粉砂质沉积物中天然气水合物分解过程的热质耦合传递机理

Natural gas hydrate in the clay-silty sand sediment is the main type of global marine gas hydrate. China successfully complicated the first global field test of gas production from hydrate in the clay-silty sediment of the South China Sea in 2017. Coupling mechanism of heat and mass transfer during hydrate dissociation is one of the main influence factors that control hydrate dissociation as well as gas and water production. In addition, coupling mechanism of heat and mass transfer during hydrate dissociation is a key scientific problem of exploiting hydrate in the clay-silty sand sediment. Based on the precious study, this project aims to conduct theoretical and experimental research about the coupling mechanism of heat and mass transfer during hydrate dissociation, by taking advantage of the existing advanced equipment and the trial-manufactured visual experimental equipment. Equations of evolutions of the permeability and heat conductivity with hydrate saturation variation in the clay-silty sand sediment can be established, through precise characterizations of key parameters for heat and mass transfer. The principle and the interaction mechanism of heat and mass transfer during hydrate dissociation in the clay-silty sediment can be illuminated through experimental investigation. Meanwhile, a coupling model of heat and mass transfer can be established by combing the multi-fields synergy theory and the previous analytical equation of heat and mass transfer with a double-moving boundary. In addition, the optimal conditions for heat and mass transfer during hydrate dissociation in the clay-silty sediment will be obtained in this project. Furthermore, hydrate dissociation experiments based on these optimal conditions are performed to verify the coupling model of heat and mass transfer by comparing the experimental and theoretical results. The research achievements in this project can provide basic data and theoretical foundation for the future exploitation of hydrate in clay-silty sand sediment in China, which plays a significant role in engineering and have important theoretical value.

粉砂质天然气水合物(NGH)是全球主要的海域NGH类型，我国于2017年实现了此种NGH的全球首次试采。NGH分解过程中的热质耦合传递机理是影响NGH分解及气液产出的主要因素，是开发粉砂质NGH的关键基础科学问题。本项目基于前期研究基础，结合现有先进设备并试制可视化实验装置，围绕NGH分解过程中的热质耦合传递机理展开实验及理论研究。通过表征传热和渗流关键参数，建立粉砂质沉积物渗透率和热导率随NGH饱和度变化的方程；通过粉砂质NGH分解实验阐明NGH分解过程中传热传质规律和相互耦合机理，结合前期研究的传热传质“双移动界面”解析方程和多场协同理论，构建热质传递耦合模型，并计算热质传递优化条件。基于获得的优化的热质传递协同条件，开展粉砂质沉积物NGH分解实验及理论结果对比，验证建立的热质传递耦合理论模型。本研究将为我国未来粉砂质NGH开采提供基础数据和理论依据，具有重要现实指导意义和理论价值。

海洋天然气水合物含碳量是所有化石能源总和的2倍，是未来全球能源发展的战略制高点。我国南海水合物资源约为800亿吨油当量，粤港澳大湾区及其邻近海域已圈定11个水合物资源开发远景区。.我国高度重视水合物资源的开发利用，将其作为能源技术革命的重要内容。《能源发展战略行动计划（2014-2020）》和《能源技术革命创新行动计划（2016-2030）》对水合物的开发利用提出了明确要求，布局加快形成勘察、开采、运输、存储、生产一体化的产业链体系。水合物的产业化开发，将极大改善我国天然气资源对外依存度高的问题，促进我国化石能源低碳转型，切实有效的保障我国的能源资源安全，促使我国在国际能源革命中掌握话语权。我国已经成功进行了两次水合物试采，第二次试采实现了探索性试采向试验性试采的转变，创造了产气总量86.14万m3和日均产气量2.87万m3的世界纪录。虽然，我国已经在水合物开采技术方面走在国际前列，但是距离正式的商业开采还有较长的距离，其中原位高效分解是制约其产气效率的重要因素，与常规油气藏资源不同的是，水合物的分解涉及固相向气液两项转变的吸热过程，因此沉积层中的热质耦合传递机理是影响其原位高效分解的重要因素。本项目通过不同尺度的室内模拟实验，研究了沉积层导热率、含水率、沉积物尺寸、沉积层渗透率等物性参数对水合物分解速率特性的影响，并建立了改进的降压分解速率模型，基于孔隙尺度实验、反应釜尺度实验、中试规模尺度实验，揭示了不同尺度模拟实验过程中，传热和传质在不同阶段对水合物分解速率的影响特性，并评估了不同分解模式下产气速率、产水速率和水合物分解速率的影响，并且对不同尺度水合物分解过程的分解前缘进行了可视化解析，厘清了水合物饱和度分布规律对储层内传热和传质特性的影响因素，并且的提出了优化降压速率建立的热质传递耦合机制。本项目的基础研究成果将对大规模尺度天然气水合物的分解，尤其是现场尺度天然气水合物的开采的高效生产方案提供基础理论支持。