ABSTRACT: Late Jurassic and Cretaceous Seals of the Vulcan Sub-Basin

Kivior, Tomasz, John Kaldi, and Richard Jones , National Centre for Petroleum Geology and Geophysics, University of Adelaide, Adelaide, Australia

The Vulcan Sub-Basin contains several structural provinces containing major petroleum fields. Paleo-oil columns found within the Vulcan Sub-Basin suggest trap breach either via top-seal or fault leakage. This paper investigates the top seal leakage aspect. The regional extent, lithological description and sealing potential of Cretaceous sediments are qualified for the first time on a regional scale.

Wireline logs correlations, based on biostratigraphic parameters, have been used to divide the Late Jurassic to Cretaceous sediments into four time continuous intervals. Seismic surveys were used to determine the regional extent of the sealing intervals. Results suggest that each of the four intervals defined is significant as a seal in different structural provinces of the Vulcan Sub-Basin.

X-ray diffraction data, wireline log signatures and lithological descriptions of the Cretaceous intervals, suggest that the sealing lithologies are mainly calcareous shales and marls. Mercury injection capillary pressures tests, performed on mud chips and cores were used to determine seal capacity. Capillary pressure results suggest hydrocarbon column heights of up to one hundred meters are supportable by the calcareous sediments of the youngest interval identified in the Cretaceous.

The study has also demonstrated that there is a direct relationship between seal capacity and present and paleo-columns oil column heights in the Vulcan Sub-basin.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia