Abstract

Maturity and petroleum generation modeling of the Paleozoic succession in the Carnarvon Basin shows that most potential source rock intervals reached their maximum generation migration during the Carboniferous–Permian and could have charged traps developed during rifting in the middle Carboniferous to Early Permian except for the Peedamullah Shelf, where generation peaked during the Cretaceous. However, identification of such traps is challenging because it is difficult to differentiate between the deformation associated with middle Carboniferous–Early Permian rifting and that of the Early Cretaceous breakup rifting. Given the presence of suitable reservoir and sealing units in most of the Paleozoic, the prime risks for this section are the volume of available source rock, trap integrity because of the long period of preservation required, and relative timing of generation vs. trap formation, such that charging of younger traps requires secondary migration.

The best Paleozoic oil-prone source beds identified in the Carnarvon Basin are thin beds in carbonate-dominated Silurian and Devonian units on the Gascoyne Platform, but Devonian source beds are restricted to the northern parts of the platform. The maturity of these units progressively increases from immature in the south-southeast to mature in the north-northwest, following increasing depth of burial in that direction. The best gas-prone source beds lie within the Lower Permian of the Merlinleigh Subbasin, and their maturity ranges from immature along the margins of the subbasin to overmature toward the center. Within the Upper Permian, the best source beds for oil and gas are in the Peedamullah Shelf, where they range from immature in the southeast to mature in the northwest.

Commercial Paleozoic petroleum has yet to be discovered in the Paleozoic of the Carnarvon Basin, but the assessment of this part of the basin is limited because few, if any, of the exploration wells drilled to date were valid tests of these objectives.

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