Accurately quantifying the concentration of CO2 and ancillary gases SOx (SO2, SO3) and NOx (NO, NO2) in formation water will be a good indicator of the extent and impact of a subsurface plume.
Raman spectroscopy is a powerful molecular vibrational application that has been employed widely for more than 70 years to analyse, non-destructively, various materials and mixtures in the laboratory.
Raman spectroscopy is based on the process of scattering light off molecules, with each type of molecule having a specific fingerprint spectrum reflecting the molecular bonding and structure of the molecule. Higher concentrations of a particular molecule result in observation of more photons at the fingerprint (spectral) energies specific to that molecule. Hence, with the correct calibration, the concentration of specific dissolved species can be determined. Raman spectroscopy has been used to analyse dissolved methane in-situ and, to a lesser extent, nitrogen and carbon dioxide in coal seam reservoirs.