COMPARISON OF PALAEOTEMPERATURE INDICATOR TECHNIQUES: AFTA, VR, FAMM AND ICA- CONSIDERATIONS FOR DESIGNING SAMPLING PROGRAMS

Abstract

A comparison of thermal maturity techniques (AFTA, VR, FAMM and ICA) in a variety of geologic settings allows an assessment of the reliability of each technique and insight into basin thermal history. Five representative sample sets are presented. In the first set, well samples from southeast Asia yield a FAMM equivalent vitrinite reflectance (VRe) value of 0.53 per cent, significantly higher than the measured VR mean of 0.43 per cent. AFTA-derived VRe indicates expected maturity levels between 0.37 and 0.45 per cent. Petrographic evaluation identified a second vitrinite population composed of reworked material which may influence the FAMM result. In the second and third cases, outcrop and well samples of Woodford Formation from Oklahoma, USA, were analysed. Facies variability in these samples may have a greater influence on FAMM VRe results than on measured VR values and AFTA VRe. A sample of jet from England gave a FAMM VRe value of 1.0 per cent with comparable AFTA VRe greater than 0.70 per cent. Measured VR values occupy a narrow range and give a well-defined mean value of 0.26 per cent with strong petrographic evidence of geochemical suppression. Based on this evidence of vitrinite reflectance suppression, the FAMM VRe value appears to represent the actual maturity level. In the final suite, samples from the Otway Basin, Australia were analysed. Measured VR (1.19 per cent) and FAMM VRe (0.82 per cent) values are consistent with AFTA VRe which constrains the maturity to greater than 0.60 per cent. The liptinite-poor nature of this sample may cause an overcorrection calculation for the FAMM VRe value. In designing a thermal history study, collection of high-quality VR data including detailed maceral descriptions and qualitative fluorescence assessments should be completed first and then combined with other maturity techniques to define the timing and magnitude of thermal events.