Should fluorescence alteration replace vitrinite reflectance as a major tool for thermal maturity determination in oil exploration

Abstract The fluorescence alteration multiple macerals (FAMM) technique is closely related to vitrinite reflectance. Until recently, fluorescence alteration study of dispersed organic matter (DOM) in sedimentary rocks has been regarded as technically difficult. With the introduction of optical microprobes equipped with small continuous wave gas lasers having a very stable output of blue radiation readily focused to 1–2 μm on the sample, this work has now become routine. FAMM has important advantages over vitrinite reflectance stemming from the possibility of resolving the data into two parameters, one related to the level of maturation, and the other related to the hydrogen-richness of a maceral. This enables the resolution of what are often difficult problems for the single parameter vitrinite reflectance technique, namely the identification of indigenous vitrinite in DOM, the recognition of caved and reworked organic matter, and the suppression of vitrinite reflectance. For these reasons, FAMM is a powerful tool for investigating vitrinite reflectance anomalies, especially those associated with unconformities. It is also well suited to investigate the tacit assumption in the vitrinite reflectance technique that all telocollinite matures along a single compositional pathway. The FAMM technique is not without problems. The range is restricted to equivalent mean random vitrinite reflectance Rm o = 0.4–1.2, the results are more sensitive to ambient temperature oxidation than vitrinite reflectance, and the technique demands a high level of technical expertise. The FAMM technique is calibrated on coals and it is therefore more likely to give high quality results on Types II and III kerogens rather than Type I kerogens which have not yet been intensively investigated. Although FAMM is unlikely to replace vitrinite reflectance, considerable confidence may be had in a maturation assessment when consistent results are obtained from these two closely related but independent techniques.

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