【作者】 杨明军；

【导师】 宋永臣；

【作者基本信息】 大连理工大学 ， 能源与环境工程， 2010， 博士

【摘要】 天然气水合物是一种高效、储量大、新型洁净能源,本文以天然沉积物中水合物形成机理及热力学特性为研究目的,利用新建的水合物相平衡测试系统,研究了堆积层中孔隙尺寸、盐分浓度、气体组成等对天然多孔介质中水合物相平衡特性的影响,定量把握其热力学特性。对阐明水合物形成机理,分布规律及其赋存状态具有重要意义。实验结果显示多孔介质中甲烷水合物容易生成、诱导时间短。在其它条件一致情况下,随着孔隙尺寸的增加,甲烷水合物相平衡曲线向高温、低压方向移动；随着盐分浓度的增加,甲烷水合物相平衡曲线向低温、高压方向移动；混合气体中随着甲烷浓度的减少,相平衡曲线向低压、高温方向移动。为了进一步研究盐分对甲烷水合物相平衡的影响,利用正交试验设计方法研究了不同离子组成和浓度条件下多孔介质中甲烷水合物相平衡特性。研究发现在本实验条件下四种阳离子对甲烷水合物相平衡影响的影响程度从大到小依次为Mg2+、Ca2+、Na+、K+。四种卤素阴离子(F-、Cl-、Br-、I-)对甲烷水合物相平衡影响效果一致；三种常规阴离子(Cl-、CO32-、SO42-)浓度对甲烷水合物相平衡影响均显著。研究发现二氧化碳初始状态的不同导致二氧化碳水合物形成过程中热力学现象发生变化。随着溶液中氯化钠浓度的增加,二氧化碳水合物相平衡曲线向低温、高压方向移动。当温度降低到冰点以下时,氯化钠溶液对二氧化碳水合物相平衡的影响很小,可以忽略。相同条件下二氧化碳水合物与甲烷水合物相平衡存在很大差异,二氧化碳水合物相平衡曲线处于高温、低压区域,也就是说二氧化碳水合物相对于甲烷水合物而言更容易形成。提出了预测含电解质溶液多孔介质中水合物的相平衡预测模型,将电解质对气-液表面张力的影响引入到预测模型；利用该模型对大体积水和多孔介质中甲烷、二氧化碳水合物相平衡进行了预测,误差分析显示,相对于传统预测模型而言本模型预测结果平均相对误差较小。计算结果同实验数据对比研究表明,该模型预测结果良好。搭建了适用于核磁共振成像(MRI)系统的二氧化碳水合物形成与分解实验测试装置；MRI追踪水中氢原子进行成像,直观的显示岩芯管中液态水分布情况,并结合MRI强度信号进行精确的分析；MRI图像显示二氧化碳水合物具有多个初始形成点和初分解始点,即多点形成、多点分解；对不同升温速度下二氧化碳水合物的分解过程进行了研究。更多还原

【Abstract】 Natural gas hydrates (NGH) is a kind of new clean energy with high efficiency and huge amounts deposits. In this study, a set of experimental device has been built up to find the formation mechanisms and thermodynamic characters of gas hydrate in natural sediment. The effects of pore size, salinity and different gas component on the formation and dissociation of hydrate in sediment have been measured. The results can provides quantitatively thermodynamic character and explain the formation mechanisms, distribution, state of stability of NGH, and provide important date for the investigation and exploration about NGH.The results indicate that the induction time of gas hydrates formation in porous media is shorter than that in bulk-water. The decrease in the pore size, induced by decreased glass bead size, leads to the enhancement in the equilibrium pressure as the salinity and the temperature are kept the same, in other words, lower temperature and higher pressure are required for the formation of methane hydrate in glass beads. While the increase of salinity makes the equilibrium pressure increase too as the pore size and the temperature are kept the same. Through the experiment of gas hydrate formation and dissociation in simulated sediments, phase equilibrium of gas hydrate composed of methane, ethane and propane has been obtained. It can be concluded that the equilibrium at the condition of decreased methane concentration needs a lower pressure and a higher temperature.The effects of anions and cations on the phase equilibrium of methane hydrate in porous media were studied by using the orthogonal experimental design. Analysis of variance demonstrated that only Mg2+ had significantly influence on the equilibrium point of methane hydrate. The influences of all halogen ions on methane hydrate phase equilibrium are similar, which can be explained by the similar mean ionic activity coefficients of sodium halides at experimental concentrations. The influences of three normal anions concentration on the equilibrium point of methane hydrate were all significant.Two kinds of hydrate formation cases were obtained due to the different initial P-T conditions of CO2. The results indicated the present of glass bead leads to the enhancement in the equilibrium pressure as the salinity and the temperature are kept the same. The increase of NaCl concentration caused the enhancement in the equilibrium pressure as the pore size and the temperature are kept the same. The effects of NaCl solution on hydrate equilibrium can be neglect when temperature was lower than ice points. This can be explained with that the vapor pressure of solution was equal to that of solid phase (ice) when the equilibrium temperature gets to ice point. Comparison of methane and CO2 equilibrium conditions shows the lower temperature and higher pressure are required for the formation of methane hydrate.An improved model was proposed to predict the hydrates equilibrium in marine sediment environment. According to the mechanical equilibrium relations to H-L-V system, interfacial energy between hydrate and liquid was corrected by the function that is expressed with temperature and electrolyte concentration when electrolyte was in pore water. The activity of water is calculated using the Pitzer model and the interfacial energy between liquid and gas is solved using the Li’s method. The model was used to predict methane hydrate equilibrium in bulk water and in porous media containing electrolyte or not. The prediction results show a good agreement with the experimental data.Since Magnetic resonance imaging (MRI) is an effective tool for hydrate investigations, a series of experiments were carried out to study CO2 hydrate formation in porous medium using it. The results indicated that the MRI data could visualize hydrate formation and was good agreement with the pressure change. The hydrate formation rate was also quantified using MRI data. The result also shows there are multi-sites for CO2 hydrates initial formation and dissociation in the experimental condition. The effects of heating rate on the hydrate dissociation were also investigated in this work.更多还原