CO2置换开采II型天然气水合物动力学规律研究

Natural gas hydrates of structure II have been found to exist widely in the permafrost of China. Exploitation methods should be developed based on the understandings of composition and character of the hydrates. CO2 replacement method has recently been more and more interest with its distinctly unique advantages. With the differences in structures, the recovery efficency of sII hydrates by CO2 repacement is higher than that of sI hydrate. However, the studies on the recovery method by CO2 replacement are for CH4 hydrate (sI) and the results obtained cannot be fully applied to the exploitation of sII gas hydrates. It is seldom reported in the literatures on the replacement of sII hydrates by CO2. Many problems related should be solved, such as phase equilibria, kinetics and mass/heat transfer problems in replacement. This item aims at solving these problems present in recovery of sII hydrates by CO2 replacement. Fundamental experiments and theoretical analysis are carried out as follows. First, based on the investigations to composition characters of sII gas hydrates deposits in Qilian Mountain permafrost, the hydrate phase equilibria data are tend to be measured for mixed gas containing CO2 to determine the directions and conditions of the replacement reaction. Second, a series of experiments on sII hydrates with different compositions and distribution characteristics will be carried out. The influence and control factors in the replacement process will be investigated concerning replacement rates and efficiencies. Third, kinetic model for sII hydrate replacement by CO2 will be studied based on the results of experiments.

我国陆域冻土区有着广泛的II型天然气水合物资源，应注意密切结合其组成和性质的特异性拟定合理开采方案。CO2置换开采方法以其独特的优势，成为国内外研究热点，由于II型水合物结构的不同，采用CO2置换开采II型天然气水合物效率高于I型水合物，但国内外对II型天然气水合物置换开采方法的研究还十分有限，在相关的相平衡、置换动力学及传质传热等方面存在许多问题尚需解决。本项目着眼于II型天然气水合物CO2置换开采中存在的问题，开展基础的实验和理论研究。首先，在深入调研祁连山冻土区II型天然气水合物组成特征的基础上，系统测定含CO2混合气体水合物的相平衡条件，分析置换反应进行的方向和条件；然后，针对冻土区水合物组成和赋存特征，进行一系列CO2置换开采II型天然气水合物的动力学实验，围绕置换速率和效率考察影响因素和控制步骤；最后，结合置换实验过程，研究CO2置换开采II型水合物的动力学模型。

我国陆域冻土区有着广泛的II型天然气水合物资源，同时，2015年广州海洋地质调查局发现南海神狐海域天然气水合物资源具有I型和II型共存的特征，因此，应针对天然气水合物的类型、组成和性质等开展试采方法研究。本项目以建立CO2置换开采II型天然气水合物资源的理论和方法为主要研究目标，研究II型天然气水合物置换反应进行的热力学机制和动力学规律等关键科学问题。首先，测定了CH4-N2-CO2混合气体水合物的相平衡条件，采用Chen-Guo水合物热力学模型分析了各组分气体在水合物大小孔中的分配规律，初步确定了置换反应进行的方向和限度；然后，开展了II型天然气水合物置换实验研究，考察了压力、水合物组成、置换气体相态、气体组成等因素对产气组成、置换速率和置换效率的影响，分析了II型水合物独特的置换模式：同晶置换和晶型转变并存，揭示了II型水合物的置换机理；接着，实验研究了II型水合物降压分解过程，发现了II型水合物不均匀分解现象，揭示了II型水合物类似于自保护效应的分解特性；最后，根据II型水合物置换机理和分解特性，建立了II型水合物置换动力学模型，相关成果可为天然气水合物试采工程与工艺提供理论依据。共发表SCI论文4篇，会议论文2篇，申请发明专利2项，培养研究生2名。