title: Classes of organic molecules targeted by a methanogenic microbial consortium grown on sedimentary rocks of various maturities.
abstract: Organic-rich shales are populated by methanogenic consortia that are able to degrade the fossilized organic matter into methane gas. To identify the organic fraction effectively degraded, we have sequentially depleted two types of organic-rich sedimentary rocks, shale, and coal, at two different maturities, by successive solvent extractions to remove the most soluble fractions (maltenes and asphaltenes) and isolate kerogen. We show the ability of the consortia to produce methane from all rock samples, including those containing the most refractory organic matter, i.e., the kerogen. Shales yielded higher methane production than lignite and coal. Mature rocks yielded more methane than immature rocks. Surprisingly, the efficiency of the consortia was not influenced by the removal of the easily biodegradable fractions contained in the maltenes and asphaltenes. This suggests that one of the limitations of organic matter degradation in situ may be the accessibility to the carbon and energy source. Indeed, bitumen has a colloidal structure that may prevent the microbial consortia from reaching the asphaltenes in the bulk rock. Solvent extractions might favor the access to asphaltenes and kerogen by modifying the spatial organization of the molecules in the rock matrix.
authors.affiliation: Laboratoire de Géologie de Lyon, CNRS UMR 5276, Ecole Normale Supérieure de Lyon, Université de Lyon, Lyon France.
authors.forename: Margaux
authors.initials: M
authors.lastname: Meslé
authors.affiliation: Laboratoire de Géologie de Lyon, CNRS UMR 5276, Ecole Normale Supérieure de Lyon, Université de Lyon, Lyon France ; Tharsis-Energy, Ecole Normale Supérieure de Lyon, Lyon France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Dromart
authors.affiliation: Institut Français du Petrole Energies nouvelles, Rueil-Malmaison France.
authors.forename: Frank
authors.initials: F
authors.lastname: Haeseler
authors.affiliation: Laboratoire de Géologie de Lyon, CNRS UMR 5276, Ecole Normale Supérieure de Lyon, Université de Lyon, Lyon France.
authors.forename: Philippe M
authors.initials: PM
authors.lastname: Oger
keywords: asphaltenes; kerogen; maltenes; methanogenic consortia; organic matter