Evaluation of the petroleum composition and quality with increasing thermal maturity as simulated by hydrous pyrolysis: A case study using a Brazilian source rock with Type I kerogen |
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| Institution: | 1. Universidade Federal do Rio de Janeiro, Instituto de Geociências, Av. Athos da Silveira, 274, Prédio do CCMN, Cidade Universitária, 21.949-900 Rio de Janeiro, RJ, Brazil;2. U.S. Geological Survey (Emeritus), Box 25046, MS 977, Denver Federal Center, Denver, CO 80225, USA;3. Basin and Petroleum System Modeling (Petrobras/E&P-EXP), Av. República do Chile, 330, Centro, 20.031-117 Rio de Janeiro, RJ, Brazil;4. Division of Geochemistry, Petrobras Research and Development Center (CENPES), Av. Horácio Macedo, 950, Cidade Universitária, 21.941-915 Rio de Janeiro, RJ, Brazil;5. Palynofacies and Organic Facies Laboratory (LAFO)/DEGL/IGEO/CCMN/UFRJ, Av. Athos da Silveira, 274 – Prédio do CCMN, Sala JI-020, Cidade Universitária, 21.941-916 Rio de Janeiro, RJ, Brazil;1. Sinopec Key Laboratory of Petroleum Accumulation Mechanisms, Wuxi Research Institute of Petroleum Geology, Sinopec Petroleum Exploration & Production Research Institute, 2060 Lihu Road, Binhu District, Wuxi, Jiangsu 214000, China;2. Department of Earth Science, Zhejiang University, Hangzhou 310027, China;1. Schlumberger-Doll Research, Cambridge, MA, United States;2. Rose Hulman Institute of Technology, Terre Haute, IN, United States;3. Advanced Photon Source, Argonne, IL, United States;1. Key Laboratory of Shale Gas Exploration and Evaluation, Ministry of Land and Resources, China University of Geosciences, Beijing (CUGB), 100083, China;2. School of Energy and Resource, CUGB, 100083, China;3. Sinopec Petroleum Exploration and Production Research Institute, 100083, China;4. China University of Petroleum, Qingdao, Shandong Province, 266580, China;5. CNOOC Gas & Power Group, Beijing, 100083, China;1. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou, Gansu Province 730000, China;2. The institute of Biology, Guizhou academy of Sciences, Guiyang 550000, China;3. Exploration and Development Research Institute, Liaohe Oilfield Company, PetroChina, Panjin 124010, China;4. University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | 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 508–131 m3/m3 during bitumen generation and remain essentially constant (81–84 m3/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. |
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| Keywords: | Brazilian Type I kerogen Hydrous pyrolysis Thermal maturation Generation and expulsion Petroleum composition and quality API gravity Sulfur content Asphaltenes Saturates Gas/oil ratio |
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