Tertiary uplift estimation from velocity data in the Eromanga Basin

Abstract

The Tertiary uplift of the Eromanga Basin over PELs 5&6 (SA) and ATP 259P (Queensland), has significantly complicated depth-porosity relationships in the important oil-bearing Hutton Sandstone, as well as altering migration pathways. Because seismic reflection data in the Eromanga Basin are focused on the lower part of the succession, they are not suitable for imaging and mapping the Tertiary unconformities. In this study, an estimate of the magnitude of Tertiary uplift across the acreage has been made by cross-plotting interval velocity and depth for the lithologically homogenous Cretaceous marine shales near the top of the succession. Deviations from a depth-velocity baseline fitted to data from the basin depocentres have enabled quantification of uplift. The uplift estimates have been used to produce pre-uplift depth structure maps which can be used to map pre-uplift hydrocarbon migration pathways. Maximum burial depth can also be calculated, providing a better predictor of porosity in the Hutton Sandstone than present burial depth.