UBC Theses and Dissertations
Storage of carbon dioxide in depleted natural gas reservoirs as gas hydrate Sun, Duo
More than 120 depleted natural gas reservoirs in Alberta, Canada have been identified as potential sites for CO₂ storage at temperature and pressure conditions at which CO₂ may form gas hydrate. Reservoir simulations presented in the literature have demonstrated the feasibility of storing CO₂ in such reservoirs. In this thesis, the injection of CO₂ in a laboratory size reservoir (packed bed of silica particles) serving as a physical model for a depleted reservoir was studied. The hypothesis was that injecting CO₂ into the reservoir at gas hydrate formation conditions will be beneficial in terms of increased CO₂ storage density. It is noted that CO₂ is stored not only as hydrate but also some is dissolved in the residual pore water (not converted to hydrate) and some as a gas in the remaining pore space. The results indicate that hydrate formation enhances the CO₂ storage density. The work also demonstrated that substances like tapioca starch added to the water in small quantities (1 wt %) delayed the onset of hydrate nucleation in the earlier stage but subsequently more CO₂ was stored as hydrate compared to the tapioca starch-free systems. The delay in nucleation decreases the risk to form a hydrate plug in the injection system. The injection of the CO₂-rich mixture (90 mol % CO₂/10 mol % N₂), which is a typical composition of a flue gas after CO₂ capture process, into a reservoir with CH4 (simulating residual natural gas) was also studied in the laboratory reservoir. It was found that the total CO₂ storage density (in hydrate, gaseous and dissolved state) decreased from 143 kg/m³ (the CO₂ injection into a CH₄ free reservoir) to 119 kg/m³. Finally, relevant phase equilibrium data were obtained in a constant volume high pressure vessel and by calorimetry. The results were found to be in good agreement with thermodynamic model calculated values within ± 40 kPa and ± 0.2 K, respectively.
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