含水合物多孔介质渗流特性及水合物分解模拟研究

发布时间：2018-08-23 10:25

【摘要】：天然气水合物作为一种储量丰富、能量密度高、燃烧清洁的潜在能源被越来越多的国家所关注，目前世界上有许多国家都已经展开对天然气水合物的研究，其中包括天然气水合物开采技术的研究以及水合物应用技术的研究等，并且已经取得了巨大的进展。天然气水合物在自然界中主要储藏在海底沉积层及永久冻土带，复杂的地质环境给水合物的开采造成了严重的困难。水合物的开采是一个复杂的过程，影响因素众多，且分解过程中气、水两相流动会极大的影响水合物的分解过程，本文通过数值模拟方法，研究了天然气水合物在多孔介质中的分解过程，以渗流力学理论和孔隙网络模型为基础，从微观层次出发，得出以下研究结论：建立了三维立方体孔隙网络模型，研究了水合物饱和度、孔径分布对水合物相平衡的影响，采用达西定律作为研究的理论基础，模拟了多孔介质中水合物生成位置不同时导致的渗透率变化，研究结果表明，无论水合物是生成于中心还是生成于壁面，渗透率都随水合物饱和度的增加而减小，并且生成于中心时渗透率的减小幅度大于生成于壁面时。同时研究了不同的孔隙率，不同的水合物饱和度条件以及水合物在孔隙中不同的位置生成时气、水两相相对渗透率的变化。当水合物生成位置是孔隙壁面时，两相相对渗透率下降较慢，而水合物生成位置是孔隙中心时，渗透率下降较快，且在壁面生成时的两相渗透率等渗点高于中心生成时，同时发现水合物无论在中心还是在壁面生成，气、液两相渗透率都不随孔隙率及水合物饱和度的变化而变化。对微观尺度下多孔介质中天然气水合物分解特性进行了影响因素敏感性分析，结果表明，水合物分解速度常数、多孔介质孔隙率、初始温度、出口压力、初始饱和度等均会影响多孔介质中天然气水合物分解速率，而多孔介质孔径分布对分解速率影响不大。本文通过数值模拟的方法研究了多孔介质中水合物饱和度与渗透率之间的关系及水合物分解特性，对于正确的进行天然气水合物开采评价具有重要的借鉴意义，，为水合物开采方法及开采技术的确定提供理论支持。
[Abstract]:As a kind of potential energy with rich reserves, high energy density and clean combustion, gas hydrate has been paid more and more attention by more and more countries. At present, many countries in the world have carried out research on gas hydrate. It includes the research of gas hydrate exploitation technology and hydrate application technology, and has made great progress. Natural gas hydrate is mainly stored in marine sediments and permafrost zones in nature. The complex geological environment makes it difficult to exploit gas hydrate. The extraction of hydrate is a complicated process, and there are many influencing factors, and the gas and water two-phase flow will greatly affect the decomposition process of hydrate. In this paper, the method of numerical simulation is used. The decomposition process of natural gas hydrate in porous media is studied. Based on the theory of percolation mechanics and pore network model, the following conclusions are drawn from the microscopic level: a three-dimensional cubic pore network model is established. The effects of hydrate saturation and pore size distribution on the phase equilibrium of hydrate are studied. Darcy's law is used as the theoretical basis to simulate the permeability change caused by the different position of hydrate formation in porous media. No matter whether the hydrate is formed at the center or on the wall, the permeability decreases with the increase of hydrate saturation, and the decrease of permeability at the center is larger than that at the wall. At the same time, the changes of relative permeability of gas and water are studied under different porosity, different hydrate saturation conditions and gas and water relative permeability when hydrate is generated at different locations in the pores. When the formation position of hydrate is on the pore wall, the relative permeability of two phases decreases more slowly, while when the location of hydrate formation is the center of the pore, the permeability decreases more quickly, and the equipermeability point of the two phase is higher than that of the center when the gas hydrate is formed on the wall. At the same time, it is found that the permeability of gas and liquid does not change with the change of porosity and hydrate saturation, regardless of the formation of hydrate in the center or on the wall. The factors influencing the decomposition characteristics of natural gas hydrate in porous media are analyzed. The results show that the rate constant of hydrate decomposition, porosity of porous media, initial temperature, exit pressure, and so on. Initial saturation and so on will affect the decomposition rate of natural gas hydrate in porous media, but pore size distribution in porous media has little effect on the decomposition rate. In this paper, the relationship between hydrate saturation and permeability in porous media and the characteristics of hydrate decomposition are studied by means of numerical simulation, which is of great significance for the correct evaluation of natural gas hydrate exploitation. It provides theoretical support for the determination of hydrate mining method and mining technology.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE312

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