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 s mall number of studies have indicated that overpressure can retard maturati on. Although some of the published information from experimental investigat ions appears to be conflicting, careful examination of the experimental con ditions shows that both vitrinite reflectance and hydrocarbon generation ar e retarded by overpressures. Overpressure appears to result in the retentio n of volatiles within the molecular structure which prevents the molecular reorganisation necessary to produce higher reflectance values. Using a data base containing vitrinite reflectance from both overpressured and normally pressured wells, a kinetic model (PresRo(TM)) has been developed in which o verpressure modifies the Arrhenius (A) factor. The model has been tested on two different basins (South China Sea and Sable), exhibiting a range of ti me-temperature-overpressure characteristics. The results suggest that the m aturity and timing of the onset of hydrocarbon generation differ significan tly from those predicted by current models. (C) 1999 Elsevier Science Ltd. All rights reserved.