Recent years, microbubble CO₂ injection technology is expected to be developed in order to improve the safety and efficiency of CO₂ storage. Although understanding of the microscale physical phenomena of water-microbubble CO₂ flow is important for the evaluation of the microbubble CO₂ injection, few quantitative analyses of its microscale flow have been conducted. In this study, numerical simulation of water-microbubble CO₂ multiphase flow was conducted by considering the mass transfer of species between water and bubbles, volume change of bubbles and surface tension effect. In order to realize the temporal evolution of the water-CO₂ interface, taking advantage of its easiness of setting up precise boundary conditions of the multiphase flow, we applied Arbitrary Lagrangian-Eulerian（ALE）Method which hardly had been applied in such water microbubble CO₂ flow. The motion of the continuous water phase and dispersed CO₂ phase were solved simultaneously by using finite element method. Our numerical simulation results showed good agreement with analytical solutions of the simple multiphase flow problems and experimental results appeared in previous researches. Through this study, we found that microbubble CO₂ is dissolved into water in a very short period and CO₂ in microbubble is substituted by gas such as N₂ and O₂ initially dissolved in water. This simulation model is of importance for understanding of the microscale physical phenomena of water-microbubble CO₂ multiphase flow, since it is difficult to acquire experiment data of microscale interaction of water and microbubble CO₂ in practice.

Diatomaceous deposits are mixtures of diatom tests（biogenic silica）and argillaceous materials. Biogenic silica migrates in the deposits as its mineral phase transforms during burial diagenesis, concentrating and diluting organic matter and argillaceous materials, and changing pore properties. The migration is considered through a simple burial diagenesis model. As a result, analytical data related to various properties including the properties of source and reservoir rocks of the Onnagawa Formation, are explained.

The migration of biogenic silica during opal-A / CT transformation emphasizes a slight compositional difference in diatomaceous deposits and forms hard（opal-CT porcelanite）-soft（opal-CT siliceous mudstone）alternating beds. The silica flows from the proto-siliceous mudstone into the proto-porcelanite, which concentrates the argillaceous materials and organic matter in the siliceous mudstone, improving its source rock potential. In addition, due to the migration, the compositional difference is emphasized even in proto-porcelanite（hard）, and light-dark colored porcelanite alternating beds are formed and become distinct. Conversely, during the opal-CT / Quartz transformation, the silica flows from the light-colored porcelanite into the dark-colored porcelanite, and the porosity of light-colored porcelanite is increased, and that of dark-colored porcelanite is decreased and chertified. Since compaction during opal-CT / Quartz transformation is more advanced than during opal-A / CT transformation, the increased porosity tends to be maintained. This phenomenon forms a double porosity reservoir in which light-colored porcelanite with high porosity and dark-colored porcelanite with dense fractures, alternate with each other.

The improvement of source and reservoir rock properties is promoted as biogenic silica migration increases. Therefore, better source and reservoir rocks are formed adjacent to each other by the diagenesis of diatomaceous deposits with more primary diatom test contents. The primary diatom test contents are estimated from the Al₂O₃/TiO₂ when chemical compositions of diatom tests and argillaceous materials are properly estimated.

In response to the recent international movement to reduce CO₂ emissions, expectations for carbon dioxide capture and storage（CCS）are increasing. CCS has been partially commercialized, but challenges remain in terms of storage potential, cost, and social acceptance. On the other hand, basalt has the potential to dispel concerns about leakage, reduce costs by early termination of monitoring, and expand storage potential through CO₂ mineralization. In this presentation, some issues and prospects of the applicability of basalt, such as storage in basalt and hot rocks, and enhanced weathering on the surface, are introduced based on the efforts of AIST.