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A Structural Re-Evaluation Of The Pendock Prospect And Surrounding Area, Carnarvon Terrace, WA

Prosser, Scott

Honours Degree, 2000

University of Adelaide

Abstract

A seismic-based structural re-evaluation of the Pendock well and the surrounding area has concluded that, while the well was slightly off structure, this was not the reason that it was dry. The target Birdrong Sandstone remains the most prospective hydrocarbon reservoir in the area, although there are also potential targets in the Palaeozoic succession.

The study area covers the Carnarvon Terrace, on the boundary of the Exmouth and Gascoyne Sub-basins, at the southern end of the Carnarvon Basin, onshore and offshore Western Australia. Early oil drilling in the late 1960s was unsuccessful and the prospectivity of the area has remained downgraded since then. 2D seismic has been collected sporadically since the 1960s to the 1990s, but only the more recently acquired data were used in this study. Seismic data were tied to the Pendock well, the only drillhole in the area.

The structural re-interpretation of the area, in conjunction with knowledge of the sedimentary patterns of the highly prospective Winning Group has shown that the Pendock Structure is an elevated fault block, and not the most prospective target for hydrocarbon exploration in the study area. Thick Cretaceous sandfilled channels may prove to be better targets. A large Devonian reef facies (Point Maud Member) lies within the fault structure.. The reef may have also contributed to the higher relief of the Pendock structure.

The most prospective plays in the area are now believed to be channel systems located in the deeper sections of the Carnarvon Terrace. The Cretaceous Winning Group, consisting of the porous Birdrong Sandstone, overlain by the regional Muderong Shale seal fills the channels. These channels occur as both incised valleys, and fault controlled features. Channel depth for the incised valleys is quite variable, with typical large channels in the order of 50 -100 m deep, and several kilometres wide. The channels located on rotated hanging fault blocks are up to 50 m deep. The deeper fault controlled channels are also covered by thicker successions of marine shales, which provide greater sealing potential than the thinned 24 m of shale over the Pendock structure.

Another potential play for the Birdrong Sandstone includes accumulations in local topographic lows on the karstified unconformity surface. Karstification is most prominent in the vicinity of the Pendock Structure where the underlying Moogooree Limestone was exposed from the Permian to Early Cretaceous. A risk factor in this play however, is the uncertainty in interconnection of the karst valleys.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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