Modeling of $CO2$-Hydrate Formation in Geological Reservoirs by Injection of $CO2$ Gas

Continuing concern about the impacts of atmospheric carbon dioxide $(CO2)$ on the global climate system provides an impetus for the development of methods for long-term disposal of $CO2$ produced by industrial and other activities. Investigations of the $CO2$-hydrate properties indicate the feasibility of geologic sequestration $CO2$ as gas hydrate and the possibility of coincident $CO2$ sequestration/$CH4$ production from natural gas hydrate reservoirs. Numerical studies can provide an integrated understanding of the process mechanisms in predicting the potential and economic viability of $CO2$ gas sequestration, especially when utilizing realistic geological reservoir characteristics in the models. This study numerically investigates possible sequestration of $CO2$ as a stable gas hydrate in various reservoir geological formations. As such, this paper extends the applicability of a previously developed model to more realistic and relevant reservoir scenarios. A unified gas hydrate model coupled with a thermal reservoir simulator (CMG STARS) was applied to simulate $CO2$-hydrate formation in four reservoir geological formations. These reservoirs can be described as follows. The first reservoir (Reservoir I) is similar to tight gas reservoir with mean porosity 0.25 and mean absolute permeability $10mD$⁠. The second reservoir (Reservoir II) is similar to a conventional sandstone reservoir with mean porosity 0.25 and mean permeability $20mD$⁠. The third reservoir (Reservoir III) is similar to hydrate-free Mallik silt with mean porosity 0.30 and mean permeability $100mD$⁠. The fourth reservoir (Reservoir IV) is similar to hydrate-free Mallik sand with mean porosity 0.35 and mean permeability $1000mD$⁠. The Mallik gas hydrate bearing formation itself can be described as several layers of variable thickness with permeability variations from $1mDto1000mD$⁠, and is addressed as a separate part of this study. This paper describes numerical methodology, model input data selection, and reservoir simulation results, including an enhancement to model the effects of ice formation and decay. The numerical investigation shows that the gas hydrate model effectively captures the spatial and temporal dynamics of $CO2$-hydrate formation in geological reservoirs by injection of $CO2$ gas. Practical limitations to $CO2$-hydrate formation by gas injection are identified and potential improvements to the process are suggested.