基于分子模拟的气体水合物结构特征及储气特性研究

doi:10.13809/j.cnki.cn32-1825/te.2022.05.015

摘要/Abstract

摘要：

天然气水合物资源丰富,是最具潜力的新能源之一。但目前天然气水合物尚未实现商业开采,其微观结构特征和储气机理亟待明确。基于SI、SII和SH型气体水合物的骨架和客体分子信息,构建并优化了3种典型水合物的分子模型。通过结构表征,明确了水合物的氢键数目、氢键长度、孔隙度、孔隙组成和孔径分布等结构特征,对比分析了3种典型水合物的微观结构差异。基于水合物骨架结构,采用巨正则蒙特卡洛方法研究了甲烷和二氧化碳的吸附行为,结合气体吸附量和吸附热阐明了3种水合物的储气特性及差异。结果表明,SII型水合物中平均氢键长度最大且数量最多,但其孔隙连通性最差;高压有利于提升水合物对气体的储气量,低温可增加水合物中气体吸附的稳定性;二氧化碳储存量虽小于甲烷,但二氧化碳吸附稳定性更强;气体在SII型水合物中的吸附量最大,在SI型水合物中的吸附热最大。

关键词: 气体水合物, 结构特征, 储气特性, 吸附, 分子模拟

Abstract:

Natural gas hydrate are rich, which is one of the most potential new energy resources with abundant resources. However, gas hydrate has not been exploited commercially at present, and its micro-structure characteristics and gas storage mechanism need to be clarified urgently. Based on the framework and guest molecular information of SI, SII and SH type gas hydrates, the molecular models of three typical gas hydrates are constructed and optimized. The hydrogen bonds number, hydrogen bonds length, porosity, pore composition, pore size distribution and other structural characteristics of hydrates are determined by structural characterization, and the micro-structure differences of three typical hydrates are compared and analyzed. Based on the hydrate skeleton structure, the adsorption behavior of methane and carbon dioxide is studied by the grand Canonical Monte Carlo method. Combined with the adsorption capacity and adsorption heat, the gas storage characteristics and differences of the three hydrates are clarified. The results show that the hydrogen bonds in SII hydrate are the longest and the most abundant, but the pore connectivity is the worst. High pressure is conducive to increasing the gas storage capacity of hydrate, while low temperature can increase the stability of gas adsorption in hydrate. Although the amount of carbon dioxide storage is smaller than that of methane, the adsorption stability of carbon dioxide is stronger. The adsorption capacity of gas in SII type hydrate is the largest, and the adsorption heat in SI type hydrate is the largest.

Key words: gas hydrate, structural characteristics, gas storage properties, adsorption, molecular simulation

中图分类号:

TE311

向雪妮,黄亮,周文等. 基于分子模拟的气体水合物结构特征及储气特性研究[J]. 油气藏评价与开发, 2022, 12(5): 825-832.

Xueni XIANG,Liang HUANG,Wen ZHOU, et al. Structural characteristics and gas storage properties of gas hydrates based on molecular simulation[J]. Petroleum Reservoir Evaluation and Development, 2022, 12(5): 825-832.

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类型	晶系	空间群	晶格参数	单品中水分子数	胞腔种类
SI	立方晶系	PM3N	a=11.82Å	46	小、大
SII	立方晶系	FD3M	a=17.14Å	136	小、大
SH	六方晶系	P6/MMM	a=12.26Å,c=10.17Å	34	小、中、大

类型	原子	X	Y	Z
SI	O₁	0.184 10	0.184 10	0.184 10
	O₂	0	0.310 00	0.115 40
	O₃	0	0.500 00	0.250 00
SII	O₁	0	0	0
	O₂	-0.092 28	-0.092 28	-0.092 28
	O₃	-0.057 44	-0.057 44	-0.244 87
SH	O₁	0.333 30	0.666 70	0.364 33
	O₂	0.867 98	0.132 02	0.500 00
	O₃	0.613 89	0.613 89	0.137 26
	O₄	0.790 99	0.209 01	0.277 65