Earth & Environmental Sciences

Wellbore integrity is one of the most critical factors for CO2 storage, subsurface resource extraction, and waste disposal. Wellbore integrity monitoring is challenging due to the general inaccessibility and high cost of well-logging operation in complex subsurface conditions. In this study, we tested a novel non-invasive approach for wellbore-integrity assessment based on time-domain reflectometry (TDR) method. With this method, a high-frequency electromagnetic pulse is sent into the borehole casing, and the reflected signals due to integrity-related impedance anomalies are recorded at the wellhead, providing rapid borehole integrity diagnosis without downhole deployment. Laboratory, numerical, and field experiments were conducted to prove the feasibility of this approach. The laboratory experiments with coaxial cable, resembling the typical wellbore, showed clear reflected signals from both of the damaged section and the end of the cable. Numerical sensitivity tests indicated that the TDR response is affected by the changes of the material in the borehole, including infilled fluids. Our field trial was conducted on an oil well (with a depth of 240 m) in the central valley region of southern California. The TDR records showed a clear reflection that matched both the calculated two-way travel time from the bottom of the borehole, as well as the numerical simulation. Our results suggested the feasibility of the TDR method for quick assessment of wellbore integrity based on wellhead only deployment.