SUMMARY AND RE-EVALUATION OF THE HIGH-TEMPERATURE ISOTOPE GEOCHEMISTRY OF METHANE

Abstract

Thirty years of research are brought together into one coherent summary of carbon and hydrogen isotope effects during the thermocatalytic production of methane from model compounds, petroleum, source rocks, and coals. The approach used by the authors and co-workers has been to pyrolyze model and natural compounds and to study the isotopic fractionations associated with molecular structure, temperature, and catalysis. The results from these experiments are summarized. A practical application of these pyrolysis experiments was the development of the pyrolysis-carbon isotope method (PCM) for determining kerogen maturity. This maturity indexing procedure is based on the isotopic difference between the total methane produced by exhaustive pyrolysis and the parent organic carbon and the mole ratio of methane to parent carbon. Data are also summarized for the thermal destruction of methane and carbon isotope exchange between methane and amorphous carbon and carbon dioxide. The latter results are important when determining the source of methane in hydrothermal fluids.