Abstract: Predictive "kinetic" Model of Smectite to Illite Evolution as a Tool for Thermal History Analysis in the West Carpathians

FRANCU, JURAJ and HARALD S. POELCHAU*

Smectite illitization is a ubiquitous process, observed in numerous sedimentary basins as a decrease of illite-smectite expandability (%S) with burial temperature. Expandability is a promising candidate as a calibration parameter in the computer simulation of basin evolution and thermal history.

Expandability was measured in core samples from Tertiary and Mesozoic basins in the West Carpathians and eastern Bohemian Massif. X-ray diffraction (XRD) patterns were evaluated using peak-fitting and comparison with computer-simulated XRD profiles (NewMod by R. C. Reynolds). Interlaboratory tests confirmed the consistency of the data sets. Expandability correlates fairly closely with vitrinite reflectance and Tmax of RockEval pyrolysis.

Burial and thermal history was modeled using PetroMod software and based on a number of deep boreholes, paleogeographic background, and organic maturity indicators. Profiles with known erosional gaps were treated separately.

The proposed "kinetic" model assumes some similarities between smectite illitization and kerogen maturation. In both cases there are starting materials (expandable I/S minerals vs immature kerogen), reaction products (illitic I/S minerals vs residual kerogen), by-products (water, ions vs oil or gas), and the process consists of a series of partial reactions which can be characterized by kinetic parameters. A distribution of activation energies and an empirical frequency factor are proposed which give a fairly good fit of the predicted vs the measured illitization paths in several basins in this area.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria