Isotope fractionation during the formation-decomposition of natural gas hydrate and its energy-environmental implications
This review provides a comprehensive analysis of the research progress concerning isotopic frac-tionation during the formation and decomposition of natural gas hydrates,focusing on three aspects:research methodologies,isotopic fractionation effects,and their energy-environmental significance. The study posits that the primary research methods for isotope fractionation effect in the formation/decomposition process of natural gas hydrates were mainly experimental simulation and natural observation. These methods reveal significant iso-topic compositional differences in fluids at various depths within the hydrate system,which are closely associated with the isotopic fractionation effects occurring during hydrate formation/decomposition. The formation/decom-position process of hydrates involves the superposition of several physicochemical processes,including dissolu-tion/desorption,phase transition,fluid transport within porous media,and oxidative consumption. The phase tran-sition process is temperature-controlled and represents a thermodynamic fractionation effect,while the dissolu-tion/desorption,fluid transport,and oxidative consumption processes are primarily governed by environmental factors such as the pore structure of the porous media,temperature,pressure,oxygen content,and are time-depen-dent,representing a kinetic fractionation effect. Currently,the isotopic fractionation effects during hydrate forma-tion/decomposition have been preliminarily applied to hydrate exploration signs,gas source identification,hydro-carbon accumulation mechanism studies,and resource assessment. They also provide new perspectives for ex-plaining the rise in atmospheric methane concentrations and the isotopic shifts towards lighter values,as well as the rapid negative isotopic excursions during global warming periods in geological history. However,existing re-search has mainly focused on the phenomenological observation and qualitative analysis of isotopic fractionation during hydrate formation/decomposition. In the future,numerical simulation and molecular dynamics simulation should be used to supplement the research methods of isotope fractionation effect of hydrate,and the characteris-tics,influencing factors,mechanism and quantitative characterization of isotope fractionation in the formation/de-composition process of gas hydrate should be systematically studied.
natural gas hydratesformation/decompositionisotope fractionationhydrate explorationmethane greenhouse effect
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