Vitrinite-inertinite Reflectance & Fluorescence Analysis of Samples from the Great South Basin

VIRF (Vitrinite-Inertinite Reflectance and Fluorescence, or VRF1) analysis has been performed on 71 cuttings samples from 8 Great South Basin (GSB) wells. The distribution and characteristics of key petrographic features in GSB wells suggest there has been more than one episode of hydrothermal activity. Asphaltic material is common in some wells and its association with pyrolytic carbon suggests that oils generated during hydrothermal high heat flow in the Paleocene may have been thermally fractionated during Eocene (or later) igneous and hydrothermal activity at some sites. This suggestion is supported by the fact that asphaltic residues are rare in Tara-1, Toroa-1 and Kawau-1A, and these are the wells which have provided encouraging hydrocarbon shows.