Assessing Exploratory Borehole Seals With Electrical Geophysical Techniques

This paper describes how time domain reflectometry (TDR) and electrical resistivity<br>logging were used to examine the integrity of seals placed in exploratory boreholes. Laboratory<br>tests were conducted in PVC columns containing layers simulating sealants and defect materials.<br>TDR or resistivity probes were installed in the columns and used to log the materials in the<br>column. Column testing showed that the TDR method could be used to identify defect types and<br>sizes. However, conduction losses limited the useful length of the TDR probe to less than 3-m.<br>Resistivity logging proved more suitable and thus field tests were conducted with the resistivity<br>probes. Resistivity logs clearly delineated portions of a borehole seal that contained either<br>sealant or defect materials.