The Concentration Changes of Major Ions in Seawater During the Methane Hydrate Formation Process
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摘要: 本文自行研制了一套甲烷水合物合成装置，模拟海洋环境甲烷水合物的生成过程，对该过程水合物生成位置、形态、反应时间、环境温压条件进行观测，同时连续测试体系海水中常量离子K+、Na+、Ca2+、Mg2+、Cl-、SO42-的浓度及海水盐度，探讨水合物生成过程的温压变化及离子浓度变化之间的关系和离子浓度的变化规律。结果表明，海水中甲烷水合物生成具有很大的随机性，在相同的初始条件下可能有不同的水合物成核、聚集过程；甲烷水合物在生成过程中，耗气量不断增加，孔隙水的盐度和海水中常量阴阳离子的浓度也在不断增加，这种变化具有较高的线性相关性(相关系数为0.9848~0.9950)，且不受甲烷水合物生成位置及状态的影响；在水合物生成过程的微环境下耗气量相同时，离子浓度存在细微的差异。这些特征为通过测定海底水合物周围孔隙水中常量离子的浓度初步推算水合物的甲烷耗气量提供了依据。
Abstract: A description of the synthetic experiment of methane hydrate is given in this paper, along with a preliminary study of ion concentration changes during the process, whilst providing important technical support for the gas hydrate geochemical exploration. In this article, the development of a set of experimental devices, which simulate the formation process of methane hydrate, is also discussed in this paper. The position and shape of hydrate, the reaction time, the temperature and pressure of the experiments were observed during methane hydrate formation. The concentrations of major ions including K+, Na+, Ca2+, Mg2+, Cl-, SO42- were continuously detected during the process to investigate the relationship among the major ion concentrations, temperature and pressure. The results show that methane hydrate forms randomly in seawater. It may have a different nucleation and agglomeration process of hydrate under the same initial conditions. There was a good positive linear relationship between the ions variation and methane gas consumption in the system with the correlation coefficients between 0.9848 to 0.9950, which was not affected by the formation position and morphology of the hydrate. The ion content had small differences under the same gas consumption in the microenvironment of the methane hydrate formation process. These important features provide the basis to make a preliminary estimate of gas consumption by using the major ion content in pore water around the methane hydrate. -
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图 1 甲烷水合物合成装置示意图
Figure 1. The sketch map of the apparatus for methane hydrate formation
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图 2 甲烷水合物生成后的位置及形态
Figure 2. Generation locations and morphology of methane hydrate in the experiment
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图 3 甲烷耗气量与海水盐度变化关系
Figure 3. The relationship between the methane gas consumption and the salinity of seawater
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图 4 甲烷耗气量相同时两组实验离子浓度的变化率
Figure 4. The change of ion concentration in the two groups of experiments with a same methane gas consumption
表 1 甲烷水合物生成过程中离子浓度的变化
Table 1 The changes of ion concentrations in the process of methane hydrate formation
合成实验 反应时间
t/h气体压力
p/MPa水合物温度
θ/℃所采水样
体积V/mL气体体积
V/mL甲烷耗气量
n/mol盐度/‰ 离子浓度ρB/(mg·L-1) Ca2+ K+ Mg2+ Na+ Cl- SO42- 第一组 0 7.9 2.0 0.0 330.0 0.0000 30.5 393 382 1233 10173 18542 2586 11 7.5 2.0 2.5 332.5 0.0713 31.5 408 391 1266 10460 18987 2593 17 7.0 2.2 2.5 335.0 0.1644 34.5 436 415 1345 10980 20118 2752 23 6.5 2.0 2.5 337.5 0.2536 36.0 454 437 1420 11570 21113 2897 35 5.5 2.0 2.5 340.0 0.4413 40.5 514 490 1601 13120 24137 3276 65 5.2 1.9 2.5 342.5 0.4915 43.0 537 505 1680 13630 25122 3466 第二组 0 8.1 2.0 0.0 330.0 0.0000 30.5 393 382 1233 10173 18542 2586 2.5 7.6 1.9 2.5 332.5 0.0914 32.0 402 395 1269 10347 19300 2717 4.5 7.4 2.0 2.5 335.0 0.1641 33.0 422 404 1302 10667 19913 2801 15 5.7 2.5 2.5 337.5 0.4947 42.5 531 510 1651 13527 25499 3565 24 5.3 2.0 2.5 340.0 0.5810 46.0 561 534 1729 14107 26823 3730 
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表 2 海水中常量离子浓度与甲烷耗气量之间的线性关系
Table 2 The linear relationship between the major ion concen-trations of seawater and the methane gas consumption
常量离子 线性方程 相关系数 Ca2+ ρ=303.37n+382.26 0.9950 K+ ρ=273.62n+371.28 0.9947 Mg2+ ρ=926.56n+1194.7 0.9933 Na+ ρ=7416.4n+9816 0.9921 Cl- ρ=14774n+17888 0.9931 SO42- ρ=2025.6n+2480.6 0.9848 注：ρ代表各常量离子的浓度，单位为mg/L；n代表甲烷的耗气量，单位为mol。
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