[H-SC07] CCUS (Carbon Dioxide Capture, Utilization, and Storage) for Climate Mitigation

[HSC07-10] Influence of cement slurry on detectability of CO₂ leakage on wellbore potential monitoring

*Takuya Horikawa^1,2, Masao Sorai^1,2 (1.Geological Carbon Dioxide Storage Technology Research Association, 2.CO2 Geological Storage Research Group, GREEN, GSJ, AIST)

Keywords:Geological Storage, Self Potential, Well Integrity, Electrochemistry

In geological CO₂ sequestration, one of the high-risk leakage pathways is the wells, especially around abandoned wells (Osada & Azuma, 2016). Therefore, monitoring the subsurface CO₂ in the vicinity of the wellbore for a long time is important for risk assessment of the leakage. The electric potential of a conductive body, often called corrosion potential, depends on the electrochemical reaction between the conductor surface and the neighboring aquifer. The negative potential anomaly is usually observed around the well because of the corrosion reaction of iron. Previous field tests showed that a potential increase of about 50 mV was observed around the wellhead in connection with CO₂ injection (Nishi and Ishido, 2022). Our experimental studies showed that when CO2 touched to the well precipitation of the corrosion products as FeCO₃ covered its surface and the following passivation brought out the increase of the corrosion potential (Horikawa and Sorai, 2023). These previous studies suggest that monitoring the electric potential of a well casing or its neighbor from ground far from the wellhead has a possibility to detect the approach of CO₂ plume to the well and the risk of leakage from the well. In this study, for predicting the potential changes due to contact with CO₂ more precisely, we attempted to a sandbox experiment to evaluate the influence of cement slurry on the potential changes.
A sandbox was composed of three horizontal layers corresponding to the reservoir, the caprock and the upper sand layer. In this study, an iron rod partially covered with cement was stuck through the layers vertically, and the electric potentials on and around the rod were measured while electrochemical reactions between the rod and solutions in the layers progressed. We attempted to measure the potentials for almost 40 days after substituting the solution in the reservoir from brine to carbonated water, and the increase of the rod potential of ~70 mV was observed 31 days after the substitution. As already reported at AGU 2022, the increase of the potential of ~40 mV was observed 15 days after the substitution in an experiment conducted under the same conditions as the present, except for the cement. These results suggest that the presence of cement slurry prolongs the time lag between contact with CO₂ and the potential change, while the magnitude of the potential change increases.
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.