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

TLDR

The authors introduce a simplified vitrinite maturation model, EASY%R[o], that predicts reflectance changes over time and temperature. EASY%R[o] employs an Arrhenius first‑order parallel‑reaction model with a distribution of activation energies to generate vitrinite reflectance versus time profiles for specified time‑temperature histories, enabling application across stratigraphic levels, reflectance ranges of 0.3–4.5 %, and heating rates from laboratory to basin‑scale. Calibration against a rigorous chemical‑properties‑based model shows that EASY%R[o] accurately predicts vitrinite reflectance for rocks subjected to igneous intrusion, geothermal fluids, and burial, and compares favorably with methods such as the Lopatin time‑temperature index.

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 .