The Post-Regional Seal Play In The Northern Carnarvon Basin.
Honours Degree, 2000
University of Adelaide
Successful petroleum exploration for targets above the Muderong Shale, the regional seal for the Northern Carnarvon Basin, is dependent on the accurate recognition and definition of the play elements that control the distribution of hydrocarbons within this succession. The recognition of reservoirs, seals, trapping mechanisms, sources and migration above the regional seal has established a framework for potential hydrocarbon accumulations in the post-Muderong succession.
Using wireline logs from wells throughout the Exmouth, Barrow and Dampier Sub-basins it has been shown that the Muderong Shale is laterally extensive and continuous. Capillary pressure data from the Muderong Shale has shown that it is an effective membrane seal, therefore seal failure is a result of migration through networks of faults and fractures.
With the exception of the concretionary carbonate reservoirs at Barrow Island, reservoir deposition during the post-regional seal succession is associated with lowstand and transgressive systems tracts. This provides excellent reservoir-seal couplets, where lowstand deposits (lowstand wedges, submarine fans) and transgressive deposits (within incised valleys) are stratigraphically trapped within clay-rich sealing facies associated with deposition during transgressive and highstand system tracts.
The source rock potential of the Muderong Shale and Gearle Siltstone is moderate and marginal respectively. Maturity data suggest that these units are currently within the oil generation zone west, of Barrow Island. Biomarker analysis, rock-eval pyrolysis and maturity modelling suggest that the Muderong Shale is currently generating oil in a trend that parallels the Alpha Arch and Rankin Platform.
The main phase of hydrocarbon migration was initiated during the Middle Miocene. This phase of migration occurred when the Upper Dingo Claystone had entered the oil window and was synchronous with fault reactivation caused by the collision between the Indo-Australian and Eurasian plates. The in-situ stress field suggests that faults orientated northeast-southwest on the basin margins and east-west in the basin centre will preferentially allow migration hydrocarbons.