多孔介质中天然气水合物相变与热质传递的非均匀性效应研究

In order to investigate the phase transition, the heat and mass transfer of the NGH(nature gas hydrate ) in porous media in the NGH accumulation and exploitation, the multi-scale experimental and theoretical studies will be carried out. Firslty, the measurement and characterization methods of the nonuniformities of the pore structure and the multi-phase distribution in porous media will be established. The characteristics of the pore structure and multi-phase distributions in different porous media will be measured. Then, the hydrate equilibrium, the formation and dissociation kinetics, the permeability and the thermal conductivity in porous media with the nonuniform pore structure will be measured by experiments. The prediction models will be established based on the experimental results. Theirs influence mechanisms will be studied and discussed. Finally, the three-dimensional simulations of the NGH formation and dissociation will be carried out by experiments to study the formation and dissociation rates, the gas-liquid seepage and the heat and mass transfer, so as to clarify theirs influence mechanisms. The three-dimensional NGH formation and dissociation theoretical model is thus established base on the NGH decomposition, the gas-liquid seepage, and heat and mass transfer. Based on the experimental and numerical studies, the phase transition and migration at the interface of the hydrate phase transition in pores of porous media in the hydrate formation and dissociation processes will be investigated, the relationship between the characteristics of the nonuniform porous microstructure and the multi phase distributions, and the macroscopic hydrate formation and decomposition characteristics will also be studied. From the pore and macro scales,the hydrate stability, phase transition and heat and mass transfer processes and the their coupling mechanism in the nonuniform structure of the porous media will be clarified.This program will provide large amount of experimental data and reliable theory model for the future NGH exploitation in China, and it is of great research value and theoretical significance.

针对天然气水合物成藏与开采研究中所需要解决的多孔介质中水合物相变特性、热质传递规律的关键科学问题，进行多尺度的实验与理论研究，建立多孔介质孔隙结构与多相分布非均匀性特征的测试表征方法，对不同多孔介质孔隙结构与多相分布的非均匀特性进行测定。进行不同多孔介质非均匀特征下水合物相平衡、形成分解动力学、渗透率与导热系数的实验研究，建立相应的理论模型，阐明其影响机制。然后采用三维实验模拟研究水合物形成分解速度、气液渗流、传热传质规律及影响机制，建立相变过程与热质传递现象的多尺度结构的耦合关系并建立三维数学模型，探悉多孔介质非均匀结构内水合物相变界面迁移特性，确定多孔介质微观结构、多相分布非均匀性特征与宏观水合物形成分解特性之间量化关系。从宏观与孔隙尺度两个层次阐明多孔介质结构非均匀性对水合物相变与热质传递过程影响机理和耦合规律。此项研究将为我国水合物开采潜力评价与方案设计提供基础数据和理论支持。

多孔介质的成分、孔隙尺寸、颗粒大小等特性对水合物的空间分布产生重要的影响，进而影响水合物的相平衡、形成分解动力学、渗透率与导热系数。这些因素互相耦合，决定了水合物相变、多相流动、传热传质等过程，最终影响水合物的形成分解过程。本项目采用实验模拟与理论模拟相结合的研究方法，首先测定了不同类型的多孔介质粒径、孔径与比表面积分布等关键参数，获得了多孔介质的微观孔隙结构。利用多孔介质中水合物相平衡实验装置进行了不同类型的多孔介质中水合物相平衡条件的测定，研究发现海底沉积物与膨润土体系中水合物相平衡压力明显高于纯水体系，并受到多孔介质比表面积的影响。开展了不同多孔介质体系下水合物生成分解实验，获得了多孔介质粒径分布、孔径分布以及含水量对水合物生成分解过程的影响。建立了多孔介质中水合物生成动力学模型，获得了多孔介质体系水合物生成过程的控制因素。设计搭建了含水合物体系多孔介质渗透率与导热系数测量实验装置，开展了不同体系的渗透率与导热系数测定，对其影响因素进行了分析，并建立了相应的理论模型。利用天然气水合物开采模拟实验平台，进行水合物三维生成以及注热法与降压法分解水合物实验，研究了水合物形成分解过程水合物藏传热传质、水合物饱和度不均匀演化过程。结合数值模拟，对水合物分解影响因素进行了敏感性分析，研究发现水合物分解存在一个明显的分解前沿，整个反应釜被该分解前沿分割成两个区域，气体和水由该界面上的水合物释放出来。在降压开采中，水合物藏渗透率和初始水合物饱和度对产气产水具有显著影响。在注热分解过程中，水合物藏渗透率和注热水温度对开采产气特性影响显著。研究阐明了多孔介质非均匀效应对水合物形成分解、气液渗流与传热传质影响机制。此项研究将为我国天然气水合物开采潜力评价与方案设计提供基础数据和理论支持。