Zhang Jidong, Yin Zhenyuan, Khan Saif A, Li Shuxia, Li Qingping, Liu Xiaohui, Linga Praveen
Institute for Ocean Engineering, Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China.
Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117582, Singapore.
Lab Chip. 2024 Mar 12;24(6):1602-1615. doi: 10.1039/d3lc00950e.
Methane hydrates (MHs) have been considered a promising future energy source due to their vast resource volume and high energy density. Understanding the behavior of MH formation and dissociation at the pore-scale and the effect of MH distribution on the gas-liquid two phase flow is of critical importance for designing effective production strategies from natural gas hydrate (NGH) reservoirs. In this study, we devised a novel high-pressure microfluidic chip apparatus that is capable of direct observation of MH formation and dissociation behavior at the pore-scale. MH nucleation and growth behavior at 10.0 MPa and dissociation thermal stimulation with gas bubble generation and evolution were examined. Our experimental results reveal that two different MH formation mechanisms co-exist in pores: (a) porous-type MH with a rough surface formed from CH gas bubbles at the gas-liquid interface and (b) crystal-type MH formed from dissolved CH gas. The growth and movement of crystal-type MH can trigger the sudden nucleation of porous-type MH. Spatially, MHs preferentially grow along the gas-liquid interface in pores. MH dissociation under thermal stimulation practically generates gas bubbles with diameters of 20.0-200.0 μm. Based on a custom-designed image analysis technique, three distinct stages of gas bubble evolution were identified during MH dissociation thermal stimulation: (a) single gas bubble growth with an expanding water layer at an initial slow dissociation rate, (b) rapid generation of clusters of gas bubbles at a fast dissociation rate, and (c) gas bubble coalescence with uniform distribution in the pore space. The novel apparatus designed and the image analysis technique developed in this study allow us to directly capture the dynamic evolution of the gas-liquid interface during MH formation and dissociation at the pore-scale. The results provide direct first-hand visual evidence of the growth of MHs in pores and valuable insights into gas-liquid two-phase flow behavior during fluid production from NGHs.
由于甲烷水合物（MHs）资源量巨大且能量密度高，它们被视为一种很有前景的未来能源。了解MH在孔隙尺度下的形成和解离行为以及MH分布对气液两相流的影响，对于设计天然气水合物（NGH）储层的有效开采策略至关重要。在本研究中，我们设计了一种新型高压微流控芯片装置，能够直接观察孔隙尺度下MH的形成和解离行为。研究了10.0MPa下MH的成核和生长行为以及伴有气泡产生和演化的解离热刺激。我们的实验结果表明，孔隙中存在两种不同的MH形成机制：（a）由气液界面处的CH气泡形成的表面粗糙的多孔型MH，以及（b）由溶解的CH气体形成的晶体型MH。晶体型MH的生长和移动会触发多孔型MH的突然成核。在空间上，MHs优先沿孔隙中的气液界面生长。热刺激下MH的解离实际上会产生直径为20.0 - 200.0μm的气泡。基于定制设计的图像分析技术，在MH解离热刺激过程中识别出气泡演化的三个不同阶段：（a）在初始缓慢解离速率下单个气泡生长并伴有水层扩展，（b）在快速解离速率下快速产生气泡簇，以及（c）气泡在孔隙空间中均匀分布的合并。本研究设计的新型装置和开发的图像分析技术使我们能够直接捕捉孔隙尺度下MH形成和解离过程中气液界面的动态演化。这些结果为孔隙中MH的生长提供了直接的第一手视觉证据，并为从NGHs开采流体过程中气液两相流行为提供了有价值的见解。
