PAYNE, DOROTHY F., and PETER J. ORTOLEVA
Laboratory for Computational Geodynamics, Indiana University, Bloomington, IN

Abstract: A New Chemical Structural Kinetic Approach to Modeling Kerogen Maturation

A new chemical kinetic approach to modeling kerogen thermal maturation and speciation is based on observed structural transformations of proto-kerogen molecules in naturally matured samples. It differs from existing thermal maturation models in that compositionally specific reactants evolve to specific intermediate and mobile products through balanced, nth order processes, by way of a network of sequential and parallel reactions. By considering sedimentary organic matter as assemblages of resistant biomacromolecules, proto-kerogen composition can be tailored to specific depositional environments rather than defined as conventional kerogen types. This model predicts hydrocarbon product speciation and relative reaction rates, which have important implications for multiphase flow modeling.

To demonstrate the approach, the thermal maturation of lignin, a major component of terrigenous proto-kerogen, is modeled. A reaction network containing 26 species and 22 reactions is constructed, based on published observed structural transformations of naturally matured lignin. The reactions include isomerization, oxidation and reduction, defunctionalization, and cross-linking processes. Output includes mole fractions of all intermediate and mobile species, functional group fractions, and elemental weight percents. The model is sensitive to the initial lignin composition and H₂O content of the system. Results are valid for maturities up to about 1.7 %Ro. The flexible design of the model allows it to be modified to account for compositionally heterogeneous source material.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas