APPLICATION OF BACKSCATTERED ELECTRON IMAGING TO THE STUDY OF SOURCE ROCKS MICROTEXTURES

Scanning electron microscope (SEM) used in backscattered electron (BSE) mode is a powerful tool for the sedimentological study of source rocks, owing to its spatial and chemical resolutions, ease and speed of operating. The obtained imaging is dependent on atomic number contrasts between the different constituents of the sample. Using the BSE mode combined with energy dispersive X-ray spectrometry, minerals and organic matter can be distinguished more clearly than with the light microscope classically used by organic petrologists. In order to describe microtextures of organic-rich sediments, particularly the disposition of the organic matter, this technique has been tested on source rocks having various sedimentological and geochemical characteristics. Accordingly, two patterns of organic matter disposition have been recognized: laminated and particulate. These dispositions can be put back into their sedimentary context, by considering the depositional environment and diagenesis. The organic matter disposition suggests the existence of organic networks which are suspected to be a major control for hydrocarbon expulsion.