High-temperature programmed pyrolysis of Paleozoic source rocks from Northern Germany and adjacent areas and its thermodynamic constraints

In order to determine the hydrocarbon generating potential of high-maturity source rocks (>2% Rmax VR), it is necessary to conduct pyrolysis experiments at high temperatures. However, kinetic and thermodynamic considerations suggest that, with increasing temperatures, the gas forming reactions become more and more unrealistic. Since there are no reliable alternative physical and chemical methods for the evaluation of late hydrocarbon potential, pyrolysis conditions have to be optimized so as to minimize the secondary degradation of methane. This necessitates the use of high-temperature programmed micropyrolysis, which permits the quick removal of pyrolysis products from the hot reaction zone. This paper discusses how a pyrolysis procedure that is similar to Rock-Eval pyrolysis was used to investigate the hydrocarbon potential of highly mature Paleozoic rocks from Northern Germany and adjacent areas. The objective of the experiments was to determine whether small amounts of dry gas, formed at maturities beyond 2% Rmax, can fill commercially interesting gas reservoirs. The finding was that coals, coaly shales, and also Cambro-Ordovician Alum Shales retain a sufficiently large methane generating potential at high maturities. In many of the rocks pyrolyzed, the kerogen clearly contained organic material of different structures and different thermal stability. These kerogen fractions decomposed one after another at different maturity stages. An isotopic inversion of the carbon in the methane released could be observed as soon as a new and more stable structure was degraded.