Hydrogen isotope study of petroleum and related organic substance

Abstract

D/H and C^(13)/C^(12) of more than 90 crude oils from all over the world and ranging from Pliocene to Cambrian and other related organic substances have been analyzed to investigate the range of the δD values of petroleum and the controlling factors. δD values of crude oils range from -85 to -181‰. Samples of non-marine origin have much narrower δD values of -142 to -163‰. Liquid petroleum distilled from Kanai gas of Alaska has a δD value of -252‰ which is the most negative δD value for petroleum samples analyzed so far. While the gas fraction can be depleted in deuterium by about 55 to 70‰ relative to the oil fraction, there is practically no detectable difference in δD values between liquid and wax fractions of crude oil. It thus appears that the variation in δD values in crude oils in general is not caused by the compositional difference. However, under unusual situations such as "oil" distilled from the Kenai gas, the effect of chemical composition can be important. Evidences also show that variation in δD values of crude oils is inherited from the source materials. There exists correlation between latitude of sampling sites and δD values of crude oils. This indicates that terrestrial organic substance is a major component of source material for most crude oils. The results also seem to support the hypothesis that the lipid fraction is the major biologic source of petroleum. It also can be concluded from the results that the hydrogen isotopic data are useful in correlation between source rocks and reservoirs of petroleum and among crude oils of common origin. There are no systematic relationships between δD and SC13 values, and between δD values and geologic ages of the crude oils analyzed so far.