Compound-specific delta H-2 and delta C-13 values of n-alkanes as a tool to unravel complex petroleum mixtures in the South Viking Graben, Norway

摘要

In order to resolve oil mixtures and for oil-source correlation purposes, both hydrogen (82H) and carbon isotope compositions (delta C-13) of n-alkanes and acyclic isoprenoid alkanes have been determined in petroleum mixtures and extracts from Jurassic source rocks of distinct organic matter type, depositional setting and lithology in the South Viking Graben, Norway. delta H-2 values vary from-80 to-140 parts per thousand for n-alkanes and from-130 to-165 parts per thousand for pristane (Pr) and phytane (Ph) in oil and condensate samples. At the same maturity level, in the main oil generative window, individual n-alkanes from most oils and condensates show a H-2-enrichment with n-alkane chain length by 15 to 50 parts per thousand. With the increase in the estimated input of hydrocarbons from terrigenous source material to petroleum mixtures, the n-alkanes (>C-20) exhibit a higher 2H-enrichment while n-alkanes (C-10-C-14) show a higher C-13-enrichment. delta H-2 values of n-alkanes (>C-20) are useful to discriminate mixed oils that were not well differentiated by delta C-13 data. delta H-2 values of individual n-alkanes from oils suggest a possible exchange of C-bound H with other hydrogen during their generation from precursor molecules. We find that delta H-2 values of n-alkanes from Jurassic source rock extracts, at the onset of oil generation, were mainly controlled by the isotopic composition of biosynthetic precursors and varied from-100 to-150 parts per thousand. Combination of carbon and hydrogen isotope compositions of n-alkanes proved to be a useful tool to discriminate Jurassic petroleum mixtures from distinct sources in the Norwegian South Viking Graben. (c) 2020 Elsevier Ltd. All rights reserved.