Previous   |    Next

doi:10.2204/iodp.proc.330.107.2012

Operations

The 91 nmi transit to Site U1376 on Burton Guyot was accomplished at an average speed of 10.1 kt. The vessel was on station at 2300 h on 26 January 2011 (all times are New Zealand Daylight Time, Universal Time Coordinated [UTC] + 13 h). A three-stand rotary core barrel coring assembly was made up with a new C-4 coring bit and mechanical bit release and deployed. The vibration-isolated television (VIT) frame was launched before the hole was spudded in order to observe the character of the seafloor and the tagging of the bit on the bottom. A rocky seabed devoid of any appreciable sediment was observed on the VIT camera. From 0300 to 0515 h on 27 January a VIT survey was undertaken to look for an area containing sediment that could support a free-fall funnel installation (should one be later required). After 2.3 h, a spot with a very small sediment pond was located.

The driller tagged the seafloor at 1514.3 meters below rig floor (mbrf; 1503.3 meters below sea level [mbsl]), 5.5 m deeper than the corrected precision depth recorder measurement, and Hole U1376A was spudded at 0705 h on 27 January (Table T1). Operations continued without incident until 1530 h on 30 January, when coring was suspended at 86.8 mbsf to change the bit, which had accumulated 72.4 rotating hours. Because of the absence of sediment cover needed to support a free-fall funnel installation, a hole marker composed of a weight, tether, and single glass float was placed on the seafloor from the VIT frame via an acoustic release. The bit cleared the seafloor at 1800 h on 30 January and was on deck at 2215 h. A new Type C-4 bit and a refurbished mechanical bit release were made up to the bottom-hole assembly and deployed.

After the drill string was tripped to 1131 mbrf, the VIT frame was deployed and both were run to 1512 mbrf. The open hole was successfully reentered at 0435 h on 31 January. Coring resumed in Hole U1376A at 0630 h and continued without incident until the allocated coring time for this site expired at 1630 h on 2 February, leaving the hole at a final depth of 182.8 mbsf. The total average recovery for the hole was 74.5%, with an excellent average recovery in basement of 75.6%. The average rate of penetration in basement was 1.8 m/h. In accordance with expedition routine, nonmagnetic core barrels were used to obtain all cores. One microsphere packet was deployed in the core catcher of Core 330-U1376A-19R at 144.4 mbsf. Prior to the recovery of all cores except 2R, 3R, and 10R, 20 bbl mud sweeps were circulated.

Following a wiper trip that displaced the borehole with 42 bbl of heavy (10.5 ppg) mud, the bit was released at the bottom of the hole. The end of pipe was positioned at the logging depth of 80.4 mbsf by 2115 h on 2 February.

The first log was conducted with the triple combination tool string, which logged the hole up from 181 mbsf in two passes. After this tool string was recovered at 0350 h on 3 February, a second logging run was conducted with the third-party Göttingen Borehole Magnetometer tool. The last tool string deployed was the Formation MicroScanner-sonic, which was run between 1335 and 1655 h and made two passes in the open hole.

The drill string was recovered when logging was concluded, and the end of the pipe cleared the seafloor at 1850 h on 3 February. Once the drill collars were set back in the derrick, the beacon was recovered, and the drilling equipment was secured, the vessel departed at 2200 h for the 391 nmi voyage to the final Site U1377 (prospectus Site LOUI-4B) on Hadar Guyot, the youngest seamount targeted during Expedition 330. The total time on Hole U1376A was 191 h, or 8.0 days (Fig. F3).

Top of page   |    Previous   |    Next