YIELDS AND CARBON ISOTOPIC COMPOSITION OF PYROLYSIS PRODUCTS FROM ARTIFICIAL MATURATION PROCESSES

Yields and isotopic comPosition of various pyrolysis products were investigated for a rich marine type source from the Upper Jurassic Kimmeridge Clay Formation onshore U.K. Three different artificial maturation processes were studied: closed, dry pyrolysis (350-degrees-C for different time intervals between 1 hr and 42 days); temperature-programmed open, dry pyrolysis (72 hr at different temperature levels between 150-degrees and 500-degrees-C); and hydrous pyrolysis (isothermally heated for 72 hr at 280-365-degrees-C). The main difference in hydrocarbon generation is observed between the open and the two closed systems, with significantly lower yields from the open system. The presence of water during the hydrous pyrolysis enhances the generation of carbon dioxide and bitumen, with maximum yields of 4.7 mmol g-1 total organic carbon (TOC) of carbon dioxide and 977 mg g-1 TOC of bitumen in the hydrous system. All three maturation processes generate hydrocarbon gases that exhibit maturity-dependent trends in isotopic composition. The main difference in the carbon isotopic composition of the products is an enrichment of the heavy isotope in the open system compared to the closed systems, with hydrous pyrolysis giving gaseous products most depleted in the heavy isotope. This effect is most pronounced for methane and carbon dioxide. None of the three methods studied produced yield and isotopic compositions which precisely match the composition of natural gases. However, the relationship between the different components are the same on a general level, and with caution the results can be considered representative for real situations.