consisted of two stages. The first stage was based on laboratory measurements and numerical modeling and the second stage was based on multi-attribute analysis. In the first stage, complex dielectric constant measurements of clean sandstones (50-400 MHz frequency range) revealed that the quality factor (Q) is strongly influenced by grain size: Q decreases as grain size decreases. Therefore, DBs are associated with relatively low Q values because they always cause grain reduction compared to the host rock. Furthermore, two-dimensional modeling of radargrams confirmed the empirically known fact that DBs appear as zones of attenuated signal in two case studies: a conceptual model of DBs and the approximate reproduction of one of the GPR cube sections. The second stage consisted of extracting the threedimensional architecture of the DBs from the GPR cube using a multi-attribute analysis. We showed that the sequential application of the edge evidence and ant-tracking attributes was able to automatically identify continuous zones of attenuated signal within the GPR cube. As a result, it was possible to extract the DBs as a geobody. The geological reliability and limitations of the geobody were evidenced by comparing sections of it with photographs of DBs exposed in similar positioning, in addition to structural measurements obtained in the field and in the geobody.Doctoral Thesis Terremotos profundos na região amazônica (Acre): mecanismos focais e parâmetros de fonte(Universidade Federal do Rio Grande do Norte, 2024-07-12) Leite Neto, Gilberto da Silva; Casas, Jordi Julià; http://lattes.cnpq.br/0012168139768170; https://orcid.org/0000-0001-9925-1587; http://lattes.cnpq.br/8005306262785305; Nascimento, Aderson Farias do; https://orcid.org/0000-0002-3961-5884; http://lattes.cnpq.br/8600906973888297; Bezerra, Francisco Hilario Rego; Carvalho, Juraci Mário de; Assumpção, Marcelo Sousa deDeep earthquakes occur at depths greater than 70 km, in the cold core of the subducting lithosphere, where the extreme pressure and temperature conditions should prevent brittle failure. Thus, alternative physical processes are necessary in order to explain the occurrence of these events. At depths exceeding 300 km, earthquakes are attributed to transformational faulting, a mechanism that relies on the presence of a metastable olivine wedge (MOW) in cold slabs. However, these events also occur in warm slabs, such as the Nazca plate, which makes explaining these phenomena even more challenging. This study aims to investigate the generating mechanism in South America by determining focal mechanisms and source parameters for a sequence of 42 deep-focus events in the Amazonian region between Peru and Brazil (2014-2022). To achieve this goal, data from several broadband stations distributed across the continent were utilized, ensuring unprecedented coverage of these events. Initially, focal mechanisms and centroid depths were determined for a total of 28 events (Mw 4.2-7.5) using the Cut-and-Paste method. The mechanisms reveal a predominance of normal faults reflecting a down-dip compression (DDC) regime. Nodal planes, oriented approximately 45º from the axis of maximum compression, indicate the formation of new faults, consistent with transformational faulting. Centroid depths demonstrate a seismic zone confined between 557 and 659 km. These observations suggest that seismicity may result from transformational faulting within a MOW preserved by a colder slab segment attached at depth to a warmer Nazca Plate. Seismic moments, corner frequencies, and radiated energies were determined for 13 events (Mw 4.8-7.4) from P- and S-wave spectra. From these parameters, stress drops (5-90 MPa) and radiation efficiencies (0.1-1.4) were calculated, revealing significant variations. The variability in radiation efficiencies suggests the coexistence of brittle and dissipative ruptures, possibly influenced by the degree of melting in the fault zone and favored by the dehydration of hydrous phases near the source. Thus, this work suggests that deep-focus earthquakes in the region result from the combination of transformational faulting and thermal runaway, the latter involving more or less melting depending on the presence of water near the source.Master Thesis Aplicação de simulação numérica e aprendizado profundo utilizando imagens de micro-ct de rochas reservatório(Universidade Federal do Rio Grande do Norte, 2024-05-23) Kiam, Thiago Noboru Leite; Xavier Júnior, Milton Morais; http://lattes.cnpq.br/3128669965557866; http://lattes.cnpq.br/8176148304942096; Lucena, Leandson Roberto Fernandes de; http://lattes.cnpq.br/4673404543485023; Marques, Manilo Soares; Soares, José AgneloCarbonate rocks constitute important reservoirs of mineral resources, however, they exhibit a high degree of anisotropy and heterogeneity, with various types of pores and scales that challenge both the industry and the scientific community. Digital petrophysical studies aim to obtain intrinsic rock parameters through the 3D rendering of X-ray microtomography images. The present study aims to classify pore types and estimate petrophysical parameters from the 3D rendering, segmentation, and numerical simulation of images of carbonate rocks from the Jandaíra Formation, Potiguar Basin, Rio Grande do Norte, Brazil. The images were acquired by X-ray microtomography, with resolution of 35 μm, and represent transverse slices of the rocks. For the treatment of slices, the ImageJ program was used. The segmentation of 3D pores was performed using the multi-Otsu method with the Simpleware ScanIP software. The segmented files were discretized and imported into the Comsol Multiphysics numerical simulator with coarse mesh density. The simulator adopts the finite element method (FEM) to perform its calculations. The simulated physics was configured to be a single-phase fluid in steady-state, laminar flow, with a density of 1000 kg/m³ and a viscosity of 0.001 Pa.s. The differential pressure between the inlet and outlet of this fluid was established at 1 Pa. Comparing with literature and laboratory-obtained values, the digital results were satisfactory and consistent. Segmentation enabled the classification of well-developed stylolites and vugs among the samples. Petrophysical estimates ranged from 0.70% to 7.99% with effective porosity and simulated permeability ranged from 7.79 mD to 3000 mD. Regarding deep learning, the Alexnet model, with SGD criterion and MSE optimizer, exhibited the best performance.Master Thesis Aplicação de interferometria sísmica passiva para extrair ondas P refletidas de alta resolução a partir de dados de fraturamento hidráulico(Universidade Federal do Rio Grande do Norte, 2023-11-13) Lopez, Joan Manuel Flores; Nascimento, Aderson Farias do; https://orcid.org/0000-0002-3961-5884; http://lattes.cnpq.br/8600906973888297; http://lattes.cnpq.br/6659596411825742; Maciel, Susanne Taina Ramalho; Medeiros, Walter Eugênio deThis study utilizes passive seismic interferometry, focused explicitly on calculating the auto-correlation function,on extracting reflections of P-waves centered on each receiver. Stacking these reflections allows for the construction of seismic sections at zero offsets. Typically, this technique uses data based on environmental noise or earthquakes. However, in this study, measurements taken during the hydraulic fracturing process in the vicinity of the Potiguar basin located in northeastern Brazil were used. Although this acquisition was not intended for a passive seismic interferometry experiment, an advantage was taken of its design and location concerning the fracturing point to evaluate the ability to construct seismic images from induced ambient noise. This geometry is composed of three main lines with three different azimuth angles, which intersect precisely at the point of fracturing located at a depth greater than 400 meters. To extract the best body wave component from Green’s function, we apply a novel variation to the commonly used processing flow. This includes the Gaussian smoothing filter, which allows a smoothed amplitude spectrum to be obtained. This spectrum may still be affected by high-energy point events that need to be further treated, for which the whitening process is considered using the division between the natural spectrum of the data versus the smoothed spectrum. After applying the inverse Fourier transform to each trace obtained for each station, they are complemented to form the resulting seismic sections, which are compared to active source seismic lines acquired close to the study area and interpreted with available geological information. Seismic images were built in 2D and projected in 3D, taking advantage of the peculiar geometry arranged for monitoring the hydraulic fracturing process. This allowed analyzing the consistency between each of the acquired lines, also considering the point of intersection between them. Within this context, we can define a result of seismic sections that have well-defined reflectors of high resolution, continuity, and a satisfactory reproduction of the limits of the different geological formations typical of the Potiguar basin, such as the Jandaira, Açu formation, and the basement top. Our work demonstrates the potential of passive seismic interferometry to generate high-resolution seismic images with highly efficient processes, considering the low relative investment level, very low environmental impact, and high-quality results.Doctoral Thesis Influência da herança estrutural do embasamento na evolução da Bacia Rio do Peixe através de abordagens geofísicas e geológicas(Universidade Federal do Rio Grande do Norte, 2023-12-13) Ramos, Gilsijane Vieira; Castro, David Lopes de; https://orcid.org/0000-0003-1110-9389; http://lattes.cnpq.br/8279954644750743; http://lattes.cnpq.br/7110486253679005; Strugale, Michael; Ferreira, Francisco José Fonseca; Gomes, Moab Praxedes; https://orcid.org/0000-0003-0836-1073; http://lattes.cnpq.br/2086362176219605; Bruna, Vincenzo LaIn this research, the role of crystalline basement structural inheritance was investigated based on the brittle reactivation of shear zones within a sedimentary basin, aiming to describe the formation and evolution of the Rio do Peixe Basin (RPB) in Northeast Brazil. The RPB was formed at the intersection of three Precambrian geological domains, highly deformed by shear zones and intruded by Neoproterozoic granitic rocks. An integrated dataset including aeromagnetic, gravity, 2D/3D seismic, and field data was analyzed to assess how Precambrian shear zones may have influenced its internal geometry. The results indicate that magnetic lineaments correlated with Precambrian shear zones persist uninterrupted in the sedimentary cover region, revealing the structural framework of the RPB. This magnetic pattern demonstrates that structures from the underlying basement significantly influenced the geometry of the basin sedimentary fill. Gravity modeling and seismic section interpretation allow the observation that inherited basement structures, particularly the shear zones delineating crustal subdomains, controlled the location and internal architecture of the rifts, as well as acted as weakness crustal zones susceptible to brittle reactivations, comprising the main normal faults of the rift phase. Furthermore, the study revealed the migration of depocenters towards the northeast, in the Brejo das Freiras sub-basin, associated with the development of the Portalegre Fault segment with NE-SW orientation, attributed to the basin-opening process. Thus, the combination of geological and geophysical data provides a current and detailed image of the half-grabens and depocenters, strongly controlled by the inherited faults of the Precambrian basement structural framework. This multidisciplinary analysis opens new research perspectives to enhance our understanding of the tectonic evolution of intraplate basins in northeastern Brazil, as well as the marginal basins located on the Brazilian Equatorial Margin. Finally, the present study of tectonic processes that influenced the RPB geological evolution can assist in comprehending the evolution of other intraplate and marginal basins in northeastern Brazil, which were also influenced by the fragmentation of tectonic plates.Doctoral Thesis Joint inversion of magnetotelluric and seismological observations: case study in NE Brazil(Universidade Federal do Rio Grande do Norte, 2023-07-18) Romero, Ana Milena Nemocón; Casas, Jordi Julia; Martínez, Xavier García; http://lattes.cnpq.br/0012168139768170; http://lattes.cnpq.br/4623014127571438; Nascimento, Aderson Farias do; https://orcid.org/0000-0002-3961-5884; http://lattes.cnpq.br/8600906973888297; Bezerra, Francisco Hilario Rego; Chaves, Carlos Alberto MorenoGeophysical methods aim at obtaining information about the subsurface rocks and fluids. To achieve this goal, different methodologies are employed to more accurately determine both the geometry and physical properties of the Earth’s strata at depth. Seismological methods recover structural and velocity information in the subsurface, while MT techniques are powerful tools to characterize the saturation of fluids, such as hydrocarbons or saline water, in subsurface rocks. Seismological or magnetotelluric (MT) measurements provide incomplete information when used independently. Combined, these techniques have the potential to considerably improve the imaging of structural features at depth. This paper evaluates the performance of joint analysis of seismological and magnetotelluric data for determination of subsurface structure beneath the Borborema Province and northern São Francisco Craton, using data collected along a N-S profile centered at the Araripe Basin. First, resistivity and S-wave velocity models were obtained through independent inversions. The velocity models were obtained through simultaneous inversion of receiver functions and dispersion curves, and revealed the presence of a layer with high velocity (4.1-4.3 km/s) below the Araripe Basin - which was interpreted as a mafic layer in the lower crust - and a decrease in velocity (< 4.3 km/s) below 120 km depth. The resistivity models were taken from an existing 3D inversion of apparent resistivity and phase curves, noting the presence of high conductivity ( 25 Ωm ) in the mantle (120 km) beneath the basin. This conductive anomaly was interpreted as material enriched with small amounts of magma derived from Mesozoic rifting processes. The joint interpretation of the results thus evidences a thinning of the lithosphere beneath the Araripe Basin, contributing to improve our understanding of the tectonic inversion processes of this basin. The performance of the joint inversion of magnetotelluric and seismological data was also investigated. The joint inversion used the same receiver functions, phase and apparent resistivity curves as the independent inversions; however, a brand-new mean phasevelocity dispersion curve had to be utilized. The inversion assumes a common seismic and resistivity structure (1D), represented by a set of layers above a half-space. Furthermore, the inversion is performed using a multi-objective genetic algorithm (GA) that efficiently exploits the parameter space. Our results demonstrate that, in spite of considerable geological complexity, it is possible to determine structurally consistent velocity and resistivity structures beneath the Borborema Province and the São Francisco Craton. The inverse (1D) models do not allowed to develop empirical relationships between resistivity and S-wave seismic velocity at crustal or mantle depths, but they were able to image an electric Moho beneath most locations within the study region.Master Thesis Geomorfologia da plataforma continental brasileira adjacente ao Delta do rio Parnaíba (PI - MA)(Universidade Federal do Rio Grande do Norte, 2023-01-30) Santos, Sarah Alves dos; Vital, Helenice; https://orcid.org/0000-0003-0462-9028; http://lattes.cnpq.br/3595069999049968; Figueiredo, Alberto Garcia de; Nogueira, Mary Lucia da SilvaThe mapping of the features present on the continental shelves contributes to the proper interpretation of the oceanic environment, which can be used for scientific, political and strategic development, to support management, for preservation of submerged areas in general and for the future of the our planet. This study was carried out on the Brazilian Equatorial Margin, on the continental shelf adjacent to the Parnaiba River Delta (PI-MA) and had as its main objective the mapping of seabed features in this region through the use of hydroacustic data (singlebeam bathymetry), supported by sedimentological data, obtained from the Brazilian Navy's National Oceanographic Data Bank - BNDO. In the laboratory, the hydroacoustic data were interpolated using the kriging and minimum curvature methods, where the kriging method proved to be more efficient in viewing the features present in the area. The integration, analysis and interpretation of data resulted in four maps of the ocean substrate: bathymetric, slope, aspect, and sediment sample distribution that can be used as relevant units (e.g., inclination, orientation, curvature and terrain, among others). In this way, it was possible to identify a sedimentary cover from fine sand to coarse sand, sand with biodetritus, shells and gravel, presence of mud and quartz sand, whose relief is associated with differente submerged features, such as sandy banks, submarine valleys, as well as the presence of plateaus, associated with rocky outcrops and reef banks; additionally, lineaments and paleovalleys on the current shelf indicate the path that the Parnaíba River took in the past.Doctoral Thesis Impactos da dissolução cárstica na permo-porosidade de rochas carbonáticas: implicações para o desenvolvimento de redes de fraturas alargadas e camadas super-k(Universidade Federal do Rio Grande do Norte, 2022-09-30) Lopes, Juliana Aparecida Gonçalves; Medeiros, Walter Eugênio de; https://orcid.org/0000-0002-6757-0572; http://lattes.cnpq.br/2170299963939072; http://lattes.cnpq.br/2489217467286848; Nascimento, Aderson Farias do; https://orcid.org/0000-0002-3961-5884; http://lattes.cnpq.br/8600906973888297; Bagni, Fábio Luiz; Balsamo, Fabrizio; Dantas, Renato Ramos da SilvaWe evaluated the impact of karst dissolution on the permo-porous system of carbonate rocks, using field data obtained from outcrops of the Jandaíra Formation (Potiguar Basin). The karst system of this formation has excellent exposures, which allow the study of karst features both in vertical and horizontal planes. The integrated and multidisciplinary approach of this thesis was carried out in two stages. The first stage was predominantly two-dimensional (2D), in which we used scanlines and aerial images of Unmanned Aerial Vehicles to characterize networks of karstified subvertical fractures. In this stage, we show that the process of fractures enlargement by karstic dissolution modifies the statistical relationships between fracture length and aperture. For early stages of karst dissolution, the length and aperture values follow approximately the classical power law distribution typical of mechanical fractures. However, as karstification progresses, fracture aperture tends to remain constant, regardless of its length. Thus, by adapting the aperture-length curve, according to the known stage of karst dissolution, it is possible to build discrete fracture models that include the effects of karstic dissolution. We call the resulting model DFKN (Discrete Fracture and Karst Network). We also show that fracture enlargement can increase the transmissivity of a karstified fracture network by up to five orders of magnitude, without changing its connectivity. The second stage of the research consists of a three-dimensional (3D) analysis of fracture networks, lithostratigraphic interfaces and karst features, based on the joint interpretation of Ground Penetrating Radar (GPR) cubes, core logs, porosity, permeability and total radiation profiles, images of borehole walls and thin sections. In this stage we verified that GPR signal attenuation zones are related to secondary alterations of carbonate rocks, which are caused by fracturing, fracture and pore enlargement, as well as stylolite dissolution. Such secondary alterations significantly increase the porosity and permeability of rocks. Fractures are the main pathways for fluid percolation, contributing to the evolution of karstification processes, especially in layers with higher primary porosity/permeability. On the other hand, layers with low primary porosity/permeability, but with a high concentration of stylolites, can also develop zones of high permeability due to the interconnection of dissolved stylolites. The attenuation/dissolution zones can compose connected volumes of high permeability and generally have tabular geometry, because they are limited by subvertical fractures and subhorizontal stratigraphic interfaces. At the reservoir scale, these tabular bodies may constitute super-k layers. In a unified view, our results contribute to a better understanding of the three-dimensional permo-porous system of fractured and karstified carbonate reservoirs.Master Thesis Caracterização de unidades de fluxo multi-escala em reservatórios fluviais: o exemplo do campo de Alto Rodrigues - Bacia Potiguar, Brasil(Universidade Federal do Rio Grande do Norte, 2022-06-24) Sena, Ewerton Soares de; Nascimento, Aderson Farias do; https://orcid.org/0000-0002-3961-5884; http://lattes.cnpq.br/8600906973888297; http://lattes.cnpq.br/8173169280831832; Antunes, Alex Francisco; https://orcid.org/0000-0002-3292-4190; http://lattes.cnpq.br/1519973126832391; Rodrigues, Marcos Allyson Felipe; Lupinacci, Wagner MoreiraPetrobras' divestment plan for mature fields created a new scenario for oil exploration and production in Brazil's onshore and shallow water sedimentary basins. Several small and medium-sized companies are acquiring these fields with the challenge of implementing projects that increase production and the recovery factor of these accumulations. Mature fields typically have more than 30 years of production and have dozens or even hundreds of producing wells, with an immense amount of rock, fluid, and associated production data. Therefore, data integration studies to generate knowledge about the producing reservoirs are mandatory, so that new production development projects can be implemented, aiming to maximize the return on capital invested in the revitalization of these fields. This study integrates geological/geophysical, petrographic/diagenetic, and petrophysical data to individualize rocks with different flow capacities producing oil in a field in the Potiguar Basin, NE, Brazil. The work used information from more than 800 vertical wells, 19 of which have rock data and petrophysical analysis. Seven wells provided most of the data for the present study because of the greater thickness of cores recovered. Implementing the multiscale approach that we presented was essential in understanding the geological aspects that influence the reservoir production capacity. At the micro scale, for example, through the study of thin sections, it was possible to identify and recognize clay minerals that occur may obstruct pore throats and, consequently, affect the permeability and productivity of the rocks. At the meso scale, the study of cores in different portions of the field allowed us to characterize the depositional systems in the area and identify factors that influence the entry of oil into the reservoir. Finally, through the correlation of rock vs. logs at the macro scale, we estimated the distribution of the flow units defined for the other wells, thus allowing the construction of maps and petrofacies sections with geological and dynamic significance. At this last scale, we visualize the geometry of the sedimentary deposits and their heterogeneities, whose understanding directly influences the planning and development of an accumulation (for example, in the definition of the production wells grid and water or steam injection in case of application of secondary recovery methods). Additionally, a methodology was developed to quantify the production capacity of the rocks from a reservoir quality index (RQI) that we validated with field production data.