--> --> Discovery of the Anisian Caley Member Petroleum System, Bedout Sub-Basin, Western Australia

2018 AAPG International Conference and Exhibition

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Discovery of the Anisian Caley Member Petroleum System, Bedout Sub-Basin, Western Australia

Abstract

In the early 1980’s, sub-commercial hydrocarbons were discovered in the Barret Member of the Lower Keraudren Formation in the Bedout Sub-basin, Western Australia. Further exploration activity in the region was dampened by the poor reservoir quality encountered in the hydrocarbon bearing sandstones, leading to a several decade hiatus. Recently, three exploration wells have targeted the underexplored, older interval of the Lower Keraudren Formation, finding improved reservoir quality in the Caley Member in particular. So far, three exploration wells have intersected the Caley Member, discovering three new hydrocarbon pools. Depositional architecture and sediment dispersal patterns of the Caley Member were influenced by the remnant tectonic elements of the East Gondwana Interior Rift, which created a deep embayment and defined a prominent shelf-slope break. The position of deltaic reservoir and source rock facies can be related to these earlier elements. Caley Member reservoir facies include distributary channels, shoreface, and proximal mouth bars. Interbedded with the reservoirs are algae-rich, lagoonal claystones that have been typed as the source rock facies of the discovered fluids. Charge access is highly efficient as a result of the interbedded nature of these reservoir and source facies. Overlying the Caley Member is the regionally continuous, hemipelagic Hove Member of the Lower Keraudren Formation, which that forms a competent regional seal and promotes lateral migration of the hydrocarbons. There is a remarkable difference between the good reservoir quality of the Caley Member sandstones and the poorer quality sandstones of the overlying strata. This difference can be related to a change in sediment provenance. A major regional unconformity separates the two intervals, defining a break from a very mature sediment source for the Caley Member and deeper section to a much more immature and potentially locally derived source for the younger section. The Barret Member sandstones above the unconformity are largely subarkose, with average permeabilites in the 10’s of mD. In contrast, the Caley Member sandstones are quartz arenites that are buried more than 500m deeper, but retain average permeabilites in the 100’s of mD. A drill stem test has confirmed the excellent gas deliverability of the Caley sandstones.