Ultrasonic Nondestructive Testing Method for Evaluation of Annular Seals

Drilling boreholes is common practice in geotechnical and geoenvironmental investigations and in various other ex­ ploration, testing, and monitoring appli­ cations. When a casing is placed in a borehole an annular space is created be­ tween the casing and the surrounding soil. If not properly sealed, this annular space can be a potential path for trans­ port of contaminants in the subsurface environment. Cross-contamination due to mixing of clean and contaminated groundwater can occur (Fig. 1). A poor annular seal can also result in loss of groundwater. There exist a number of methods to evaluate the integrity of annular seals. The most common methods used for in situ evaluation of seals around casings are: water level monitoring, pressure testing, and cement logging (Driscoll 1986). Two other less frequently used methods for evaluating cement seals are temperature logging and radioactive logging (Driscoll1986). A summary of existing in situ seal evaluation methods and their advantages and disadvantages is presented in Table 1. The limitations of the existing meth­ ods (Table 1) indicate that there is need for a simple, yet sensitive testing method to evaluate the wide range of commonly used casings and sealants. The method should also allow for re­ petitive testing after seal placement to monitor the performance of a seal over time. For this reason, a nondestructive testing method that uses ultrasonic prin­ ciples was developed.