Quantitative measurement of carbon isotopic composition in CO2 gas reservoir by Micro-Laser Raman spectroscopy

The use of Micro-Laser Raman spectroscopy technology for quantitatively determining gas carbon isotope composition is presented. In this study, ¹²CO₂ and ¹³CO₂ were mixed with N₂ at various molar fraction ratios to obtain Raman quantification factors (F_12CO2 and F_13CO2), which provide a theoretical basis for calculating the δ¹³C value. And the corresponding values were 0.523 (0 < C_12CO2/C_N2 < 2) and 1.11998 (0 < C_13CO2/C_N2 < 1.5) respectively. It has shown that the representative Raman peak area can be used for the determination of δ¹³C values within the relative errors range of 0.076% to 1.154% in ¹³CO₂/¹²CO₂ binary mixtures when F_12CO2/F_13CO2 is 0.466972625. In addition, measurement of δ¹³C values by Micro-Laser Raman analysis were carried out on natural CO₂ gas from Shengli Oil-field at room temperature under different pressures. The δ¹³C values obtained by Micro-Laser Raman spectroscopy technology and Isotope Ratio Mass Spectrometry (IRMS) technology are in good agreement with each other, and the relative errors range of δ¹³C values is 1.232%-6.964%. This research provides a fundamental analysis tool for determining gas carbon isotope composition (δ¹³C values) quantitatively by using Micro-Laser Raman spectroscopy. Experiment of results demonstrates that this method has the potential for obtaining δ¹³C values in natural CO₂ gas reservoirs.