Effects of clay minerals and biosurfactants on isotopic and molecular characteristics of methane encaged in pressure vessel gas hydrates

The stable isotope values of carbon (delta C-13(methane)) and hydrogen (delta H-2(methane)) from methane molecules trapped in gas hydrates are useful for differentiation of methane from microbial and thermal origins, providing valuable information during hydrocarbon exploration. Recent studies have reported catalysis of methane hydrates when smectite clays and biosurfactants are present in hydrate-hosting sediments, but catalytic influences on the values of delta C-13(methane) and delta H-13(methane) are not well documented. In this study, pressure vessel methane hydrates were formed from solutions in contact with smectite clays (montmorillonite and nontronite) and biosurfactants (rhamnolipids and surfactin). Experiments show less than 1% differences in values of delta C-13(methane) between free and encaged molecules and up to 10% variations in values of delta H-13(methane) between free and encaged molecules. Notably, methane consumption increased in methane hydrates formed from solutions containing biosurfactants and biosurfactant-smectite mixtures. Results presented here indicate that a hydrate formed in the presence of smectite clays and biosurfactants are characterized by small shifts in free and encaged values of delta C-13(methane) and delta H-13(methane) and do not complicate interpretation of gas origin. In contrast, methane consumption in hydrates formed under the catalytic effect of smectite clays and biosurfactants modifies gas wetness, obscures gas origin and complicates interpretation of thermal maturity. (C) 2013 Elsevier Ltd. All rights reserved.