RECURRENCE OF TECTONIC EVENTS OVERPRINT IN THE CARBONIFEROUS VILA VELHA SANDSTONES OF THE ITARARÉ GROUP, PARANÁ BASIN, SOUTH BRAZIL

This paper describes the tectonic control on the depositional and post depositional evolution of the lateCarboniferous glacial Itararé Group in the eastern flank of the Paraná Basin, southeast Paraná State. Emphasiswas given on the structural and stratigraphic organization of the Vila Velha sandstone, an outcrop analogue tosubsurface reservoirs in the Ponta Grossa – Itararé petroleum system. The study was based on satelliteimage and digital elevation model analysis, aerial photograph interpretations (1:25.000 and 1:10.000), detailedvertical stratigraphic profiles, descriptive, kinematic and dynamic analysis of deformational structures andgeological mapping. The results suggest a series of tectonic events related to Phanerozoic evolution of theSouth American Platform that can be observed in the Vila Velha sandstone. In the studied area, the ItararéGroup was deposited unconformably on a Devonian basement affected by tectonism triggered by the Eo-Hercynian orogeny during Late Devonian to Late Carboniferous times. Distribution of the lowermost glacialfacies of the Itararé Group and its spatial relationship with major tectonic features suggest tectonic controlduring the first depositional phase in the Late Carboniferous. The second depositional phase was marked bydeposition in marine, glaciomarine and shoreline environments due to deglaciation. This episode produceda 100 m thick and highly heterogeneous sand-rich succession (Vila Velha sandstone). Structural analysisshowed that these sandstones were affected by at least three brittle deformational events, which appear asfracture systems and fault zones visible on remote sensing images and direct outcrop observation. The firstdeformation event generated north-northeast fracturing and northeast sinistral strike-slip faulting, exemplifiedby the Fortaleza Fault, probably related to Fini-Hercynian intraplate stress propagation induced by the PermianLa Ventana-Cabo orogeny recorded in the Sierras Australes of Buenos Aires. The second event is recorded bynorthwest fractures and normal faults clearly related to the Early Cretaceous extensional and magmatic eventdue to the South-Atlantic rifting. This event produced the uplift of the Ponta Grossa Arch and the developmentof regional northwest structures that cross almost the entire basin, like the Rio Alonzo lineament. Patterns ofsedimentation and superimposed tectonic deformations observed in the Vila Velha sandstone provide astratigraphic/structural anisotropy that control flow units and fluid circulation within the porous media.O presente trabalho avalia o controle tectônico na deposição e deformação do intervalo basal doGrupo Itararé no sudeste do Estado do Paraná e sua influência na anisotropia de reservatórios análogos. Apartir da análise estrutural do arenito Vila Velha, a observação das relações espaciais entre a conformaçãodos estratos e as estruturas descritas e o mapeamento geológico de detalhe, propõe-se um modelo deevolução tectono-sedimentar para a área. O Grupo Itararé foi depositado em contexto glacial, glácio-marinhoe costeiro, tendo sido afetado por vários eventos tectônicos que influenciaram a sedimentação e deformarama seção sedimentar. A descrição do arcabouço estrutural/estratigráfico sugere uma história tectônica complexa,do Carbonífero ao Eocretáceo, com estruturas tectonicamente ativas durante a deposição e a suareativação em eventos tectônicos posteriores. A natureza da sedimentação e a deformação tectônicasuperimposta em múltiplos eventos imprimiram no arenito intensa anisotropia, com diferentes escalas deheterogeneidades estruturais e estratigráficas que limitam unidades de fluxo e controlam a circulação defluidos no meio poroso

SHALLOW REFLECTION SEISMIC SURVEY: A STUDY OF THE VILA VELHA SANDSTONE IN THE STATE OF PARANÁ, BRAZIL

A técnica de sísmica de reflexão rasa é analisada como aplicação no imageamento de potencialreservatório fraturado. Os métodos, procedimentos e equipamentos utilizados neste tipo de trabalho sãodescritos de forma crítica. O levantamento sísmico passou inicialmente pela aquisição de dados de refraçãoe análise de ruído para prover informações da resposta sísmica da área. Assim, definiram-se os parâmetrosa ser empregados na aquisição dos dados de sísmica de reflexão rasa de alta resolução, que constitui oobjeto principal da pesquisa. O processamento dos dados é feito de forma expedita, apenas para possibilitara correlação com a geologia e validar a escolha dos parâmetros de aquisição. Os resultados sísmicos sãocorrelacionados com os de poço e mapeamento. A sísmica de reflexão rasa é assim pioneiramente utilizadacomo ferramenta no imageamento de arenitos fraturados do Grupo Itararé, gerando imagens sísmicas queauxiliam no entendimento da geologia da área e subsidiam o estudo de modelagem de uma situaçãoaflorante, análoga a potenciais reservatórios fraturados.Shallow depth reflection seismic is analyzed with respect to its applicability to imaging a fracturedpotential reservoir. Methods, procedures and equipments used in this type of survey are critically discussed.Initially, refraction and walkaway data were acquired to provide information on the seismic response of thestudy area and so determining the high resolution, shallow depth reflection seismic acquisition parameters,which constitutes the main target of the research. A quick data processing is carried out simply to allow for thecorrelation of the seismic data with geological information and to validate the choice of the acquisitionparameters. Seismic results are correlated with borehole and surface geology data. The use of shallow depthreflection seismic is so applied for the first time to make the image of the fractured sandstones of the ItararéGroup, generating seismic images which contribute to the geological knowledge of the study area and givesupport to the study of outcrops which resemble fractured potential reservoirs

THE USE OF RESISTIVITY METHOD IN FRACTURED SANDSTONES CHARACTERIZATION OF ITARARÉ GROUP PARANÁ BASIN

Geoeletric surveys were carried out on sandstones of Itararé Group, Paraná Basin, as a contribution to a comprehensive research project on fractured reservoirs (Modres Project). The main objective of this study to determine the resistivity of fractured rocks from Itararé Group Paraná Basin. Particularly fractures acting as barriers or conduits influencing resistivity by diferential water percolation. The study area involves the Rivadávia Farm, located close to the Vila Velha Park, formed by rocks of Campo Mourão Formation, represented by a thick portion of psamitics rocks informally called Arenitos Lapa-Vila Velha. The field survey was carried out on a regular mesh with fifteen parallel lines, with 10 meters spacing. Several dipole-dipole electrode spacing were used, including 5, 10, 20, 30 and 40 meters. Data processing started with the apparent resistivity pseudosections plot, followed by of 2D inversion models. Inversion results allow to correlate the resistivity values with diverse geologic features, particularly with the layers geometry and the contact between different lithologies. It was observed that the structural conditioning, represented by fractures and faults, influences the resistivity values. Resistivity highs had been correlated with mapped faults, possibly indicating closed type of faults, while lows can indicate open ones, with higher porosity which propitiate water percolation. The results show high values (thousand of Ohm.m), somehow uniformly distributed, even in the most sandy levels, indicating very low permeability for the Itararé sandstones.Como contribuição a um projeto de pesquisa abrangente de modelos análogos a reservatórios fraturados (Projeto Modres), foram realizados ensaios geoelétricos nos arenitos do Grupo Itararé, Bacia do Paraná. O principal objetivo deste estudo consiste em determinar as respostas de resistividade dos arenitos fraturados do Grupo Itararé. Particularmente interessa a detecção de fraturas e seu comportamento hidráulico (atuando como barreiras ou condutos) influenciando a resistividade, e, neste contexto, apresenta uma nova contribuição ao entendimento do Grupo Itararé. A área de estudo envolve a Fazenda Rivadávia, localizada perto do Parque Estadual de Vila Velha. Geologicamente a área é formada por rochas da Formação Campo Mourão, Grupo Itararé, Bacia do Paraná, sendo representadas por uma porção sedimentar arenosa chamada informalmente de Arenitos Lapa-Vila Velha. O levantamento de campo foi realizado sobre uma malha com quinze linhas paralelas e distanciadas 10 metros. Vários espaçamentos foram utilizados no arranjo dipolo-dipolo, incluindo 5, 10, 20, 30 e 40 metros. O processamento dos dados iniciou-se com a plotagem em pseudo-seções de resistividade aparente, seguida da geração das seções modelos de resistividade através de inversão 2D. Os resultados obtidos permitem correlacionar os valores de resistividade com diversas feições geológicas, mais especificadamente com a geometria das camadas e o contato entre litologias diferentes. De maneira geral, foi observado que o condicionamento estrutural, representado pelas fraturas, influenciam os valores de resistividade. Altos de resistividade foram correlacionados a fraturas mapeadas, possivelmente indicando que estas se encontram fechadas, enquanto que baixos podem indicar fraturas mais abertas, maior porosidade e com conseqüente maior facilidade de percolação de água. Os resultados mostram valores muito altos (milhares de Ohm.m), até certo ponto distribuídos de forma uniforme, mesmo nos níveis mais arenosos, indicando que a permeabilidade dos arenitos é muito baixa

Bayesian and multivariate methods applied to favorability quantification in recôncavo Basin and Ribeira Belt, Brazil

A methodology to define favorable areas in petroleum and mineral exploration is applied, which consists in weighting the exploratory variables, in order to characterize their importance as exploration guides. The exploration data are spatially integrated in the selected area to establish the association between variables and deposits, and the relationships among distribution, topology, and indicator pattern of all variables. Two methods of statistical analysis were compared. The first one is the Weights of Evidence Modeling, a conditional probability approach (Agterberg, 1989a), and the second one is the Principal Components Analysis (Pan, 1993). In the conditional method, the favorability estimation is based on the probability of deposit and variable joint occurrence, with the weights being defined as natural logarithms of likelihood ratios. In the multivariate analysis, the cells which contain deposits are selected as control cells and the weights are determined by eigendecomposition, being represented by the coefficients of the eigenvector related to the system's largest eigenvalue. The two techniques of weighting and complementary procedures were tested on two case studies: 1. Recôncavo Basin, Northeast Brazil (for Petroleum) and 2. Itaiacoca Formation of Ribeira Belt, Southeast Brazil (for Pb-Zn Mississippi Valley Type deposits). The applied methodology proved to be easy to use and of great assistance to predict the favorability in large areas, particularly in the initial phase of exploration programs. © 1998 International Association for Mathematical Geology

The Itajaí group, state of Santa Catarina, Crazil : example of sedimentation in a foreland basin.

A análise estratigráfica do Grupo Itajaí permitiu individualizar quatro associações faciológicas em um contexto de bacia flexural de antepaís, tendo-se verificado significativa mudança tanto no suprimento como na sucessão vertical de fácies, quando comparados os estágios inicial e final da sedimentação. A primeira associação constituiu-se de depósitos continentais a plataformais retrogradantes com aporte da margem cratônica, a N-NW. A segunda registra uma sedimentação em condições subaquosas profundas, com paleocorrentes para S-SW. A terceira reflete condições transgressivas, com depósitos pelíticos que avançaram em direção à margem norte da bacia. A quarta e última associação encontra-se representada por depósitos costeiros progradantes, com suprimento da margem orogênica, aS-SE.8ased on stratigraphic analysis of the Itajaí Group, four facies units are defined in a foreland basin context. Depositional characteristics indica te a significant change both in sedimentary supply and in the vertical succession of facies from the initial to final stages of stratigraphic evolution. The first unit is composed of retrograding continental to platform deposits, with supply from the N-NW cratonic margin. The second unit records sedimentation under deepwater conditions, with paleocurrents toward the S-SW The third unit reflects transgressive conditions, with pelitic deposits onlapping the northern margin of the basin. The fourth unit, overlying the other three, consists of prograding coastal systems, with supply from the orogenic margin of the basin, coming from S-SE

Structural analysis of the deforming tectonics of the Itajaí Basin, Santa Catarina, Brazil.

Structural analysis of the Itaja" Group has confirmed and increase in deformation magnitude from NW to SE, toward the more deformed zone of the Dom Feliciano mobile belt. This condition is in agreement with the predicted characteristics of a foreland basin deformed in a convergent environment. Two families of tectonic structures were recognized, both corresponding to different deformation phases and associated stress fields. The first represents the late collisional phase of the orogenic cycJe, which caused the development of reverse faults, asymmetric folds, and a conjuga te system of strike-slip faults. The progressive evolution of this convergence led to the change from a frontal to an oblique collision, with dextral-reverse kinematics. The second phase records a post-collisional extensional pulse, leading to the reactivation of earlier structures and inversion of movements along the conjugate system of strike-slip faults