多孔質体における超臨界CO₂の流動挙動に関する室内実験ならびにシミュレーション研究

抄録

The quantitative estimation for the amount of storage and leakage of injected CO₂ under the environment of underground is necessary for risk assessment of carbon dioxide capture and storage (CCS) . In addition, permeability characteristics of supercritical CO₂ and water in porous media are very important parameter in order to predict migration of injected CO₂ dependent on time and space.
In this study, using sand column, we conducted experimental study on flow behavior of supercritical CO₂ and water in porous media. Grain size and temperature were changed as an experimental parameter. Using experimental data for flow behavior such as discharge rate of fluids, differential pressure between inlet and outlet of sand column, we conducted a numerical simulation for this laboratory-scale experiment in order to clarify permeability characteristics of supercritical CO₂ in porous media. As relative permeability model for simulation, the extended Corey model that N_krg and N_krw as indexes were introduced into the original one was used. By changing the values of N_krg and N_krw, history matching of flow behavior and pressure change during both of CO₂ and water injection processes was carried out and the shapes of relative permeability curves that allowed us to reproduce CO₂-water multi-phase flow behavior were optimized.
Comparison of the optimized relative permeability curves in the process of CO₂ injection indicated that 1) water mobility was relatively high compared with that of CO₂ when grain size was large and 2) relative permeability to CO₂ became higher under the condition below critical point of CO₂. In addition, we interpreted transport phenomena of CO₂ after shutoff of CO₂ injection on the basis of relative permeability curves obtained for water injection process. As a result, it was found that 1) liquid CO₂ easily migrated into geological formation in the cases of small grain size and low temperature and 2) dissolved CO₂ migration due to groundwater flow contributed to the change of CO₂ distribution under the condition of high water saturation.