Carbon isotopic balance of kerogen pyrolysis effluents in a closed system

We have devised an experimental method for calculating isotopic mass balances for the 12C and 13C in the pyrolysis products from a type II kerogen during artificial maturation in a closed system. The method also enables a study of the isotopic evolution of cracking products versus kerogen transformation ratios. The type II kerogen (Paris Basin) was at the onset of catagenesis. Pyrolysis was carried out in a confined closed system under isothermal conditions, at several temperatures (275–350 °C) and times at a constant pressure of 10 Mpa. Under these conditions, the kerogen transformation ratios covered a range from 1% to 87%. Pyrolysis effluents were separated into hydrocarbon gases (C1–C5), non-hydrocarbon gases (CO, CO2, H2, H2S), C6–C14 products soluble in pentane (C6–C14 saturated, C6–C14 aromatics), C14+ products soluble in pentane (C14+ saturated, C14+ aromatics, resins 1), C14+ products soluble in dichloromethane (asphaltenes and resins 2) and residue insoluble in dichloromethane. Validation of mass and atomic carbon balances plus δ13C measurements was checked carefully in order to obtain accurate isotopic mass balances. Mass balances on pyrolysis products were higher than 97.7% of the initial kerogen amount. The δ13C fractionation observed between different pyrolysis products reached 18‰, but only 2‰ between different C14+ fractions within the range of pyrolysis conditions.