低渗双重介质中水合物相变动力学及其控制机制研究

Natural gas hydrate (NGH) is a kind of new and clean energy resource that has the most application potential in the future. Huge amount of NGH has been confirmed to exist in the Shenhu Area of the South China Sea and the Qilian Mountain permafrost of the Qinghai-Tibet plateau. It is of great importance to exploit NGH effectively for solving the problem of energy shortage and ensuring the sustainable development of the economic society of China. The phase transition kinetics of natural gas hydrate as well as its controlling factors is one of the basic scientific problems during the exploitation process of NGH. Based on the geological conditions of the Qilian Mountain permafrost hydrate deposits, this program aims to carry out the experimental and theoretical investigations of the NGH phase transition kinetics in double-porosity media containing pores and fractures with low permeability. The characteristic physical parameters of the matrix and the fractures in the core samples are measured experimentally during hydrate formation and dissociation. The key parameters, such as the thermodynamic state of the system, the reaction driving force, and the phase saturations, are also monitored during the whole life of natural gas hydrate (including the nucleation, the growth, the agglomeration, and the dissociation) to illuminate the main factors controlling the NGH phase transition kinetics. Combined with the double media theory, new models which describe the gas hydrate phase equilibrium, the hydrate formation and dissociation kinetics, and the multi-phase fluid flow in double-porosity rocks are then established by coupling them with the medium properties. Furthermore, these models are further coupled with the numerical simulator of gas hydrate, and their parameters are validated and modified based on the experimental data. This program will provide basic data and theoretical support for the gas hydrate exploitation from permafrost hydrate deposits of China.

天然气水合物（NGH）作为一种未来最具潜力的新型洁净能源，在我国南海海域以及青藏高原冻土区储量巨大，有效开发NGH对于解决我国能源短缺问题以及确保我国经济社会可持续发展意义重大。自然界中水合物相变动力学及其控制机制是NGH资源开发的基础科学问题之一。本项目基于我国冻土区水合物藏地质条件，开展低渗透型孔隙-裂隙双重介质中NGH相变动力学实验及基础理论研究。通过在线测量水合物生成与分解过程中岩芯样品基质与裂隙特征物理参数及其变化，以及水合物颗粒成核、生长、聚结、与消融的全生命周期中体系热力学状态、反应驱动力、各相饱和度等关键参数，阐明水合物相变动力学主控因素；结合双重介质理论，建立耦合介质特性的含孔隙-裂隙岩体中NGH相平衡模型、生成与分解动力学模型、及多相渗流模型；将其与水合物数值模拟软件进行耦合，结合实验数据，验证并修正模型参数。本项目研究将为我国冻土区水合物开采提供基础数据和理论支持。

作为一种低碳高效的新型清洁能源，天然气水合物（NGH）广泛分布于我国南海及青藏高原冻土区，实现水合物资源商业开发对于确保我国能源安全、助力“双碳”目标的实现等具有重要意义。本项目基于我国青藏高原冻土区天然气水合物成藏地质环境，针对双重介质中水合物生成与分解相态变化规律、动力学过程、及多相渗流规律等关键科学问题开展实验及基础理论研究。首先，在低孔隙度低渗透率细砂岩双重介质中实验测量了甲烷水合物相平衡条件，并根据测试结果对不同水合物相平衡模型进行了对比和验证。然后，采用数值模拟的方法，开展了多孔介质中水合物生成动力学及气-液-固三相空间分布特性研究，验证了动力学模型的可靠性，获得了水合物生成过程的时空演化规律，揭示了三相物质分布的非均质性及其控制机制。在此基础上，合成了含水合物多孔介质样品，开展了水合物分解实验和数值模拟研究，揭示了降压幅度、井筒加热方式（连续加热和间歇加热）以及井筒布局形式对水合物分解动力学及热传递的影响机制，定量表征了系统的传热行为；此外，从强化传热的角度出发，提出了一种新型的多策略联合开采法：电加热和注室温水联合降压法，并实验验证了其有效性及高效性。接着，开展了冰点以下冰冻型水合物分解与产气特性研究，建立了耦合水合物自保护效应的与多孔介质物理特性相关的水合物分解动力学模型，结合实验数据分析了固相冰对气液两相流动的抑制效应，阐明了水合物自保护效应、注热速率以及井筒降压幅度对冰点以下水合物分解动力学的耦合作用机制。基于改进和修正后的水合物数值模拟器，采用新型五点水平井系统，开展了祁连山冻土区低渗水合物藏降压联合注热法开采模拟研究，揭示了不同开采模式下气液两相渗流与水合物分解的相互作用机制。研究成果为我国未来冻土区水合物资源开发提供了重要的基础数据和理论支持。