한국 포항분지 심부 대염수층 내 감압정 운영을 통한 이산화탄소 주입성 증진 연구

Abstract

In this study, the simulation of CO2 injection into the first field-scale CO2 storage, a saline aquifer in the Pohang basin, offshore South Korea was conducted to estimate CO2 storage capacity and injectivity. We analyzed the effect of using a relief well on improving CO2 storage capacity and injectivity of the aquifer. The Pohang basin where the sand layers are dominated is one of the sedimentary basins in South Korea and it is considered to be potential for CO2 storage site. The geological model of Pohang basin has closed boundary along east-south-west side, thus there would be drastic pressure build-up while injecting CO2. From the results of our simulation, when installed a CO2 injection well in syncline structure, the western margin of anticline structure of target storage site, the maximum storage capacity was calculated as 468 kton with 200 ton/day of injection rate. However, when installed a relief well near the CO2 injection well, the maximum storage capacity was increased to 681 kton which is about 45% larger than the case without the relief well. With the operation of the relief well, CO2 injection rate was also increased 4 times from 200 ton/day to 800 ton/day in comparison to the case without the relief well. To avoid early CO2 breakthrough, the relief well may be installed farther than 750 m from the CO2 injection well in the north direction and the pumping rate may be maintained below 1,800 ton/day.|본 연구에서는 신규 탐사를 통해 이산화탄소 지중 격리 적정 후보지로 해석된 한국 포항분지 내 대염수층을 대상으로, 감압정을 활용한 이산화탄소 저장용량 및 주입성 증진 연구를 수행하였다. 포항 분지 지질 모델을 활용한 시뮬레이션 수행 결과, 수평 방향으로 지층의 3면이 단층에 의해 닫힌 경계를 이루고 있어 이산화탄소 주입에 따른 급격한 압력의 상승이 발생함을 확인하였다. 이에 따라 주입정 1공만을 운영하는 경우 200 ton/day 이하의 속도로 주입하는 것이 적정한 것으로 나타났으며 이때의 최대 가능 저장 용량은 46.8만 톤으로 산정되었다. 반면, 주입정 인근에 감압정 1공을 추가적으로 운영하는 경우, 대염수층 내 물 생산을 통해 주입 압력을 낮춤으로써 주입 속도를 감압정 운영 이전에 비해 4배 빠른 속도인 800 TPD까지 높일 수 있음을 확인하였다. 또한 감압정 운영 설계 요소들에 대한 최적화를 수행한 결과, 물 생산으로 인한 이른 시점에의 이산화탄소 돌파를 막기 위해서는 감압정을 주입정 북쪽 방향에 0.75 km이상 떨어진 지점에 설치하는 것이 바람직하였으며, 이때 물 펌핑 속도는 1,800 ton/day 이하로 설정해야함을 확인하였다. 감압정을 운영할 경우 최대 가능 저장 용량은 68.1만 톤으로, 주입정 운영을 하지 않은 경우에 비해 약 45% (21.3만 톤) 이상 크게 높은 것으로 산정되었다. 이를 통해 감압정 운영은 이산화탄소 저장용량 및 주입성을 크게 증진시킬 수 있음을 확인하였다.; In this study, the simulation of CO2 injection into the first field-scale CO2 storage, a saline aquifer in the Pohang basin, offshore South Korea was conducted to estimate CO2 storage capacity and injectivity. We analyzed the effect of using a relief well on improving CO2 storage capacity and injectivity of the aquifer. The Pohang basin where the sand layers are dominated is one of the sedimentary basins in South Korea and it is considered to be potential for CO2 storage site. The geological model of Pohang basin has closed boundary along east-south-west side, thus there would be drastic pressure build-up while injecting CO2. From the results of our simulation, when installed a CO2 injection well in syncline structure, the western margin of anticline structure of target storage site, the maximum storage capacity was calculated as 468 kton with 200 ton/day of injection rate. However, when installed a relief well near the CO2 injection well, the maximum storage capacity was increased to 681 kton which is about 45% larger than the case without the relief well. With the operation of the relief well, CO2 injection rate was also increased 4 times from 200 ton/day to 800 ton/day in comparison to the case without the relief well. To avoid early CO2 breakthrough, the relief well may be installed farther than 750 m from the CO2 injection well in the north direction and the pumping rate may be maintained below 1,800 ton/day.