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Spigolon A.L.D.,Federal University of Rio de Janeiro | Spigolon A.L.D.,Petrobras | Lewan M.D.,U.S. Geological Survey | de Barros Penteado H.L.,Petrobras | And 2 more authors.
Organic Geochemistry | Year: 2015

Hydrous pyrolysis (HP) experiments were used to investigate the petroleum composition and quality of petroleum generated from a Brazilian lacustrine source rock containing Type I kerogen with increasing thermal maturity. The tested sample was of Aptian age from the Araripe Basin (NE-Brazil). The temperatures (280-360. °C) and times (12-132. h) employed in the experiments simulated petroleum generation and expulsion (i.e., oil window) prior to secondary gas generation from the cracking of oil. Results show that similar to other oil prone source rocks, kerogen initially decomposes in part to a polar rich bitumen, which decomposes in part to hydrocarbon rich oil. These two overall reactions overlap with one another and have been recognized in oil shale retorting and natural petroleum generation. During bitumen decomposition to oil, some of the bitumen is converted to pyrobitumen, which results in an increase in the apparent kerogen (i.e., insoluble carbon) content with increasing maturation. The petroleum composition and its quality (i.e., API gravity, gas/oil ratio, C15+ fractions, alkane distribution, and sulfur content) are affected by thermal maturation within the oil window. API gravity, C15+ fractions and gas/oil ratios generated by HP are similar to those of natural petroleum considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous age. API gravity of the HP expelled oils shows a complex relationship with increasing thermal maturation that is most influenced by the expulsion of asphaltenes. C15+ fractions (i.e., saturates, aromatics, resins and asphaltenes) show that expelled oils and bitumen are compositionally separate organic phases with no overlap in composition. Gas/oil ratios (GOR) initially decrease from 508-131m3/m3 during bitumen generation and remain essentially constant (81-84m3/m3) to the end of oil generation. This constancy in GOR is different from the continuous increase through the oil window observed in anhydrous pyrolysis experiments. Alkane distributions of the HP expelled oils are similar to those of natural crude oils considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous age. Isoprenoid and n-alkane ratios (i.e., pristane/n-C17 and phytane/n-C18) decrease with increasing thermal maturity as observed in natural crude oils. Pristane/phytane ratios remain constant with increasing thermal maturity through the oil window, with ratios being slightly higher in the expelled oils relative to those in the bitumen. Generated hydrocarbon gases are similar to natural gases associated with crude oils considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous, with the exception of elevated ethane contents. The general overall agreement in composition of natural and hydrous pyrolysis petroleum of lacustrine source rocks observed in this study supports the utility of HP to better characterize petroleum systems and the effects of maturation and expulsion on petroleum composition and quality. © 2015 Elsevier Ltd.

Van de Wetering N.,University of Queensland | Mendonca Filho J.G.,Palynofacies and Organic Facies Laboratory LAFO DEGL IGEO CCMN UFRJ | Esterle J.,University of Queensland
International Journal of Coal Geology | Year: 2013

A high-resolution study (n = 66) was conducted on Late Permian coal measures of the Bowen Basin, Australia, to observe palynofacies changes during peat accumulation over time. Palynofacies were determined using polytopic vector analysis (PVA) to derive end members with variable compositions that reflected fine scale environmental changes, within and between seams, of the Kaloola Member. Palynofacies reflect a three-stage succession within the palaeo- peat-forming environments from stable, anoxic conditions at the base, progressing to variable, oxic conditions toward the top of each seam. In cases where a seam was capped by tuff, rather than siliciclastic sediment, anoxic conditions similar to the bottom of each seam occurred. The results corroborate previous interpretations of palaeofloral communities and provide a new palynofacies model that integrates environmental progression within the coal seams in the Late Permian coal measures of the Bowen Basin. A complementary study of palynological assemblages recognised a shift from Dulhuntyspora sp., to Protohaploxypinus sp. in the lower Kaloola Member, indicating a change in pollen/spore source. Associations between dispersed palynomorphs and coal phyterals of parent flora remain tenuous beyond class rank, due to poor preservation and taxonomic bias inherent within the sample space. This is the first such palynofacies study to be conducted in the Bowen-Sydney-Gunnedah basin complex, thus opening the way for future work examining regional changes in palynofacies, expressed in both coal and siliciclastic sediments. © 2013 Elsevier B.V.

Mendonca Filho J.G.,Palynofacies and Organic Facies Laboratory LAFO DEGL IGEO CCMN UFRJ | Sommer M.G.,Federal University of Rio Grande do Sul | Klepzig M.C.,Federal University of Rio Grande do Sul | Mendonca J.O.,Palynofacies and Organic Facies Laboratory LAFO DEGL IGEO CCMN UFRJ | And 6 more authors.
International Journal of Coal Geology | Year: 2013

Permian sedimentary rocks of the Rio Bonito Formation, Paraná Basin, in the Santa Catarina state, Brazil, contain three important coal seams, in a descending order: Barro Branco, Bonito Superior and Pre-Bonito Superior. Artinskian carbonaceous shale samples corresponding to the so called "Bonito coal" were sampled at the mine face of the coal bed ofthe Bonito I underground mine. These samples were analyzed in order to discuss their petrographical, geochemical, palynological, and paleobotanical characteristics. Palynologicalanalyses demonstrated abundant and well-preserved palynomorphs showing a dominance of bisaccate pollen grains related to gymnospermic plants. Wood fragments preserved as coalified compression show the presence of lycophyta. Palynofacies on samples demonstrated good results for the recognition of preserved organic matter and changes in paleoenvironmental conditions along the sedimentary sequence. Palynofacies and palynological analyses indicate changes in paleoecological conditions that have favored the development of different plant communities during the depositional time span from a forested gymnosperm at the baseto a lycophyte, arborescent plant dominated scenario at the top suggesting a shift to coastal environment. The microscopic maceral-group analyses reveal a predominance of liptinite and vitrinite over inertinite, while among microlithotypes, carbargilite is abundant. The joint occurrence of inertinite as a maceral in the carbonaceous rock and charcoal in associated shales suggests that the mire and near surroundings were regularly subject to wildfires. Mean random vitrinite reflectance (Rr) varies from 0.88 to 1.04%. The liptinite spectral fluorescence parameters obtained for samples show the Λmax values varying from610 to 650 indicating equivalent vitrinite reflectance (Rreq) values from 0.83 to 1.10%. These results show that the equivalent vitrinite reflectance (Rreq) correlates well with the measured vitrinite reflectance (Rr). The "Bonito Coal" is a high-volatile bituminous coal according to the ISO, 11760: 2005 standard. Total organic carbon varies from 2.4 to 44.0 wt.% and sulfur is present in moderate to high contents. GC-MS analyses evidenced a predominance of even saturated hydrocarbons and the presence of aß-hopanes and aßß-steranes. © 2012 Elsevier B.V.

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