天然气水合物微观弹性性质的模拟研究及应用

发布时间：2018-06-19 14:04

本文选题：天然气水合物 + 微观结构　；参考：《西南石油大学》2015年硕士论文

【摘要】：天然气水合物形成于低温、高压。在自然界中主要存在于陆地永久冻土层及海底沉积层中,貌似冰雪,可直接点燃；1m3的天然气水合物可以释放约164m3的甲烷天然气,可高效清洁燃烧；目前已发现的水深三千米以内天然气水合物中甲烷的碳总量相当于全世界已知传统化石能源(煤、石油和天然气)总量的两倍以上,是不可多得的战略能源。要对天然气水合物资源进行勘探与开发,钻井是最直接和主要的技术手段,成功钻取天然气水合物是整个资源开发的关键,故需要对天然气水合物在钻井过程中力学性质的变化情况进行探讨研究。本文首先对天然气水合物的基本性质及结构稳定性进行了探讨,包括基本物理性质、地层物理特征、化学性质、微观分子结构以及晶体构成等,并通过设置模拟实验,根据第一性原理,采用密度泛函理论计算方法研究微观状态下内嵌分子对水合物分子结构的形成、稳定性的影响以及外加电场作用下天然气水合物分子结构的变化；其次,因天然气水合物分子间作用力为范德华力,分子晶体间表现为弱相互作用,故先针对尿素、冰和石墨三种体系,通过CASTEP模块确定对分子晶体进行弹性模量计算应选用的最佳应变值,从而进行天然气水合物分子结构的晶胞模拟,较为精确地计算出天然气水合物的弹性模量值,分析出天然气水合物的微观弹性性质随压力变化的规律,为宏观钻井过程中的压力控制提供理论基础；再次,探究了天然气水合物的形成条件与成藏机理,讨论其在永久冻土区和海洋区的储集特征及分布特点；最后分析了天然气水合物钻探过程中的钻井参数和难点,并结合前面模拟实验中总结的微观力学性质和宏观的形成条件,提出了使用控压钻井技术开采天然气水合物的合理建议,对复杂工况下天然气水合物稳定性的控制进行了分析。通过上述研究,本篇论文对天然气水合物的基本性质、结构、形成与成藏给出了更加清晰的认识；不仅从微观上得出了天然气水合物的结构稳定性、外加电场作用的表现和压力对天然气水合物微观弹性性质影响规律,也从宏观上提出了天然气水合物钻井的压力控制方法,为实际工程中高效开采天然气水合物提供理论指导和帮助。
[Abstract]:Natural gas hydrate is formed at low temperature and high pressure. In nature, which mainly exists in land permafrost and submarine sediments, it looks like ice and snow, and can directly ignite 1 m3 of natural gas hydrate, which can release about 164m3 methane gas and can be burned clean and efficiently. The total carbon content of methane in gas hydrate has been found to be more than twice that of conventional fossil energy (coal, oil and natural gas) in the world, which is a rare strategic energy. To explore and develop natural gas hydrate resources, drilling is the most direct and main technical means, and successfully drilling natural gas hydrate is the key to the whole exploitation of natural gas hydrate. Therefore, it is necessary to study the change of mechanical properties of natural gas hydrate during drilling. In this paper, the basic properties and structural stability of natural gas hydrate are discussed, including the basic physical properties, stratigraphic physical characteristics, chemical properties, micromolecular structure and crystal composition, etc. According to the first principle, the density functional theory (DFT) method is used to study the influence of embedded molecules on the formation of hydrate molecular structure, the influence of stability and the change of natural gas hydrate molecular structure under the action of external electric field. Because the intermolecular force of natural gas hydrate is van der Waals force and the interaction between molecular crystals is weak, therefore, three kinds of systems, urea, ice and graphite, are first used. The optimum strain value for calculating elastic modulus of molecular crystal is determined by CASTEP module, and the unit cell simulation of the molecular structure of natural gas hydrate is carried out, and the elastic modulus value of natural gas hydrate is calculated more accurately. The microelastic properties of natural gas hydrate vary with pressure, which provides a theoretical basis for pressure control in macro drilling. Thirdly, the formation conditions and reservoir forming mechanism of gas hydrate are discussed. The reservoir characteristics and distribution characteristics in permafrost and marine areas are discussed, and the drilling parameters and difficulties in the process of gas hydrate drilling are analyzed. The reasonable suggestion of using controlled pressure drilling technology to exploit natural gas hydrate is put forward, and the control of gas hydrate stability under complex working conditions is analyzed. Through the above research, this paper gives a clearer understanding of the basic properties, structure, formation and accumulation of natural gas hydrate, and not only from the microscopic point of view, the structure stability of natural gas hydrate is obtained. The effect of external electric field and pressure on the microscopic elastic properties of natural gas hydrate is studied. The pressure control method for gas hydrate drilling is also put forward from the macroscopic view. It provides theoretical guidance and help for high efficiency exploitation of natural gas hydrate in practical engineering.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P618.13

【参考文献】