多孔介质中天然气水合物降压分解特性研究

发布时间：2018-03-22 21:12

本文选题：天然气水合物　切入点：分解特性　出处：《大连理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：天然气水合物是一种固态的、非化学计量的、束缚有气体分子的笼型冰状晶体化合物,主要分布于冻土与海洋沉积物中的高压低温区域,其巨大的储量被认为是未来潜在能源。鉴于目前不同水合物储藏开采的可行性以及经济性问题,降压开采被认为是水合物三种开采方法中最有效率的,且可以联合其他开采技术同时使用,因此研究沉积物中水合物降压开采过程的分解特性对于水合物储藏的利用具有重大意义。本文实验研究了产气压力和多孔介质导热系数对甲烷水合物降压分解特性的影响,分析了水合物二次生成和结冰现象的诱因,最后从储层显热和外围传热两方面讨论了传热因素对水合物降压分解的影响。研究表明,产气压力的降低以及储层导热系数的增大能够有效提高水合物的分解速率,水合物的整个降压产气过程可以分为三个阶段：自由气的排出、储层显热的消耗、以及外围传热驱动下的水合物分解阶段。第一阶段,储层中自由气开始产出,但甲烷水合物仍未分解；第二阶段,储层中水合物沿着相平衡线整体同时分解,水合物分解所需热量主要来自储层显热,而在第三阶段,储层压力降至产气压力,水合物分解则转变为外围传热作用下的由外向内分解。由于储层显热和外围传热的不足,水合物二次生成和结冰现象常出现在储层内部靠近产气井的区域,但在高导热系数储层中并未发生。此外,本文还引入了斯特藩数(Ste)和水合物分解速率常数(Kd)来研究储层显热和外围传热的对水合物降压分解的影响,结果表明两个传热因素是水合物降压分解的主要驱动力,但两者大小均取决于水合物储层的产气压力。同时,本文还建立了水合物降压分解的数值模型,在Darcy定律中考虑了重力项对气水两相渗流速度的影响,通过与本文实验结果的对比,验证了该模型的准确性,并分析了降压产气过程中储层压力、温度以及水合物饱和度的分布。研究表明,外部传热主要经储层侧面和下盖层传入储层内部,并证明了水合物由初期的空间整体分解转变为外部传热主导的由外向内分解的过程。
[Abstract]:Natural gas hydrate is a solid, non-stoichiometric, gaseous molecules bound cage ice crystal compounds, mainly distributed in frozen soil and marine sediments in the high-pressure low-temperature region, Its huge reserves are considered to be potential sources of energy in the future. Given the feasibility and economy of exploiting different hydrate reserves, depressurized extraction is considered to be the most efficient of the three methods of hydrate extraction. And can be used in conjunction with other mining technologies, Therefore, it is of great significance to study the decomposing characteristics of hydrate depressurization in sediments. The effects of gas production pressure and thermal conductivity of porous media on the decomposing characteristics of methane hydrate are experimentally studied in this paper. The inducement of hydrate secondary formation and ice formation is analyzed. Finally, the influence of heat transfer factors on hydrate decomposing is discussed from two aspects of reservoir sensible heat transfer and peripheral heat transfer. The reduction of gas production pressure and the increase of reservoir thermal conductivity can effectively increase the decomposition rate of hydrate. The whole process of reducing pressure and producing gas of hydrate can be divided into three stages: the discharge of free gas and the consumption of sensible heat in reservoir. In the first stage, the free gas in the reservoir begins to produce, but the methane hydrate is not decomposed, in the second stage, the hydrate in the reservoir is decomposed simultaneously along the phase equilibrium line. The heat needed for hydrate decomposition mainly comes from the sensible heat in the reservoir. In the third stage, the reservoir pressure drops to the gas production pressure, and the hydrate decomposition is transformed into the outer to inner decomposition under the action of the peripheral heat transfer, because of the deficiency of the reservoir sensible heat and the peripheral heat transfer. The secondary formation and ice formation of hydrate often occur in the area near the gas-producing well inside the reservoir, but not in the reservoir with high thermal conductivity. In this paper, Stean and Kd) are introduced to study the effect of reservoir sensible heat and peripheral heat transfer on hydrate decomposing. The results show that two heat transfer factors are the main driving forces of hydrate decomposing. But both of them depend on the gas production pressure of hydrate reservoir. At the same time, a numerical model of gas hydrate decomposing is established, and the influence of gravity term on gas-water two-phase percolation velocity is considered in Darcy's law. The accuracy of the model is verified by comparing with the experimental results in this paper, and the distribution of reservoir pressure, temperature and hydrate saturation in the process of reducing pressure and gas production is analyzed. The external heat transfer is mainly transmitted to the reservoir interior through the lateral and lower caprock layers, and it is proved that the hydrate has changed from the space integral decomposition in the initial stage to the outer to internal decomposition process dominated by the external heat transfer.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE311

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