Petroleum Generation and Expulsion: Process Understanding and Application to Norwegian North Sea Source Rocks

Initial geochemical screening of the Upper Jurassic Mandal formation (TOC, Rock-Eval) identifies a very prone petroleum source rock that is situated in the maturity window to generate petroleum. Nevertheless, composition and amounts of predicted hydrocarbons reveals significant discrepancies to actual accumulations encountered in identified trap structures. Petroleum generation and expulsion models for petroleum source rocks are relatively simplistic, often combining kinetic descriptions of oil (often C5+) and gas (C1-4) generation with arbitrary sorption threshold values and a basic permeability description of the source rock. While generally satisfactory for assessing bulk volumes generated and expelled from a source rock such approaches omit a range of chemical and physical details of the processes and effects involved, which may be critical for predicting the amount and type of retained and expelled fluids, and changes of these amounts and compositions as a function of maturity. Barren petroleum accumulations in potential trap structures could likely be attributed to delayed expulsion due to adsorption thresholds varying from commonly applied sorption models (e.g. Pepper and Corvi, 1995). Brief comparisons drawn to several Upper Jurassic source rocks as the Draupne formation indicate high lateral variability in deposition and preservation of organic matter of this Upper Jurassic main source rock of the central North Sea petroleum system.


  • quantifying the in-place retained petroleum as a function of TOC, kerogen type, rock maturity and mineralogy + comparison to expelled/accumulated petroleum compositions using MPLC, GC-MS, GC-IR-MS, FT-ICR-MS
  • developing more realistic sorption descriptions including influence of kerogen type on molecular and physical structure and influence of fluid type generated
  • generating compositional kinetic descriptions for individual source rock units coupled with a new expulsion/retention model applicable for conventional and unconventional petroleum system assessments 
Schematic visualization of a hydrocarbon prospect (after Tissot & Welte, 1984) showing compositional changes of generated petroleum when migrating within the source rock and expelled to the carrier bed. Question marks represent the processes of e.g. fractionation and retention that are under investigation in this project


  • Prof. Brian Horsfield 
  • Volker Ziegs

Partners & Funding:

  • Det Norske Oljeselskap ASA