含裂隙多孔介质中天然气水合物分解动力学机理研究

As a kind of new and potential energy resource with the most application prospect in the future, natural gas hydrates (NGH) have been proved to exist widely in the Shenhu Area of the South China Sea and the Qilian Mountain permafrost of the Qinghai-Tibet plateau. It is of great strategic significance to carry out the investigations of the NGH exploitation techniques for the energy security and the sustainable development of the economic society of China. The dissociation kinetics of the natural gas hydrate as well as its influencing mechanisms in porous media is one of the basic scientific problems during gas production from natural gas hydrate reservoirs. This program aims to build an visualized simulator for the experimental and theoretical investigations of the NGH dissociation kinetics in different kinds of natural porous media containing fractures. The characteristic parameters of the core samples, such as the grain size, the pore size, and the distribution of the internal fractures and voids, are measured experimentally. The key parameters including the thermodynamic state of the system, the dissociation surface area, and the reaction driving force are also measured during hydrate dissociation to illuminate the effects of the physical properties of the fractured porous media on the NGH dissociation kinetics. Combined with the double media theory, a new kinetic model coupled with the effects of the fractures is then established for hydrate dissociation. This model is relevant to the properties of the porous media, the phase saturations, and the reaction driving force. In addition, the kinetic model is further embedded into the numerical simulator, and its parameters are validated and modified by comparing the experimental results with the results of the numerical simulations. This program will provide basic data and theoretical support for the NGH exploitation from permafrost hydrate deposits of the Qinghai-Tibet plateau.

作为未来最具应用前景的潜在新能源之一，天然气水合物(NGH)已被证实广泛存在于我国南海以及青藏高原冻土区，开展NGH开发技术研究对于我国能源安全及经济社会可持续发展具有重大战略意义。多孔介质中天然气水合物分解动力学及其影响机制是自然界中NGH资源开发的基础科学问题之一。本项目研制可视化实验装置，开展不同类型的含裂隙多孔介质中NGH分解动力学实验及基础理论研究。通过实验测量含裂隙岩芯样品的粒径、孔径、内部裂隙与孔隙分布特征参数，以及水合物分解过程中的热力学状态、分解界面面积、反应驱动力等关键参数，阐明裂隙型多孔介质物理特性对NGH分解动力学的影响机制。结合双重介质理论建立耦合裂隙影响的，与多孔介质特性、各相饱和度、反应驱动力相关的NGH分解动力学模型，并将其融入水合物开采数值模拟软件。通过实验与数值模拟结果对比，验证并修正模型参数。本项目研究将为我国冻土区NGH开采提供基础数据和理论支持。

天然气水合物是一种清洁、高效的潜在新能源，为我国第173个矿种，在我国南海以及青藏高原冻土区储量巨大。开展天然气水合物开采理论及技术研究，对于优化能源结构、保障我国能源安全等具有重大战略意义。本项目基于我国冻土区水合物成藏地质环境，开展了含裂隙多孔介质体系水合物分解动力学实验及基础理论研究。首先，成功研制一套三维水合物生成及分解模拟实验装置，在实验测量多孔介质渗透率、孔隙度等基础物性参数基础上，合成了不同类型含水合物多孔介质实验样品。然后，开展了降压法以及降压联合电加热法结合不同垂直井布置方式下水合物分解动力学特性，获取了含裂隙多孔介质中水合物分解热力学条件，明确了降压幅度、加热速率、及开采井位置对水合物分解的影响。接着，基于多相渗流理论及传热传质理论，开展了单垂直井降压联合电加热分解水合物实验与数值模拟研究，建立了不同热流的理论计算模型，并以此改进了三维数值模拟器，获得了控制水合物分解的降压驱动力和注热驱动力的定量表征方法；通过分析温度及水合物饱和度三维空间分布演化特征，阐明了两种驱动力对水合物分解的耦合作用机制及其与传热的相互关系，获取了热损的定量计算数学模型。基于改进的数值模拟软件，在中试规模三维模拟实验系统中开展了双水平井降压与注热水联合开采天然气水合物实验与数值模拟研究，分析了水合物饱和度和注热速率对多孔介质中水合物分解动力学的影响，明确了水合物的分解主要受多孔介质内传热传质过程控制。研究成果为我国未来冻土区天然气水合物开采积累了大量的基础实验数据和可靠的理论预测模型。