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Marine and
Petroleum Geology
II1~.~ .,il
ELSEVIER Marine and Petroleum Geology 16 (1999) 355-377
A vitrinite reflectance ic model incorporating overpressure
retardation
. Carr*
Advanced Geochemical Systems Ltd, Towles Fields, Burton on the Wolds, Leicestershire, LEI2 5TD, UK
Received 31 December 1996; receivedin revised form 8 March 1998; accepted 1 October 1998
Abstract
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 anisation necessary to produce higher
reflectance values. Using a database containing vitrinite reflectance from both overpressured and normally pressured wells, a ic
model (PresRoTM) 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.
© 1999 Elsevier Science Ltd. All rights reserved.
Keywords." maturity; overpressure;retardation
I. Introduction differences in interpretation illustrate the lack of funda-
mental understanding of the effects of pressure on the
Overpressures, that is fluid pressures above hydro- processes of maturation and hydrocarbon generation.
static, mon in many sedimentary basins, and Exploration drilling r