In assessment of fine-grained unconventional reservoir rocks, discrimination of kerogen (primary, detrital organic matter (OM)) from bitumen (a diagenetic product of kerogen maturation) can be difficult, even at the SEM scale. To explore the nature of these systems, Milliken et al. describe observations of low-maturity, and presumably bitumen-free, samples of Pliocene-Pleistocene marine sapropels. The data illustrate the diversity of organic-matter-hosted pore systems, providing a useful baseline for identification of these fundamentally different OM types in mature OM-rich mudrocks, and highlighting some of the challenges. Knowing the proportion of detrital versus diagenetic organic matter in these types of mudrocks has significant implications for understanding the nature of petroleum systems in unconventional reservoirs.
SEM petrography of eastern Mediterranean sapropels: analogue data for assessing organic matter in oil and gas shales by Kitty L. Milliken, Lucy T. Ko, Maxwell Pommer, and Kathleen M. Marsaglia