地质流体状态方程

段振豪; 刘荣; 孙睿

地质流体状态方程

段振豪^{1, 2, 3,},
刘荣³,
孙睿^{1, 3}

1.
中国科学院地质与地球物理研究所, 北京 100029
2.
Department of Chemistry, University of California, San Diego, CA 92093, USA
3.
中国地质大学资源学院, 湖北武汉 430074

基金项目:

国家杰出青年基金项目 40225008

详细信息

作者简介:
段振豪(1959-), 男, 研究员(教授), 主要从事分子地球化学和流体地球化学工作.E-mail: Duanzhenhao@yahoo.com

中图分类号: P628
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- 被引次数: 0
出版历程
- 收稿日期: 2004-08-31
- 刊出日期: 2004-11-25

Modeling Geological Fluids to High Temperatures and Pressures

DUAN Zhen-hao^{1, 2, 3
,},
LIU Rong³,
SUN Rui^{1, 3}

1.
Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
2.
Department of Chemistry, University of California, San Diego, CA 92093, USA
3.
Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China

摘要

摘要: 几乎所有的地球化学过程都有地质流体参加, 定量地了解地质流体的物理化学性质是定量研究地球化学过程的基础.100多年以来, 广大化学和实验地球化学工作者做了大量的实验测定工作, 可是所有这些工作之和, 仅仅覆盖地球范围内一个不大的温压空间, 远远不能满足地球化学研究的需要.近年来, 我们试图通过分子水平上的研究, 结合热力学和统计力学方面的知识, 在重现前人实验结果的基础上, 研究实验工作者没有或不能研究的温压和成分空间, 得到了一系列能够精确预测地质流体在广阔的温压范围内的物理化学性质的状态方程.这些状态方程不仅能够重现实验数据, 而且具有良好的外延能力, 可以应用于地球化学领域诸多方面的研究.重点讨论了几个状态方程(包括纯流体状态方程含水溶液状态方程和含盐-水-气的状态方程) 在预测流体的溶解度、相平衡、化学位和PVT性质方面的应用.简要介绍了近年来笔者应用分子动力学和蒙特卡罗模拟在地质流体研究方面所取得的成果
- 天然流体 /
- 热力学模型 /
- 物理化学性质 /
- 状态方程 /
- 分子动力学模拟
Abstract: Methodsfor predicting the thermodynamic properties of natural fluids over a large range of concentration, temperature and pressure are presented. With careful choice of phenomenology and parameterization, predictions can be made with accuracies similar to the experimental data.Resultspresented for the NaCl-CO₂-CH₄-H₂O system suggest that these modeling methods can be used to extrapolate experimental measurements to high pressure and temperature regions difficult to access by experimental methods. For species such as CH₄ and CO₂, which are nonpolar and weakly interacting, a corresponding states representation yields results that are highly accurate and depend on only two temperature and pressure independent parameters. Predictions with such models of fluid/fluid coexistence at high temperature and pressures are within experimental accuracy. The role of molecular dynamics and Monte Carlo simulations in developing thermodynamic representations of natural system are discussed. For closed shell and nonpolar systems, simulation results agree very well with experimental data. Polar systems (H₂O) at sufficiently high temperatures are also well described. On the other hand, the simulations for polar systems at low temperatures yield results only in qualitative agreement with data. Efforts to improve simulation methods for these systems are in progress.
- natural fluid /
- thermodynamic model /
- physical chemistry properties /
- equation of state /
- molecular dynamics simulation

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图 1 地球内部的地质作用过程涵盖的温度-压力范围, 其中“Data”标志的区域表示已有的实验数据涵盖的温度-压力范围

Fig. 1. Temperature and pressure regimes corresponding to earth processes. The "Data" area indicates the region in which well characterized experimental data can be found

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图 2 状态方程(Eq. (1)) 对纯CH₄压缩因子的预测结果与实验数据的比较

图中Z=PV/RT, 实线和虚线表示状态方程的预测结果, 空心矩形、空心圆、实心圆、实心矩形代表的实验数据分别取自Deffet and Ficks (1965), Din (1961), Francesconi and Kristische (1978), Tsiklis and Linshits (1967)

Fig. 2. Comparison of the measured compressibility factor for CH₄ with predictions of Eq. (1)

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图 3 CO₂-H₂O体系的气-液相平衡

图中实线代表我们的状态方程的预测结果, 实心和空心的圆、矩形和三角形分别代表不同温度下的实验数据, 这些实验数据取自Todheide and Franck (1963)

Fig. 3. Phase coexistence for the system CO₂-H₂O. The solid line is the prediction of the EOS. Experimental data from Todheide and Franck (1963)

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图 4 CH₄-H₂O体系的气-液相平衡

图中实线代表我们状态方程的预测结果, 实心圆代表的实验数据取自Welsch (1973), 实心三角代表的实验数据取自Sultanov and Skripka (1971)

Fig. 4. Phase coexistence for the system CH₄-H₂O. The solid line is the prediction of the EOS. Experimental data from Welsch (1973) (solid circles), Sultanov and Skripka (1971) (solid triangles)

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图 5 CO₂-H₂O混合体系中CO₂和H₂O的逸度与相同温压条件下纯CO₂和纯H₂O逸度的比值随体系组成的变化关系

图中的曲线表示状态方程的预测结果, 在虚线部分对应的组成范围内体系处于两相区, 连接对角的两条直线代表理想混合状态对应的逸度的比值

Fig. 5. Ratio of mixture fugacities to end-member fugacities of CO₂ and H₂O in their mixtures at 300 ℃ and 700 ℃. The dashed lines show the two-phase region. The diagonal solid lines represent ideal mixing

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图 6 H₂O-N₂体系在超临界区的相分离现象

对比态方程的预测结果与实验数据的比较, 实验数据取自VanHinsberg et al. (1993)、Costantino (1991)

Fig. 6. Supercritical fluid/fluid phase coexistence in the binary system H₂O-N₂

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图 7 CO₂-H₂O体系的热焓

图中实线为对比态方程的预测结果, 矩形代表Dawe and Snowdon (1974)的实验数据

Fig. 7. Prediction of the Enthalpy model for the CO₂-H₂O system (solid lines). Data from Dawe and Snowdon (1974)

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图 8 对比态方程预测的CO₂-H₂O体系的热焓-温度-密度相(依据此图可以获得地热井的喷出温度和气/液比)

Fig. 8. Enthalpy-temperature-density relationships for CO₂-H₂O mixtures. The steam ratio and wellhead temperature for a geothermal well can be obtained from this diagram

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图 9 CO₂-CH₄体系的气液相平衡

图中实线代表蒙特卡罗吉布斯系综模拟方法的模拟结果, 圆和三角形代表Al-Sahhaf et al. (1983)的实验数据

Fig. 9. Phase equilibria for the binary CO₂-CH₄ system calculated by the MC Gibbs Ensemble simulation (solid lines). Experimental data from Al-Sahhaf et al. (1983).

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图 10 CO₂-CH₄-N₂三元系的气-液相平衡——蒙特卡罗吉布斯系综模拟结果与Al-Sahhaf (1990)的实验数据的比较

Fig. 10. Phase equilibria of the ternary system CO₂-CH₄-N₂ calculated via a MC Gibbs Ensemble simulation vs. experimental data

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图 11 文中第三部分介绍的状态方程预测的NaCl-H₂O-CO₂体系的PVTX性质与实验数据的比较

图中实线代表状态方程的预测结果, 实心圆代表Gehrig (1980)的实验数据, 虚线代表相边界, 虚线下方为两相不混溶区, 虚线上方为单相区

Fig. 11. Comparison of experimental PVTX properties in the ternary NaCl-H₂O-CO₂ with the prediction of the EOS of section 3. Data from Gehrig (1980). The dashed line is the phase boundary. The liquid and vapor two-phase field is below this boundary. The single fluid phase field is above this boundary

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图 12 NaCl-H₂O-CO₂体系的气液相平衡(温度等于500 ℃, 压力为2 000×10⁵ Pa)——状态方程的预测结果与Frantz et al. (1992)的合成流体包裹体实验数据的比较

Fig. 12. Calculated phase equilibria vs. data measured by the synthetic fluid inclusion method in the ternary NaCl-H₂O-CO₂ for T=500 ℃, P=2 000×10⁵ Pa. Data from Frantz et al. (1992)

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图 13 NaCl-H₂O-CO₂体系的气液相平衡(温度等于500 ℃, 压力为1 000×10⁵ Pa)——状态方程的预测结果与Frantz et al. (1992)的合成流体包裹体实验数据的比较

Fig. 13. Calculated phase equilibria vs. data measured by the synthetic fluid inclusion method in the ternary NaCl-H₂O-CO₂ for T=500 ℃, P=1 000×10⁵ Pa. Data from Frantz et al. (1992)

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图 14 文中第三部分介绍的状态方程预测的NaCl-H₂O-CH₄体系的摩尔体积与实验数据的比较

图中实线代表状态方程的预测结果, 实心圆表示Krader and Frank (1987)测定的实验数据

Fig. 14. Comparison of the experimental volumes/mole in the ternary system NaCl-H₂O-CH₄ with the prediction of the EOS of section 3. Data from Krader and Frank (1987)

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图 15 状态方程预测的NaCl-H₂O-CH₄体系的气-液不混溶相边界和共结线与Lamb et al. (1996)测定的合成流体包裹体实验数据的比较

Fig. 15. Comparison of experimental immiscibility boundary and tie-lines (synthetic fluid inclusion method) with the prediction of the EOS for the ternary NaCl-H₂O-CH₄ system at 500 ℃ and 1 000×10⁵ Pa. Data from Lamb et al. (1996)

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表 1 对比态方程对氮气和纯水体系PVT性质的预测结果

Table 1. Experimental PVT data vs. the corresponding state and other EOS

表 2 H₂O-CO₂体系的PVTX性质——对比态方程的预测结果与实验数据的比较

Table 2. Comparison of experimental PVTX data in the system H₂O-CO₂ with the corresponding state EOS

表 3 状态方程对高温高压条件下NaCl-CO₂-H₂O体系的密度的预测结果

Table 3. Prediction of density at high temperatures and pressures in the system NaCl-CO₂-H₂O

表 4 笔者建立的NaCl-H₂O-CH₄-CO₂体系状态方程与实验数据以及Bowers-Helgeson方程(1983)的比较

Table 4. EOS of this study is compared with experimental data and with the EOS of Bowers-Helgeson (1983)

表 5 采用RWK2势能函数对水的PVT性质的模拟结果

Table 5. Simulated PVT properties for water using RWK2 model

表 6 盐-水体系的PVTX性质——模拟结果与实验数据的对比

Table 6. PVTX properties of salt-H₂O system simulated results vs. experimental data

表 7 流体体系热力学性质的实验数据涵盖的温-压范围

Table 7. Thermodynamic measurements on fluid systems

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