不同尺度下模拟天然气水合物的降压分解

发布时间：2018-01-07 21:18

本文关键词：不同尺度下模拟天然气水合物的降压分解　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：天然气水合物是未来最有希望的清洁能源之一。近年来,天然气水合物由于在多年冻土和深海底部的大量存在,越来越多的人正在广泛关注天然气水合物的提取、运输和利用。目前,在全世界各国学者和科研人员的共同努力下,有关水合物实验、模拟、开采、理论等方面都取得了巨大的进展。水合物有关知识体系正在不断地补充、完善之中。经过各国有关学者和科研人员的刻苦努力,天然气水合物分解动力学和生成动力学相关理论已经得到了长足的发展,提出了合适的模型并得到了实验的验证。然而,利用现有成熟模型来模拟大尺度条件下水合物分解的还较少。本论文在现有模型的基础上,建立了不同尺度下天然气水合物岩芯中水合物降压分解的二维轴对称数学模型,其中包括水、气、水合物三相和水组分、水合物组分、甲烷气体组分三种组分。对建立的数学模型自行编写UDF程序在Fluent中对该模型进行求解及分析。通过改变有关边界条件和热力学条件以及比表面积等参数来获得不同的压力、温度、饱和度、产气率、产水率、吸热量分布特性和随时间变化的情况,进而形成大尺度下水合物分解的相关理论。研究结果表明:天然气水合物分解速率是岩芯物理热力条件、周围环境热条件、以及出口压力的敏感函数;多孔介质岩芯中孔隙率和各相相对渗透也是影响水合物分解和气体生产过程的重要因素;靠近分解前缘位置的温度首先会随着水合物的分解降低,然后随着岩芯与周围环境的自然热对流温度会上升至环境温度;提高环境温度会使水合物分解速率加快,同时气体生成速率和水生成速率也会加快;降低出口压力会使水合物分解速率加快,气体生成速率和水生成速率也会随之加快;编写的UDF程序为模拟多孔介质岩芯中的水合物分解提供了方便,为以后的研究打下了坚实的基础;在天然气水合物MH降压分解过程中,随着时间的推移,水合物开始从压力出口开始分解,朝着远离出口的方向进行,气相和水相的饱和度逐渐增加;在大尺度天然气水合物岩芯的模拟中可以得到类似于小尺度模型中的结论。
[Abstract]:Natural gas hydrate is one of the most promising clean energy in the future. In recent years, natural gas hydrate exists in permafrost and deep sea bottom. More and more people are paying more and more attention to the extraction, transportation and utilization of natural gas hydrate. At present, with the joint efforts of scholars and researchers from all over the world, the hydrate experiment, simulation and exploitation are concerned. Great progress has been made in theory and so on. The knowledge system of hydrate is being continuously supplemented and perfected. Through the hard work of scholars and researchers concerned in various countries. The related theories of gas hydrate decomposition kinetics and formation kinetics have been greatly developed, and the appropriate model has been put forward and verified by experiments. There are few mature models to simulate hydrate decomposition in large scale. This paper is based on the existing models. A two-dimensional axisymmetric mathematical model of gas hydrate depressurization in natural gas hydrate core at different scales is established, which includes water, gas, hydrate three-phase, water component and hydrate component. Three components of methane gas. UDF program is written to solve and analyze the mathematical model in Fluent. By changing the boundary conditions, thermodynamic conditions and specific surface area. Equal parameters to get different pressures. Temperature, saturation, gas yield, water yield, heat absorption distribution and changes over time. The results show that the rate of gas hydrate decomposition is a sensitive function of the core physical and thermal conditions, the surrounding thermal conditions, and the exit pressure. The porosity and relative permeability of each phase in the core of porous media are also the important factors affecting the hydrate decomposition and gas production process. The temperature near the front edge of decomposition decreases with the decomposition of hydrates, and then increases to the ambient temperature with the natural heat convection temperature of core and surrounding environment. At the same time, the rate of gas formation and the rate of water formation will also be accelerated by increasing the ambient temperature. Lowering the outlet pressure will accelerate the rate of hydrate decomposition, and the rate of gas formation and water formation will also accelerate. The UDF program is convenient for simulating hydrate decomposition in porous media core and lays a solid foundation for future research. In the process of gas hydrate MH decomposing, with the passage of time, the hydrate begins to decompose from the pressure outlet, moving away from the exit, and the saturation of gas phase and water phase increases gradually. In the simulation of large scale gas hydrate cores, a conclusion similar to that in the small scale model can be obtained.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE642

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