结合水对泥质粉砂水合物储层性质影响机制研究

There is a sharp distinction between the properties of sandy reservoir and pelitic siltstone reservoir of natural gas hydrate, causing the theory and technology for sandy reservoir cannot be fully applied to exploration and exploitation of the pelitic siltstone reservoir in the South China Sea(SCS). A deep understanding of the characteristics of the gas hydrate reservoir in SCS is a necessary foothold for the development of novel theories and methods. The predominant feature of the gas hydrate reservoir in SCS is that the content of bound water in sediments is quite high. The bound water locates at the interface of hydrate/sediment, which is strongly linked to gas hydrate occurrence, clay expansibility and the heat-mass transfer in sediments. The bound water is used as an entry point in this project that aims at its influencing mechanism on the properties of pelitic siltstone reservoir of gas hydrate in SCS. First, investigate the composition of minerals in gas hydrate-bearing sediments in SCS and analyze the content of different type water in clay minerals and its changing rule. After that, measure the equilibrium conditions between loosely bound water and gas hydrate, and develop a thermodynamic model. On the basis, operate experimental studies on the thermal conductivity and permeability of gas hydrate-bearing sediments. Analyze the effects of the presence of bound water on the process of heat-mass transfer in hydrate-bearing sediments. Actively explore the interdisciplinary of electro-chemical at mineral/water interface, themodynamic/kinetics of gas hydrate, poromechanics and heat transfer theory for new problems and concepts. Finally, provide a useful reference for the development of technological theories applied to gas hydrate reservoir in SCS.

南海天然气水合物储层为泥质粉砂型，储层性质具有自身特异性，现有针对砂质类型水合物储层的理论和技术不能满足南海水合物勘探和开发的需要，深入认识南海水合物储层特性，是建立新理论新方法的立足点。南海水合物储层的显著特征是结合水含量很高，结合水介于沉积物和水合物之间，与水合物赋存特征、黏土矿物膨胀性以及储层热-质传递过程密切相关。本项目以结合水为切入点，研究其对泥质粉砂水合物储层性质的影响机制。首先，充分调研南海储层矿物组成，分析黏土矿物中不同类型水的相对含量及变化规律；然后，测定弱结合水-水合物相平衡条件，建立结合水体系水合物热力学模型；在此基础上，分别开展储层渗透和导热性质实验研究，分析结合水赋存和物性对水合物储层热-质传递过程的影响，积极探索固/液界面电化学与水合物热/动力学、渗流力学、传热学等多学科的交叉与融合，发现新问题提出新概念，为建立适合我国水合物资源特点的技术理论体系提供参考。

南海天然气水合物为泥质粉砂型储层，结合水含量很高，与砂质类型储层有很大差异。本项目针对南海天然气水合物的储层特征，以结合水为切入点，研究了结合水对泥质粉砂水合物形成、相平衡、渗透性质和导热性质的影响机制。观测了结合水体系水合物形成特征，发现黏土矿物中弱结合水能够形成水合物，而强结合水很难形成水合物，在水合物形成过程中，弱结合水有序地从扩散双电层的外层向内层转化为水合物；采用逐步升温法测定了弱结合水水合物相平衡条件，结果表明，黏土介质中水合物形成条件高于砂质沉积物。研究发现结合水与黏土矿物表面距离越近，结合水的活度越低，弱结合水水合物形成条件越高，反之，弱结合水水合物的形成条件逐渐趋近于自由水水合物，据此建立了结合水体系水合物相平衡模型，将气体水合物热力学理论拓展应用到黏土结合水体系水合物；研究了天然气水合物分解前后泥质粉砂沉积物渗透性质的衰减特征，揭示了水合物分解过程结合水含量增加对泥质粉砂储层的损害机理，发现防膨剂具有抑制黏土矿物膨胀和调控泥质粉砂沉积物渗透性的作用；研究了结合水对黏土质沉积物导热性质的影响，理论分析发现结合水体系水合物的相变可引起沉积物热阻的突变，黏土矿物比表面积越大且表面结合力越强，结合水含量越高，相应沉积物导热系数越大，越有利于水合物分解过程中的热量传输。所取得的研究成果可为泥质粉砂型水合物开采提供理论基础。本项目运行期间，在能源化工类期刊发表SCI检索论文10篇，授权发明专利2项，培养博士研究生4名。