Olefins of radiogenic origin in crude oils

Crude oil samples irradiated by 60Co γ-irradiation have been investigated for olefins. Olefin concentrations were found to increase in oils in the proportion with the irradiation dose. No influence of S and/or asphaltene concentrations in oils on olefin formation was observed. The olefin hydrocarbons were found to be generated mainly through non-selective dehydrogenation of saturated hydrocarbons in the oils, rather than cleavage of C-C bonds of aromatic and/or resinous compounds. Structures of the laboratory-prepared radiogenic olefins were studied (by GC,1H and 13C NMR) and compared with structures of alkenes isolated from Paleozoic and Precambrian oils. The results of comparison do support the radiolytic concept of olefin formation in crude oils. There are also reported data on the olefin concentrations measured in about 700 oils from 5 basins of the Former Soviet Union, in which the age of oil formations ranges from Precambrian up to Cainozoic. A tendency for olefins to occur more often in oils from old and cold deposits has been established.