Water as an oxygen source for the production of oxygenated compounds (including CO2 precursors) during kerogen maturation

In order to study the generation of oxygen-rich species which may act as CO2 precursors, the interaction of sedimentary organic matter and water during hydrous pyrolysis has been investigated using 18O labelled water. Model compound experiments were conducted with a series of compounds (3,4-dimethylphenol, dodecanoic acid and xanthene) in order to assess their levels of simple homogeneous exchange of oxygen with hot water. While dodecanoic acid underwent extensive oxygen exchange (98%), dimethylphenol underwent restricted oxygen exchange (13%) and xanthene showed no exchange. A comparison of the dimethylphenol model compound experiments in H218O with dimethylphols generated by Kimmeridge Clay kerogen, under identical conditions, showed marked differences in levels of 18O incorporation (approx. 13% for the model compound and 40% for the kerogen-derived products) suggesting neogenic phenol formation during hydrous pyrolysis. The implications of this inferred water oxygen addition to sedimentary organic matter during kerogen degradation will undoubtedly affect mass balance calculations of the generation of oxygen-rich species from sedimentary organic matter and thus have a potential impact on mass balance assessments of the generation of CO2 and its precursors in petroleum basins. The results also have major implications for oxygen mobility between organic matter and water in hydrothermal systems and possibly for lower temperature reactions in petroleum systems