Analysis of Carbon Dioxide/Methane Mixing Process in Rock Cores for Underground Natural Gas Storage

Dispersion coefficients are determined, and entry/exit effects during gas displacement experiments in porous media are characterized. Two methods are proposed for measuring concentration breakthrough profiles: using an X-ray scanner for internal core measurements and a Raman spectrometer for postcore measurements. The experimental setup includes a coreflooding system with X-ray scanning capabilities and a high-pressure Raman probe. A description of the data processing of X-ray and Raman signals to derive concentration profiles and calculate mixing coefficients is presented. Results from the experiments are discussed, including mixing coefficients for CO2 displacing CH4 and CH4 displacing CO2, and their variations with pressure, temperature, and flow velocity. Dispersion coefficients are found to be higher with CH4 as the displacing fluid compared to CO2, suggesting higher mixing during gas injection in underground gas storage with a CO2 cushion. The study extends the analysis to the structure promising for underground storage in Poland, analyzing dispersion coefficients and other parameters for gas injection and production scenarios. The proposed methods show promise for characterizing mixing processes and optimizing UGS operations, with potential applications in studying other gases such as higher hydrocarbons or H2 for future energy developments.