[H-SC06] CCUS (Carbon Dioxide Capture, Utilization, and Storage) for Climate Mitigation

[HSC06-P04] Numerical Investigation of Self-potential Monitoring for Offshore Geological Storage of CO₂

*Yuki Kano^1,2, Takuya Horikawa^1,2, Yuji Nishi^1,2 (1.Geological Carbon Dioxide Storage Technology Research Association, 2.National Institute of Advanced Industrial Science and Technology, Geological Survey of Japan)

Keywords:CO2 geological Storage, Numerical simulation, Geophysical monitoring, Self-potential, Geobattery

Injecting oxidizing substance such as CO₂ in the deeper formation causes self-potential (SP) changes by electrokinetic and electrochemical mechanisms due to the streaming effect and/or change of redox environments. The metallic well casing acts as a vertical electronic conductor connecting regions of differing redox potential, and SP anomalies of negative polarity near the well is caused by a mechanism known as “geobattery” (Bigalke and Grabner, 1997). The change of the streaming potential caused by the CO₂ geological storage would be relatively small compared with the effects of shallow ground water flow. On the other hand, previous field tests found observable SP increase around the wellhead in association with CO₂ injection due to geobattery mechanism at some onshore sites (Nishi and Ishido, in press). To monitor this change of SP can be convenient method to detect a CO₂ breakthrough and/or a leakage along the well in the CO₂ geological storage site.
In Japan and the Nordic countries, main targets of CO₂ geological storage will be the offshore sites. The salinity of the formation water will be high in such sites, and it results in low resistivity of the formations. The change of SP at the ground surface would be relatively small due to the shallow low-resistivity zone (Kano, 2021). Long directional well installed at the offshore site will be also a challenge with the SP monitoring for the offshore geological storage of CO₂.
At Tomakomai CCS project site in Japan, SP monitoring at the wellhead was started to develop a low-cost monitoring method and obtain knowledge of the SP monitoring operation at the offshore CCS site (Horikawa, 2022). In this study, we conducted numerical simulations on CO₂ injection into a saline aquifer under the seafloor referring to the geometric layout and physical properties of the Tomakomai site. Calculated results were compared with the monitoring results and used to investigate the applicability of the SP monitoring to the offshore geological storage of CO₂.
Fluid flow simulations were carried out using the reservoir simulation code “STAR” (Pritchett, 2002) with the equations of state “SQSCO2” (three pore components: H2O, CO2 and NaCl) (Pritchett, 2008), and then the changes of SP data were calculated using STAR’s “Redox Electrical Postprocessor” (Pritchett, 2003).
This presentation is based on results obtained from a project (JPNP18006) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) and the Ministry of Economy, Trade and Industry (METI) of Japan.

References
Bigalke, J., and Grabner, E.W. (1997): The geobattery model: a contribution to large scale electrochemistry. Electrochimica Acta 1997; 42:3443-3452.
Horikawa, T. (2022): Developments Low-Cost Monitoring Techniques using Microgravity and Self-Potential (in Japanese). Institute for Geo-Resources and Environment, GREEN Report 2021. AIST04-C00014-20: 14-15.
Kano, Y. (2021): Numerical Investigation of “Geobattery” Monitoring based upon CO2 Geological Storage. Presentation at AGU Fall Meeting 2021. Dec. 13-17, 2021, New Orleans, LA & online.
Nishi, Y. and Ishido, T. Self-Potential Monitoring for Geologic Carbon Dioxide Storage. In Geophysical Monitoring for Geologic Carbon Storage (eds Huang, L.). John Wiley & Sons, Inc in press:303-320.
Pritchett, J.W. (2002): STAR User’s Manual Version 9.0, SAIC Report Number 02/1055
Pritchett, J.W. (2003): Verification and Validation Calculations Using the STAR Geophysical Postprocessor Suite. SAIC Report Number 03/1040; 2003.
Pritchett, J.W. (2008): New “SQSCO2” equation of state for the “STAR” code, SAIC.