# AAPG Bulletin

Abstract

Volume: 74 (1990)

Issue: 10. (October)

First Page: 1559

Last Page: 1570

Title: Evaluation of a Simple Model of Vitrinite Reflectance Based on Chemical Kinetics (1)

Author(s): JERRY J. SWEENEY and ALAN K. BURNHAM (2)

Abstract:

We present a simplified version of a vitrinite maturation model, complete with sample spreadsheet, based on changes in vitrinite composition with time and temperature. The simplified model, called EASY%R[o], uses an Arrhenius first-order parallel-reaction approach with a distribution of activation energies. EASY%R[o] has been calibrated to a more rigorous model of vitrinite maturation based on the chemical properties of coal vitrinite. With EASY%R[o], a profile of vitrinite reflectance vs. time can be obtained for a given stratigraphic level if the time-temperature history for that level has been estimated. When applied to multiple stratigraphic levels, EASY%R[o] can be used to compute profiles of the percent of vitrinite reflectance with depth for comparison with borehol data and to optimize thermal history models. EASY%R[o] can be used for vitrinite reflectance values of 0.3 to 4.5%, and for heating rates ranging from those in the laboratory (1 degree C/week) to those in slowly subsiding geologic basins (1 degree C/10 m.y.). Examples of model applications range from sedimentary rocks heated by an igneous intrusion to a variety of burial histories. Vitrinite maturation predicted by EASY%Ro is compared to other methods currently being used, such as the Lopatin time-temperature index, level of organic maturity, and other approaches using a single activation energy. Our model successfully estimates vitrinite reflectance due to thermal metamorphism of sedimentary rocks heated by igneous intrusions, geothermal fluids, and burial in a variety of basin setting .

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