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

[HSC06-P03] Self-potential measurements around a metal casing when the acidified water flows through a sandbox

*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:Carbon Dioxide Geological Storage, Self potential, Well integrity

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 self-potential (SP) method, which is a technique for measuring spontaneously generated potential differences between two measurement points, has a promising potential to detect the approach of CO₂ to the well and the risk of leakage from the well. For example, it is well known that negative SP anomalies are observed near a conductor connecting regions with different redox environments (Maineult, 2016). Moreover, Ishido et al. (2013) numerically showed that injection and migration of CO₂ caused the change of the redox environment around the bottom of the metal casings and a potential variation of up to 80 mV was observed on the ground. However, few experiments have been performed to focus on the SP changes of the well induced by the approach of CO₂.
The possible causes of the SP change when CO₂ approaches the casing are the pH decrease of the pore water due to the dissolution of CO₂ and the additional redox reaction between HCO₃^-, CO₃^2- and the material of the casing, e.g., iron. In the simple sandbox experiment, we observed a temporal increase of the electric potential of an iron rod coinciding with an injection of a small amount of carbonated water near the bottom of the rod (Table 1). Additionally, we also observed that the potential returned to its initial value after the injection. Next, in order to interpret more quantitatively the potential changes caused by approaching the carbonated water, we made a new sandbox apparatus and measured the potential distribution in the sandbox added to the rod potential as the solution flowed through the sandbox (Fig. 1). The new sandbox apparatus has three horizontal layers, corresponding to the reservoir, the caprock and the upper sand layer respectively. In our presentation, the results and discussion of the flow-through experiments will be presented.
This presentation is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) and the Ministry of Economy, Trade and Industry (METI) of Japan.