[H-SC06] CCUS (Carbon Dioxide Capture, Utilization, and Storage) for Climate Mitigation

[HSC06-02] Effects of geochemical reactions on a relationship between geomechanical and hydrological properties of caprocks in storing CO₂ geological processes

*Takashi Fujii¹, Masao Sorai¹, Yasuki Oikawa¹, Xinglin Lei¹, Manami Kitamura¹ (1.National Institute of Advanced Industrial Science and Technology)

Keywords:CO2 geological storage, geochemical, geomechanics, permeability

In the course of CO₂ injection, a fluid pressure build up will occur mechanical stresses and deformations with seismic events within storing CO₂ reservoir system. Majority of mineral component in caprocks (mudstone and shale) is clay minerals, which could react under conditions of CO₂ storage reservoir and play an essential role in connecting other minerals, e.g., quartz, feldspar groups. It is well-known that the occurrences of mineral dissolution and precipitation should require to a geological time scale (i.e., millions of years). Batch experiments of sandstone, shale, and dolomite for short terms in several weeks under supercritical CO₂ (scCO₂) conditions have been conducted so far. Their results indicated that K-feldspar, albite, dolomite, and cement were dissolved and then precipitated montmorillonite as the secondary minerals. It is further indicated that resulting mineral dissolution and precipitation phenomena with scCO₂-saturated brine aging led to reducing strength induced by changes of effective porosity of rock matrix in comparison to untreated materials. It can therefore, be said that, even though terms of geological CO₂ storage were very short such as several weeks, clay minerals and feldspars could dissolve through mineral trapping process, except for the precipitation of secondary minerals (e.g., carbonates). Up to now, it has been identified that geochemical (GC) reactions had effects on each geomechanical (GM) and hydrological (HY) properties of the rock matrix, but interactions among GC, GM, and HY have rarely been investigated. The purpose of this study is to examine experimentally geochemical reactions (i.e., mineral dissolution, secondary mineral precipitation) of caprocks under conditions of geological storage of CO₂ (40°C, 10MPa) and to determine how such reactions provide impacts on both geomechanical and hydrological behaviors of rocks.