Thermodynamic gas hydrate inhibition for CO2 injection in depleted gas reservoirs

For carbon capture and storage, underground depleted reservoirs, saline aquifers and salt caverns can store carbon dioxide (CO 2 ) permanently to reduce the CO 2 concentration in the atmosphere. This study focused on the formation and equilibrium conditions of CO 2 hydrates formed in a pure water phase containing thermodynamic inhibitors (methanol, monoethylene glycol, diethylene glycol, triethylene glycol). The pure water system was used as reference system. The formation of CO 2 hydrates was investigated in a pressure range of about 1.5 MPa – 8.0 MPa and thus also under different CO 2 aggregate phases (gaseous and liquid) and in a temperature range of 263 K – 284 K adapted from the project field specifications. The novelty of the present study was the investigation of the possible subcooling prior to gas hydrate formation without memory effect. A possible subcooling without gas hydrate formation at a cooling rate of 0.1 K/min was found to be between 5.2 K – 16.1 K. This is an important outcome of the study, as it implies that CO 2 injection without gas hydrate forming still seems to be possible although operating conditions are already submerged into the gas hydrate stability zone. In addition, the main novelty was the investigation of a possible synergy effect of mixtures of 18 wt% methanol/monoethylene glycol solution at different mole concentrations. The synergy effect of these two nonionic thermodynamic inhibitors were found to be small (0.5 K). The gas hydrate experimental setup is described. The experiments were carried out in good agreement of the equilibrium data with various literature values.