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盐类对甲烷水合物稳定性影响研究进展

Research Progress on the Effect of Salts on the Stability of Methane Hydrate

  • 摘要: 甲烷水合物稳定性主要控制着甲烷水合物稳定带的厚度,温度、压力、孔隙水盐度和气体组分等因素影响着水合物稳定带的厚度。甲烷水合物的形成与地层水关系密切,而地层水中的各种盐离子(Cl-、Na+、Mg2+、SO42-、Ca2+)以及过渡金属(Fe、Mn、Cu、Co、Ni等)会影响天然气水合物的形成和分解条件。因此,研究盐类对甲烷水合物的稳定性认识有助于更加深入了解天然气水合物的成藏条件。本文分析了氯化物、硫酸盐、碳酸盐三大盐类对甲烷水合物稳定性的影响:同一盐类不同盐度条件下,随着盐度的增加,甲烷水合物相平衡曲线向低温高压偏移。总结了不同盐类和阴阳离子对甲烷水合物的抑制作用大小:在相同浓度、不同盐类条件下,盐类浓度在1.0~1.5 mol/L时盐类对甲烷水合物的抑制作用大小为MgCl2 > CaCl2 > NaCl > KCl,盐类浓度大于1.5 mol/L时CaCl2的抑制作用较强;阴离子对甲烷水合物的抑制作用大小争议较大,阳离子中Mg2+对甲烷水合物的抑制作用最强。从目前的研究成果来看,已有数据与实际地质条件还存在一定差距,需要在真实实验条件下加强氯化物-硫酸盐-碳酸盐-甲烷-水体系的详细研究。本文提出,将高压可视反应腔与显微激光拉曼技术相结合,有望准确获取天然气水合物稳定形成时的温压条件,明确盐类和阴阳离子的抑制作用大小,以及盐类和离子特性如何影响水合物的形成和稳定,以便为未来的水合物勘探开发提供参考。

     

    Abstract: The thickness of the methane hydrate stable zone is mainly controlled by the stability of methane hydrate. The temperature, pressure, pore water salinity, and gas component affect the thickness of the hydrate stable zone. The formation of methane hydrate is closely related to the formation of water. Various salt ions in formation water (Cl-, Na+, Mg2+, SO42-, Ca2+, and transition metals Fe, Mn, Cu, Co, Ni) can affect the formation and decomposition conditions of natural gas hydrate. Therefore, studying the effect of salts on the stability of methane hydrates is helpful to better understand the reservoir-forming conditions of methane hydrate. The effects of chloride, sulfate and carbonate on the stability of methane hydrate are evaluated in this paper. With the increase of salinity, the phase equilibrium curve of methane hydrate migrates to low temperature and high pressure under the same salinity condition. The inhibitory effects of different salts and anion and cation on methane hydrate are summarized. Under conditions of the same concentration and different types of salts, when the concentration of salt ranges from 1 to 1.5 mol/L, the inhibition effect of salt on methane hydrate is MgCl2 > CaCl2 > NaCl > KCl. When the concentration of salt is larger than 1.5 mol/L, the inhibitory effect of CaCl2 on methane hydrate is stronger. The inhibitory effect of anions on methane hydrate is controversial, and the inhibitory effect of Mg2+ on methane hydrate is the strongest. From available research results, there is still a gap between the existing data and the actual geological conditions. It is necessary to strengthen the detailed study on chloride-sulfate-carbonate-methane-water systems under actual experimental conditions. It is proposed that the combination of the high-voltage visual reaction chamber with Micro Laser Raman Spectroscopy is likely to accurately obtain the stable temperature and pressure conditions of gas hydrate formation, clarify the inhibitory effect of cations and anions, and understand how salts and ion affect the formation of hydrate and its stability, which will provide reference for the future exploration and development of hydrate.

     

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