摘要
文章从研究方法、同位素分馏效应及其能源-环境意义3个方面,综述了天然气水合物形成/分解过程中同位素分馏的研究进展.天然气水合物形成/分解过程中同位素分馏效应的研究方法主要为实验模拟和天然观测.以往研究表明,天然气水合物系统内不同埋深的流体存在显著的同位素组成差异,这与天然气水合物形成/分解过程中的同位素分馏效应密切相关.天然气水合物的形成/分解涉及溶解/脱溶、相变、多孔介质内流体传质以及氧化消耗等多个物理化学过程的叠加.相变过程受温度控制,属于热力学平衡同位素分馏效应;而溶解/脱溶、传质和氧化消耗过程主要受多孔介质孔隙结构、温度、压力和氧气含量等环境因素控制,并与时间相关,属于动力学非平衡同位素分馏效应.目前,天然气水合物形成/分解过程中的同位素分馏效应已初步应用于天然气水合物勘探标志、气源判识、成藏机制研究和资源量评估,并为解释现今大气中甲烷浓度上升和同位素反转变轻、地质历史时期全球升温与同位素快速负偏提供了新的视角.然而,目前关于天然气水合物形成/分解过程中同位素分馏效应的研究方法仍较为匮乏,现有手段主要聚焦于同位素分馏的现象观测和定性分析.未来,应采用数值模拟、分子动力学模拟等方法对天然气水合物同位素分馏效应的研究方法加以补充,并系统开展天然气水合物形成/分解过程中同位素分馏特征、影响因素、机理及定量表征的研究.
Abstract
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.
维普
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