Experimental study of vitrinite maturation: effects of temperature, time, pressure, water, and hydrogen index

Lignite samples were artificially matured in sea water over a wide range of temperature and time (250–450°C and up to 305 days) in a confined-pressure system. The reflectance evolution of vitrinite-like macerals in the run products was found to fit an empirical power law rate model. These experiments confirm that the evolution of vitrinite reflectance is controlled more by temperature than time. The empirical model is reasonably consistent with the kinetic model of Burnham and Sweeney (1989) implying that the mechanism for vitrinite reflectance development at the experimental conditions may not differ significantly from that in nature. This simple rate equation is particularly useful to incorporate into the algorithm of a basin modeling program. Additional experiments confirm that the evolution rate of reflectance of vitrinite depends highly on the original hydrogen content (as measured by hydrogen index) in its precursor materials. Other factors such as water pressure, fluid chemistry, fluid flow, the presence of oil or Type I organic matter and methane or CO2 partial pressures were found to play only minor roles in the development of vitrinite reflectance.