TROUBLESHOOTING VITRINITE REFLECTANCE PROBLEMS USING FAMM: A GIPPSLAND AND OTWAY BASIN CASE STUDY

Abstract

'Fluorescence alteration of multiple macerals' (FAMM) is a multi-parameter microprobe technique developed by CSIRO to provide the petroleum industry with an objective method of estimating thermal maturity of organic matter in sedimentary rocks. The technique is closely related to vitrinite reflectance methods, although the identification of vitrinite is not necessary; FAMM is based on the fluorescence alteration characteristics of vitrinite, inertinite and liptinite macerals in a sample. It is a powerful tool for the identification of casings, reworked material and hydrogen-rich (perhydrous) vitrinite, and has the capacity to correct for the effects of vitrinite reflectance suppression.The technique has been tested on Cretaceous coals from the Latrobe Group in Volador-1, offshore Gippsland Basin, where the identification of vitrinite is unequivocal, and on dispersed organic matter (DOM) in various clastic lithologies from the Cretaceous Waarre and Eumeralla Formations intersected by Flaxmans-1 and Port Campbell-4, onshore Otway Basin, where the identification of vitrinite is difficult and subjective.For the Volador-1 sequence, the FAMM-derived vitrinite reflectance (equivalent reflectance) and the measured vitrinite reflectance (VR) are similar, although the VR data are more scattered about the VR-depth regression line. The variability in the vitrinite reflectance data is largely due to compositional variation in the vitrinite. This variation however does not affect the equivalent vitrinite reflectance data to the same degree.In the sections intersected by Flaxmans-1 and Port Campbell-4, FAMM data indicate that vitrinite reflectance suppression is responsible for the large deviations of the measured values from the VR—depth regression line. In some of these samples the suppression effect may be as much as 0.20 per cent absolute.The FAMM technique offers a valuable supplement to VR determinations, or even a valid alternative in many practical situations.