Operations at Site 1198 (proposed site CS-05A) began when a beacon was dropped precisely on site coordinates at 1636 hr on 7 February 2001. Because the strong current moved the beacon before it landed on the seafloor, the vessel was offset 150 m to the southeast of the original coordinates to compensate for the displacement. The precision depth recorder indicated a water depth of 322.2 m.
Hole 1198A was spudded with the advanced piston corer (APC) at 2030 hr on 7 February (Table T2 in the "Leg Summary" chapter; Tables T1, T2). The water depth determined from the drill string measurement and the recovered mudline was 319.4 m. Coring advanced to the APC refusal depth at 203.0 mbsf, and average recovery for this interval was 102.2%. Cores were oriented starting with Core 194-1198A-3H. Downhole temperature measurements were attempted at 33.5, 62.0, 90.5, 119.0, 147.5, 176.0, and 203.0 mbsf.
Subsequent coring with the extended core barrel (XCB) deepened the hole to 251.5 m. The first XCB core had 29% recovery, and the subsequent four cores had zero recovery. Based on the experience at Site 1197 with XCB coring in the corresponding seismic stratigraphic interval (Megasequence C), the hole was abandoned in favor of a new hole to be cored with the rotary core barrel (RCB).
The vessel was offset 20 m east of Hole 1198A. Hole 1198B was spudded with the RCB at 2125 hr on 8 February. After drilling ahead with a center bit to 195.7 mbsf, coring resumed and deepened the hole 4 m into acoustic basement to a total depth of 522.6 mbsf. During the process, the drill string became stuck after cutting Core 194-1198B-6R (243.6 to 253.3 mbsf) and had to be worked free by pulling up to 220 kilopounds (kips). During the working of the stuck drill pipe, circulation was maintained, with a maximum pump pressure of 800 psi and a mud pump output of 450 gal/min or 90 strokes/min. To reduce the potential for further hole problems, coring was interrupted twice to make a wiper trip from 385.1 to 183.0 mbsf and from 397.6 to 385.1 mbsf, and the annulus was flushed frequently with sepiolite flushes.
Average recovery for the interval 195.7-359.1 mbsf (Cores 194-1198B-1R through 17R) was 9.98 m, or 6.1%. Recovery for the interval 359.1-522.6 mbsf (Cores 194-1198B-18R through 34R) was 65.2%. The average recovery for the entire hole was 35.7%.
After the last core was recovered, the hole was flushed and displaced with sepiolite, the bit was released on bottom, and the bit was pulled back to 91.8 mbsf in preparation for logging.
Only one pass with the triple combination tool (triple combo) was made in the upper portion of the open hole. The tool was unable to descend below 235.5 mbsf because of a narrowing hole diameter caused by the collapse of the upper part of the hole (presumably the interval poorly recovered in the cores). While attempts were made to move the tool past the tight spot, the hole diameter narrowed down to ~4 in and trapped the triple combo tool string. After the tool was worked free, the hole was logged up from 231 mbsf to the seafloor. Above 192 mbsf the hole was found to be dramatically enlarged, reflected by a maximum opening of the caliper to >17 in. It was decided not to make any further logging runs because of the deteriorating hole condition.
The logging equipment was rigged down, and the drilling assembly was tripped to the surface. The beacon failed to release from the tether. The vessel departed at 0430 hr on 11 February, ending operations at Site 1198 and returning to Site 1196.