A novel PFG-NMR method to determine CO2 solubility in geological carbon storage

Solubility is a dominant trapping mechanism for geological carbon storage (GCS). CO${}_2$ dissolution into aquifer water, mainly affected by formation pressure, temperature and salinity, which in turn regulate water molecules self-diffusion coefficient(D${}_0$). Here we measured CO${}_2$ solubility in DI water, in 50 kppm and 100 kppm NaCl solutions at different pressures and temperatures. Then, a self-diffusion coefficient experiment, using the pulsed-field gradient nuclear magnetic resonance (PFG-NMR) technique, was conducted to investigate how the different conditions affect CO${}_2$ dissolution. Results show that the diffusion coefficient in aqueous phase containing dissolved CO${}_2$ increases with temperature, and decreases inversely with pressure, due to increased CO${}_2$ dissolution. Additionally, clear, well-defined correlations between D${}_0$ and the CO${}_2$ dissolved fraction were found in all experiments. These correlations gave rise to a novel method to assess CO${}_2$ solubility by measuring D${}_0$ via PFG-NMR. This method is fast and provides an assessment of solubility trapping during GCS site screening or storage processes.