Application of fluorescence microscopy in coal petrology and oil exploration

Abstract

SUMMARY Fluorescence microscopy of polished surfaces allows more satisfactory study and identification of the hydrogen‐rich constituents (liptinites) that are the precursors of petroleum and which, in soft brown coals, fine‐grained clastic and carbonate sediments can hardly be detected using normal reflected light. Diagnostic properties of liptinites and lipoid substances are their colour, intensity and variation of fluorescence (both colour and intensity) during irradiation which may allow distinction of organic and inorganic constituents in coals and bituminous shales. Fluorescence properties also change with increasing degree of diagenesis (‘rank’) of organic matter, although organic constituents cease to fluoresce beyond the medium‐volatile, bituminous‐rank stage. In this paper fluorescence microscopy as a means of studying the rank of coaly and lipoid substances in sedimentary rocks is discussed after a brief description of the method. The influence of facies on fluorescence properties is considered and the relative merits of fluorescence and reflectance measurements in different parts of the rank range are discussed. The importance of fluorescence microscopy in petroleum exploration is also emphasized. Finally, consideration is given to the future of fluorescence microscopy in relation to the ‘bituminization range’ of coalification which has important implications to both petroleum generation and to the coking and hydrogenation of coals.