Carbon isotopic balance of kerogen pyrolysis effluents in a closed system

We have devised an experimental method for calculating isotopic mass balances for the C-12 and C-13 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 degrees 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 (C-1-C-5), non-hydrocarbon gases (CO, CO2, H-2, H2S), C-6-C-14 products soluble in pentane (C-6-C-14 saturated, C-6-C-14 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 delta C-13 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 delta C-13 fractionation observed between different pyrolysis products reached 18 parts per thousand, but only 2 parts per thousand between different C14+ fractions within the range of pyrolysis conditions. (c) 2005 Elsevier Ltd. All rights reserved.