Geomorphology and seismic stratigraphy of the early Cretaceous delta in the Vlaming Sub-basin and implications for seal quality

Abstract

The early Cretaceous South Perth Shale has been previously identified as the regional seal in the offshore Vlaming Sub-basin. The South Perth Shale is a deltaic succession, which infilled a large palaeotopographic low in the Early Cretaceous through a series of transgressive and regressive events. A study undertaken at Geoscience Australia has shown that the seal quality varies greatly throughout the basin and in places has very poor sealing properties. A re-evaluation of the regional seal based on seismic mapping determined the extent of the pro-delta shale facies within the South Perth Shale succession, which provides effective sealing capacity. New sequence stratigraphic interpretation, seismic facies mapping, new and revised biostratigraphic data and well log analysis were used to produce palaeogeographic reconstructions which document the distribution of depositional facies within the South Perth Shale and reveal the evolution of the early Cretaceous deltas. Our study documents spatial variations in the seal quality and re-defines the extent and thickness of the regional seal in the offshore central Vlaming Sub-basin. It provides an explanation for the lack of exploration success at some structural closures and defines constraints on the possible location of valid plays.