Sho Ogata

An enhanced geothermal system using carbon dioxide (CO2) for both reservoir creation and thermal energy extraction has attracted attention; however, studies on the CO2 fracturing of volcanic rocks under geothermal conditions are lacking. This study aimed to elucidate CO2 fracturing characteristics and processes in geothermal volcanic rocks via integrated lab-scale fracturing experiments and numerical simulations of basalt and andesite at 250°C and a confining pressure of 30 MPa. Moreover, it pro

The aim of the present research was to establish a case study for the prediction of the unknown EDZ (Excavation Damaged Zone) distribution using a numerical analysis calibrated by replicating the trends in the EDZ observed from one of the representative underground research fields in Japan (Horonobe URL). In this study, a 2D numerical analysis using a damage model, which can determine rock deformation and fracturing simultaneously, is presented. It was calibrated to reproduce the excavation of t

The aim of the current study was to establish a validated numerical model for addressing the changes in permeability and reactive transport behavior within rock fractures based on the fluid pH under coupled thermal-hydraulic-mechanical-chemical (THMC) conditions. Firstly, a multi-physics reactive transport model was proposed, considering the geochemical reactions that depend on the temperature, stress, and fluid chemistry conditions (e.g., fluid pH and solute concentrations), as well as the chan

A novel coupled thermal-hydraulic-mechanical-chemical (THMC) simulator for fractured porous rock was developed in the present study based on explicit fracture models. This work is an attempt to describe the spatial coupled phenomena sensitive to fracture generation within rock masses by using explicit fracture representation. The simulator was then applied to numerically predict the long-term evolution in the permeability of a rock mass working as a natural barrier within a geological disposal f

A multi-physics simulator, with geochemical reactions that depend on the pH condition, was proposed. The simulator was validated by replicating the measurements of the evolving permeability and the solute concentrations in a single rock fracture obtained from flow-through experiments under different pH conditions. Then, the changes in fracture permeability during the virtual long-term flow-through tests were predicted by assuming the permeant under various pH, stress, and temperature conditions.

We improved our coupled thermo-hydro-mechanical-chemical (THMC) simulator by adopting the dual porosity model to predict the long-term permeability change of the fractured rocks. The model evaluates influence of the geochemical reaction on the evolution of the permeability in fractured rock. Pressure solution that may occur both at grain contacts and the contacting asperities within fractures was incorporated in the model. By using the developed THMC numerical model, long-term prediction of rock

高レベル放射性廃棄物地層処分システムの安全性を担保する上で，熱・水・応力・化学連成作用による廃棄体周辺岩盤の水理学特性変化の把握は必須である．特に，廃棄体処分坑道掘削時に形成されるき裂で生じる地化学反応は岩盤の長期透水性変化を予測する上で考慮すべき事象である．そこで，本研究では損傷理論を用いたき裂発生・進展と，き裂領域内での鉱物溶解・沈殿プロセスを導入した熱・水・応力・化学連成解析モデルを構築し，放射性廃棄物地層処分施設近傍の岩盤の透水性変化の長期予測解析を実施した．その結果，坑道掘削に伴うき裂発生・進展により増加した坑道周辺の透水性が，き裂内部で生じる地化学現象（圧力溶解）により時間の経過とともに低下する傾向が得られた．