本文選題：天然氣水合物 + 微觀結(jié)構(gòu)　； 參考：《西南石油大學》2015年碩士論文

【摘要】：天然氣水合物形成于低溫、高壓。在自然界中主要存在于陸地永久凍土層及海底沉積層中,貌似冰雪,可直接點燃；1m3的天然氣水合物可以釋放約164m3的甲烷天然氣,可高效清潔燃燒；目前已發(fā)現(xiàn)的水深三千米以內(nèi)天然氣水合物中甲烷的碳總量相當于全世界已知傳統(tǒng)化石能源(煤、石油和天然氣)總量的兩倍以上,是不可多得的戰(zhàn)略能源。要對天然氣水合物資源進行勘探與開發(fā),鉆井是最直接和主要的技術(shù)手段,成功鉆取天然氣水合物是整個資源開發(fā)的關(guān)鍵,故需要對天然氣水合物在鉆井過程中力學性質(zhì)的變化情況進行探討研究。 本文首先對天然氣水合物的基本性質(zhì)及結(jié)構(gòu)穩(wěn)定性進行了探討,包括基本物理性質(zhì)、地層物理特征、化學性質(zhì)、微觀分子結(jié)構(gòu)以及晶體構(gòu)成等,并通過設(shè)置模擬實驗,根據(jù)第一性原理,采用密度泛函理論計算方法研究微觀狀態(tài)下內(nèi)嵌分子對水合物分子結(jié)構(gòu)的形成、穩(wěn)定性的影響以及外加電場作用下天然氣水合物分子結(jié)構(gòu)的變化；其次,因天然氣水合物分子間作用力為范德華力,分子晶體間表現(xiàn)為弱相互作用,故先針對尿素、冰和石墨三種體系,通過CASTEP模塊確定對分子晶體進行彈性模量計算應(yīng)選用的最佳應(yīng)變值,從而進行天然氣水合物分子結(jié)構(gòu)的晶胞模擬,較為精確地計算出天然氣水合物的彈性模量值,分析出天然氣水合物的微觀彈性性質(zhì)隨壓力變化的規(guī)律,為宏觀鉆井過程中的壓力控制提供理論基礎(chǔ)；再次,探究了天然氣水合物的形成條件與成藏機理,討論其在永久凍土區(qū)和海洋區(qū)的儲集特征及分布特點；最后分析了天然氣水合物鉆探過程中的鉆井參數(shù)和難點,并結(jié)合前面模擬實驗中總結(jié)的微觀力學性質(zhì)和宏觀的形成條件,提出了使用控壓鉆井技術(shù)開采天然氣水合物的合理建議,對復(fù)雜工況下天然氣水合物穩(wěn)定性的控制進行了分析。 通過上述研究,本篇論文對天然氣水合物的基本性質(zhì)、結(jié)構(gòu)、形成與成藏給出了更加清晰的認識；不僅從微觀上得出了天然氣水合物的結(jié)構(gòu)穩(wěn)定性、外加電場作用的表現(xiàn)和壓力對天然氣水合物微觀彈性性質(zhì)影響規(guī)律,也從宏觀上提出了天然氣水合物鉆井的壓力控制方法,為實際工程中高效開采天然氣水合物提供理論指導(dǎo)和幫助。
[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.
【學位授予單位】：西南石油大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：P618.13

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