Abstract
Carbon capture and storage (CCS) is considered a key technology for reducing CO2emissions into the atmosphere. Nonetheless, there are concerns that if injected CO2migrates in the crust, it may trigger slip of pre-existing faults. In order to test if this is the case, covariations of carbon, hydrogen, and oxygen isotopes of groundwater measured from Uenae well, southern Hokkaido, Japan are reported. This well is located 13 km away from the injection point of the Tomakomai CCS project and 21 km from the epicenter of September 6th, 2018 Hokkaido Eastern Iburi earthquake (M 6.7). Carbon isotope composition was constant from June 2015 to February 2018, and decreased significantly from April 2018 to November 2019, while total dissolved inorganic carbon (TDIC) content showed a corresponding increase. A decrease in radiocarbon andδ13C values suggests aquifer contamination by anthropogenic carbon, which could possibly be attributable to CCS-injected CO2. If such is the case, the CO2enriched fluid may have initially migrated through permeable channels, blocking the fluid flow from the source region, increasing pore pressure in the focal region and triggering the natural earthquake where the brittle crust is already critically stressed.
Highlights
There is a global consensus that some form of carbon capture and storage (CCS) technology is necessary to reduce CO2 emission associated with fossil fuel combustion into the atmosphere (IPCC Special Report, 2005)
The δ13C of total dissolved inorganic carbon (TDIC) in groundwater from the Eniwa well decreased over time, from −18.5‰ to −20.9‰, except for October 2017, while TDIC concentration remained constant at 0.68 ± 0.03 mmol/L, except for the most recent sample
The ratio is almost constant, at 0.66 ± 0.04 Ra, at the Laforet site located far from the Ishikari-Teichi-Toen Fault Zone (ITTFZ) (Figure 1). These results suggest that a mantle helium component was slightly enriched in the ITTFZ subsurface region fluids after the M6.7 earthquake
Summary
There is a global consensus that some form of carbon capture and storage (CCS) technology is necessary to reduce CO2 emission associated with fossil fuel combustion into the atmosphere (IPCC Special Report, 2005). The majority of research into this technology has focused on securely isolating CO2 from the Earth’s surface and storing it in a reservoir which is sealed by an impermeable cap rock (Johnson et al, 2005; Michael et al, 2011) This strategy should prevent CO2 from leaking into the closest areas around the injection well but it may promote horizontal flow of CO2-rich fluids through available permeable horizons. We collected groundwater samples from wells used for producing commercial bottled mineral water at Uenae and Eniwa sites, located 13 and 29 km from the CCS Tomakomai site, respectively (Figure 1). Carbon isotopes were measured at the Atmosphere and Ocean Research Institute, University of Tokyo, Japan with a conventional continuous flow mass spectrometer (Delta V plus, Thermo Fisher) after standard decarbonation with phosphoric acid. Experimental errors on carbon isotopes and TDIC concentrations were calculated by repeated measurements of standard samples. A smaller amount of CO2, approximately 100 tons, was injected into the deeper reservoir
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