OPERATIONS

Leg 185 ended and Leg 186 officially began with the first line ashore at 2018 hr on Monday 14 June 1999 in Yokohama, Japan (all times are reported in local ship time, which is Universal Time Coordinated + 9 hr). Because of the large amount of casing to be used during Leg 186, the riser (casing) hold had to be emptied and rearranged. The following casing was loaded: 8 joints of 20-in casing (94 lb/ft; ~13.86 m/joint; total length = ~111 m), 83 joints of 16-in casing (75 lb/ft; ~12.70 m/joint; total length = ~1054 m), 156 joints of 10-in casing (40.5 lb/ft; ~12.98 m/joint; total length = ~2024 m), and 179 joints of 4-in casing (10.5 lb/ft; ~11.64 m/joint; total length = ~2084 m).

Port call activities included a number of tours, which were managed by the Ocean Research Institute (ORI) and the Japan Marine Science and Technology Center (JAMSTEC), and a reception hosted the evening of 16 June by the ORI. All Ocean Drilling Program/Texas A&M University (ODP/TAMU) and Sedco employees plus scientists from Legs 185 and 186 were invited. The reception was attended by many dignitaries, including consulate personnel from various member countries and many Japanese scientists involved with the future of ocean drilling, particularly through the OD21 initiative. In the end, port call extended a day longer than anticipated owing in part to a strike by the Yokohama dock workers that fortunately extended only through the weekend. The extra time during the weekend was used to assemble the battery packs for the borehole instruments and to replace the aft crane boom on the port side of the ship.

The JOIDES Resolution departed Yokohama at 1145 hr on Monday 21 June. Traveling the 363-nmi transit at an average speed of 11.9 kt, we arrived at Site 1150 (JT-1C) at 1830 hr on 22 June and began drilling operations. The initial beacon deployed was released and recovered because it was not as close to the desired site location as we would have liked. A second beacon was released at 2047 hr and, because we would be spending a significant number of days at this site, a back-up beacon was deployed at 2145 hr.

Hole 1150A was spudded at 0530 hr on 23 June using the advanced hydraulic piston corer/extended core barrel (APC/XCB) coring system in a water depth of 2680.8 m (2692.2 meters below rig floor [mbrf]). Cores 3H through 12H were oriented using the Tensor tool. Three successful Adara temperature tool (Adara) measurements were taken on Core 3H at 26.7 mbsf, Core 6H at 55.2 mbsf, and Core 9H at 83.7 mbsf. An overpull of 60,000 lb after the third Adara run led us to cancel any further Adara measurements.

Biogenic methane was present throughout the APC-cored interval, which led us to cease APC coring. The gas content coupled with the tendency of the APC to pack material fully in the core liners resulted in the explosive ruptures of the core liners for Cores 10H and 11H. We believed rotary coring would alleviate some of the propensity of the liners to explode even if the gas remained present in the cores; therefore, APC coring was terminated before reaching any typical refusal point. Overpull at that point was running a mere 15,000-20,000 lb for non-Adara deployments.

XCB coring began with Core 13X and continued through Core 76X to a depth of 722.6 mbsf. Methane gas continued to be present in the cores at the same level; however, there was only a single exploding core liner incident with the XCB and this occurred before we removed the liner from the core barrel. The Davis-Villinger temperature probe (DVTP) was successfully run twice during the XCB-cored interval: once after Core 13X at 116.4 mbsf and again after Core 18X at 164.4 mbsf. The three Adara data points, two DVTP data points, and the single Adara mudline temperature measurement combined to define a very linear temperature gradient of 28.9°C/km. There were no hydrocarbon safety issues while drilling this hole. Biogenic methane was present for the entire section cored with head space data averaging around 3% methane and 1-2 ppm ethane.

Hole 1150A was cored to a total depth (TD) of 722.6 mbsf. The maximum drill string deployed was 3414.8 mbrf. A total of 566.40 m of core was recovered for an average of 78.4% of the section cored. Penetration rates varied from 99 m/hr in the surface sediments to just under 20 m/hr at TD. The entire XCB-cored section of 610.4 m was cored at an average rate of penetration (ROP) of 35.1 m/hr. Of the 112.2 m penetrated with the APC system, 118.25 m of core was recovered (105.4% recovery), and, of the 610.4 m penetrated with the XCB system, 448.15 m (73.4%) of core was recovered (Table T1, also available in ASCII format). The APC/XCB drilling assembly was pulled clear of the mudline at 1415 hr on Saturday 26 June 1999.