Campos Basin Research Articles

Spatial Mobility: analysis of the demographic census data and the BlaBlaCar application

Empirical data is the starting point for the analysis of human mobility, since it allows the calibration and validation of models and, therefore, a set of data sources are useful for this analysis: censuses; Origin and Destination surveys; measurement of money flows and phone calls; GPS tracking of cell phones or other sources; means of payment of public transportation systems; among others. The registration of trips by apps is a way to capture human movements in space and, if on the one hand the companies usually do not provide social and demographic information of their users and the data are limited to the universe of customers registered on the platforms, on the other hand, the digital footprints of millions of individuals are recorded by several devices all the time in an uninterrupted way. The objective of this paper is to analyze human mobility in two selected regions in the state of Rio de Janeiro: the Metropolitan Region of Rio de Janeiro and an area composed of 26 municipalities near the North and Northwest regions of the state of Rio de Janeiro, using data from the BlaBlaCar application and the 2000 and 2010 Demographic Censuses. An initial hypothesis is to look for patterns indicating the use of the application for home-work mobility, hypothesis that was initially refuted for the Metropolitan Region, in view of the dense network of public transport apparently minimizes the relevance of rides. However, this same hypothesis, although not confirmed, was not refuted for the Campos Basin region, which showed a high proportion of trips made internally at times and days of the week consistent with a typical home-work movement.

Tectono‐stratigraphic evolution of the rift and post‐rift systems in the Northern Campos Basin, offshore Brazil

AbstractThe Campos and Santos Basins have been a focus of subsurface studies since the discovery in 2006 of large accumulations of hydrocarbons in the Early Cretaceous rift and post‐rift strata below Aptian evaporites. In this study, regional 2D seismic lines, a 3D seismic survey and well data were interpreted to reconstruct the tectono‐stratigraphic evolution of the rift and post‐rift stages in the northern sector of the Campos Basin. Detailed 3D seismic interpretation and geological modelling were used to subdivide the pre‐salt sedimentary record. This revealed a diachronous strain distribution along the Guriri Fault System (GFS), a roughly NE‐SW striking fault‐bounded horst that was a focus of rift‐related deformation. The syn‐rift succession is interpreted to be the product of two episodes of rifting (RP1 and RP2) with contrasting fault activity patterns and lithostratigraphy. Volcaniclastics and coarse siliciclastics of RP1 were deposited under WNW‐ESE transtension that formed discontinuous half‐grabens followed by extensive erosion and tectonic inversion. Structurally controlled bioclastic rudstones and hybrid deposits characterize RP2 and were deposited in elongated half‐grabens that delimit the GFS horst, which developed under an NW‐SE extension. Deposition under increasingly less tectonically active transitional and post‐rift stages dominated by thermal subsidence gradually led to the healing of the rift‐related structural relief. Selective reactivation of rift faults testifies active tectonic inversion through compression from immediate post‐rift throughout evaporite deposition. These interpretations are put into the context of recent geochronological data of onshore dyke emplacement and the new age constraints for the end of deposition of the pre‐salt sequence. Therefore, we propose an earlier onset on rifting in the Campos Basin, at the Berriasian.

CFD Analysis of The Heave and Pitch Motion of Hull Mode

This work aims to predict numerically the vertical motions (heave and pitch) of a Wigley ship model heading over regular waves at Campos Basin, Brazil. Critical levels of periods and amplitudes from waves are determined based on historical data, these are re-dimensioned to a small scale and used as input data to the model. The flow is assumed to be incompressible and viscous with mass and momentum fluxes being conserved. The Computational Fluid Dynamics (CFD) software ANSYS Fluent which makes use of the finite volume method (FVM) is employed to solve continuity and the unsteady Reynolds Averaged Navier-Stokes (RANS) equations with a Shear-Stress Transport (SST) κ-ω turbulence model. The air-water interface is modelled via the Volume of Fluid (VOF) method. An UDF (User Defined Function) is set to simulate only these two degrees of freedom for the ship motion and different sea conditions are simulated with Response Amplitude Operators (RAOs) being compared to experiments, with a good agreement being found. The Campos Basin wave from the Southwest direction with a 1-year occurrence period is a wave with the highest dimensionless value resulting in a 0.172 of heave and the wave that has a North direction with a 1-year occurrence period is a wave with the highest dimensionless value resulting from the 0.097° pitch.

Estimation of the Size and Type of Porosity in an Albian Carbonate Reservoir of the Campos Basin, Southeastern Brazil

Abstract —The Albian carbonates of the Quissama Formation in the Campos Basin, southeastern Brazil, are important oil reservoirs. They make part of a carbonate platform that formed along the eastern coast of Brazil and the western coast of Africa during the Albian, which resulted in the opening of the South Atlantic Ocean. Subsequently, this reservoir was subjected to different postdepositional diagenetic processes. The present study utilized geophysical well logs to estimate the porosity of this reservoir, based on density, neutron porosity, and sonic logs. The estimates do not show good results when compared with the laboratory measurements. Then, exploring the fact that these logs are obtained with different physical principles, a multiple linear regression and an artificial neural network with Bayesian stochastic approach were applied, which resulted in a better porosity estimate. As porosity is a petrophysical parameter considered significant in the characterization of reservoirs, it was used, hereafter, to estimate permeability and water saturation of the reservoir, applying empirical equations. From there, it was not enough just to estimate the porosity, but was necessary to know what type it is. For this purpose, the concepts of the electrical formation factor, cementation coefficient, tortuosity, and anisotropy were used. With them, the zones with primary intergranular and interparticle porosity as well as secondary porosity, such as fractures, fissures, and vugs, were mapped. It was concluded that, with studies of this type, it is also possible to identify the connected and nonconnected porosities, which permits estimation of the effective porosity along the well.

Characterization of heavy oils from the Campos Basin, Brazil: Free biomarkers in oils, adsorbed and occluded in asphaltene structures

The Campos Basin is considered an important Brazilian petroleum province, with the most of its oils consisting in a mixture of biodegraded and non-biodegraded oils, which is related to more than one generation and migration pulse coupled with biodegradation events during successive stages of reservoir filling. Its turbidites reservoirs are also structural controlled through faults generated by halokinesis comprising the main route of oil migration from underlying source rocks. Throughout the biomarkers analyses of free hydrocarbons in oil, adsorbed, and occluded in the asphaltene structures, samples from different oilfields, and distances from the main fault responsible for its reservoirs filling, were comprehensive studied. The gas chromatography coupled mass spectrometer (GC-MS) methodology was applied. The results of biodegradation, source, and thermal maturation parameters reveals that the free and adsorbed saturated hydrocarbons are similarly altered, but differ in biodegradation degrees and pathways between oils, while occluded hydrocarbons and all fractions of aromatic compounds are well preserved. The predominance of biodegradation process over the recharge is suggested for distant samples from the main fault in each area, contributing to the local models of oil migration. The occluded hydrocarbons showed source similarities regardless of oilfield. According to thermal maturity based on unaltered aromatics compounds, the occluded hydrocarbons showed lower mature ratios than those free. This study introduces the application and limitations concerning biodegradation, source, and thermal maturation inferences from occluded hydrocarbons in asphaltenes covering Brazilian oils, in view to improve a concise geochemical tool in petroleum exploration.

Characterization of Deep-Water Submarine Fan Reservoir Architecture: AB120 Reservoir in the Campos Basin

The exploration of deep-water submarine fan reservoirs has become a prominent research area for hydrocarbon discovery and recovery. However, the high operational costs render efficient exploration of this type of reservoir crucial, and the pivotal foundation lies in studying reservoir architectures. A case study of deep-water submarine fans in the Albacora Leste oilfield in Brazil is presented along with a characterization of the underground reservoir architecture based on well-log and seismic model fitting. A sedimentary microfacies distribution model is systematically established for each reservoir based on a detailed stratigraphic framework with a well-seismic joint characterization method and various types of data (e.g., geological, well-log, and seismic data). The results are as follows: the sedimentary microfacies of the deep-water submarine fans in the study area can be subdivided into tongue-shaped-lobe, muddy-channel, sandy-channel, and contourite deposits. Owing to data abundance and quality constraints, the architecture of the target layer in the study area was characterized based on Level 4 architectural elements. The AB120 Reservoir consisted of three complex channels (I, II, and III) and two tongue-shaped complex lobes (I and II). Complex channels I and III were the first and last to be deposited, respectively, and complex lobe I was deposited earlier than complex lobe II. Complex channels II and III supply complex lobes I and II, respectively. Vertically, complex lobe II was composed of three single lobes formed at different stages, the youngest of which was distributed over the largest area. Complex lobe II has already been drilled and is currently under development. However, complex lobe I has not yet been developed. This study has great practical significance for the effective development of deep-water submarine-fan reservoirs in this area and is of considerable theoretical significance for the advancement of deep-water sedimentology.

A diversity preservation method for expensive multi-objective combinatorial optimization problems using Novel-First Tabu Search and MOEA/D

Expensive multi-objective combinatorial optimization problems have constraints in the number of objective function evaluations due to time, financial, or resource restrictions. As most combinatorial problems, they are subject to a high number of duplicated solutions. Given the fact that expensive environments limit the number of objective function evaluations, the existence of duplicated solutions heavily impacts the optimization process due to poor diversity and low convergence speed. This paper proposes the Novel-First Tabu Search, a greedy-strategy mechanism that uses Knowledge-Assisted Local Search methods to preserve the population diversity and increase the exploration and exploitation ability of MOEA/D. Experiments are conducted on constrained, unconstrained, multimodal, deceptive, linear, convex, and non-convex Pareto Front multi-objective combinatorial optimization benchmark problems. This paper also conducts an experiment on the real-world, expensive problem of Well Placement Optimization using a benchmark case based on the Namorado oil field, located in the Campos Basin, Brazil. The experimental results and performance comparison with state-of-the-art algorithms demonstrate that the proposed design significantly preserves diversity and increases convergence without violating the constraint in the number of objective function evaluations.

Western boundary currents drive sun-coral (Tubastraea spp.) coastal invasion from oil platforms

Most marine species have a planktonic larval phase that benefit from the surface oceanic flow to enhance their dispersion potential. For invasive species, the interaction of environmentally resistant larvae with different flow regimes and artificial substrates can lead to complex larval dispersion patterns and boost geographic expansion. In the Southwest Atlantic, the invasive corals Tubastraea spp. (sun-coral) have been recorded biofouling on oil platforms since the late 1980s. These platforms are considered important vectors for the established populations throughout the Brazilian coast. However, we still do not know how the position of these structures relative to regional flow contribute to the natural dispersion potential of these invaders on a regional scale. Herein, we used an eddy-resolving ocean model (ROMS) and an Individual Based Model (IBM-Ichthyop) to simulate the natural dispersion patterns of sun-coral larvae from all oil platforms on Brazilian oil-producing basins, for the austral summer and winter along 6 years (2010–2015) in 90-day simulations. We found that mortality rates by advection were significantly higher during the winter (p = 0.001) and when sources of larvae were compared throughout this season (p = 1.9 × 10–17). The influence of two western boundary currents and persistent eddy activity contribute to the dispersal of larvae to distances up to 7000 km. The effectiveness of each oil-producing basin as vectors for the entire Brazilian coastline, measured as the percentage of larval supply, highlights the importance of the northern Ceará (59.89%) and Potiguar (87.47%) basins and the more central Camamu (44.11%) and Sergipe-Alagoas (39.20%) basins. The poleward shift of the Southern branch of the South Equatorial Current during the winter causes larvae released from the Sergipe-Alagoas and Camamu basins to enter the North Brazil Current, expanding their dispersion towards the north. The Brazil Current disperses larvae southwards, but strong mesoscale activity prevents their dispersion to the coast, especially for those released from the oil platforms on Campos and Santos basins. Within this complex hydrodynamic setting, a few source areas, like those in the Sergipe-Alagoas and Camamu basins, can potentially contribute to the spread of larvae along nearly all the Brazilian coast. Therefore, oil platforms act as possible chronic sources of sun-coral propagules to the coast, emphasizing the urgency for a more detailed set of actions to control and monitor these invasive exotic species.

Three new species of Microlaimus (Nematoda: Microlaimidae) from the South Atlantic.

Three new species of Microlaimus are described from the continental shelf of the Campos Basin, southwest Atlantic, Brazil. Microlaimus campiensis sp. n. differs from all other species in the presence of two anterior testes, slender spicules with enlarged proximal ends, 7–11 pre-cloacal papilliform supplements, and females with a pair of constriction structures, one on each branch of the ovary. Microlaimus alexandri sp. n. shows sexual dimorphism in the size of the amphidial fovea, which occupies 100% of the diameter of the corresponding area in the male; the buccal cavity provided with five teeth and a slightly cuticularized cuticular ring. Microlaimus vitorius sp. n. has four longitudinal-lateral rows of glands associated with small pores, one seta and three pores small pre-cloacal, and the gubernaculum has a triangular base. An amendment to the diagnosis of the genus is proposed, where the number of teeth was modified.

Fast diagnosis of reservoir simulation models based on 4D seismic similarity indicators

In the last ten years, 4D seismic (4DS) data acquisition is evolving to permanent reservoir monitoring (PRM) systems where sensors are installed at the ocean-bottom, collecting seismic data according to the project's monitoring demand. Simultaneously, reservoir management workflows evolved to include uncertainties, where multiple reservoir models may be considered. Model-based approaches for developing and managing a field rely on error minimizations between modelled and measured data, traditionally from well production data, and eventually adapted to 4DS data. This study presents a fast, robust and unsupervised workflow to provide a comprehensive diagnosis of multiple reservoir simulation models using similarity indicators with observed 4DS. The methodology comprises a seismic forward modelling to convert hundreds of models from the reservoir engineering domain to the seismic domain. The diagnosis includes a novel region-by-region approach to compare the predicted synthetic seismic response with the observed 4DS anomalies using ternary maps generated from Gaussian mixture models (GMM), in addition to a magnitude metric. The methodology is tested in an ultra-deep turbidite field from the Campos basin in Brazil with a PRM system that captured various 4DS anomalies of different polarity, magnitude, shapes and sizes over several production and injection years. The contributions of this work are demonstrated in four applications: (1) feedback on various iterations of geomodelling, (2) feedback on well and seismic data assimilation, (3) quick evaluation of a new seismic monitor, and (4) ranking models for further decision-making studies. The workflow advantages are proved along the model-based reservoir management outline. For application (1), we successfully flagged which 4DS anomalies were being honored in the simulation models and quantified the impact of introducing features interpreted from seismic monitors in the geomodelling. For application (2), we quantified simulation model improvements provided by data assimilation. For application (3), we rapidly evaluated the quality of the seismic monitor against the existing simulation models as soon as the new seismic acquisition and processing was complete, validating the requirement to re-visit the simulation models. Finally, the workflow was crucial to select best models, out of hundreds, for the decision-making process, in application (4).

Capitellidae (Annelida) from the Brazilian Continental Margin (SW Atlantic): new occurrences of three genera and description of new species

The Brazilian Continental Margin hosts several deep seafloor landscapes. However, this deep margin is still poorly studied and monitored, compared to coastal and continental shelf areas, historically limited to areas of particular economic interest. Some studies financed by the Brazilian oil and gas company have been conducted off Southeast (SE) Brazil (Esprito Santo and Campos Basins) as part of the environmental licensing process for resource exploration. Similar results showed that annelid polychaetes dominated on the continental shelf and upper slope. Within a wide bathymetric range, Capitellidae species belonging to three different genera represented new records for Brazil: Mastobranchus Eisig, 1887, Peresiella Harmelin, 1968, and Polymastigos Green, 2002. Mastobranchus braziliensis sp. nov. was found in shallow waters (20147m) of both Esprito Santo and Campos Basins; Peresiella megapapilata sp. nov. occurred from 21 to 446m of both Esprito Santo and Campos Basins; and Polymastigos profundus sp. nov. inhabited greater depths (9901361m) of the Esprito Santo Basin only. Three new species are described and compared to other species of the respective genus, the diagnosis of some genera amended and the type material of Mastobranchus loii Gallardo, 1968 redescribed. Although the three genera have the same number of thoracic chaetigers, they present several morphological differences, and the current effort being made is to translate those differences into characters to be included on the generic diagnosis of each genus. Additionally, two new morphological characters were proposed for the family, the shape of thoracic chaetigers and depth of intersegmental groove.

Enhancing vertical resolution with 4D seismic inversion

In this work, we applied a Bayesian time-lapse (4D) seismic inversion to a deep-water heavy oil field located in the Campos Basin (Brazil). In this procedure, the differences of seismic amplitudes of baseline and repeated surveys are the input to calculate the changes in acoustic impedances. To ensure the quality of the results, the parametrization of the inversion was performed by analyzing the anomalies resolution and signal-to-noise ratio with different values of input parameters, and the estimates are crosschecked with the results of a petroelastic modeling applied to the dynamic model. Results show a relevant improvement in the vertical resolution of estimated acoustic impedances in comparison to the amplitude data in a thin reservoir (with thickness ranging from 15 to 45 m). This improvement was possible because of the high-quality of acquired seismic amplitudes (permanent reservoir monitoring) and because of the data variability that is controlled in the Bayesian 4D inversion algorithm. The high resolution of Bayesian inverted results enabled a more detailed vertical zoning of the reservoir, revealing important geological features, such as channels in the main interval and below the reservoir's base, and improved the understanding of the fluid movement over time, enabling the analysis of the injection efficiency and by-passed oil zones as well as the aquifer movement. This information is important to update the static model, by improving the definition of geological features, and to calibrate dynamic models, in the future, by adding the inverted acoustic impedance maps into the data assimilation procedure.

Boron and Lithium Isotopic Signatures of Nanometer-Sized Smectite-Rich Mixed-Layers of Bentonite Beds From Campos Basin (Brazil)

AbstractBoron and lithium were analyzed in three nanometer-sized (<20, 20-50 and 50-100 nm) separates of two Santonian (85.8-83.5 Ma) bentonite samples collected closely in the Campos Basin along the southeastern Atlantic coast (Brazil). The B and Li data give various trends that suggest varied crystallization conditions for separates that consist of overwhelming smectite with less than 9% illitic layers. The δ11B of the few illitic tetrahedral sites from one of the samples remains quite constant, while its contents are strictly correlated with those of K, which suggests that illitization proceeded by interaction with pore fluids of the host sediments that supplied the K. In the second sample, the δ11B of the illite layers from the two coarser fractions is indicative of an early volcanic origin, while the smaller size fraction also interacted with sedimentary fluids. Favored by octahedral substitutions of the smectite layers, the δ7Li is more strictly regulated by a volcanic link. In turn, the information of the B and Li isotopic compositions and contents from studied mixed-layers suggests a various origin for the few illite layers of the smectite-rich I-S that contain more B than the smectite layers that host more Li. The difference appears to be sample-site and crystal-size dependent, fueled by pore fluids of the hosting turbidites.

Deep-water oil-spill monitoring and recurrence analysis in the Brazilian territory using Sentinel-1 time series and deep learning

Oil spills are a worldwide concern since they cause environmental problems and financial losses. Automatic detection plays a crucial role in rapid decision-making to reduce damage. In this context, deep learning and remote sensing are powerful tools with successful applications in many regions. However, there are still no studies on deep-water zones and in the Brazilian territory. The present research has three contributions: (1) create an oil spill dataset on the Brazilian region, (2) compare state-of-the-art deep learning models for this task, and (3) propose a novel application on the Campos Basin (Brazil's largest producer) using Sentinel-1 time series to identify more susceptible regions, encompassing 138 images from 2016 to 2021. The experts manually labeled the dataset with confirmation from the oil company and federal inspection, resulting in 800 images with 512 × 512 spatial dimensions and their respective annotations (600 for training, 125 for validation, and 75 for testing). The study compared three semantic segmentation architectures (U-net, DeepLabv3+, and LinkNet) with four backbones (ResNet-101, ResNet-50, Efficient-net-B0, and Efficient-net-B3) resulting in 12 models. The U-net with the Efficient-net-B3 backbone presented slightly better results (98% accuracy, 75% precision, 78% recall, 76% F-score, and 62% IoU). The time-series analysis considered images with 8,192 × 11,264 spatial dimensions. The entire image classification used a sliding window approach with a 128-pixel stride (averaging the overlapping pixels). Moreover, recurrence analysis detected the more susceptible areas and eliminated the look-alike. False-positive features have a high spatial presence, but with low recurrence (rarely reaching 3 events), which facilitates their elimination using a threshold recurrence. This novel analysis for oil spills is suitable for understanding the patterns along the time and providing regions for the authorities in real-time.

Characterization of Volcanic Reservoirs; Insights from the Badejo and Linguado Oil Field, Campos Basin, Brazil

Characterization of Volcanic Reservoirs; Insights from the Badejo and Linguado Oil Field, Campos Basin, Brazil

Strike-Slip Salt Tectonic Structures Associated with Basement-Involved Faults: Analogies between the Frade Field and Surrounding Region in the Campos Basin, Offshore Brazil and the Zagros Fold-and-Thrust Belt, Iran

Strike-Slip Salt Tectonic Structures Associated with Basement-Involved Faults: Analogies between the Frade Field and Surrounding Region in the Campos Basin, Offshore Brazil and the Zagros Fold-and-Thrust Belt, Iran

Facies Architecture of Lava Flows of the Cabiúnas Formation in Campos Basin, Se Brazil

Facies Architecture of Lava Flows of the Cabiúnas Formation in Campos Basin, Se Brazil

Multi-scale and multi-technique characterization of hybrid coquinas: A study case from the Morro do Chaves Formation (Barremian-Aptian of Sergipe-Alagoas Basin, Northeast Brazil)

The coquinas are carbonate rocks with variable content of siliciclastics and have a complex porous framework that implies an issue for their characterization as reservoirs. Furthermore, these rocks are considered important reservoirs due to the giant accumulations in the Campos and Santos basins (Coqueiros and Itapema formations, respectively), increasing the interest in understanding and characterizing these complex and heterogeneous lithologies. In this context, this study aims to introduce a novel method of petrophysical characterization of coquinas through a multi-technique and multi-scale approach in a continuous well core of approximately 135 m, drilled in the “Atol Quarry”, São Miguel dos Campos County, Alagoas State. Based in mineralogical content, x-ray attenuation and pore type, seven tomofacies were defined using computerized tomography and allowed a representative sampling (plugs and thin sections). Five rock types were defined based textural aspects (tomofacies and petrography) and petrophysical data (routine core analysis and micro-computerized tomography). The rock types were compared to well logs, establishing boundary values and distributed along the whole well, in an upscaling process from thin-section and plugs (microscopic scale) to the well core (macroscale). The Morro do Chaves Formation core was divided into two portions: upper portion, with better reservoir quality and greater influence of mineral dissolution; and lower portion, a poor reservoir quality portion influenced by cementation processes. The upscaling method using the concepts of tomofacies and rock types proved to be a successful way to improve the understanding of reservoir characterization in heterogeneous of complex limestone successions, which can improve the recovery factor and aid in the field development. • Coquina carbonate rock types and electrofacies. • Multi-technique and multi-scale approach. • Influence of depositional and diagenetic controls at petrophysical parameters. • Reservoir compartmentation observed due to upscaling approach.

Calculation of the 1D Lithofacies Discrimination Attribute driven by Rock Physics Modelling of Maastrichtian Reservoirs from the High Block of the Roncador Field, Campos Basin

ABSTRACT. The use of impedances derived from seismic and well data is a powerful methodology aiming geophysical reservoir characterization. However, impedance calculation often lacks geological information, being up to the interpreter associate it with the computational and physical parametrizations behind the inversion process. This scenario may lead to ambiguous or even erroneous interpretations. Thus, we propose an approach of Elasto-Facies Association (EFA) driven by rock physics modelling, in an attempt to bring more geological correlation in comparison with other widely used techniques (probabilistic, unsupervised or neural networks). This analysis is based on depth trends for P-wave velocity, which, for this case, clearly revealed the dependence of elastic properties on diagenetic effects as grain sorting, cementation and mechanical compaction. Thus, we investigated how these effects impact on seismic amplitudes and elastic impedances and their correlation with petrophysical properties for reservoir and non-reservoir rocks of intervals of interest. Finally, we applied the AVOImpedance technique (AVOI), creating a new attribute based on the projection of Acoustic Impedance (AI) and Elastic Impedance (EI2), named Lithological Discrimination Attribute (LDA). It was successful in characterizing the main lithological clustering and properly discriminating the Elasto-Facies for Maastrichtian reservoirs from the High Block of the Roncador Field.Keywords: AVO analysis, seismic inversion, rock physics, reflection coefficients modelling, elastic impedances analysis. Cálculo do Atributo de Discriminação de Litofácies 1D através de Modelagem de Física das Rochas para os Reservatórios Maastrichtiano do Bloco Alto do Campo de Roncador, Bacia de CamposRESUMO. A utilização das impedâncias derivadas dos dados sísmicos e de poços gera um importante conjunto de informações que auxilia na caracterização geofísica do reservatório. Entretanto, o cálculo das impedâncias carece de integração com as informações geológicas, sendo responsabilidade do intérprete associá-las às parametrizações computacionais do algoritmo de inversão. Isso pode frequentemente produzir resultados ambíguos ou erro nas interpretações. Assim, nós propomos um estudo das Elasto-Fácies Associadas (EFA), baseado em modelos de física de rochas, atribuindo assim um modelo mais geológico do que outras técnicas largamente utilizadas (probabilística, não-supervisionada ou redes neurais). Essa análise é baseada nas tendências das velocidades de onda-P com a profundidade, o que revelou uma estreita dependência com os efeitos diagenéticos, como seleção, cimentação e compactação mecânica. A partir dessa constatação, investigamos como esses efeitos influenciam as amplitudes sísmicas, impedâncias e propriedades petrofísicas das rochas reservatório e não-reservatório dos intervalos de interesse. Por fim, aplicamos a técnica de Impedância de AVO (AVOI) gerando um atributo, baseado na projeção das impedâncias acústica (AI) e elástica (EI2), chamado Atributo de Discriminação de Litofácies (LDA). Ele obteve sucesso na caracterização dos principais agrupamentos litológicos e discriminou adequadamente as Elasto-Fácies para reservatórios Maastrichtianos do Bloco Alto do Campo de Roncador.Palavras-chave: análise de AVO, inversão sísmica, física de rochas, modelagem dos coeficientes de reflexão, análise das impedâncias elásticas.

Thin-skinned extensional salt tectonics, counterregional faults, and the Albian Gap of Brazil

Thin-skinned extension detached on salt is mostly well understood. Faults may dip basinward or landward (counterregional) and intersect the top salt or equivalent weld at cusps/rollers. The polarity of faulting may switch over time, and with sufficient extension, the oldest suprasalt strata separate into rafts with intervening younger depocenters. Salt may break through extensionally thinned overburden to grow as passive diapirs, which can widen during ongoing extension but collapse if the salt supply cannot keep pace with extension. Counterregional normal faults are the most debated structures as they may form by: extension, with the footwall moving basinward relative to the hanging wall; or progressive basinward salt expulsion but only vertical movement of the overburden. Extensional counterregional structures are characterized by: (i) strata that predominantly thicken into the bounding structures, but with areas of basinward thinning due to fault/salt geometry and displacement transfer; (ii) highly elongate plan-view geometries; and (iii) the presence of coeval distal translation and contraction. The most controversial counterregional system is the Albian Gap of the Santos Basin, Brazil. We use the criteria above to argue that it formed by post-Albian thin-skinned extension, with little/no extension during the Albian. This contrasts with the Campos Basin along strike to the NE, where Albian and later extension were accommodated on basinward-dipping faults, and is explained by the rift architecture and consequent base-salt dip. The Aptian salt dipped basinward in the Campos Basin and extension was therefore triggered by Albian gravity gliding. However, the base salt dipped landward over a large area of the northern and central Santos Basin, so that Albian gravity gliding was minimal and Late Cretaceous progradational loading drove gravity spreading and the development of the counterregional system. Accommodation for sediment within the Albian Gap was provided in part by stretching and consequent thinning of the underlying salt.