Interlaboratory Application of Raman CO₂ Densimeter Equations: Experimental Procedure and Statistical Analysis Using...

Area of Science:

• Geochemistry
• Spectroscopy

Background:

• Raman spectroscopy measures CO2 fluid density via Fermi diad split (Δ).
• Existing Raman CO2 densimeter equations show interlaboratory variability, yielding different density values for the same Δ.
• This variability limits the universal application of published calibration equations.

Purpose of the Study:

• To investigate the influence of experimental parameters on Raman CO2 densimeter calibration.
• To develop a new calibration equation and assess instrument-dependent variability.
• To statistically analyze existing equations at a population level using bootstrapped confidence intervals.

Main Methods:

• Calibrated a new Raman CO2 densimeter equation using a bottom-up approach.
• Acquired CO2 spectra with varying spectral resolutions.
• Developed bootstrapped confidence intervals for density estimates of existing equations.

Main Results:

• Raman densimeter equations calibrated with similar spectral resolution yield CO2 density values within standard errors.
• Statistical analysis confirms CO2 densities calculated by equations calibrated at similar spectral resolution are equivalent at 95% confidence.
• Each Raman densimeter has a statistically defined limit of applicability (minimum Δ value) beyond which density errors increase.

Conclusions:

• Equations calibrated at similar spectral resolutions are suitable for interlaboratory application.
• Instrument-dependent variability can be minimized by standardizing spectral resolution during calibration.
• Establishing a minimum Δ value for each densimeter improves the accuracy and reliability of CO2 fluid density measurements.