The impact of thermal maturity level on the composition of crude oils,assessed using ultra-high resolution mass spectrometry |
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Affiliation: | 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. State Key Laboratory of Petroleum Resources and Prospecting, College of Geosciences, China University of Petroleum, Beijing 102249, China;2. China Southern Petroleum Exploration and Development Corporation, Haikou 570216, China;1. ExxonMobil Research & Engineering Company, 1545 Route 22 East, Annandale, NJ 08819, United States;2. ExxonMobil Upstream Research Company, 3120 Buffalo Speedway, Houston, TX 77098, United States;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Fuxue Road 18, Changping District, Beijing 102249, PR China;2. College of Geosciences, China University of Petroleum, Fuxue Road 18, Changping District, Beijing 102249, PR China;3. Research Institute of Experiment and Testing, PetroChina Xinjiang Oilfield Company, Karamay 843000, Xinjiang Province, PR China;1. The State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 511 Kehua Street, Wushan Road, Tianhe District, Guangzhou, GD 510640, PR China;2. Sinopec Key Laboratory of Petroleum Accumulation Mechanisms, Wuxi Institute of Petroleum Geology, Sinopec Petroleum Exploration and Production Research Institute, 2060 Lihu Road, Binhu District, Wuxi, JS 214126, PR China;3. Department of Earth Science, Zhejiang University, Hangzhou, ZJ 310027, PR China |
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Abstract: | We have examined, using a 12 Tesla FTICR-MS instrument, the impact of varying thermal maturity level on a suite of 9 related crude oils charged from source rocks covering most of the liquid petroleum generating portion of the oil window (0.68–1.11% vitrinite reflectance equivalent (%Re)). The sample suite was analyzed as whole oils under three different conditions, electrospray ionization (ESI) in positive and negative ion mode to analyze basic and acidic components, respectively, and atmospheric pressure photoionization (APPI) in positive ion mode, for sulfur and hydrocarbon species.Increasing oil maturity level had a strong influence on the composition of all compound classes in the oils with several major observations evident:The relative apparent abundances of all heteroatom containing compound classes detected in this study, using all ionization modes, decrease systematically with increasing oil maturation levels. Both aromatic hydrocarbons, detectable in APPI mode, and NSO compound classes (detectable in both ESI and APPI modes), as broad classes, are becoming more aromatic (shift to a greater predominance of higher DBE group members) and dealkylated (decreasing average molecular mass of individual compound groups), with increasing maturation level in the oil suite. Several putative oil maturity level dependent, molecular ratios were identified in the study. Of particular note, the relative abundance ratios of heteroatom compound classes tentatively identified as alkylated carbazoles, quinolines and benzothiophenes, compared to their benzannulated homologues are very sensitive to maturation level. Several groups of compounds show interesting and specific carbon number distributions, suggesting there may be hints of specific molecular markers in the FTICR-MS data. One observation of note is the strong increase in the relative abundance of protonated hydrocarbon components with DBE 5. We speculate this might reflect the presence of previously unreported higher molecular weight diamondoid (diamantane) species in oils with up to 40 carbon atoms or more, at advanced maturity levels. Such species may prove very valuable as molecular markers in highly mature fluids, such as those currently being produced from some shale reservoirs. Covariation of quantitative GC–MS data for alkylated hetero aromatic sulfur and nitrogen compounds in this oil suite, together with the corresponding FTICR-MS data from compounds believed to be, based on accurate mass, alkylated sulfur and alkylated nitrogen compounds, suggests that FTICR-MS already has some very rudimentary quantitation capabilities. |
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Keywords: | Thermal maturity Crude oil Shale oil FTICR-MS Polar compounds Sulfur compounds Nitrogen compounds Oxygen compounds Diamondoids Highly alkylated diamantanes |
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