Raman spectroscopic characterization of the CO 2 -N 2 gaseous system at 24–300°C and 2–40 MPa and applications

CO2 and N2 are important gas components of deep-sourced geological fluids. To establish a quantitative method for the study of these fluids, we used a high-pressure optical cell, a heating–cooling stage, and a laser Raman spectrometer to examine pure CO2 and N2 gases and nine CO2-N2 gaseous mixtures at 24–300°C and 2–40 MPa. The results show that the CO2 Fermi diad split and the peak area ratios of the ν1 band of N2 to the upper band of CO2 are considered to be the best for determining pressure and composition, respectively. The quantitative Raman analysis method developed in this study for the determination of the CN2/CCO2 molar ratio was verified by measuring those in synthetic N2-CO2-H2O fluid inclusions. The developed method has also been applied to the analysis of natural fluid inclusions in quartz from Donghai for the determination of both the CN2/CCO2 molar ratio and pressure.