GSA Connects 2021 in Portland, Oregon

Paper No. 135-7
Presentation Time: 9:50 AM


DOIRON, Kelsey1, SAUER, Peter E.1, SCHIMMELMANN, Arndt1, DROBNIAK, Agnieszka2, MASTALERZ, Maria2 and BRASSELL, Simon1, (1)Earth and Atmospheric Sciences, Indiana University, 1001 East 10th Street, Bloomington, IN 47408, (2)Indiana Geological and Water Survey, Indiana University, 611 North Walnut Grove, Bloomington, IN 47405-2208

The conventional paradigm attributes the process for generation of most economically viable petroleum reserves to thermal cleavage of C-C bonds within sedimentary organic matter. There is increasing evidence, however, that alternative chemical pathways yield non-microbial CH4 generation at low temperatures. Samples of two immature shales (Cretaceous Second White Specks Formation, SWSF; Ro = 0.42 % and Devonian New Albany Shale, NAS; Ro = 0.51 %) were subjected to hydrous heating experiments in sealed Pyrex® ampoules at low temperatures (80 or 100 °C) over long-term periods (14 to 36 months). Utilizing 2H-enriched water at three levels of 2H-enrichment (-137 ‰ to 2H2O) in these experiments provided an opportunity to evaluate the role of water in CH4 generation at temperatures insufficient to achieve thermal cleavage of C-C bonds. Free CH4 was produced from both source rocks heated at 80 °C and 100 °C, with the latter temperature producing slightly higher yields of CH4 (relative to organic C contents) for NAS, and greater CH4 generation from the SWSF. Moreover, CH4 from the hydrous maturation experiments conducted at 100 °C exhibited higher δ13C values for both samples compared with those at 80 °C, matching the expectation for δ13CH4 values to increase with increasing maturity. δ2H values for CH4 generated from samples treated with 2H-enriched water confirm incorporation of water. In addition, the samples treated with 2H-enriched water at 100 °C maturation experiments yielded significantly higher δ2H values for generated CH4 than those conducted at 80 °C, indicating greater hydrogen incorporation from 2H-enriched water. The evidence for incorporation of 2H derived from 2H-enriched water in hydrous maturation experiments demonstrates that water incorporation is a key process in CH4 production at low temperatures (80-100 °C) that precludes cleavage of C-C bonds, and further supports a role for catalytic processes in petroleum generation in natural systems.