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

[HSC07-15] Modelling of permeability change caused by CO₂ hydrate in sand layer using numerical simulation

*Toru Sato¹, Ayumu Nono², Junji Alan Yamaguchi¹ (1.Department of Ocean Technology, Policy, and Environment, Graduate School of Frontier Sciences, University of Tokyo , 2.Department of Systems Innovation, Faculty of Engineering, University of Tokyo)

Keywords:Effective permeability, Pore-scale simulation, CO2 hydrate, Lattice Boltzmann method, Phase field model

Carbon dioxide capture and storage is an efficient technology to reduce CO₂ emission. One of the reservoirs of CO₂ is an aquifer in the sub-seabed geological formation under a caprock. However, there is a risk of CO₂ leakage even though such probability is extremely low. When the water depth of a storage site is large: say, about 400 m or more, leaked CO₂ changes its form to gas hydrate, which may block CO₂ rise in the sediment. To estimate the sealing potential of CO₂ hydrate, it is necessary to evaluate effective permeability of the sediment after CO₂ hydrate forms. In this study, a series of numerical models were used to investigate microscopic hydrate distribution that essentially controls the effective permeability. The method consists of packing sand grains within microscopic computational domains, arranging water and CO₂ phases in the pore space of the packed sand grains, placing multiple hydrate nuclei, and growing hydrate in the pores of the sand grains. First, we derived a value of the interface mobility of CO₂ hydrate by fitting calculated growth rate of a hydrate spherule to a measurement in the literature. Then, CO₂ hydrate formation was simulated within microscopic computational domains consisting of sand grains and water-CO₂ two phases. Finally, efficient permeability was estimated using the results of the simulation of water flow through the pore space, regarding the formed hydrate as a solid. The calculation results indicated the differences in hydrate distribution in the pore space and in resulting effective permeability, depending on hydrate saturations, initial water saturations, and contact angles of water on the sand surface.