Research and Institute of Innovative Technology for the Earth (RITE) had undertaken a five-year project beginning in 2000 with the goal of pursuing R&D to establish the underground storage of carbon dioxide (CO_2). Technical basis of the underground storage of CO_2 is offered by underground gas storage and enhanced oil recovery. But, it is important for starting the commercial scale CO_2 storage in Japan to provide assurance that CO_2 can remain trapped underground for very long periods and does not create local health and safety problems for humans or the ecosystem. Then, this paper discussed the behavior of CO_2 when CO_2 was injected and migrated upward from deep saline formations. The geological model was based on the aquifer offshore Japan that might be considered as one of candidate sites. As the result, it becomes clear that care should be taken not to create channels of leakage in the seal rock by controlled the injection rates and safe injection pressure for CO_2 during the injection phase because the pressure of the aquifer increases gradually as CO_2 injected. Moreover, it can be considered that a release of CO_2 from the seafloor does not occur explosively because the CO_2 velocity is very low even if a large-size, vertical pathway may occur in rock units in the worst-case scenario.
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