A comparison of pyrolysis products with models for natural gas generation

Abstract Hydrous pyrolysis, using progressive heating from 150 to 365°C, is used to study the generation and isotopic composition of hydrocarbon gases and carbon dioxide. Different source rocks from the Draupne, Heather, Dunlin and Brent Formations in the North Sea, a Miocene brown coal from Germany, a coal from the Middle Jurassic Ness Formation in the northern North Sea and a rich marine type source from the Late Jurassic Kimmeridge Clay Formation onshore UK are studied. The experimental results are related to vitrinite reflectance as a maturity reference parameter and to existing models for natural gas generation. Hydrous pyrolysis simulates the observed isotopic composition of natural systems fairly closely. The largest deviations are found for methane, which is most sensitive to fractionation effects. The obtained results mainly reflect variations in source rock type and initial isotopic composition. Different maturity-dependent trends are found between coal-derived and marine type II-derived gases. Trends in the experimental data fit well with basic assumptions of existing models for natural gas generation.