摘要
煤层气的分馏效应是指运移过程中气体组份和同位素值发生变化的现象.分馏机理的探讨对煤层气的运移聚集具有重要指导意义.本文以吸附势理论为指导,以等温吸附实验数据为依据,对甲烷碳同位素和多组分气体分馏机理进行了探讨.确定了4种分馏机理的存在:(1)解吸-扩散-运移不仅造成甲烷碳同位素分馏,而且造成多组分气体分馏.13CH4因其吸附势普遍高于12CH4而具有优先吸附、滞后解吸的特征,12CH4更容易发生运移分馏.二氧化碳与甲烷相比,具有优先吸附、滞后解吸的特征,特别是在高压下,甲烷具有强的分馏效应;(2)发生在地下水径流带的溶解作用使得13CH4被优先溶解并被运移至滞留区聚集,12CH4保留在原地;(3)浅部次生生物气的产生造成甲烷碳同位素变轻的假象;(4)高温裂解气的生成造成甲烷碳同位素变重的假象.4种分馏效应都引起浅部甲烷碳同位素变轻,深部变重,这已为众多的实例所证实.
Fractionation effect of coalbed gas is a phenomenon that gas composition and isotope change during the process of migration. Fractionation mechanisms have an important significance in coalbed gas migration and accumulation. Based on measured isotherm data of methane and carbon dioxide on coal, the fractionation mechanisms of methane carbon isotope and multi-component gas is discussed with adsorption potential theory in the paper. Four fractionation mechanisms can be identified： （1） Desorption-diffusion-migration results in fractionations of methane carbon isotope and multi-component gas. The adsorption po tential of ^13CH4 on coal is higher than ^12CH4. This implies that the coal is preference for ^13CH4 adsorption and postponement for ^13CH4 desorption, and it is favorable for ^12CH4 fractionation. The coal is preference for CO2 adsorption and postponement for CO2 desorption compared with that for CH4. Methane has strong fractionation effect, especially at high pressure. （2） Dissolution which takes place in transmission zone of groundwater made ^13CH4 preferential to dissolve and migrate to the stagnant zone for accumulation, and ^12CH4 keeps in-situ. （3） Biogenic methane generated in shallow part of basin results in methane carbon isotope to light. （4） Cracked gas in high-temperature causes methane carbon isotope to heavy. The four kinds of fractionations cause methane carbon isotope to light in shallow part, and heavy in the deep part has already been confirmed in the previous investigations.
出处
《河南理工大学学报（自然科学版）》
CAS
2006年第4期295-300,共6页
Journal of Henan Polytechnic University（Natural Science）
基金
国家"973"项目(2002CB211705)
国家自然科学基金重点资助项目(50534070)
关键词
煤层气
吸附势
分馏机理
解吸-扩散-运移
Coalbed Gas
Adsorption Potential
Fractionation Mechanism
Desorption-diffusion-migration
