Transit to Site 1131

Because of long-period swell (~3 m high) and the resulting heave, which averaged 1.5 m with excursions over 2.0 m, operations in water depths less than 300 m were precluded. Thus, we proceeded to alternate Site GAB-08A. The 46-nmi transit required 4.6 hr at an average speed of 10.0 kt. A beacon was launched at 1338 hr on 16 November, initiating Site 1131. A second beacon was deployed, as required for shallow-water operations.

Hole 1131A

The ship was stabilized on position, and an APC/XCB BHA was run to the seafloor. Hole 1131A was spudded at 1605 hr on 16 November. The bit was positioned at 339 mbrf, and Core 1H recovered 3.39 m, indicating a water depth of 333.6 mbsl. APC coring advanced to 60.4 mbsf. Cores 3H–7H were oriented, and an Adara tool heat-flow measurement was made during Core 4H. A nonmagnetic cutting shoe and a steel 10-finger core catcher were run on Cores 3H, 5H, and 7H. Recovery of Core 7H required 70 kips overpull; therefore, APC coring was terminated in favor of the XCB system. H2S (86 ppm; headspace analysis) was detected in Core 4H (26.9 mbsf). H2S alert procedures were implemented, including use of breathing apparatus. H2S concentrations reached a maximum of 156,600 ppm in a vacutainer sample (359.6 mbsf), but ambient air readings remained below 10 ppm. No H2S was detected below Core 56X (>511.3 mbsf)

XCB coring advanced from 60.4 to 616.9 mbsf with 56.3% recovery. Recovery was minimal below 540.2 mbsf in presumed mixed chalk and chert, and five XCB hard-formation shoes were destroyed. Hydrocarbon gases up to C5 were detected beginning with Core 38X (338.3 mbsf), and the coring rate was controlled to allow proper gas monitoring. However, C2+ volumes were extremely low and subsequently diminished downhole; C1/C2 varied primarily as a function of methane fluctuation. Coring was terminated near the depth objective because of poor recovery in cherts.

Hole conditions appeared to be excellent, and the bit was pulled to 102 mbsf without a conditioning trip for logging. Logging tools were run in the following order (depths of penetration are included): (1) triple combo from 578 mbsf, 39 m off bottom, to the mudline in two passes; (2) FMS-Sonic from 573 mbsf to the end of pipe; and (3) WST tool from 567 mbsf to the end of pipe, recording eight check-shot stations. With an improving forecast and diminishing long-period swell, continued operations at Site 1131 were postponed for a return to Site 1129. After plugging the hole with mud, the drill string was retrieved, both beacons were recovered, and the rig was secured for transit at 1800 hr on 19 November, ending Hole 1131A.

Transit Back to Site 1131 (Hole 1131B)

The ship was moved in DP mode from Site 1129 back to Site 1131 to complete a second APC/XCB hole. The 2-nmi transit required 1 hr at 2 kt. A beacon was dropped at 0335 hr on 20 November, and the ship was positioned ~40 m north of Hole 1131A.

Hole 1131B

Hole 1131B was spudded at 0545 hr on 20 November. The bit was positioned at 342.0 mbrf, and Core 1H recovered 8.40 m, which indicated a water depth of 331.4 mbsl. APC coring advanced to 65.4 mbsf with 94.0% recovery. Cores 3H–7H were oriented and an Adara tool heat flow measurement was taken on Core 6H. The nonmagnetic shoe and flapper core catcher with a steel 10-finger core catcher were deployed on Cores 3H, 5H, and 7H. H2S was detected in Core 5H at 46 mbsf, and H2S alert procedures were implemented. XCB coring extended the hole from 65.4 to 105.8 mbsf with 83.3% recovery. A DVTP was deployed after Core 12X at 105.8 mbsf. The hole was plugged with mud, the beacon recovered, the rig secured for transit, and the vessel was under way for Site 1132 at 1730 hr, on 20 November.

To 182 Summary of Engineering and Drilling Operations for Site 1132

To 182 Table of Contents