【作者】 于涛；

【导师】 宋永臣；

【作者基本信息】 大连理工大学 ， 能源与环境工程， 2012， 硕士

【摘要】 天然气水合物是自然界中天然气存在的一种特殊形式,主要分布在深海沉积层和陆域永久冻土带中。我国的青藏高原冻土区幅员广阔,面积可达150万平方公里。近年来在青藏高原冻土区实施的一系列的地质学、地球物理和地球化学的调查和研究,证实了其具备良好的天然气水合物赋存条件和找矿前景。2008年和2009年,我国在祁连山冻土区实施了“祁连山冻土区天然气水合物科学钻探工程”,成功钻获天然气水合物的实物样品。本文以DK-3井内的天然气水合物的产出特征作为依据,利用目前世界上较先进的水合物开采模拟软件TOUGH+HYDRATE,并采用垂直单井降压法,对青藏高原祁连山冻土区天然气水合物藏的开发潜力进行数值模拟。为了全面且系统地评价根据实地参数建立的模型的产气能力,分别引用了绝对指标和相对指标,并在降压分解的过程中设置了三种不同的井筒压力(1MPa、1.5MPa和2.5MPa)。模拟结果显示,井筒压力为1.5MPa时,水合物分解产气速率和储层内总气体产出速率都较为适中,储层内的累计产气总量相对最大,开发潜力明显优于其他两种情况。对井筒压力为1.5MPa时天然气水合物储层内的温度、水合物饱和度、气体饱和度和盐度的空间分布随时间的演化进行数值模拟研究,结果显示,水合物在分解过程中没有出现冰阻现象,也未见二次水合物的生成,但有一部分游离气体滞留在了储层内未被产出。在最大分解时间内,水合物储层的有效分解半径不到20m,实际分解的水合物质量仅占整个模拟系统中天然气水合物总量的2.3%。通过上述的分析和讨论可以看出,对青藏高原祁连山冻土区天然气水合物藏采用垂直单井降压法开采不具有经济可行性。更多还原

【Abstract】 Natural gas hydrate is a special form of the existence of natural gas, which is mainly distributed both in the deep marine sediments and in the terrestrial permafrost regions. The Qinghai-Tibet Plateau permafrost in China has a vast expanse with a total area up to150×104km2. In recent years, a series of geological, geophysical, and geochemical investigations and studies were conducted in the Qinghai-Tibet Plateau permafrost, resulting in the confirmation of the favorable occurrence conditions and prospecting potential for gas hydrates in this region. In2008and2009, the scientific drilling project of gas hydrate in the Qilian Mountain permafrost was implemented in China, with the discovery of gas hydrate samples successfully.Based on the output characteristics of gas hydrates at the DK-3drilling site, we take advantage of currently one of the world’s most advanced hydrate simulator TOUGH+HYDRATE to numerically simulate the development potential of gas hydrate deposits in the Qilian Mountain permafrost, Qinghai-Tibet Plateau using a single vertical well by depressurization. In order to evaluate the gas production potential of hydrates in the model built by the field parameters comprehensively and systematically, we employ the absolute index and the relative index respectively, and set three different cases of wellbore pressure (1MPa,1.5MPa and2.5MPa) during the dissociation process by depressurization. The simulation results indicate that when the wellbore pressure is set to1.5MPa, the CH4production rate of hydrate dissociation and the total CH4production rate in the reservoir both show moderately, and the cumulative CH4volume produced from the reservoir is relatively the largest, with the development potential better than the other two cases obviously. Then we numerically simulate the evolution of spatial distributions of temperature, hydrate saturation, gas saturation and water salinity in the reservoir for the wellbore pressure of1.5MPa, which indicates that ice obstacle does not appear and secondary hydrate is not observed, however, a large volume of free gas remains in the reservoir instead of being produced. During the maximum dissociation time, the effective radius of gas hydrate dissociation in the reservoir is less than20m, and the actual quality of gas hydrate dissociation only accounts for2.3%of the total quality of gas hydrates in the simulation system. Through the above analysis and discussions, we can conclude that the method of a single vertical well by depressurization for the development of gas hydrate deposits in the Qilian Mountain permafrost, Qinghai-Tibet Plateau is not economically feasible.更多还原