Abstract:

In order to study the formation of methane hydrate in porous media with different particle sizes, quartz sand with particle sizes of 0.075—0.5mm, 0.5—1mm, 1—2mm and 2—3mm were used as porous media. The hydrate formation experiment was carried out at an initial pressure of 7.0MPa and a temperature of 0.5℃, and then the sampling observation and delamination were performed. Results showed that with the increase of medium particle size, the initial rate of formation and the amount of hydrate formation in the pores of quartz sand were decreased gradually, the hydrate began to form during aeration process in three particle sizes of 0.075—0.5mm, 1—2mm and 2—3mm, and there was a large amount of hydrate formation in particle size of 0.5—1mm during the hydrate formation process. The particle size of 0.5—1mm had the maximum gas consumption of 0.47mol, and gas consumption in particle size of 2—3mm was the minimum of only 0.05mol. According to the sampling observation, the methane hydrate on the surface of these four quartz sand bodies was mainly distributed evenly among the particles with dispersed or cemented into blocks. However, it was different from the result that the amount of hydrate in the upper part of sand body was more than that in the lower part of sand body by decomposition method. There was only a large amount of hydrate accumulation occurred on the top of quartz sand with 0.5—1mm. Therefore, it was inferred that when there was a large void in the upper part of a medium system with a certain particle size, the hydrate may be enriched in the void. The experimental result had certain reference value for the prediction of hydrate occurrence area and morphology in natural environment.

Key words: particle size, quartz sand, methane hydrate, formation process, gas consumption, decomposed gas, distribution

摘要：

为了研究不同粒径多孔介质体系中甲烷水合物的形成，本文采用粒径分别为0.075~0.5mm、0.5~1mm、1~2mm和2~3mm的石英砂作为多孔介质，在初始压力7.0MPa、温度0.5℃条件下进行水合物形成实验并进行取样观察、分层分解，得出不同粒径大小石英砂中甲烷水合物形成及分布的特征。结果表明：随着石英砂粒径的增大，石英砂砂体中的水合物形成量和初始水合物形成速率在逐渐减小；在粒径为0.075~0.5mm、1~2mm和2~3mm石英砂中，充气过程中水合物便开始形成，且并未出现明显的水合物大量形成阶段，而在粒径为0.5~1mm石英砂体系中出现了水合物大量形成的阶段；通过计算发现，0.5~1mm石英砂体系的气体消耗量最大，为0.47mol，2~3mm石英砂体系的气体消耗量最小，仅为0.05mol；在这4种粒径的石英砂体表面的甲烷水合物主要以分散状均匀分布于颗粒之间或胶结成块，但这一观察结果与通过分解的方法所得到的石英砂上部水合物形成量大于下部的结果存在差异；重复实验也发现，仅在粒径为0.5~1mm石英砂顶部出现了水合物大量富集的现象，因此推断认为在一定粒径的介质体系同时上部存在较大空隙时，水合物有可能会在空隙中大量富集存在。这一实验结果对自然环境中水合物的赋存区域及形态的预测具有一定的参考价值。

关键词: 粒径大小, 石英砂, 甲烷水合物, 形成过程, 气体消耗量, 分解气体量, 分布