天然气水合物分解过程中的传热传质数值模拟研究

发布时间：2018-11-25 11:26

【摘要】：进入21世纪以来,我国经济高速发展,经济发展和能源不足之间的矛盾日益突出。另外,我国依然以煤、石油、天然气等常规化石能源为主导能源,可再生能源所占比例很少,环境问题迫在眉睫。因此,寻找无污染的替代性能源意义重大。天然气水合物是成藏于深海沉积物或者陆地永冻层的一种新的能源,因其储量丰富、能量密度高、燃烧无污染等特点,被国际能源界公认为未来最具潜力的替代性能源。天然气水合物的分解过程是一个复杂的相变传热传质过程,分解速率主要受气、液两相流及传热,水合物分解动力学等因素的影响。通过大量的文献调研,建立了水合物分解的二维数学模型。降压分解过程中,由于没有额外的热量注入,盖层传热、导热及井底压力(BHP)等都是影响水合物分解的重要因素,将相关参数进行分离,采用单一的直井模拟了水合物在不同的盖层温度、多孔介质导热系数及井底压力下的分解过程;注热水分解过程中,注热水的速度、温度等均是重要的影响因素,选取不同的注热水速度和注热水温度,分别模拟了水合物在一维系统及二维径向系统中的分解过程,得到了储层内的温度分布,分解前缘分布以及产气速率和累积产气量的变化规律。通过对模拟结果归纳并分析,得到了以下结论:1.盖层温度越高,分解前缘越快地深入到水合物层中心,产气速率和产气量越大,产气持续时间越长。2.多孔介质导热系数越大,相同模拟时间后,储层内的整体温度越低,分布越均匀;导热系数较小时,其对产气量的影响较明显,随着导热系数增大,其对产气量的影响逐渐减弱。3.井底压力越小,分解前缘处的温度越低,越多的显热可用于水合物的分解;盖层温度较低时,井底压力对产气量的影响较大,随着盖层温度升高,井底压力的影响逐渐被削弱。4.注热水分解过程中,水合物的分解过程可以看成是移动的边界消融过程,边界处温度变化较快.,储层被分成3个区域,即完全分解区域、正在分解区域和未分解区域,正在分解区域只存在于一段狭小的区域内;增加注水速度或温度会提高产气速率,但对最终产气量影响不大。
[Abstract]:Since entering the 21 st century, the contradiction between economic development and energy shortage has become increasingly prominent. In addition, China still takes coal, oil, natural gas and other conventional fossil energy as the dominant energy, renewable energy accounts for a small proportion, environmental problems are imminent. Therefore, it is of great significance to find alternative energy sources without pollution. Natural gas hydrate is a new energy source formed in deep-sea sediments or terrestrial permafrost. Because of its rich reserves, high energy density and non-pollution combustion, gas hydrate is recognized as the most potential alternative energy in the future by the international energy community. The decomposition process of natural gas hydrate is a complex phase change heat and mass transfer process. The decomposition rate is mainly affected by gas, liquid two-phase flow and heat transfer, hydrate decomposition kinetics and so on. A two-dimensional mathematical model of hydrate decomposition is established through a lot of literature research. Due to no additional heat injection, heat transfer in caprock, heat conduction and bottom hole pressure (BHP) are the important factors influencing hydrate decomposition, so the related parameters are separated. A single vertical well is used to simulate the decomposition process of hydrate under different capping temperature, thermal conductivity of porous media and bottom hole pressure. In the process of hot water injection decomposition, the velocity and temperature of hot water injection are all important factors. The decomposition process of hydrate in one dimensional system and two dimensional radial system is simulated by selecting different water injection velocity and injection temperature. The temperature distribution, decomposition front distribution, gas production rate and cumulative gas production rate in the reservoir are obtained. The simulation results are summarized and analyzed, and the following conclusions are obtained: 1. The higher the caprock temperature, the faster the decomposition front reaches to the center of hydrate layer, the higher the gas production rate and the gas production rate, the longer the gas production duration. 2. The larger the thermal conductivity of porous media is, the lower the overall temperature of reservoir is and the more uniform the distribution is after the same simulation time. When the thermal conductivity is small, the effect on gas production is obvious, and with the increase of thermal conductivity, the influence on gas production gradually weakens. The lower the bottom hole pressure, the lower the temperature at the front edge of decomposition, and the more sensible heat can be used to decompose hydrate. When the temperature of caprock is low, the influence of bottom hole pressure on gas production is greater. With the increase of capping temperature, the influence of bottom hole pressure is weakened gradually. In the process of hot water injection decomposition, the decomposition process of hydrate can be regarded as a moving boundary ablation process, and the temperature at the boundary changes rapidly. The reservoir is divided into three regions, that is, the completely decomposed region, which is being decomposed and the undecomposed area. The decomposing region exists only in a narrow region; Increasing water injection rate or temperature can increase the gas production rate, but has little effect on the final gas production.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE31

【相似文献】