A vitrinite reflectance kinetic model incorporating overpressure retardation

The models currently used to predict maturation and hydrocarbon generation in petroleum basins use time and temperature as controlling parameters. A small number of studies have indicated that overpressure can retard maturation. Although some of the published information from experimental investigations appears to be conflicting, careful examination of the experimental conditions shows that both vitrinite reflectance and hydrocarbon generation are retarded by overpressures. Overpressure appears to result in the retention of volatiles within the molecular structure which prevents the molecular reorganisation necessary to produce higher reflectance values. Using a database containing vitrinite reflectance from both overpressured and normally pressured wells, a kinetic model (PresRo(TM)) has been developed in which overpressure modifies the Arrhenius (A) factor. The model has been tested on two different basins (South China Sea and Sable), exhibiting a range of time-temperature-overpressure characteristics. The results suggest that the maturity and timing of the onset of hydrocarbon generation differ significantly from those predicted by current models. (C) 1999 Elsevier Science Ltd. All rights reserved.