oa Evidence for the Role of Water in Ch4 Generation from Long-Term, Low Temperature Experimental Maturation of Immature Shales

The conventional paradigm for generation of economically viable petroleum reserves involves thermal cleavage of C-C bonds within sedimentary organic matter. However, there is evidence for alternative chemical pathways yielding non-microbial methane generation at low temperatures. In addition, assessing the role of water in methane generation at temperatures lower than those required for it to form by thermal cracking represents a critical step for evaluating processes likely involved in catalytic methanogenesis. Previous pyrolysis experiments of source rocks in the presence and absence of water have yielded insights on the role of water in CH4 generation at a range of maturities including late-stage thermogenesis. Our studies explore the role of catalytic pathways in CH4 generation by experiments simulating maturation of immature source rocks at temperatures insufficient to achieve thermal cleavage of C-C bonds. These hydrous maturation experiments demonstrate that immature shales can generate CH4 at temperatures (80–100 °C). They establish the potential to yield δ13C values <-70 ‰ commonly associated with microbial gas by early CH4 generation at low maturity levels. Incorporation of 2H derived from 2H-enriched water in these hydrous maturation experiments confirms the role of water in catalytic processes generating CH4 at low temperatures.