多孔介质中天然气水合物相平衡影响因素研究

doi:10.13745/j.esf.sf.2024.11.18

摘要/Abstract

摘要：

天然气水合物主要蕴藏于海底沉积物与大陆冻土层中,深入研究多孔介质中水合物的相平衡及其影响因素,对于了解海底沉积物中水合物的形成机制、分布范围和储量评估具有重要意义。当前的相关实验研究大多聚焦于合成多孔介质,而天然沉积物因结构和成分复杂,对水合物相平衡特征影响的研究仍需进一步深化。本文综述了水合物在不同孔径多孔介质中的相平衡变化,全面分析了孔径、粒度以及表面润湿性对水合物相平衡的具体影响。研究揭示,多孔介质产生的强毛细管力会导致水的活性降低,进而抑制水合物的形成,且在纳米尺度范围内具有临界值。此外,较小的多孔介质粒度会增加成核位点和反应界面,从而缩短诱导时间,有利于水合物的成核和生长。至于表面润湿性(亲水和疏水)对水合物形成的影响,目前学界观点尚待统一,但多数研究倾向于认为疏水表面相对亲水表面能更好地促进水合物的形成。

关键词: 天然气水合物, 多孔介质, 相平衡, 毛细管效应, 表面润湿性

Abstract:

Natural gas hydrates are primarily distributed in seafloor sediments and continental permafrost. Research on hydrate phase equilibrium and its influencing factors in porous media is of great significance for understanding the formation kinetics, distribution range, and reserve estimation of hydrates in seafloor sediments. Most current experimental studies focus on synthetic porous media, while the impact of natural sediments on hydrate phase equilibrium characteristics requires further exploration due to their complex structures and compositions. This article reviews the changes in the phase equilibrium of hydrates in porous media with varying pore sizes, comprehensively analyzing the specific effects of pore size, particle size, and surface wettability on hydrate phase equilibrium. Studies have shown that the strong capillary force generated by porous media can reduce water activity, thereby inhibiting hydrate formation, with a critical value observed in the nanoscale range. Additionally, smaller porous media particle sizes increase nucleation sites and reaction interfaces, reducing induction time and promoting the nucleation and growth of hydrates. Regarding the impact of surface wettability (hydrophilic vs. hydrophobic) on hydrate formation, academic opinions remain divided. However, most studies suggest that hydrophobic surfaces promote hydrate formation more effectively than hydrophilic surfaces.

Key words: gas hydrate, porous media, phase equilibrium, capillary effect, surface wettability

中图分类号:

管文, 杨海琳, 卢海龙. 多孔介质中天然气水合物相平衡影响因素研究[J]. 地学前缘, 2025, 32(2): 153-165.

GUAN Wen, YANG Hailin, LU Hailong. Research on factors affecting the phase equilibrium of natural gas hydrates in porous media[J]. Earth Science Frontiers, 2025, 32(2): 153-165.

图/表 12

图1 水合物晶体结构图(据文献[1]修改) a—Ⅰ型;b—Ⅱ型;c—H型;d—Ⅰ型水合物立方单元晶胞;e—Ⅱ型水合物立方单元晶胞;f—H型水合物笼六边形单元晶胞。

Fig.1 Crystal structure of clathrate hydrate: (a) Structure Ⅰ; (b) Structure Ⅱ; (c) Structure H; (d) Cubic unit cell of the clathrates I structure; (e) Cubic unit cell of the clathrates Ⅱ structure; (f) Hexagonal unit cell of the clathrate H structure. Modified from [1].

图2 水合物相平衡及水合物稳定带底界

Fig.2 Phase equilibrium and stability zone of hydrate

表1 纳米尺度多孔介质

Table 1 Porous media of nanoscale

多孔介质	粒径/μm	气体	参考文献
硅胶	0.007	CH₄, C₃H₈	[18]
高硅氧玻璃	0.01,0.03,0.05	CH₄	[13]
硅胶	0.002,0.003,0.005,0.007	C₃H₈	[25]
硅胶	0.003,0.005,0.007	CH₄, CO₂	[10]
硅胶	0.006,0.015,0.03	CH₄, CO₂	[20]
高硅氧玻璃	0.004,0.006,0.01,0.03, 0.05,0.1	CH₄, CO₂, C₃H₈	[19]
多孔硅玻璃	0.009 2,0.015 8,0.030 6	CH₄, CO₂	[21]
硅胶	0.002,0.003,0.005,0.007 5	CH₄	[8]
硅胶	0.002,0.003,0.005,0.007 5	CH₄	[26]
硅胶	0.003,0.005,0.007 5	C₂H₆	[27]
蒙脱石	0.009	CH₄	[28]

图3 不同孔径范围的多孔介质中CO2水合物相平衡T-p条件(据文献[19⇓-21]修改)

Fig.3 T-p conditions of CO2 hydrate phase equilibrium in porous media with different pore size ranges. Modified from [19⇓-21].

图4 MIL-53水合物形成和解离过程中的p-T曲线(据文献[34]修改) a—MIL-53中的CO2水合物相平衡图;b—MIL-53中的CH4水合物相平衡图;c—CO2水合物p-T曲线;d—CH4水合物p-T曲线。

Fig.4 p-T curves during the formation and dissociation of hydrates in MIL-53: (a) Phase equilibrium diagram of CO2 hydrate in MIL-53; (b) Phase equilibrium diagram of CH4 hydrate in MIL-53; (c) p-T curve of CO2 hydrate; (d) p-T curve of CH4 hydrate. Modified from [34].

图5 水含量为20%(质量分数)的不同沉积物中甲烷水合物的相平衡条件(据文献[38]修改)

Fig.5 p-T conditions for phase equilibrium of methane hydrates in different sediments with 20% water content(mass fraction). Modified from [38].

图6 不同粒度的石英砂、硅胶中水合物相平衡(据文献[51-52]修改) a—CO2-CH4;b—CO2-H2。图中成分含量为质量分数。

Fig.6 (a) CO2-CH4 and (b) CO2-H2 hydrate phase equilibrium in quartz sand and silica gel with different particle sizes. Modified from [51-52].

图7 CH4水合物和CO2水合物形成的诱导时间(据文献[5,41,50]修改) a—活性炭中CH4水合物形成的诱导时间;b—硅砂中CH4水合物形成的诱导时间;c—浮石和火烧硬红土中CO2水合物形成的诱导时间。

Fig.7 Induction time of CH4 hydrate formation in activated carbon (a) and silica sand (b); CO2 hydrate formation in pumice and fire-hardened red clay (c). Modified from [5,41,50].

图8 亲水、疏水表面示意图(a)和固体颗粒对甲烷水合物成核的影响柱状图(b)(据文献[53]修改)

Fig.8 Schematic representation of hydrophilic and hydrophobic surfaces (a); Column diagram of the effect of solid particles on methane hydrate nucleation (b). Modified from [53].

图9 疏水性纳米二氧化硅的水合物促进机制(a)、亲水性纳米二氧化硅CH4分子与H2O分子的分布(b)和亲水性二氧化硅的表面基团(c)(据文献[55]修改)

Fig.9 Mechanism of hydrate promotion for hydrophobic nano-SiO2 (a); Distribution of CH4 molecules and H2O molecules on the surface of hydrophilic nano-SiO2 (b); Surface groups of hydrophilic SiO2 (c). Modified from [55].

图10 不同CO2浓度的混合气体水合物在多孔介质中的相平衡(据文献[51-52]修改) a—CH4-CO2;b—CO2-H2。图中成分含量为质量分数。

Fig.10 Phase equilibria of gas mixture hydrates with different CO2 concentrations: (a) CH4 with CO2 and (b) CO2 with H2 in porous media. Modified from [51-52].

图11 多孔介质中孔隙水盐度对水合物相平衡的影响(据文献[51]修改) 图中成分含量为质量分数。

Fig.11 The effect of pore water salinity on hydrate phase equilibrium in porous quartz sand. Modified from [51].

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