本文選題：分子動力學　切入點：蒙特卡洛模擬　出處：《西南石油大學》2017年碩士論文　論文類型：學位論文

【摘要】：納米孔隙中流體的輸運性質是頁巖氣等致密油氣藏開發(fā)、多孔納米材料研發(fā)的基礎科學問題。由于氣體在納米級孔隙中流動受到尺寸效應的影響,常規(guī)的流體力學理論已經(jīng)無法適用。本文基于分子動力學理論和軟件,在前人研究的均一壁面基礎上,模擬了碳納米孔隙中甲烷的輸運過程,分析了甲烷在超臨界狀態(tài)下的滑移流以及過渡流;通過在不同壁面結構的石墨多孔介質模型中,模擬了甲烷在該多孔介質中的分布及擴散過程,揭示了甲烷在納米孔隙裂縫中與固體壁面粒子相互作用的微觀機理;最后,通過建立Ⅰ類和Ⅱ類干酪根有機質的分子模型,模擬了不同溫度下甲烷在干酪根基質單元中的吸附和擴散行為,計算了所產(chǎn)生的吸附熱和擴散活化能。論文的主要內容和結論為:(1)通過甲烷在兩個不同孔徑的石墨孔隙中的分子動力學模型,發(fā)現(xiàn),石墨孔隙的開孔方向變化會導致甲烷與孔隙壁面的勢能作用發(fā)生變化,并影響甲烷的流動性質;在過渡流中,甲烷軸向速度的徑向分布波動劇烈,石墨六晶格面是一種非常光滑的壁面,甲烷在這種壁面的孔隙中的流動速度快,且邊界滑移長度大;甲烷的平均速度隨著微觀孔隙尺度的增加而增加,且軸向速度的徑向分布波動變緩。垂直于石墨晶格面的孔隙中,甲烷流動的平均速度低于平行于石墨晶格面孔隙中的甲烷流速。在滑移流中,孔隙方向垂直于石墨晶格面時,速度分布與切向動量協(xié)調系數(shù)ζ=0.6的Maxwell滑移理論值符合較好;當壁面原子為單層石墨卷成的納米管時,速度分布與ζ=0.1的Maxwell滑移理論值符合較好;而在孔隙方向平行于石墨晶格面的孔隙中,兩側近壁面處的甲烷速度為0,以致整體徑向速度分布偏離了 Maxwell滑移理論值。在方向相同的孔隙中,滑移程度隨驅動力的增大而增大,質量流量逐漸增大。隨著驅動力的增加,滑移長度增加的趨勢不斷減小,流動摩擦阻力系數(shù)隨著驅動力和雷諾數(shù)的增加而減小,減小的幅度隨著驅動力的增加在降低。(2)通過構建的孔徑為1～5nm的石墨多孔骨架,模擬了甲烷在溫度為280K和320K下的分布形態(tài)和擴散性質。研究發(fā)現(xiàn),甲烷主要吸附在石墨的六晶格壁面處,其面積越大,吸附數(shù)越多,在該壁面構成的孔隙中停留的時間越長;甲烷的吸附層是在溫度與分子間勢能相互耦合作用下形成的,溫度對甲烷擴散的影響與固體結構原子排列關系不大。(3)通過構建的Ⅰ類和Ⅱ類干酪根有機質分子模型,模擬了甲烷在不同溫度中的等溫吸附和擴散過程。研究發(fā)現(xiàn),干酪根對甲烷的吸附數(shù)隨溫度的升高而減少,且溫度每升高20K,甲烷吸附量大約減少25%,吸附規(guī)律符合Langmuir等溫吸附特征。Barneet Ⅱ類干酪根對甲烷的吸附量約為樺甸Ⅰ類干酪根的3.37倍。甲烷更容易從Ⅰ類干酪根中解吸出來。溫度每升高40K,擴散系數(shù)大約增加2.3倍。甲烷在Ⅰ類干酪根張擴散系數(shù)大于Ⅱ類,表面其在Ⅰ類干酪根中的擴散速度更快。
[Abstract]:The nano pore fluid transport properties in shale gas is tight oil and gas reservoir development, basic scientific problems of porous nano materials development. The gas flow in nanoscale pores by size effect, the conventional theory of fluid mechanics has been unable to apply. The molecular dynamics theory and software are based on a previous study in based on the surface to simulate the transport process of methane, carbon nano pores, analyzes the methane slip in the supercritical state flow and transition flow; through the graphite porous medium model with different wall structure, simulate the distribution and diffusion of methane in the porous medium, the microscopic mechanism of methane and solid surface the wall cracks in the nano porous particle interactions revealed; finally, through the establishment of molecular type kerogen organic matter model was simulated under the different temperature of methane in cheese base The adsorption and diffusion behavior of matter in the cell, resulting in a calculation of the heat of adsorption and diffusion activation energy. The main contents and conclusions as follows: (1) by molecular dynamics model in two different diameter of the graphite in the pores of methane that changes the direction of hole graphite will lead to effects of methane and pore wall surface the potential change of flow and influence the nature of methane; in transitional flow, the radial distribution of the axial velocity fluctuation of methane is intense, graphite six lattice plane is a very smooth surface, flow rate of methane in the pore wall in fast, and the boundary slip length; the average velocity increases with the increase of methane the micro pore scale, radial distribution and axial velocity of the slow wave perpendicular to the graphitic lattice. The pore, the average speed is lower than that of methane methane flow velocity parallel to the graphite lattice plane in the pores. The slide Advection in the direction perpendicular to the porous graphitic lattice plane, the velocity distribution and the tangential momentum accommodation coefficient zeta =0.6 Maxwell slip in good agreement with the theoretical value; when the wall atoms of graphene coiled nanotubes, Maxwell theory slip velocity distribution and zeta values of =0.1 in good agreement; and in the direction parallel to the graphitic pore the pore lattice, the velocity of methane on both sides near the wall is 0, so that the overall radial velocity distribution deviates from the theoretical value. The Maxwell slip in the same direction in the pore, with the degree of slip driving force increases with the increase of mass flow increased gradually. With the increase of driving force, the slip length increased gradually decreased flow, the friction coefficient decreases with the increase of driving force and the Reynolds number, reduces with the increase in driving force decreased. (2) through the construction of the aperture is 1 ~ 5nm of graphite porous skeleton, a simulation At the temperature of alkane distribution and diffusion properties of 280K and 320K. The study found that methane mainly adsorbed on the surface of the graphite lattice wall six, the area is larger, the adsorption number in the wall of the pore to stay longer; the adsorption layer is formed on the temperature and methane molecules the potential interaction under the influence of temperature on methane diffusion and solid structure of atomic arrangement has little relationship. (3) through the construction of class I and class II kerogen organic molecular model, simulation of isothermal adsorption and diffusion process of methane at different temperatures. The study found that the number of kerogen on methane adsorption to decrease with increasing temperature, and the temperature is increased by 20K, reducing the methane adsorption capacity of about 25%, adsorption accords with Langmuir isothermal adsorption characteristics of.Barneet class II kerogen adsorption of methane is about 3.37 times that of Huadian type I kerogen methane more easily. Desorption from the first class kerogen. When the temperature is increased by 40K, the diffusion coefficient is increased by 2.3 times. The diffusion coefficient of methane in type I cheese kerogen is larger than that of type II, and its diffusion speed is faster in the first class kerogen.

【學位授予單位】：西南石油大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ127.11;TB383.1

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