Maturation and migration processes in intact source rock micro plugs induced by chemical and thermal treatment: A new approach combining Rock-Eval pyrolysis and organic petrography

This study proposes a new approach to investigate hydrocarbon generation and migration processes in petroleum source rocks under laboratory conditions. For the first time, programmed open-system pyrolysis using a Rock-Eval 6 instrument is applied on small, polished source rock plugs to induce changes in the type and distribution of solid bitumen, which is qualitatively investigated by means of organic petrography before and after treatments. This approach allows us to directly visualize the evidence of solid bitumen (SB) formation and distribution after the following treatments: (1) thermal extraction (300°C for 3 min), (2) chemical extraction of the surface using dichloromethane (DCM), and (3) artificial maturation up to 400 to 500°C. After each step, the surface of micro plugs was digitally scanned to allow a comparison of specific areas of interest before and after the treatments.

After thermal extraction, the volume of observed SB in the early- and moderately mature samples slightly increased, while most of the thermally mobilized bitumen from inside the plug was evaporated. The initial solid bitumen was not or hardly affected by thermal extraction at 300°C for 3 min, i.e. it was thermally stable at this temperature. After DCM treatment, SB in the early mature samples was almost completely dissolved. While some SB was dissolved in the moderately mature sample showing more mature and stable SB. After the artificial maturation, the volume of SB in early- as well as in moderately mature samples increased, indicating the presence of new SB due to bitumen migration from the plug.