ARE VANADYL PORPHYRINS PRODUCTS OF ASPHALTENE KEROGEN THERMAL BREAKDOWN/

The idea was examined that during early stages of thermal maturation o f source rocks or petroleums, the release of bound vanadyl (VO2+) porp hyrins (P) from the immature asphaltenes or kerogen could contribute t o an increase in extractable VO2+-P. To simulate such a change in the laboratory, the Dead Sea 'floating' asphalt and total organic (bitumen + kerogen) fractions of the La Luna and Serpiano carbonaceous sedimen tary rocks were heated at controlled temperatures (100, 200, 300 and 4 00 degrees C) for different periods of time. Residual (and altered) as phaltenes or kerogens were then separated from the heated products and analysed for VO2+-P content by electron spin resonance. Three conclus ions were reached: (1) thermal degradation of immature asphaltenes or kerogen generated no or very little (<1 wt%) extractable VO2+-P during simulated maturation of petroleums or source rocks and thus by infere nce during natural maturation; (2) petroleum VO2+-P by far are those t hat were saved from incorporation into asphaltenes or kerogen precurso rs (or young asphaltenes or kerogen) during diagenesis; and (3) a high VO2+-P content of a petroleum is not an indication of its immaturity. (C) 1997 Elsevier Science Ltd.