As part of a program to evaluate the utility of integrated geoelectrical methods for subsurface structural mapping and groundwater resource investigation in the semiarid eastern margin of the Parnaiba basin in Brazil, several vertical electrical soundings (VES) and transient electromagnetic (TEM) and tensorial audiomagnetotelluric (AMT) measurements were carried out along a 250-km-long east‐west transect (passing through major towns and cities) and a 127-km-long north‐south profile (passing through small farm settlements). The various data sets have been jointly processed using a novel integration scheme and a constrained 1-D inversion technique to yield the resistivity structure underneath each observation station. Regularized 2-D inversion of static‐shift‐corrected, dual‐mode AMT data provided additional deep structural information and, together with the joint 1-D results, enabled an assessment of the distribution of aquifers and major structural controls in the region. The east‐west regional geoelectrical model evokes a picture of a gently dipping succession of conductive and resistive units in good agreement with the alternating shaly and sandy formations evinced from preexisting borehole data and previous geological studies. The geoelectric models also show the presence of the large‐scale Transbrazilian lineament and other graben‐like structures, previously inferred from aeromagnetic data, which may have some control on groundwater distribution. The agreement with geology and aeromagnetic interpretation emphasizes the importance of integrated geoelectrical surveying as a complementary or independent means of obtaining useful stratigraphic and structural information for hydrogeological studies in this region.

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Carbonate reservoirs represent a large portion of the world’s oil and gas reserves, exhibiting specific characteristics that pose complex challenges to the reservoirs’ characterization, production, and management. Therefore, the evaluation of the relationships between the key parameters, such as porosity, permeability, water saturation, and pore size distribution, is a complex task considering only well-log data, due to the geologic heterogeneity. Hence, the petrophysical parameters are the key to assess the original composition and postsedimentological aspects of the carbonate reservoirs. The concept of reservoir petrofacies was proposed as a tool for the characterization and prediction of the reservoir quality as it combines primary textural analysis with laboratory measurements of porosity, permeability, capillary pressure, photomicrograph descriptions, and other techniques, which contributes to understanding the postdiagenetic events. We have adopted a workflow to petrofacies classification of a carbonate reservoir from the Campos Basin in southeastern Brazil, using the following machine learning methods: decision tree, random forest, gradient boosting, K-nearest neighbors, and naïve Bayes. The data set comprised 1477 wireline data from two wells (A3 and A10) that had petrofacies classes already assigned based on core descriptions. It was divided into two subsets, one for training and one for testing the capability of the trained models to assign petrofacies. The supervised-learning models have used labeled training data to learn the relationships between the input measurements and the petrofacies to be assigned. Additionally, we have developed a comparison of the models’ performance using the testing set according to accuracy, precision, recall, and F1-score evaluation metrics. Our approach has proved to be a valuable ally in petrofacies classification, especially for analyzing a well-logging database with no prior petrophysical information.

ABSTRACT. The applicability of the Transient Electromagnetic (TEM) geophysical method for stratigraphic mapping and hydrogeological delineation has been tested in terrestrial part of the Campos Basin in Brazil. The study area is located within the fluvial plain of Paraíba do Sul River, at the W edge of the continental portion of the Basin, geologically consisting of Tertiary and Quaternary sediments and a gneissic basement. Around 32 central loop TEM soundings were made with 10 or 20 m-sided transmitter loops, to map the conductive and/or resistive zones in the subsurface, which were correlated with lithology from a drilled borehole in the test area, whose location was indicated by the present study. In general, the one-dimensional (1D) models constructed for the TEM field data suggest a 3-layer resistivity structure characterized by a resistor-conductor-resistor pattern. The shallow section of 100-500 ohm.m and 50 m average thickness is interpreted as correlating with clay and shaly sand formations. The intermediate layer, with thickness around 20 m and resistivity less than 10 ohm.m, corresponds to clay. The basal resistor of 10-100 ohm.m at depths of more than 60 m at most sites is interpreted as the combined signature of the basal conglomerates, shaly sands and crystalline basement. Comparison with borehole data shows that the zone corresponding to the conductive geoelectrical units contains many thin layers of clay and sand that cannot be individually resolved by the TEM data and that there are no thick aquifers in the investigated area. In addition to that the shaly sand sediments have iron rich clays, which pollute groundwater, deeper resistive layers formed by conglomerates are considered the main aquifers of this area.Keywords: transient electromagnetic, inverse one-dimensional interpretation, Campos Basin, stratigraphic mapping, hydrogeological delineation. RESUMO.A aplicabilidade do método geofísico Transiente Eletromagnético (TEM) foi testada na parte terrestre da Bacia de Campos, Sudeste do Brasil, no mapeamento estratigráfico e no delineamento hidrogeológico. Aárea do estudo, situada na borda W da porção continental da bacia e dentro da planície fluvial do Rio Paraíba do Sul, consiste geologicamente de sedimentos Terciários e Quaternários sobre um embasamento gnáissico. Os trabalhos de campos consistiram de 32 sondagens com o arranjo loop central, com uma extensão lateral 10 ou 20 m. O objetivo central do levantamento foi o de mapear as zonas condutoras e/ou resistivas em subsuperfície, as quais foram correlacionadas com a litologia de um poço perfurado naárea estudada, cuja localização foi indicada a partir deste estudo. Em geral, os modelos unidimensionais (1D) resultantes da interpretação dos dados de campo sugerem uma estrutura de três camadas, a qualé caracterizada por uma intercalação resistorcondutor-resistor. A seção rasa, de 100-500 m de resistividade e uma espessura média de 50 m,é interpretada como estando constituída por formações areno-argilosas.A camada intermediária, com espessura em...

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This work combines the outcomes from the electron spin resonance (ESR) analysis of crude oils with the results of their chemical composition from elemental analysis (CHN), gas chromatography with flame ionization detection, Fourier-transform ion cyclotron resonance mass spectrometry using electrospray ionization in negative mode [ESI(−) FT-ICR MS], and Fouriertransform infrared spectroscopy analyses, searching for correlations to identify paramagnetic constituents associated with the presence of vanadyl species and free radicals in three Brazilian oils and in their resin and asphaltene fractions. The ESR analysis of the light oil SO02 (43°API) was able to differentiate it from biodegraded oils C19 (25°API) and C10 (19°API), through the quantification of free radicals in C19 (10.60 au) and C10 (9.39 au) when compared to SO02 (6.16 au), as a result of the electron paramagnetic resonance present in compounds that make up their polar fractions. The ESR response of the C19 resin fraction was the one that came closest to the oil's response, probably due to the greater relative abundance of compounds of N and NO classes in the C19 oil, observed through the results of the FT-ICR MS analysis. The ESR technique was also able to differentiate the biodegraded oils, due to the higher response of the vanadyl species in the C19 oil when compared to the C10 oil. O 2 compounds (carboxylic acids) present in high abundance in the C10 oil confirmed that it had undergone more extensive biodegradation than the C19 oil, and we suggest that this oxidation process may have decreased the response of the vanadyl species signal. The knowledge of the existing correlation between the response of the ESR technique of oils and their chemical composition aims at the application of this technique in the oil characterization during exploration, production, and refining operations.

ID ENTI FI CATI ON OF L1Tl10 TYPES IN WELL WGS OF NAMO RADO FI ELD (CAM POS BASIN, BRAZI L) AND MARACAIBO fAKE ( VENEZUE LA) APPIXING M ULTI VARIED STA TlS71CSThe identificationof lithotypes along a borehole is one of the most important contributions of boreholegeophysics to geological studies inside the petroleum industry. However, it is a difficulttask, because the measurementsperformed in the wellexpress the changes of the physical propertiesand, not necessarily, the lithological variations. This work shows a methodology based on discriminant analysis technique for the identification of lithotypes in well logs, by means of the association between the physical property variations andthe lithological types indepth. The geophysical logs applied for the evaluation of this methodo logy were gammaray (GR), sonic (Dn, neutronic porosity (PI/IN), density (RHOS) and resistivity (ILD). In this form, we tested this scheme in two wells of Namorado Field (Campos Basin, Brazi l) and another two of Maracaibo Lake (Venezuela). The obtained resultsare interesting in the sense of the automatic identification of lithotypes using well logs. Thus, the optained results allowto observe an excellent agreement between the well log interpretations or thegeological column descriptions of the well and the lithological typesidentified by the method.Keywords:discriminant analysis,geophysical logging,Campos Basin, Maracai boLake.Resumo A identificacao de litotipos ao longo de urn poffo euma das contnbulcoes mais importantes da geoffsica aos estudos geol6gicos dentro da industria de perrolec. Entretanto, e uma das tarefas mais dificeis, porque as medidas executadas no poco expressamasmudancasdas propriedades ffsicase, nne necessariamcnte,as variacocs litol6gicas. Este trabalho mostraumametodologia bascada na tecnica da analisediscriminante para a identiflcacao de Iitotipos nos perfis de poffos, onde procuramos a associacao entre as variacocs das propriedades fisicas e os tipos litol6gicos em profundidade. Os perfis geoflsicos utilizados para a avaliacao desta metodologia saoraiosgama(GR),scmco (D7), porosidade neutronica (PI IIM, densidade (RI/OB) e resistividade (lID). Desta lonna, testamos 0 esquema desenvolvido em dois pocos do Campo de Namorado (Bacia de Campos, Brasil) e em outros dois do Lagc Maracaibo (Venezuela). Os resultados obtidos sao intercssantes no sentido da identificacao automaticade litotipos usando perfis de poco. Assim, os resultados obtidos perrnite urn excelente acordo entre as interpretacoes dos perfis ou as colunascstratigraficas dos pecos e os tipos Iitol6gicos identificados pelo mcrodo.Palavras-chave:analisediscriminante,gcoffsica de poco. Baciade Campos, Lago Maracaibo.INTRODU<;:AO Atualmente, muitos estudos mostram uma boa aplicabilidade das tecnicas da analise estatistica multivariada no processamento e interpretacao de dados geofisicos (Couto 1994). No caso da geofisica de poco, uma das aplicacoes freqUentemente apresentada trata da identificacao e da separacao das eletrofacies e a sua associacao as d...