Artificial maturation of a Type I kerogen in closed system: Mass balance and kinetic modelling

The aim of this work was to apply a kinetic scheme proposed by Behar et al. [2008, Organic Geochemistry 39, 1-22] to a Type I kerogen of lacustrine origin. There it was demonstrated, based on experiments performed in closed pyrolysis system on a kerogen of marine source (Type II) and lignite (Type III), that the major proportion of generated hydrocarbons (Hcs) does not originate from the initial kerogen. Indeed, kerogen decomposes mainly into heavy NSO compounds. Subsequently, these NSOs rapidly undergo secondary cracking to generate hydrocarbons and a new NSO fraction. Consequently, HCs have multiple sources: a minor part comes from the kerogen itself, whereas the major part is derived from secondary cracking of the two types of NSOs. In the present work, an immature Type I kerogen was pyrolysed in a closed pyrolysis system from 275 to 350 degrees C with residence time between 1 h and 27 days. The kinetic scheme was optimised on the basis of the same framework as that proposed in our previous study and an excellent fit was obtained between experimental and optimised data. This kinetic scheme was used to compare our results with those obtained in open system pyrolysis and on an aliquot of the same sample matured in a closed pyrolysis system under hydrous conditions [Ruble et al., 2001, American Association of Petroleum Geologists Bulletin 85, 1333-1371]. In hydrous experiments, the results demonstrate very good prediction of the total HC fraction, which is recovered in both the tarry bitumen and the expelled oil. This means that, as far as the generation process is concerned, the rate and total amount of generated HCs are similar in both hydrous and non-hydrous closed systems. In an open system, the total HC yield is similar to that obtained in a closed system but the generation rate is significantly lower. (C) 2010 Elsevier Ltd. All rights reserved.