地质流体状态方程

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．

Modeling Geological Fluids to High Temperatures and Pressures

Methods for 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. Results presented for the NaCl-CO_2-CH_4-H_2O 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 CH_4 and CO_2, 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 (H_2O) 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.