Abstract
An experiment of CO2 gas injection into the shallow confined aquifer has been conducted, and subsurface thermal environment change caused by effects of CO2 gas injection was observed. Subsurface temperature increase was found in the injected aquifer, excepting the temporary drop of temperature in the injection well. The part of subsurface temperature increase was formed from the depth of 44m to 48m, and the temperature increase was most significant around the upper surface of the aquifer at the depth of 47m. This suggests that injected CO2 gas expanded along the upper surface of the aquifer. Moreover, groundwater quality variation showed decrease of pH and increase of ORP accompanying the dissolution of CO2 gas. It was considered that the increase of subsurface temperature was caused by generated heat accompanying oxidization of iron minerals in the aquifer. The part of temperature increase was recognized 35 days after the end of the injection, although it was shrinking with time progress. This suggests that effects of subsurface thermal environment change remain for a long period in spite of the shallow aquifer around the depth of 50m.
