MODELING OF THERMAL MATURATION AND HYDROCARBON GENERATION IN 2 PETROLEUM SYSTEMS OF THE TAROOM TROUGH, AUSTRALIA

Thermal maturity modeling, using first-order reaction kinetics, of a P ermian and a Triassic source rock in the Taroom trough was employed to determine the time over which petroleum generation, migration, and ac cumulation occurred, and to explain the observed distribution of oil a nd gas. Modeling shows that the maximum paleotemperatures were attaine d in these two source rock units by burial at the south end of the Tar oom trough during the Late Cretaceous. In the north, maximum paleotemp eratures were caused by increased heat flow as well as burial to maxim um 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 wh ere structural-stratigraphic traps had formed in response to Triassic compressional deformation. Kinetic modeling supports biomarker and oth er geochemical evidence that the oil and gas currently produced from s andstone reservoirs were sourced mainly from the carbonaceous shales o f the Upper Permian Blackwater Group. Hydrocarbon output from the Midd le Triassic Snake Creek Mudstone was minor, but sufficient to produce a second petroleum system, North of the study area, early (Triassic) g eneration 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 o f the region.