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doi:10.2204/iodp.proc.341.106.2014

Operations

Transit to Site U1420

After a 30 nmi transit from Site U1419 averaging 9.2 kt, the vessel arrived at the fourth expedition site. The vessel stabilized over Site U1420 at 0345 h (UTC – 8 h) on 14 July 2013, and the positioning beacon was deployed at 0400 h.

Hole U1420A

After lowering the thrusters and hydrophones, the vessel switched from cruise mode to dynamic positioning mode and drill floor activities began. The rotary core barrel (RCB) components for the bottom-hole assembly (BHA) were assembled and run to the seafloor. The top drive was then picked up. The camera system was deployed for a seafloor survey. Following the survey, at 0850 h the seafloor was tagged with the bit at 248.2 meters below sea level and the camera system was pulled back to the surface. Hole U1420A was spudded at 1045 h on 14 July 2013. Coring continued from Core 341-U1420A-1R through Core 78R (0–749.2 m drillers depth below seafloor [DSF]) (Table T1). Because of increasing torque on the drill string, a ~200 m wiper trip was completed, preceded by 50 bbl of mud. Coring continued from Core 79R through Core 106R (749.2–1020.8 m DSF). Recovery over the entire hole was problematic because of the presence of numerous large clasts that continually jammed the core catchers and prevented core recovery. A total of 106 rotary cores were taken over a 1020.8 m interval, with 139.91 m recovered (14%) (Fig. F4).

A total of 570 bbl of high-viscosity mud was used for hole cleaning during coring operations. At the completion of coring, the hole was cleaned by circulating 50 bbl of high-viscosity mud. The rotary shifting tool (RST) was run into the hole on wireline to release the bit for logging. While running in the RST, torque on the rotating drill string increased to 500 A. The tool was pulled back and removed. After some hole remediation, another 75 bbl sweep was pumped, and the end of pipe was pulled back to 981.2 m DSF. The RST tool was run into the hole again, and the bit was released in the hole at 983.6 m DSF. After another run of the RST to shift the mechanical bit release sleeve back into logging position, the hole was displaced with 450 bbl of 10.5 ppg mud for logging. After displacing the hole with mud, the end of the pipe was raised up to logging depth (93.3 m DSF).

A modified logging tool string termed the Sonic-induction tool string, measuring gamma ray, borehole diameter, sonic velocity, and resistivity, was run to 288 m wireline log depth below seafloor (WSF). The tool string was 44 m long. After repeated attempts to run the tool string deeper into the hole, the string was pulled back to the BHA and another pass to 288 m WSF was performed. After logging up with the final pass, the tool string entered and became stuck in the BHA. The Kinley crimper was then rigged up, the crimper was deployed, and the logging cable was crimped, securing the tools in the BHA. The Kinley cutter was then deployed, and the logging cable was cut and pulled back to surface. The drill string was then pulled back to surface, the logging tools removed from the BHA, and the BHA secured. The thrusters and hydrophones were pulled at 0100 h 22 July. Total time spent on Hole U1420A was 189.25 h.

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