Areas W07-16 and W07-17
Exmouth Plateau, Carnarvon Basin
Carnarvon Basin Geology
Hydrocarbon Habitat
The Carnarvon Basin is Australia’s most prolific hydrocarbon-producing
basin; 77.8 MMbbls or 12.4 GL of oil, 925 bcf or 26.2 BCM of gas and 37.8
MMbbls or 6.0 GL of condensate were produced in 2005 (http://www.doir.wa.gov.au/mineralsandpetroleum/Publications.asp).
This represents more than half of Australia’s total hydrocarbon production.
During 2005 a total of 58 wells were drilled in the basin including 25 new
field wildcats, 13 extensions and 20 development wells (http://www.doir.wa.gov.au/mineralsandpetroleum/0D311793CCD44D60B1C1730FB59451C9.asp).
The majority of the hydrocarbons discovered to date in the Carnarvon Basin are reservoired in top porosity beneath the Early Cretaceous Muderong Shale, which forms the regional seal. The presence of this effective regional seal is a major contributing factor to exploration success in the basin (Baillie and Jacobson, 1997). One of the notable exceptions is the Barrow Island oil field, where the oil-bearing Windalia Sandstone of the Muderong Shale is top-sealed by the Aptian Windalia Radiolarite. Another exception is the Maitland gas accumulation, in which Paleocene sandstone is the reservoir. Intra-formational seals are also an important element of hydrocarbon accumulations in the basin, resulting in stacked hydrocarbon-bearing reservoirs beneath a regional unconformity surface. Individual pools in gas accumulations on the Rankin Platform are top sealed by a combination of the regional seal and intra-formational claystones. Figure 3 shows the major oil and gas accumulations discovered in the Carnarvon Basin.
The main trap styles in the basin are drape anticlines, horsts, fault roll-over
structures and stratigraphic pinch-outs beneath the regional seal. The stratigraphic
level of top porosity, ranging from the Late Triassic Mungaroo Formation
to the Early Cretaceous Mardie Greensand beneath the regional seal, generally
becomes progressively younger inboard.