天然气水合物沉积物传热特性及对开采影响研究

发布时间：2018-10-31 13:34

【摘要】：天然气水合物是一种世界公认的最具潜力的清洁新能源,目前我国对水合物勘探开采研究正进入关键突破阶段。传热特性对水合物高效开采有至关重要的影响和控制作用,本文以水合物开采过程中面临的高效性关键问题为研究背景,针对水合物沉积物有效导热系数、储层传热因素,分解过程传热变化规律以及对开采影响展开重点研究。为了探明水合物沉积物导热特性,本文自主开发了一种高压低温原位测量多孔介质中水合物有效导热系数的实验方法和系统,获取了水合物沉积物在不同孔隙度、多孔介质、饱和度、温度等多因素作用下的有效导热系数变化规律。并基于不同维度的实验数据,建立了水合物沉积物有效导热系数经验关联式,对比证明该经验关联式能够较好预测THF水合物沉积物和水饱和沉积物的有效导热系数。系统研究了水合物沉积物开采过程中储层的宏观传热因素,实验发现闷罐式水合物热开采过程是导热控制型分解模式,证明沉积物导热系数和开采温度决定了开采效率。实验得出高导热系数多孔介质材料对水合物分解的促进作用主要体现在水合物的分解后期,它能够提高沉积物分解温度、产气速率和累积产气量,抑制冰的生成,进而提高水合物的开采效率。结合Ste的计算证明沉积物的显热在降压开采的快速降压阶段控制着水合物的开采效率,较高的Ste在快速降压阶段能促进水合物的分解,提高开采温度并抑制结冰现象,当Shj30%,显热对水合物促进作用显著减弱。研究发现Qov在降压开采后期热传递和水合物开采效率上起到主导控制作用,Qov能够显著的提高水合物开采效率,随着水合物饱和度增加,Qov对开采的促进作用增强。而随着Qov的持续增加,对水合物的促进作用反而逐渐减弱,水合物的开采效率也逐渐降低。探讨了水合物开采过程中的传热影响机理,对三种开采技术的传热影响与开采效率关系进行了系统的对比分析,证明沉积层的显热和抑制结冰是提高降压开采效率的关键因素；能源利用率和水合物饱和度是决定注热开采效率的关键；联合开采具有可观的产气效率,是一种最具应用前景的开采技术。实验获取了水合物分解过程不同阶段导热系数变化规律,发现了水合物分解速率、气水迁移是控制水合物分解过程沉积物导热系数变化的主要因素。建立了一种高压低温下多孔介质中水合物分解过程传热系数法原位测量方法,获取了水合物沉积物内部传热系数与分解速率和产气速率的协同变化规律,实验证明了水合物分解过程中的相态变化和气液流动是传热系数变化的主要驱动力。在水合物快速分解阶段,传热系数随着水合物的分解和产气输出呈现出快速上升趋势,水合物降压开采过程中的传热系数随着Shi的升高呈现出先增高后降低的规律。
[Abstract]:Natural gas hydrate is recognized as the most potential clean new energy in the world. At present, the research on hydrate exploration and exploitation in China is entering a critical breakthrough stage. The heat transfer characteristic has the vital influence and the control function to the hydrate high efficiency exploitation. This paper takes the high efficiency key problem in the hydrate mining process as the research background, aiming at the hydrate sediment effective thermal conductivity, the reservoir heat transfer factor. The variation of heat transfer in decomposition process and its influence on mining are studied. In order to investigate the thermal conductivity of hydrate sediments, an experimental method and system for in-situ measurement of effective thermal conductivity of hydrate in porous media at high pressure and low temperature were developed, and the effective thermal conductivity of hydrate sediments in different porosity and porous media was obtained. The variation of effective thermal conductivity under the action of saturation, temperature and other factors. Based on the experimental data of different dimensions, an empirical correlation formula for the effective thermal conductivity of hydrate sediments is established. It is proved that the empirical correlation can better predict the effective thermal conductivity of THF hydrate sediments and water-saturated sediments. The macroscopic heat transfer factors of reservoir in the process of hydrate sediment exploitation are systematically studied. The experimental results show that the thermal recovery process of gas hydrate is a thermal conductivity controlled decomposition mode, which proves that the thermal conductivity and exploitation temperature of sediment determine the recovery efficiency. The results show that the effect of high thermal conductivity porous media on hydrate decomposition is mainly reflected in the later stage of hydrate decomposition, which can increase the decomposition temperature, gas production rate and cumulative gas production rate of sediment, and inhibit the formation of ice. Furthermore, the extraction efficiency of hydrate is improved. Combined with the calculation of Ste, it is proved that the sensible heat of sediment controls the extraction efficiency of hydrates in the stage of rapid depressurization. The higher Ste can promote the decomposition of hydrates, raise the extraction temperature and restrain the phenomenon of ice formation in the stage of rapid depressurization. The promoting effect of sensible heat on hydrate is obviously weakened. It is found that Qov plays a leading role in controlling heat transfer and hydrate recovery efficiency in the later stage of depressurized mining, and that Qov can significantly improve the hydrate extraction efficiency. With the increase of hydrate saturation, the effect of Qov on mining is enhanced. However, with the increase of Qov, the promotion of hydrate becomes weaker and the recovery efficiency of hydrate decreases gradually. The influence mechanism of heat transfer in hydrate mining is discussed. The relationship between heat transfer effect and extraction efficiency of the three mining technologies is systematically compared and analyzed. It is proved that the sensible heat of sediment layer and the inhibition of ice formation are the key factors to improve the efficiency of depressurization mining. Energy utilization ratio and hydrate saturation are the key factors to determine the efficiency of heat injection extraction, and combined mining is the most promising mining technology for its considerable gas production efficiency. The variation of thermal conductivity in different stages of hydrate decomposition is obtained experimentally. It is found that the rate of hydrate decomposition and gas-water migration are the main factors controlling the variation of sediment thermal conductivity during hydrate decomposition. A method of in-situ measurement of heat transfer coefficient of hydrate decomposition process in porous medium at high pressure and low temperature was established. The synergistic variation of heat transfer coefficient with decomposition rate and gas production rate in hydrate sediment was obtained. The experimental results show that the change of phase state and gas-liquid flow are the main driving forces for the change of heat transfer coefficient in the process of hydrate decomposition. In the rapid decomposition stage of hydrate, the heat transfer coefficient increases rapidly with the decomposition of hydrate and gas output, and the heat transfer coefficient increases first and then decreases with the increase of Shi.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TE37

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