ANALYSIS MODELING OF LEAKAGE RISK OF DEEP GROUNDWATER AND CARBON DIOXIDE DUE TO GEOLOGIC CARBON DIOXIDE STORAGE IN A PROSPECTIVE STORAGE SITE IN THE GYEONGSANG BASIN, KOREA

A series of analysis modeling of leakage risk of deep groundwater (brine) and carbon dioxide (CO₂) due to geologic CO₂ storage in a prospective storage site in the Gyeongsang Basin, Korea was performed using a behavior prediction model and a leakage risk analysis model to validate their applicability. The prospective storage site is composed of five Cretaceous sedimentary geologic formations, and a thick sandstone layer in the Hasandong Formation is considered as a target formation for geologic CO₂ storage. Above the target formation, four alternating thick shale layers (aquitards) and thin sandstone layers (aquifers) exist as a multiple layer system. In this study, several virtual abandoned wells at various locations are considered as leakage pathways for deep groundwater and CO₂ leakage into the overlying four aquifers. A series of prediction modeling of behavior of deep groundwater and CO₂ in the target formation was performed first using a behavior prediction model TOUGH2 (Pruess et al., 1999, 2012) to obtain spatial and temporal distributions of the pressure, temperature, and saturation of deep groundwater and CO₂ as well as the mass fraction (solubility) of CO₂ in deep groundwater along the upper boundary of the target formation beneath the overlying cap rock. These spatial and temporal distributions are used as input data in the next leakage risk analysis modeling. A series of analysis modeling of leakage risk of deep groundwater and CO₂ through the virtual abandoned wells was then performed using a leakage risk analysis model CO₂-LEAK (Kim, 2012). The analysis modeling results show that CO₂ injection can cause deep groundwater (brine) and CO₂ (both free fluid and aqueous phases) leakage into the overlying four aquifers through the abandoned wells. In that case, brine leaks first, aqueous phase of CO₂ then leaks, and free fluid phase of CO₂ leaks finally. The analysis modeling results also reveal that deeper alternating aquitards and aquifers (multiple layer system) can act as a natural barrier keeping shallower (ground or near surface) aquifers from leakage of deep groundwater and CO₂. This work was supported by the Geo-Advanced Innovative Action (GAIA) Program funded by the Korea Environmental Industry and Technology Institute (KEITI), Ministry of Environment, Republic of Korea.