【作者】 陈敏；

【导师】 曹志敏； 业渝光；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2005， 硕士

【摘要】 天然气水合物（Gas Hydrates）是21世纪一种重要的潜在能源,主要分布于大陆边缘的海底沉积物和大陆上的永久冻土带中。然而由于天然气水合物的不稳定性以及其中含有大量的甲烷,也使它成为地质灾害和全球气候变化的诱发因素。 对天然气水合物的基础性研究,尤其是天然气水合物实验室模拟研究非常必要。在实验室模拟天然气水合物的生成环境,探索水合物的生成机制不仅花费资金少、风险低,而且极具理论价值。目前取得的关于天然气水合物的元素地球化学数据,大部分是来源于天然气水合物区域的沉积物或沉积物岩芯中的孔隙水,在取样过程中天然气水合物大部分已分解,所以不能如实的反映水合物层的真实情况。加之对水合物生成过程中元素地球化学行为的模拟实验,现阶段研究成果还比较少,研究的程度亦不够深入。因此我们想通过实验模拟手段来研究由于水合物的形成而引起的离子浓度变化以及氢、氧同位素分馏特征。 本文为此设计了一套实验流程,提出了直接测定天然气水合物生成过程中海水中元素变化的实验方法,探讨了不同影响因素（温度、压力、振动、过滤方式和沉积物颗粒大小等）对实验结果的影响,选择了最佳实验条件。 在两种体系下（天然海水—甲烷体系和沉积物—天然海水—甲烷体系）对天然气水合物形成过程中离子浓度的变化进行了初步研究,结果表明,水合物形成过程中由于排盐作用的影响,离子浓度都有不同程度的增高,但只有K⁺、Sr²⁺和Cr^-离子能较好地反映由水合物排盐作用引起的溶液浓度变化,因此我们认为,K⁺、Sr²⁺和Cr^-离子在孔隙水中的浓度异常是指示天然气水合物存在的重要标志。 在沉积物—天然海水—甲烷体系中,通过对六种不同粒度的沉积物中离子浓度在水合物反应前后变化的研究,我们发现沉积物粒度太大或太小都不利于水合物的生成。在天然海水—甲烷体系中,我们通过对水合物生成前后溶液中的Cl^-离子浓度和氢、氧同位素成分的分析,研究了天然气水合物形成过程中氢、氧同位素的分馏情况。实验测定了氢、氧同位素的分馏系数,证明了氢、氧重同位素易于富集在水合物中。结合世界各地富含天然气水合物沉积层孔隙水的同位素组更多还原

【Abstract】 Gas hydrate is one of the most important potential energy resources, distributing mainly in marine sediments beside continental slopes and continental perennial frost zones. On the other hand, owing to its instability and high percents of methane contents, gas hydrates is a factor inducing geological hazards and global climate changes.To understand more about gas hydrates, it is necessary to strengthen basic studies, especially in experimental simulations. Advantage of studying the environments and mechanisms of gas hydrates through laboratory modeling not only include its low costs and low risk, but also include its high theoretic importance. At present, elements geochemical data about gas hydrates are from sediments containing gas hydrates and related pore fluids. Due to the instability of gas hydrates, sampling processes are often unable to guarantee the actual situations of the gas hydrates strata. As a whole, studies on elements geochemistry during gas hydrates forming processes are relatively inadequate. Purposes of this study are to illustrate the changes in ionic concentrations and characteristics of hydrogen and oxygen isotopic fractionation during gas hydrates formation through experimental simulation.To achieve the goal, an experimental flow is designed; method of determining the element concentrations instantly through the gas hydrates forming processes is proposed. With the experimental data, factors affecting the experimental results, including temperature, pressure, vibration, filter type and sediment sizes, are in turn discussed. At the end, an optimal experimental condition is proposed.Preliminary studies of ionic concentration changes in marine water-methane system and sediment-marine water-methane system showed that, concentrations for many ions increased during gas hydrates forming period, due to the salt exclusion process. Among them, several ions (including Na~+、Sr~2+ and Cl~-)concentrations variation correlated well with the salt exclusion process. Their anomalies in porewaters might be important indicators of gas hydrates. Studies of the sediment-marine water-methane system also showed that, medium sediment size is propitious to the genesis of gas hydrates.In the marine water-methane system, concentration changes of chlorine ion, hydrogen and oxygen isotope composition were determined. Fractionation factors of H and O isotope showed that, the heavier isotopes have an aptitude to concentrate in gas hydrates. Considering the ubiquitous isotope anomalies in the sediment pore-waters rich in gas hydrates, we think that salt exclusion during gas hydrates formation is the cause for these anomalies.更多还原