天然气水合物降压分解过程传热控制机理研究

In recent years, large amount reserves of permafrost and marine natural gas hydrate were discovered in China, exploiting the hydrate resources with high efficiency became a major topic in the hydrate resource utilization. The heat transfer in hydrate-bearing sediments is the main controlling factor for hydrate decomposition by depressurization, and determines the rate and efficiency of hydrate dissociation. Therefore, heat transfer becomes a key problem for the hydrate efficient decomposition. Under this background, this project aims at the heat transfer control mechanism for natural gas hydrates dissociation by depressurization. The point heat source measurement and microfocus X-ray CT experimental method and simulation will be used to investigate the heat transfer during the whole process of hydrate decomposition. Moreover, considering the reservoir structure and the time varying characteristic of pore gas, water and hydrates, the time varying regularity of the dominant factors for the heat transfer process in the hydrate-bearing sediments will be analyzed in detail. The depressurization-induced driving effect and collaborative control principle will be mainly ascertained in decomposition process, which associate with the intrinsic inner heat in the reservoir, effective thermal conductivity and the convection in the hydrate-bearing sediment. The internal relationship between the heat transfer of hydrate-bearing sediment and the decomposition efficiency of natural gas hydrate by depressurization would be established. Finally, this study will reveal the heat transfer control principle and mechanism in the natural gas hydrate decomposition process by depressurization, and provide the theoretical basis for the high efficiency exploitation of natural gas hydrate in the future.

近年我国相继探明大规模陆地、海洋天然气水合物资源，对其高效开采成为我国天然气水合物资源利用面临的重大课题。传热作为天然气水合物降压分解进程的主控因素，决定了天然气水合物分解速率和效率，是制约天然气水合物降压开采高效性的关键问题。本项目以此为背景，利用天然气水合物点热源测量与微焦X射线CT可视化实验技术以及数值模拟方法，对沉积物中天然气水合物降压分解开展全历程传热分析；考虑储层结构以及孔隙气、水、天然气水合物等多因素的时变特征，研究天然气水合物降压分解进程中传热主控因素的时变规律；重点解析沉积物储层自身内热源、天然气水合物沉积物有效导热、以及沉积物中气水对流换热，对天然气水合物降压分解进程的驱动作用与控制原理；探明天然气水合物沉积物储层传热与降压分解高效性之间的内在联系；最终阐释沉积物中天然气水合物降压分解进程的传热控制机理，为我国天然气水合物资源高效开采利用相关研究提供基础理论依据。

近年我国相继探明大规模陆地、海洋天然气水合物资源，对其高效开采成为我国天然气水合物资源利用面临的重大课题。传热作为天然气水合物降压分解进程的主控因素，决定了天然气水合物分解速率和效率，是制约天然气水合物降压开采高效性的关键问题。本项目已此为背景，利用构建的天然气水合物降压分解实验平台，基于陆相与海域天然气水合物储层温度范围，实验室模拟生成不同温压条件下，不同赋存结构的天然气水合物沉积物，分析了 天然气水合物二次生成与结冰现象、不同上下盖层热对流对于水合物降压分解速率与分解效率的影响；利用构建的天然气水合物有效导热系数原位测量装置，基于点热源测量方法结合CT可视化观测对甲烷水合物沉积物有效导热系数进行测量，探明了甲烷水合物沉积物有效导热系数随饱和度的变化规律，以及水合物分解过程中有效导热系数的变化规律；利用自主开发的天然气水合物降压分解模拟系统，数值模拟了渗透率对天然气水合物降压开采过程中分解速率以及开采效率的影响控制作用，结果表明，高渗透率沉积层可以有效促进压力的传播，使得水合物呈现空间分解特性，在低渗透率沉积层中，环境传热控制的轴向分解特性更为显著，其分解速率对环境传热的依赖性更大，而且，储层渗透率越大，越容易导致水合物的快速分解，进而导致快速的产气速率。以上研究成果阐释沉积物中天然气水合物降压分解进程的传热控制机理，为我国天然气水合物资源高效开采利用相关研究提供基础理论依据。