Site 1143 (Proposed Site SCS-9)

After the hydrophones and thrusters were extended and the vessel located on position, the corrected precision depth recorder (PDR) depth referenced to the dual elevator stool (DES) was obtained and indicated 2782.4 m. The advanced hydraulic piston corer (APC) and extended core barrel ( XCB) bottom-hole assembly was made up and deployed. During the tripping of the drill string, the vessels TRUONG SA-12 and SOUTH TUG 156 remained visible until nightfall. At 2200 hr, the SOUTH TUG 156 moved away from the site and was lost to radar. The TRUONG SA-12 lingered in the area and kept us company until the site was abandoned.

Hole 1143A

Hole 1143A was spudded with the APC at 0330 hr on 4 March. Piston coring advanced to 190.4 meters below seafloor (mbsf) with excellent recovery (102%). The cores were oriented starting with Core 3H. APC refusal resulted when Core 21H did not allow a full stroke into the indurated sediment. The hole was deepened with the XCB to the depth approved by the Pollution Prevention and Safety Panel (PPSP), 400 mbsf. The average recovery for the entire hole was 95%. Only a trace amount of methane was measured at concentrations <10 ppm. No higher hydrocarbons were detected. Downhole temperature measurements were obtained using the APC temperature tool (APCT) before the retrieval of Cores 4H, 7H, 11H, and 16H, at 31, 60, 98, and 145 mbsf, respectively. A temperature gradient of 84°C/km was calculated from these data.

Three wireline logging runs were planned. After the hole was flushed with a 30-bbl mud treatment, it was displaced with an additional 100 bbl of sepiolite. During the pipe trip to the logging depth of 86 mbsf, the driller did not observe any increased weight caused by a restriction in the size of the hole. The first log was conducted with the triple combo tool suite. Results of the first run determined that the hole was in generally good condition below 210 mbsf and provided satisfactory results below this depth. Above 210 mbsf, there were alternating swollen clays and washouts as large as 45 cm. Several tight spots were measured, and a 3-hr wiper trip was performed the next tool string was deployed. Later deployment of the Formation MicroScanner (FMS) and sonic tool combination encountered an obstruction in the hole at <20 m below the bit. Several attempts to pass this obstruction proved fruitless. The mud pumps were used in an attempt to hydraulically push the tool suite past the hole constriction, but this maneuver gained only about 3 m. A moderate overpull was required to free the tool from the mud. After recovering the logging tool, the drill pipe was lowered past the obstruction to a depth of 163 mbsf and then pulled back with the bit positioned at 134 mbsf. The second deployment of the FMS required well over an hour for the logging tool to be worked through the clays. The hole was logged in one pass from 380 to ~158 mbsf. The planned deployment of the geological high-resolution magnetic tool (GHMT) was canceled. The logging equipment was disassembled, and the drill string was pulled clear of the seafloor.

Hole 1143B

The vessel was offset 20 m east for Hole 1143B. Before coring was begun in this hole, a bottom-water temperature measurement was obtained with the APCT. At 0130 hr on 7 March, Hole 1143B was spudded with the APC. The inferred seafloor depth from the mudline recovery was 2783.5 m. After advancing to 175.4 mbsf, APC refusal resulted when Core 19H did not effect a full stroke. The hole was deepened with nine XCB cores to 258.2 mbsf, which was considered the target depth for this hole. All piston cores were oriented starting with Core 3H. The bit cleared the seafloor at 0010 hr on 8 March. The average recovery for the hole was 95%.

Hole 1143C

The vessel was offset 10 m east, and the last hole of the site was spudded with the APC at 0100 hr on 8 March. The seafloor depth calculated from a presumed mudline recovery of 9.4 m was 2784.5 m, but hole-to-hole correlation showed that the top of the core was actually 4 m below the mudline. The hole was APC cored to 177.4 mbsf. The piston cores were oriented starting with Core 3H. The hole was deepened with the XCB to 286 mbsf when approval was received to extend the depth of the hole to 500 mbsf. XCB coring continued until 2315 hr on 9 March when the last core (54X) was recovered from 500 mbsf. The average recovery for the hole was 96%. The average recovery for the site was 95%.

The drill pipe was pulled out of the hole and cleared the seafloor at 0045 hr on 10 March. As the drill string was being recovered, both primary and backup beacons were retrieved, and the hydrophones and thrusters were retracted. The bit was at the rotary table at 0530 hr, and by 0545 hr the drilling equipment was secured for the voyage to the next site. At 0655 hr, a submarine periscope was clearly visible as it crossed our bow and pursued a reciprocal course that brought it within one-quarter mile of the starboard side of our vessel. The JOIDES Resolution cleared Dangerous Grounds at 1300 hr at 10°0´N, 113°17.1´E.

Operations-Site Survey

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