Multi-Component Modelling of Hydrocarbon Charges: Challenges and Developments
Ulrich Ritter, Hans Borge, Are Tømmerås, and Hermann M. Weiss
SINTEF Petroleum Research, Basin Modelling Department, Trondheim, Norway
Modelling of petroleum generation and migration has to date mainly been approached in terms of “bulk” flow of gas and oil. The need for more detailed prediction of petroleum quality has so far only been sporadically addressed. Main challenges in devising multi-component models are to (a) develop an economically viable experimental design that allows also quantification of heavy hydrocarbons and NSO compounds, which make up a large percentage particularly of newly generated petroleum; (b) develop software that allows to separate the simultaneous effects of primary generation and cracking that are inherent in closed-system pyrolysis experiments; (c) identify and quantify the processes that lead to changes of petroleum composition during expulsion and migration. We chose C1, C2 to C5, C6 to C14 saturates, C6 to C14 non-saturates, C15+ saturates, C15+ non-saturates and NSO compounds as pseudo-components. C1 to parts of C15+ are analysed by closed-system micro-scale sealed vessel (MSSV) pyrolysis. Parts of C15+ and NSO have to be derived from large-vessel heating experiments and analysis by TLC-FID (Iatroscan) or semi-preparative liquid chromatography (MPLC), with scaling of the two data sets being the main challenge. Once one single experimental data set has been established, our in-house software KING is used to build both stoichiometrically and kinetically plausible generation, cracking- and redistribution (GCR) models. The interaction of primary generation from kerogen and secondary cracking of oil in a closed system distorts kinetic parameters as well as the potential of the different pseudo-compounds. KING therefore requires closed-system- as well as some open-system experiments in order to derive kinetic constants and the “true” generation potential. Post-generation modification of petroleum occurs during expulsion and primary and secondary migration, usually resulting in strong depletion of NSO compounds and weak to moderate depletion of aromatics. Software PriMig has quantified some of these processes in the source rock, using models based on polymer solution theory and adsorption in nano-pores (Dubinin-Radushkevitch equation). The effect of clay-complex-formation is under investigation. The multi-component capabilities of the secondary migration simulator SEMI have been extended in order to handle a sufficient number and range of mobile compounds. Assuming monolayer adsorption of asphaltenes and resins at the inner surface of pores of the carrier rock, either small charges, very unfocused-, or very long migration pathways have to be invoked in order to explain observed depletion of NSO compounds.
AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands