[H-SC07] CCUS (Carbon Dioxide Capture, Utilization, and Storage) for Climate Mitigation

[HSC07-P10] Effect of sediment particle size on self-sealing of CO₂ hydrate

Toshiki Terahata¹, Yuna Arai¹, *Yoshihiro Konno¹, Yusuke Jin² (1.The University of Tokyo, 2.National Institute of Advanced Industrial Science and Technology (AIST))

Keywords:Permeability, Core flooding test, Subsea sediment, Global warming

CCS is attracting attention as a promising means to reduce greenhouse gas. In Japan, storage of CO₂ in aquifers with a shieling layer is assumed, but it is unclear whether sufficient potential can be secured. Therefore, in addition to storage in aquifers, hydrate CCS using self-sealing of CO₂ hydrate is being considered. Previous studies show that there is a relationship between the particle size of sand and the rate of gas hydrate formation. In order to gain insight into performing hydrate CCS, this study conducted an experiment of liquid CO₂ injection into a layered core and analyzed the effect of sediment particle size on the formation and self-sealing of CO₂ hydrate experimentally.
Two types of artificial sediments, Toyoura standard sand and Tohoku silica sand No. 8, were packed in sequence from the bottom end of the core to create a layered core. Liquid CO₂ was injected from the bottom end of the core under conditions of 7.5 MPa and 8.5 °C. Temperature and pressure in the core were measured. The result shows that CO₂ hydrate formed non-uniformly and partial blockage was observed; however, complete self-sealing was not achieved. In addition, a large amount of liquid CO₂ was observed close to the boundary between Toyoura standard sand and Tohoku silica sand No. 8 and not much CO₂ hydrate formed there. This phenomenon may be attributed to the fact that liquid CO₂ could not enter the Tohoku silica sand No. 8 layer, which has high capillary pressure, and stagnated near the boundary, resulting in the elimination of pore water and the lack of water necessary for the formation of CO₂ hydrate. It is found that the non-uniform CO₂ hydrate may form and the stagnation of liquid CO₂ will occur especially near the boundary of layers with different particle size, which may hinder hydrate formation.