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ABSTRACT: Pitfalls in Hydrocarbon Generation Modeling

Thomas T. Y. Ho, Craig F. Schiefelbein

An interlaboratory study was conducted to compare pyrolysis-based methods used to determine kinetic parameters (E, A) for hydrocarbon generation. Aliquots of five well-known source rocks, composed of different kerogen types, were analyzed by three different laboratories using published dry pyrolysis methods. Samples included lacustrine source rocks from the Green River Fm (USA) and Lower Cretaceous

of West Africa (type I); Middle Eastern Cretaceous and Jurassic source rocks (type II); and a South China Sea Tertiary source rock (type III). Pyrolysis data were used to derive the kinetic parameters. Two of the labs used curve fitting techniques that employ a single Arrhenius constant (A) and indirectly distribute the activation energies within a relatively narrow range (40 to 70 and 35 to 65 Kcal/mole). The third lab used a time-slice technique, variable Arrhenius constants, and directly determined the activation energies that can be distributed over a wider range (20 to 80 Kcal/mole).

The results of the study indicate that although the different approaches often provide similar average values of activation energy, significant differences in the distribution of E values can result in unrealistic maturation levels defining the oil generation window. For example, these different approaches can shift the modeled top of the oil window by up to 2000 f in a basin with a typical heating rate (2°F/Ma).

It will be demonstrated that the validity of the modeling results should be established by comparison with other data such as hydrocarbon-generation profiles (based on C15+ extract data) and hydrous pyrolysis experimental results.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990