Significant drilling challenges can exist when drilling in mature fields or in reservoirs that are subject to various geomechanical stress regimes associated with overpressure, tectonic stress, and depletion. Despite mitigation efforts to reduce stuck-pipe occurrences, drilling problems leading to stuck pipe still occur. When conventional techniques used to free the drillstring are ineffective, wireline logs are often run to determine the stuck depth of the drilling assembly and to release the pipe above the free point.
The traditional free-point (FP) logs used to determine the depth of stuck pipe are based on a measurement of strain when stress is applied to the pipe between two points. These measurements are taken at specific intervals and require the tool arms to firmly grip the pipe to prevent movement that could mask the strain measurement. This simple method is difficult to implement reliably. Because it depends on the skill of the specialist operator, pipe-recovery operations include "more art than science." A new technology, based on electromagnetic measurements, can now make a continuous FP log. The log consists of two passes, with and without stress applied to the pipe. By comparing the two responses, service company specialists and drilling engineers can interpret the log without the need for highly-experienced personnel.
This paper reviews several cases from the Middle East and provides information about the tool response in various parts of the drilling assembly. It also reviews pipe-recovery techniques that are recommended depending on the FP log response and the specific drilling assemblies, such as drill collar, drill pipe, crossovers, and jars. The pipe-recovery techniques discussed include explosive back-off techniques, explosive pipe severing, and various pipe cutters. The case study examples demonstrate the improved efficiency and reliability of determining stuck-pipe intervals and subsequent successful pipe recovery.