液态CO2原位置换整形天然气水合物的形态研究

CO_2置换法在开采天然气(CH_4)水合物资源的同时,能将温室气体(CO_2)以稳定的水合物形式永久封存并保持海底地质结构的稳定。探究液态CO_2原位置换整形天然气水合物的过程形态,验证水合物的形态结构是否会破坏,对实际开采技术的研发具有关键意义。利用自行设计的可视化反应釜对液态CO_2置换整形天然气水合物进行实验观测研究。结果表明:①在置换过程中,原位CH_4水合物分解的同时生成CO_2水合物,并保持过程中水合物的整形结构稳定的第二类原位置换过程是可以实现的;②在实际工程应用中,采用液态CO_2在相应的相平衡压力条件下,对大规模的天然气水合物藏进行第二类原位置换,可望获得较高的水合物藏置换开采效率。实验结果为进一步研究液态CO_2置换天然气水合物开采工艺提供了直观的过程现象。

Morphology on in-situ replacement of bulk methane hydrates with liquid carbon dioxide

Natural gas hydrate, existing wildly below the ocean floor and in permafrost zones, is expected to be future energy source. Replacement of CH₄ in natural gas hydrate by CO₂, CH₄-CO₂ replacement, has been considered as a promising way for simultaneous CH₄ production and CO₂ sequestration. Exploring the morphology of CO₂ in-situ replacing CH₄ in bulk hydrates to test whether the morphology structure of bulk hydrates would be destroyed has a significant meaning in the development of exploitation technology. In this study, morphological changes of liquid CO₂ in-situ replacing bulk CH₄ hydrates in a self-designed horizontal cylinder are recorded by CCD camera. The results show that the dissociation of CH₄ hydrates and the formation of CO₂ hydrates occur in the hydrate phase simultaneously without destroying the morphology structure of bulk hydrates. Using liquid CO₂ to in-situ replacement for large-scale natural gas reservoirs under corresponding pressure,a higher efficiency of exploitation can be achieved. This result can provide intuitive phenomena for the study of replacement techniques.