2:30 PM - 2:45 PM
[HSC06-16] Relationship between CO2 storage and hydrate sealing layer in hydrate CCS
Keywords:Permeability, CCS, Core flooding test, Subsea sediment, Global warming
CCS is being considered to mitigate climate change because of global warming. It is not clear whether the storage in aquifers assuming the existence of sealing layer, which is considered as a main method in Japan, has sufficient potential. Therefore, the feasibility of hydrate CCS using CO2 hydrate self-sealing as a method to supplement the storage in aquifers has been discussed. In this study, to clarify the conditions under which CO2 can be sequestered in hydrate CCS, we conducted experiments of liquid CO2 injection into several cores, each consisting of sands with different particle size, and experimentally analyzed and compared the hydrate distribution and the presence of sealing.
Three types of cores were prepared using two simulated sediments, Toyoura standard sand and Tohoku silica sand No. 8. One contained only Toyoura standard sand, another contained only Tohoku silica sand No. 8, and the last one was filled with Toyoura standard sand and Tohoku silica sand No. 8 in sequence from the bottom end of the core. The inside of the cores were maintained at 7.5 MPa and 8.5 ℃, and the same amount of liquid CO2 was injected at a constant flow rate from the bottom end of the cores. The pressure and temperature in the cores were measured and the formation behavior of CO2 hydrate was analyzed. The results of the experiments showed that hydrate formation in the core was confirmed in each experiment, but the demonstration of sealing varied from experiment to experiment. In some experiments, the formation of a hydrate sealing layer that could withstand maximum pressure difference of about 5.5 MPa was confirmed, while in other experiments only partial blockage was observed. The difference in this phenomenon can be attributed to the uneven formation of CO2 hydrate in the horizontal plane and the heterogeneity of the blockage in the flow channel. In addition, there was an experiment in which sealing was confirmed and another in which it was not, even when the same core was used. The result of the latter experiment could be attributed to the fact that the hydrate sealing layer did not form homogeneously as a result of the stochastic nature of hydrate formation and insufficient hydrate growth. From the above, it is important to form the hydrate sealing layer as homogeneously as possible to realize hydrate CCS, and it is necessary to investigate methods to achieve it.
Three types of cores were prepared using two simulated sediments, Toyoura standard sand and Tohoku silica sand No. 8. One contained only Toyoura standard sand, another contained only Tohoku silica sand No. 8, and the last one was filled with Toyoura standard sand and Tohoku silica sand No. 8 in sequence from the bottom end of the core. The inside of the cores were maintained at 7.5 MPa and 8.5 ℃, and the same amount of liquid CO2 was injected at a constant flow rate from the bottom end of the cores. The pressure and temperature in the cores were measured and the formation behavior of CO2 hydrate was analyzed. The results of the experiments showed that hydrate formation in the core was confirmed in each experiment, but the demonstration of sealing varied from experiment to experiment. In some experiments, the formation of a hydrate sealing layer that could withstand maximum pressure difference of about 5.5 MPa was confirmed, while in other experiments only partial blockage was observed. The difference in this phenomenon can be attributed to the uneven formation of CO2 hydrate in the horizontal plane and the heterogeneity of the blockage in the flow channel. In addition, there was an experiment in which sealing was confirmed and another in which it was not, even when the same core was used. The result of the latter experiment could be attributed to the fact that the hydrate sealing layer did not form homogeneously as a result of the stochastic nature of hydrate formation and insufficient hydrate growth. From the above, it is important to form the hydrate sealing layer as homogeneously as possible to realize hydrate CCS, and it is necessary to investigate methods to achieve it.