Modelling of thermal maturation and hydrocarbon generation in two petroleum systems of the Taroom Trough, Australia

Abstract

Thermal maturity modeling, using first-order reaction kinetics, of a Permian and a Triassic source rock in the Taroom trough was employed to determine the time over which petroleum generation, migration, and accumulation occurred, and to explain the observed distribution of oil and gas. Modeling shows that the maximum paleotemperatures were attained in these two source rock units by burial at the south end of the Taroom trough during the Late Cretaceous. In the north, maximum paleotemperatures were caused by increased heat flow, as well as burial to maximum depth. In the southern part of the study area, the Permian-Triassic source rocks started expelling hydrocarbons during the Jurassic-Early Cretaceous. These hydrocarbons migrated updip to the east and west where structural-stratigraphic traps had formed in response to Triassic compressional deformation. Kinetic modeling supports biomarker and other geochemical evidence that the oil and gas currently produced from sandstone reservoirs were sourced mainly from the carbonaceous shales of the Upper Permian Blackwater Group. Hydrocarbon output from the Middle Triassic Snake Creek Mudstone was minor, but sufficient to produce a second petroleum system. North of the study area, early (Triassic) generation of hydrocarbons and subsequent (Jurassic-Cretaceous) burial resulted in an overmature Permian section, at present able to generate only dry gas. The bulk of its hydrocarbons most likely have seeped to the surface. Only late-mature expulsion products, which subsequently migrated southward, could have contributed to the petroleum reserves of the region.