Hydrate Plugging and Flow Remediation during CO2Injection in Sediments

Successful geological sequestration of carbon depends strongly on reservoir seal integrity and storage capacity, including CO(2)injection efficiency. Formation of solid hydrates in the near-wellbore area during CO(2)injection can cause permeability impairment and, eventually, injectivity loss. In this study, flow remediation in hydrate-plugged sandstone was assessed as function of hydrate morphology and saturation. CO(2)and CH(4)hydrates formed consistently at elevated pressures and low temperatures, reflecting gas-invaded zones containing residual brine near the injection well. Flow remediation by methanol injection benefited from miscibility with water; the methanol solution contacted and dissociated CO(2)hydrates via liquid water channels. Injection of N(2)gas did not result in flow remediation of non-porous CO(2)and CH(4)hydrates, likely due to insufficient gas permeability. In contrast, N(2)as a thermodynamic inhibitor dissociated porous CH(4)hydrates at lower hydrate saturations (<0.48 frac.). Core-scale thermal stimulation proved to be the most efficient remediation method for near-zero permeability conditions. However, once thermal stimulation ended and pure CO(2)injection recommenced at hydrate-forming conditions, secondary hydrate formation occurred aggressively due to the memory effect. Field-specific remediation methods must be included in the well design to avoid key operational challenges during carbon injection and storage.