Simplified Prediction of the Proceeding of Mineral Trapping of CO₂ Based on Experimental Study

Implications for CO₂ Storage site Selection in Japan

Abstract

We conduct CO₂-water-rock interaction experiments at a temperature of 25 °C and pressure of 1 MPa to investigate rock dissolution phenomena and to predict long-term CO₂ fixation efficiency. The rock samples selected for our experiments are basalt, granodiorite and tuffaceous sandstone.
Our experiments show that tuffaceous sandstone provides the fastest acid-neutralizing reaction (the fluid reacting with tuffaceous sandstone shows the highest pH) . However, most cations eluted from tuffaceous sandstone and granodiorite may be caused by dissolution of constituent carbonate minerals, which will not contribute to the long-term CO₂ mineral fixation. On the other hand, basalt shows the fastest Si release rate corresponding to silicate mineral dissolution.
We conduct a long-term CO₂ fixation efficiency simulation using Ca, Mg and Fe release rates. On the assumption that (1) CO₂ injection rate to be 1,000 ton/day (2) injection time period to be 50 years (total amount of injected CO₂ is 18,250,000 t) (3) target aquifer porosity 20% (4) CO₂ density 500 kg/m³ (5) injected CO₂ to groundwater volume ratio 1:1, the time required for mineral fixation of 18,250,000 tons of CO₂ is simulated to be about 180 years for granodiorite, about 15,000,000 tons of CO₂ fixed as a carbonate mineral in 200 years for basalt and 4,000,000 tons of CO₂ fixed in 200 years for tuffaceous sandstone. This simulation data strongly suggests that the geochemical trapping of CO₂ will proceed much faster than the results of previous studies and is an important mechanism not only for long-term but for shorter-term security of CO₂ storage.