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doi:10.2204/iodp.proc.340.103.2013

Operations

Transit to Site U1393

After a 347 nmi transit from San Juan, Puerto Rico, that included an unplanned diversion to a rendezvous point just off the coast of Antigua to pick up a Siem Offshore crew member, the vessel arrived at the first expedition location, Site U1393. The vessel stabilized over Site U1393 at 1800 h on 6 March 2012. All times reported in this volume are given in ship local time, which was Universal Time Coordinated (UTC) – 4 h. The position reference was a combination of GPS signals and a single acoustic beacon. The positioning beacon was deployed at 0112 h on 7 March. It was recovered at 1527 h on 8 March at the conclusion of operations at Site U1393.

Site U1393

For the Site U1393 coring summary, see Table T1.

Hole U1393A

The bottom-hole assembly (BHA) was picked up and drifted, followed by running drill pipe to bottom. There were no problems running the drill string into the hole. Prior to the start of coring operations, a seafloor survey was conducted to site a favorable location to spud possible holes at the site. A clockwise spiral on a 20 m center was conducted. The survey identified a large megablock southeast of the preliminary location, and our first hole was adjusted to 20 m west of the original location. The subsea camera system failed at the end of the survey, and the vibration-isolated television frame with camera was pulled back to the surface. A single hole was then cored at this site. Hole U1393A was cored to 47.5 meters below seafloor (mbsf) with an 11 inch diameter advanced piston corer (APC)/extended core barrel (XCB) BHA that was 135.75 m long. A mudline core with the APC established a water depth of 926 mbsl. The second APC core bounced off the formation, and we changed to the XCB bit. Coring conditions proved to be very difficult, and recovery was very poor. Coring was terminated at 0515 h on 8 March 2012 when the XCB failed, leaving part of the XCB core barrel in the hole. The remainder of the XCB BHA was retrieved by wireline. The drill string was then pulled clear of the seafloor, the top drive was set back, and the drill string was tripped to the surface while the vessel began its 5.3 nmi transit to Site U1394. At 1025 h on 8 March the bit cleared the rotary table, ending Hole U1393A. The depth objective at the site was 250 mbsf, and this appeared to be unreachable with the tools planned for the site. Overall core recovery for Site U1393 was 11% of the 47.5 m cored. Two APC cores were attempted before refusal was reached. Core recovery was 4.36 m for the 4.4 m advance. An additional five XCB cores were attempted to 47.5 mbsf with only 1.05 m of core recovered. Most of the recovery consisted of small-diameter pieces of volcanic debris. Two holes were originally planned for this site, but because of the poor drilling conditions, the second hole was canceled.

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