Monitoring CO2 intrusion and associated geochemical transformations in a shallow groundwater system using complex electrical methods.
The risk of CO(2) leakage from a properly permitted deep geologic storage facility is expected to be very low. However, if leakage occurs it could potentially impact potable groundwater quality. Dissolved CO(2) in groundwater decreases pH, which can mobilize naturally occurring trace metals commonly contained in aquifer sediments. Observing such processes requires adequate monitoring strategies. Here, we use laboratory and field experiments to explore the sensitivity of time-lapse complex resistivity responses for remotely monitoring dissolved CO(2) distribution and geochemical transformations that may impact groundwater quality. Results show that electrical resistivity and phase responses correlate well with dissolved CO(2) injection processes. Specifically, resistivity initially decreases due to increase of bicarbonate and dissolved species. As pH continues to decrease, the resistivity rebounds toward initial conditions due to the transition of bicarbonate into nondissociated carbonic acid, which reduces the total concentration of dissociated species and thus the water conductivity. An electrical phase decrease is also observed, which is interpreted to be driven by the decrease of surface charge density as well as potential mineral dissolution and ion exchange. Both laboratory and field experiments demonstrate the potential of field complex resistivity method for remotely monitoring changes in groundwater quality due to CO(2) leakage.
Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, California 94720, United States. BDafflon@lbl.gov
Baptiste
B
Dafflon
Yuxin
Y
Wu
Susan S
SS
Hubbard
Jens T
JT
Birkholzer
Thomas M
TM
Daley
John D
JD
Pugh
John E
JE
Peterson
Robert C
RC
Trautz
D002245:Carbon Dioxide / Q000032:analysis*; D057965:Carbon Sequestration; D004553:Electric Conductivity; D004784:Environmental Monitoring; D055593:Geological Phenomena; D060587:Groundwater / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D014874:Water Pollutants, Chemical / Q000032:analysis*
D014874:Water Pollutants, Chemical; D002245:Carbon Dioxide