Raman spectroscopic characterization of the CO₂-N₂ gaseous system at 24–300°C and 2–40 MPa and applications

ABSTRACT

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 C_N2/C_CO2 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 C_N2/C_CO2 molar ratio and pressure.

KEYWORDS:

• CO₂-N₂ gaseous system
• Raman spectroscopy
• quantitative analysis
• fluid inclusion

Acknowledgments

We thank Dr. Yanbin Wang for the careful editorial handling and an anonymous reviewer for the insightful and constructive suggestions, which greatly helped to improve the manuscript. Special thanks go to Dr. Nanfei Cheng for critical reading and comment on early versions of the manuscript. We are indebted to Dr. Li Xu for providing Donghai quartz crystals with CO₂-N₂-bearing fluid inclusions. We thank Dr. Jing Fang for frank discussion and useful information on the experimental setup. Dr. Ying Chen and Maokang Hu are acknowledged for their help in the experimental methods. Dr. Ye Wan is thanked for proofreading the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China under grant numbers 42130109 and 41973055; and Natural Science Foundation of Hainan Province of China under grant number 423MS106.