Monitoring of CO₂ Well Plug Integrity. Electrical Response of Cement/CNF Sensor to Mechanical Load, Water Saturation and Carbonation

CO₂ storage wells will eventually need to be permanently plugged and abandoned. Subsidence, fault/fracture reactivation or chemical degradation can all adversely affect well plug integrity leading to CO₂ leakages. Thus, monitoring of well plug integrity should be of high priority for CO₂ storage. There are materials whose properties change upon application of mechanical stress or chemical alterations that could be tested for well plug integrity sensing. One of them is cement with conductive fibres. In this paper we summarize SEP FARAWELL project results describing electrical response of conductive composites made of well cement and carbon nanofibers (CNFs) in response to load, carbonation, and water saturation changes. The results show that bulk resistivity of well cement/CNF composites changes upon application of the three stimuli mentioned above thus the material proves promising for monitoring applications.