T<623.15K,P<100MPa条件下CO_2—H_2O体系相关热力学参数计算新方法

A New Method Used to Calculate the Homogenization Pressure and Related Thermodynamic Parameters of CO_2—H_2O System at T<623.15K and P<100MPa

根据CO2—H2O体系均一法测温过程中出现的部分均一和完全均一现象,采用最新的热力学参数及相关模型,分别建立相应的热力学方程。根据同一体系的摩尔体积在均一法测温升温过程中几乎不变的特征可知,部分均一与完全均一状态下,体系的摩尔体积近似相等。据此对影响摩尔体积的充填度进行微调,通过迭代运算,直至两种条件下的摩尔体积近似相等,从而可以获得精确的摩尔体积和充填度,进而获得体系中的CO2含量、完全均一压力以及流体包裹体的总密度等热力学参数。本方法只需提供部分均一温度和完全均一温度以及部分均一方式便可求取相关热力学参数,符合地质研究方法和思路。该方法只适用于完全均一温度低于623.15K、完全均一压力小于100MPa以及最后均一至液相或临界点的CO2—H2O流体包裹体体系。对比研究表明,该方法也适用于盐度低于6%的NaCl—CO2—H2O流体体系,所获得的热力学参数相对误差在10%左右。

According to the partial homogenization and total homogenization features of the CO2—H2O system during heating process, we establish a thermodynamic model based on the latest thermodynamic parameters and related models. The molar volumes of the same one fluid inclusion are nearly same in partial homogenization state and total homogenization state.. Following this law, we adjust the approximately measured filling factor of the fluid inclusion using an iteration method until getting a same molar volume. At the same time, the accurate filling factor value is obtained. With this value, the molar fraction of CO2-rich phase, total homogenization pressure, overall molar volume and other relevant parameters can be obtained. Other thermodynamic parameters, such as molar fraction of CO2-rich phase, total homogenization pressure, overall molar volume, can also be gained based on the accurate filling factor value calculated. A new software based on this method is developed, which can be applied to the CO2—H2O system at T<623.15K, P<100MPa with total homogenization to liquid phase or critical phase. Comparative studies show that the software can also be extended to low salinity (<6%) CO2—H2O system within a relative error of 10%.