Before the last core in Hole 1271B was retrieved, we decided not to displace the hole with sepiolite (as routine prior to logging) because of concerns with hole stability. The core recovery had been low throughout the coring operations (recovery = ~19.7%), and most of the recovered cores were fragmented pieces suggesting potential unstable hole conditions. Our thought was that displacing the volume of the hole with mud might fracture the formation and loosen more rock fragments that could potentially cause a risk to the logging tool strings. The operational strategy was to acquire logging data as quickly as possible to minimize any risks to the tools, starting with the triple combination (triple combo) geophysical tool string and followed by the Formation MicroScanner-sonic tool string.
Drilling operations reached a total depth of 104.5 mbsf, and the mechanical bit release was used to leave the rotary core barrel bit at the bottom of the hole. Shortly after releasing the bit, high torque, loss of circulation, and drag conditions were experienced while placing the BHA at logging depth. Ultimately, the BHA was placed at a logging depth of 3627 meters below rig floor, or 31 mbsf.
After the triple combo was rigged up, a conflict between the telemetry cartridge, the Accelerator Porosity Sonde (APS), and the Dual Induction–Phasor Resistivity Tool (DIT-E) was encountered. The telemetry cartridge was displaying a low voltage signal and both the APS and the DIT-E were displaying conflicting signals. Exchanging telemetry cartridges resolved the conflict.
Sea conditions were calm with ~1-m heave while the triple combo tool string was being deployed. During deployment of the first tool string, an obstruction was encountered at a logging depth of 35 mbsf, or 4 m below the end of the BHA. Three unsuccessful attempts were made to get past this obstruction by raising and lowering the tool string. In order to test the possibility that the bit had not released (since the distance to the apparent obstruction was so small), the tool string was raised until it was inside the pipe and the drill string was raised ~10 m. On lowering the tool string, the same total wireline length was deployed before the tool reached the obstruction, indicating the tool was several meters beyond the end of the pipe; thus, the bit must have been released. After three more attempts to pass the obstruction, logging operations were terminated. The wireline logging operations took ~7.5 hr from rig-up to rig-down.