As the problem of global warming becomes more serious, more efforts are needed to reduce CO2 emissions, and CO2 sequestration is considered to be one of the most effective ways to reduce greenhouse gases. The study of natural gas hydrates has become more innovative, with huge hydrate-forming zone (HFZ) that can be effectively used to sequester CO2. In order to accurately characterize the formation and dissociation of CO2 hydrate, we have fitted the hydrate phase equilibrium to precisely control the chemical reaction by temperature and pressure. By injecting CO2 into the HFZ for 30 years, the permeability and porosity around the wellbore dropped to 1.55 × 10-3 mD and 0.056. Plugging occurred which prevented gas injection. Then we proposed thermal stimulation, increasing injection pressure and hydraulic fracturing to enhance sequestration. Thermal stimulation can restore stratigraphy conditions to initial conditions. The CO2 was injected into the reservoir successfully with a sequestration volume of 5.50 × 107 m3. Also, the injection rate decreased slowly, allowing for long-term sequestration. In contrast, the physical methods, such as increasing injection pressure and hydraulic fracturing, can only increase the rate for a short time, and the sequestration increased from 4.23 × 107 m3 to 4.42 × 107 m3 and 4.34 × 107 m3, respectively. These results demonstrate that the most important measures to enhance sequestration by mitigating hydrate plugging are destabilizing hydrate and restoring injection loss.
Keywords CO2 hydrate, CO2 sequestration, hydrate phase equilibrium, thermal stimulation