Temporal variations in pore water and gas geochemistry in shallow marine sediments over four years following offshore CO2 injection in Yeongil Bay, South Korea
1Carbon Capture & Storage (CCS) Research Center, Kongju National University, Gongju 32588, South Korea.
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Summary
A four-year study of an offshore carbon capture and storage (CCS) project in South Korea found no significant CO2 leakage. Geochemical analysis revealed that natural processes, not injected CO2, influenced pore water and gas in marine sediments.
Area of Science:
- Geochemistry
- Environmental Science
- Marine Geology
Background:
- Carbon capture and storage (CCS) is crucial for mitigating anthropogenic CO2 emissions.
- An offshore CCS demonstration project injected 100 tons of CO2 into a deep saline aquifer in Yeongil Bay, South Korea.
- Monitoring the impact of CO2 injection on marine sediment geochemistry is essential for assessing CCS viability.
Purpose of the Study:
- To investigate the potential impact of CO2 injection on pore water and gas geochemistry in shallow marine sediments.
- To differentiate between anthropogenic CO2 effects and natural geochemical processes.
- To assess the integrity and potential leakage of the offshore CCS demonstration project over four years.
Main Methods:
- Repeated sampling and geochemical analyses of pore water and gases before and up to four years post-injection.
- Analysis of total alkalinity (TA), dissolved inorganic carbon isotopes (δ13C), gas-phase CO2, and major/trace elements (Ca2+, Sr2+, Mg2+, SO42-, Mn, Fe).
- Seismic data interpretation to identify features like acoustic blanking and the sulfate-methane transition (SMT).
Main Results:
- No significant changes in TA, δ13C, or gas-phase CO2 concentrations were observed, indicating negligible CO2 leakage.
- Spatial variations in geochemistry were attributed to natural processes: microbial organic matter degradation, carbonate precipitation, and marine silicate weathering (MSiW).
- Sites with acoustic blanking and shallow SMT showed high TA and CH4, indicative of methanogenesis and carbonate precipitation, with enhanced MSiW at some locations.
Conclusions:
- The pore water and gas chemistry in Yeongil Bay remained stable over the four-year monitoring period.
- Geochemical variations were predominantly controlled by natural diagenetic processes and sources, not by anthropogenic CO2 migration from the CCS project.
- The study demonstrates the resilience of the marine sediment system to the injected CO2 and supports the negligible leakage assumption for this CCS demonstration.