多孔介质中天然气水合物注热水分解理论及实验研究

【作者】 李明川；

【导师】 赵金洲； 樊栓狮；

【作者基本信息】 西南石油学院 ， 油气田开发工程， 2005， 博士

【摘要】 据估计,全球天然气水合物中甲烷碳含量达10¹⁶kg或含有20×10¹⁵m³的甲烷气,相当于全世界已知煤炭、石油和天然气等常规化石燃料总碳储量的两倍。天然气水合物作为一种重要的后继能源,具有替代石油和天然气的广阔前景;在能源危机日益严峻的21世纪,被公认为是具有良好前景的后续清洁能源。地球上广泛的分布着天然气水合物资源,主要分布于海洋水深大于300～500m的海底沉积物之中和寒冷的高纬度区域。天然气水合物以固体形式存在,是不可移动和渗透的,必须将其分解才能释放出其中的天然气气体资源;但在目前的技术条件下,还难以开采。 天然气水合物是在一定条件下由气体或挥发性液体与水相互作用过程形成的白色固态结晶物质,外观像雪或松散的冰,其存在需要低温（0～10℃）和高压（>10MPa）条件的保障,这即是天然气水合物赖以稳定存在的相平衡条件。从多孔介质相平衡和受力情况出发,分析了多孔介质对天然气水合物形成过程的影响:相平衡曲线向左移动,相比自由液面需要更低的温度和更高的压力;毛细管半径越小,多孔介质对其影响越明显;实验证实了多孔介质缩短了水合物形成过程诱导区和成长区,冰成天然气水合物过程并没有诱导区直接进入成长阶段,且能形成均一稳定的水合物。 人们根据天然气水合物的相平衡曲线提出了以破坏相平衡为基础的常规分解方法:热激法、压力下降法和化学试剂法。在对比注热水分解方法的优势基础上,分析了注热水分解方法的可行性。论文从天然气水合物的分解三阶段（注热水阶段、水合物分解阶段和开采气体阶段）出发,建立了相应的数学模型。在此基础上建立了水合物一维分解前缘模型:质量传递、能量守恒、动量守恒偏微分方程;并利用有限差分格式,对其进行线性化求解,绘制了相应的程序迭代流程。利用作者自行编制的小型C语言算法程序对分解模型进行了参数拟合,粒径、温度和注入速率对参数都有不同程度的影响,温度对拟合参数的影响不及注入速率的影响大。 在实验室中,自行设计并搭建了多孔介质中天然气水合物形成/注热水分解一维实验平台。实验中将冰粉和石英砂等体积混合,在一定条件下完全形成天然气水合物,利用温度热电偶和电阻来监测反应的进程。 （1）通过实验数据分析和理论的拟合,结果仅相差1.14min,误差为8.21%。 （2）对于小流量25ml/min的注入速率,温度对天然气水合物的影响较小,实验值最大更多还原

【Abstract】 It’ s reported that natural gas hydrates over the world contain total methane carbon 10~16Kg or methane gas 20x 10~15 m3, this amount equal twice total carbon reserves of coals, oils and natural gases etc conventional fossi fuels around the earth. Natural gas hydrate, which will replace the status of oil fenatural gas in the future, has been voted an important cleanly energy sources in 21 century when energy sources present austere emergencies. Great amount natural gas hydrates that exit in solid distributing widely in sediments porous medium which locate under the seabed more depth 300~500m ocean and in permafrost deposit on high-latitude. It presents immobile and impenetrabile for natural gas hydrates exit in solid, thus must be decomposed to release naturl gases . It’ s impossible to exploit these solid samples for the poor technology condition these days.Natural gas hydrates that look like ice crystal are formed from gases or volatile liquid and water under a certain condition. The lower temperature and higher pressure must be required for natural gas hydrates extence, namely the phase equilibrium of natural gas hydrate exits steady. The infection on formation process of natural gas hydrates in porous medium has been analyzed from the condition of phase equilibrium in sediments and function of force: the curves of phase equilibrium shift to left exhibits lower temperature and higher pressure than the free exterior; and the radius of capillary is less, the clearer for infection of porous medium is. The induction time of formation for natural gas hydrate is abridged by experimental results, there exits no induction time to the formation process of natural gas hydrates from ice-form, but can form the symmetrical steady natural gas hydrates.The routine methods that based on phase equilibrium for decomposition of natural gas hydrates have been provided through the breakage to the curve of phase equilibrium: thermal stimulation method, depressurization method and chem. inhibitor method. The feasibility of hot water injection for natural gas hydrates has been given based on the advantage of decomposition for hot water injection. The mathematic models for dissociation of natural gas hydrates have been built from the three stages for dissociation of natural gas hydrates (the stage of hot water injection, the stage of dissociation of natural gas hydrates and the stage of exploitation gases). One-dimensional models of dissociation frontal brim fornatural gas hydrates have been established through this information, partial differential equations of mass transport, energy conservation and momentum conservation have been proposed and been solved through the finite difference for linear solution, and the flow charts for program alternate been drew. Parameters on models of dissociation have been drafted through utilizing the little C programs that author own wrote. The different infection on grain radius, temperature and velocity of injection to parameters have been analyzed, including the infection of velocity of injection shows more larger than that of temperature.In lab a set one-dimensional experimental device has been designed and built for the formation/dissociation of injection hot water on natural gas hydrates in porous medium by oneself. Natural gas hydrates are formed through admixtures of parts of quartz and ice-power under a certain condition in lab, this process of reaction is being inspected by thermocouple and resistance.(1)Error between drafting models and experimental data is presented only 8.21%, and disparity 1. 14min through analyses of data and draft theory.(2)To the little injection velocity 25ml/min, little infection to dissociation of natural gas hydrates happens for temperature; maximal error of experimental values shows 13. 71% and nearly overlaps on the curve drafted. But that of injection velocity presents larger than temperature and maximal error exits 27.273%, higher 14% than temperature.(3)Consistencies are kept between temperature and resistance to measure of the dissociation frontal brim for natural gas hydrates through analysis of data in experiments.更多还原