Hydrogen Imbalance in Petroleum Source

Abstract The average molar hydrogen concentration relative to carbon is always higher in petroleum than the source organic matter and thus it becomes a serious concern for the theory of organic origin. On the other hand, abiogenic theory of petroleum generation do not have this problem because hydrogen is available even deep inside the earth either due to serpentinization or by chemical reactions of freshly cut ferromagnesian mineral surface with water. Although available hydrogen thus favours abiogenic theory for petroleum generation, but the field and other laboratory evidences in favour of organic origin are so convincing that it is very difficult to accept generation of petroleum other than the organic source. In this work attempt has been made to critically review this hydrogen imbalance problem within a fence of organic origin of petroleum. Though the organic matter is deficient in hydrogen, yet it can generate petroleum if its deficiency is compensated by some other source. Fischer-Tropsch (FT) synthesis, in which coal and organic biomass is catalytically converted to liquid petroleum using water gas as a source of hydrogen, experimentally supports the above statement. Many of the recent workers believe petroleum is generated from organic matter and the deficient hydrogen is made available from the subsurface water. This is further supported by hydrous pyrolysis and also by isotope exchange reactions with water. In this paper critical review is made to understand the limitations of these supporting evidences. High pressure temperature conditions in FT synthesis cannot be a model for natural petroleum generation and thermodynamically it can be shown that it is nearly impossible to spontaneously convert dead organic matter to petroleum compounds. An alternate solution is proposed here suggesting petroleum is possibly generated using dominantly the lipids of organic matter that has higher H/C compared to petroleum.