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ABSTRACT: Thermal history modeling using organic matter maturation data from normal pressure systems in the Offshore Carnarvon Basin, Northwest Shelf, Australia

He, Sheng, Mike Middleton, and Lindsay Collins , Curtin University of Technology, Perth, Australia

The Offshore Carnarvon Basin consists of a series of the Jurassic-Cretaceous rifting sub-basins as a result of lithospheric thinning and oceanic crust spreading associated with the breakup of the Gondwana continent. Two subsidence and thermal periods can be recognized in the evolution of the Offshore Carnarvon Basin. The period of rifting, lasting from the late Early Jurassic to Early Cretaceous, resulted in tens of kilometers of sediments being deposited in the rift grabens, and up to 2000 m of sediments were eroded on the uplift areas of the eastern and northern rift shoulders. The period of post-rifting is characterized by thermal subsidence in the Cretaceous.

Vitrinite reflectance and Tmax profiles from several exploration wells in various tectonic units with normal pressure systems have been selected for this modeling using a temperature-time basin model. The study indicates that the maturity profiles did not undergo the retardation by paleo-overpressure systems during their rifting thermal history. However, some vitrinite reflectance profiles have been corrected for suppression due to hydrogen-rich vitrinite. The study suggests that normal pressure is not an important factor in organic matter maturation, and the proposed basin model is capable of modeling thermal history using maturation data in normal pressure systems. The rift thermal model can provide a good fit to the vitrinite reflectance and Tmax profiles and present day geothermal field. The peaks of rift heat flow in the rift garbens and Exmouth Plateau ranged from 60 to 80 mW/m2, while the rift shoulders experienced a lesser rifting thermal increase.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia