WAARRE SANDSTONE DEVELOPMENT WITHIN THE PORT CAMPBELL EMBAYMENT

Abstract

The Late Cretaceous Waarre Formation is recognised as the principal reservoir unit throughout the Port Campbell Embayment, where a number of small gas fields were discovered and developed in the late 1970s and the early and mid- 1980s.

The Waarre Formation can be subdivided into four units, identified as Unit A, a basal fining upward sequence; Unit B, a medial siltstone with interbedded calcareous sandstones; Unit C, a coarse- grained porous sandstone (the primary gas reservoir); Unit D, a ferruginous siltstone/sandstone sequence.

The Upper Waarre, Units C and D, represents a variety of environments unique to a beach barrier- system, including back- water lagoons, swamps, tidal channels, tidal deltas, and beach sands. The development of an Upper Waarre sandstone- beach- barrier model, the identification of various facies, and the construction of regional palaeogeography leads to an understanding of sedimentary deposition during Waarre times.

Recent drilling has shown the Upper Waarre to extend laterally in an easterly direction and, as proposed by the depositional model, development of the prospective Waarre Unit C gas sands in a restricted linear east- west zone.

By combining the complex structural history of the Port Campbell Embayment and the resultant structures developed with the depositional model of the Waarre Formation, major migration pathways, and thick (>50 m) overlying seals, exploration throughout the embayment can be directed towards prospective gas reservoirs within the Waarre, Unit C, sandstone bodies.