A chemical kinetic model of vitrinite maturation and reflectance

Abstract

A chemical kinetic model is presented that uses Arrhenius rate constants to calculate vitrinite elemental composition as a function of time and temperature. The model uses distributions of activation energies for each of four reactions: elimination of water, carbon dioxide, methane and higher hydrocarbons. The resulting composition is used to calculate vitrinite reflectance via correlations between elemental composition and reflectance. The correlations are derived from published measurements. The model is valid for %Ro values from slightly less than 0.3 to slightly greater than 4. Model calculations are compared to published vitrinite data from both laboratory experiments and sedimentary columns where adequate thermal histories are available. Calculated and measured %Ro values generally agree within 0.1 at low rank and 0.4 at high rank, which is comparable to uncertainties in the experimental values. This confirms our starting premise that vitrinite reflectance is properly described by standard chemical kinetics with activation energies that extrapolate from laboratory to geological maturation temperatures. The model indicates that the relationship between the extent of oil generation and vitrinite reflectance is nearly independent of heating rate.