Further Evaluation of the Expulsion and Primary Migration Scheme PRIMIG
Joachim Rinna, Arnt Grøver, and Matthias C. Daszinnies
SINTEF Petroleum Research, NO-7465 Trondheim, Norway
Assessing the quantities and compositions of hydrocarbons expelled from source rocks relies not only on hydrocarbon generation modelling but also on a profound simulation of expulsion from the kerogen and primary migration within the source rock (Stainforth and Reiders, 1990). For example, from lab experiments it is known that coals may generate as much heavy compounds as a conventional type II kerogen. However, retention processes in the source rock subject the initial generated products to secondary cracking, and a shift to lighter hydrocarbons (condensates, gas) is often seen in coal associated petroleum play types. Therefore substantial compositional changes in the hydrocarbon phase composition may occur before the generated hydrocarbons migrate out of the source rock. This composition change depends on the delicate balance between kerogen type, primary generation kinetics, absorption in the polymer-like kerogen, adsorption in nanopores and on clay minerals within the source rock, and secondary cracking.
A process and stacked filter based expulsion and retention primary migration scheme called PRIMIG (Ritter and Grøver, 2006) has been developed in order to assess both the retention potential within the source rock and the compositional change in the resulting hydrocarbon phase. It simulates the main three processes within the source rock (absorption in polymer-like kerogen, adsorption on vitrinite and inertinite, and adsorption on clay minerals; Fig. 1) responsible for retention of the initially generated hydrocarbon product which makes it available for subsequent secondary cracking.
The Late Jurassic Hekkingen formation is regarded as an important source for many Mesozoic play types in the Barents Sea. However, geochemical studies indicate rather moderate initial hydrogen indices between 200 and 350 mg HC/g TOC (Ohm, 2008) and consequently suggest a significant contribution of land-derived organic matter with associated vitrinite macerals. Here we will systematically test and discuss how changes in the source rock characteristics will influence the composition of the hydrocarbon phase migrating out of the source rock. The obtained results will be utilised within a secondary migration model at regional scale (Daszinnies et al, 2012).
Figure 1. Data flow in PRIMIG, showing the stacked structure of the sequential retention scheme .
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AAPG Search and Discovery Article #120098©2013 AAPG Hedberg Conference Petroleum Systems: Modeling the Past, Planning the Future, Nice, France, October 1-5, 2012