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doi:10.2204/iodp.proc.340.107.2013

Operations

Transit to Site U1397

After a 113.0 nmi transit from Site U1396 in cruise mode, the vessel arrived at Site U1397. The vessel stabilized over Site U1397 at 1945 h on 18 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 2010 h on 18 March. At the end of operations at Site U1397, the beacon was sent an acoustic command to release. The beacon was retrieved at 2200 h on 23 March.

Site U1397

Site U1397 consists of two holes (Table T1). The original plan called for two holes to be cored to ~314 mbsf. The first hole was successfully cored and was terminated at a total depth of 265.5 mbsf. The second hole was cored to a depth of 253.5 mbsf. Logging plans originally included a vertical seismic profile (VSP) experiment, but this was canceled when the diameter of the hole proved too large to use the Versatile Seismic Imager (VSI). Sixty-six cores were recorded for the site. There were two drilled intervals. The advanced piston corer (APC) was deployed 35 times. The cored interval with the APC was 225.7 mbsf with a recovery of 226.17 m of core (100.2%). The extended core barrel (XCB) was deployed 31 times. The cored interval with the XCB was 284.1 mbsf with a recovery of only 49.49 m of core (17%). Overall recovery for Site U1397 was 54%. Hole U1395B was successfully logged with both the Formation MicroScanner (FMS)-sonic and triple combination (triple combo) logging strings. Total time spent at Site U1397 was 127.0 h.

Hole U1397A

The vessel arrived at Site U1397 and was in position at 1950 h on 18 March 2012. After an uneventful pipe trip, the top drive was picked up and the bit was spaced out to spud Hole U1397A. The initial corrected precision depth recorder (PDR) reading was 2489.5 meters below rig floor (mbrf). The bit was initially set at 2484.5 mbrf, and the hole was spudded at 0422 h on 19 March. The seafloor depth was calculated from the length of the first core (0.3 m) to be 2493.7 mbrf (2482.2 mbsl). Orientation was performed with the FlexIt tool on the first nine cores. Nonmagnetic core barrels were used for APC coring for Cores 340-U1397A-1H through 17H. Advanced piston corer temperature tool (APCT-3) measurements were taken on Cores 5H through 7H. An APCT-3 measurement was attempted on Core 3H, but the electronics failed and data could not be downloaded. The majority of the piston cores were incomplete strokes, and the hole was advanced by recovery. After reaching refusal with the APC, the XCB was deployed, and XCB coring continued to 265.5 mbsf. Coring was terminated after Core 35X, short of the 314 mbsf target depth, because of time constraints. Difficult hole conditions contributed to lengthening the coring time required to advance the hole. Nineteen piston cores were taken over a 117.3 m interval with a total recovery of 118.1 m of core. Fifteen XCB cores were taken over a 143.80 m interval. Only 26.10 m were recovered (18%), and the hole was terminated at 265.5 mbsf. Overall core recovery for Hole U1397A was 55%. After the completion of XCB coring, the drill string was pulled back with the top drive still installed, and the bit cleared the seafloor at 0055 h on 21 March, ending Hole U1397A. Total time spent in Hole U1397A was 53.25 h.

Hole U1397B

After clearing the seafloor from Hole U1397A, the vessel was offset 20 m east and Hole U1397B was spudded at 0252 h on 21 March 2012. The seafloor depth was calculated from the length of the first core to be 2492.9 mbrf (2481.4 mbsl). Nonmagnetic core barrels were used for all cores. APCT-3 measurements were taken on Cores 340-U1397B-3H, 4H, and 7H. Similar to Hole U1397A, most of the piston cores were partial strokes and the hole was advanced by recovery. After reaching refusal with the APC on Core 17H, the XCB was deployed, and XCB coring continued to 265.5 mbsf. Coring was terminated after Core 33X short of the 314 mbsf target depth because of time constraints. Difficult hole conditions lengthened the coring time required to advance the hole. Seventeen piston cores were taken over a 108.4 m interval with a total recovery of 108.07 m of core. Sixteen XCB cores were taken over a 140.30 m interval. Only 23.39 m were recovered (17%), and the hole was terminated at 253.5 mbsf. Overall core recovery for Hole U1397B was 53%. At the conclusion of coring, Hole U1397B was conditioned with a 30 bbl high-viscosity mud sweep. Hole conditions at the end of coring were very bad, and the top drive had to be left in to pull back. Both rotation and circulation were required while the drill string was pulled back to ~220 mbsf. The hole was not displaced with logging mud because the mud would have simply pumped away during the necessary circulation. The drill string was then pulled back to 2645 mbrf, the top drive was set back, knobbies were added to the drill string, the bit was set at 81.6 mbsf, and the pipe was hung from the blocks. The Schlumberger wireline was then rigged up for logging and the triple combo was deployed. Because of hole conditions, we decided to not include the two nuclear sources in the triple combo tool string. Two successful passes were made to a depth of 221.1 mbsf. The tool string was then pulled back to surface and rigged down. The FMS-sonic tool string was then picked up. The tool was run to 210.3 mbsf and two passes were made over the length of the open hole. The second pass was only able to reach ~205 mbsf because of bridging or infilling in the hole. The tools were then recovered to the surface and rigged down. At the beginning of the last logging run, the driller noted overpull on the drill string of 70 klbs. After the FMS-sonic was laid out, the top drive was picked up and, using rotation and overpull, the drill string was worked free from the formation. The knobbies were then laid out, the top drive was set back, and the drill string was pulled from the hole. The bit cleared the rotary table at 0240 h, and the drill floor was secured at 0245 h on 24 March, ending Site U1397 and Hole U1397B. The vessel then proceeded underway to Site U1398. Total time spent on Hole U1397B was 73.75 h.

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