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doi:10.2204/iodp.proc.320321.110.2010

Operations

Unless otherwise noted, times are local ship time, which was Pacific Standard Time (Universal Time Coordinated [UTC] – 7 h).

Transit to Site U1338

The transit to Site U1338 (proposed Site PEAT-8D) began at 1625 h on 2 June 2009, after recovering all thrusters/hydrophones and shifting control to cruise mode on the bridge. The transit was uneventful. In relatively mild seas and moderate wind the vessel averaged 10.5 kt for the 324 nmi transit. Thrusters and hydrophones were lowered and at 2320 h on 3 June, and control was switched from bridge cruise mode to dynamic positioning mode.

Site U1338

As at the previous site, the position reference was a combination of the Global Positioning System and an acoustic beacon on the seafloor. At 0005 h on 4 June, the same positioning beacon (FSI BAP-547, SN 1010, 15.0 kHz, 208 dB) used on the previous site was deployed. Four holes were drilled at this site using the APC/XCB coring systems. The last hole (U1338D) was limited to only three cores to be used in the labs for processing demonstrations during the upcoming expedition. Hole U1338B was wireline logged using the triple combo, FMS-sonic, and VSI tool strings. The APCT-3 was deployed in Holes U1338A and U1338C. Overall recovery for Site U1338, using both APC and XCB coring systems, was 97%. Basement was recovered in two of the four holes drilled at the site.

Hole U1338A

Rig floor operations commenced at 2330 h on 3 June. The top drive was picked up, and the drill string was spaced out, placing the bit at 4196.0 m drilling depth below rig floor (DRF) or 3.4 m above the "corrected" precision depth recorder depth of 4199.4 m DRF. The first APC barrel recovered was empty, so the bit was lowered an additional 5.0 m to 4201.0 m DRF and another attempt for mudline was made. This time the barrel obviously contacted the mudline; however, the small amount of core recovered was completely destroyed by the sloshing of the water column above. For the third attempt, the bit was repositioned an additional 3.0 m lower at 4204.0 m DRF. This time the barrel recovered 2.7 m of core, and an official seafloor depth was established at 4210.8 m DRF. APC coring continued through Core 24H to 221.2 m DSF using nonmagnetic coring assemblies and the FlexIt core orientation system. Overpull forces of 100,000 lb and the need to drillover the APC barrel led to the use of steel core barrels beginning with Core 25H. APC coring was eventually ended with Core 26H at 240.2 m DSF. All barrels fully stroked; however, the last three cores (24H through 26H) required 100,000 lb overpull and drillover to extract from the formation. Five successful APCT-3 measurements were obtained with Cores 5H, 7H, 9H, 11H, and 13H at 40.7, 59.7, 78.7, 97.7, and 116.7 m DSF, respectively. Average core recovery for the APC was 105%. XCB coring continued with Cores 27X through 44X, achieving an average recovery of 56%. A small piece of basement was recovered in the core catcher of Core 44X, to a total depth of 4620.8 m DRF for Hole U1338A (410.0 m DSF). XCB coring performance was highly variable, with some cores achieving near 100% recovery and others recovering <1% and sometimes zero. In the areas of little or no recovery there were diatom-rich intervals and/or porcellanite (baby chert) found in the surrounding cores. Just as in the earlier holes at Site U1337, these proved to be the troublesome areas for recovery and were targeted in later Holes U1338B and U1338C in an attempt to complete recovery for the section. Overall recovery for Hole U1338A, using both APC and XCB coring systems, was 84%. The drill string was pulled clear of the seafloor at 1900 h on 6 June, officially ending operations in Hole U1338A.

Hole U1338B

Operations in Hole U1338B officially began when the drill string cleared the seafloor at 1900 h on 6 June. The drilling line was slipped and cut while the ship was offset 20 m west of Hole U1338A. With the drill bit placed at 4208.0 m DRF to optimize the core gaps between holes, the APC was deployed and once again a water core was recovered. After checking the drill string tally it was discovered that the driller was off by a single joint of drill pipe. This single was added to the string, and with the bit positioned at the same depth, Hole U1338B was spudded at 2330 h on 6 June. Core recovery with APC Core 1H determined the seafloor depth as 4209.9 m DRF. Except for a short drilled interval of 2.5 m to adjust the core breaks, continuous APC coring continued through Core 20H to 188.1 m DSF using the FlexIt core orientation system and nonmagnetic coring assemblies. FlexIt and steel core barrels were then used as APC coring continued through Core 42H to 387.4 m DSF. At the time of drilling, Hole U1338B was the second deepest APC hole in ODP and IODP history, surpassing the 378.0 m DSF depth achieved during Expedition 320 in Hole U1335B. APC extraction overpull reached 100,000 lb on 19 of the 42 cores taken, including the last 11 APC cores. Full stroke was achieved on all but two cores (30H and 31H) from 276.1 to 282.9 m DSF. Coincidentally, the shear pressure for these two cores was inconclusive, so this may have been the reason for the incomplete stroke. Drillover was required on 13 cores, including the last 10. Except for Cores 30H and 31H, shear pressures were consistent throughout the coring process at 2800 psi. Core liner issues were relatively mild. The Core 1H liner was broken, the liner for Core 13H was cracked at the bottom, and the liner of Core 42H was recovered split. Average core recovery for the APC was 104%. Coring continued with three XCB cores (43X through 45X) to 416.1 m DSF. Basement was recovered in Core 45X. Overall the XCB coring system recovered 58% of the interval penetrated. Recovery was problematic with the XCB, and the material that was recovered suffered significantly from the typical "biscuiting" effect. Total depth of Hole U1338B was 4626.0 m DRF (416.1 m DSF). Overall core recovery using both APC and XCB coring systems was 101%. In preparation for downhole logging, the hole was swept clean with 50 bbl of attapulgite mud. A wiper trip revealed no ledges or bridges, and no fill was identified at total depth. The lockable float valve was locked open, the hole was displaced with heavy 10.5 ppg logging mud, and the end of pipe was placed at 84.7 m DSF. Rig-up for wireline logging began at 2145 h on 9 June. Three logging strings were deployed. The triple combo and the FMS-sonic tool reached total hole depth of 416.1 m WSF. The third and final logging string consisted of the VSI. This tool reached total hole depth and shooting stations were conducted at ~15 m stations. All VSP logging was done during daylight hours to conform with established IODP mammal watch protocols, including a preshooting mammal watch and soft start procedures for the air guns. Wireline logging in Hole U1338B was successfully concluded and all logging equipment was rigged down by 1615 h on 11 June. The drill string was pulled back until the bit cleared the seafloor at 1655 h on 11 June, officially ending operations in Hole U1338B.

Hole U1338C

Operations in Hole U1338C officially began when the drill string cleared the seafloor at 1655 h on 11 June. The ship was offset 20 m to the west of Hole U1338B. The drilling line was slipped and cut and the Rigwatch drawworks/block position encoder was recalibrated. The drill bit was placed at 4204 m DRF (same as Hole U1338A) to optimize the core gaps with respect to Holes U1338A and U1338B. The APC was deployed, and, for the third time at this site, a water core was recovered. Because 2.7 m of core had been recovered in Hole U1338A with the bit at the same depth, it was suspected that vessel heave, induced by a large long-period swell from the south, had impacted bit depth by being on the high side of the swell when the core was taken. The drill string was lowered another 3 m, and the bit was repositioned at 4207.0 m DRF. Hole U1338C was spudded at 2135 h on 11 June. The 3.83 m of core recovery with APC Core 1H determined the seafloor depth at 4212.7 m DRF. APC coring continued through Core 21H to 189.8 m DSF using the FlexIt core orientation system and nonmagnetic coring assemblies. FlexIt and steel core barrels were then used as APC coring continued through Core 44H to 396.9 m DSF. Core 45H appeared to fully stroke, and drillover was required to extract it from the formation. Retrieval was delayed because a bent core barrel initially prevented the core barrel from being pulled back up the drill string. Repeated jarring with the wireline jars eventually sheared the overshot pin. The sinker bar string was recovered, and the FlexIt core orientation tool was removed. The sinker bar assembly was redeployed, and the core barrel was immediately recovered without any further incident. It was deemed prudent at this point to not use the FlexIt tool for the remainder of coring. Coring continued through Core 47H to a total depth of 414.4 m DSF, at the time setting a new depth record for the APC. This surpassed the standing record set on 7 August 1992 (ODP Leg 145) when the APC penetrated to a total depth of 398.3 m DSF in Hole 882A. APC extraction overpull reached 100,000 lb on Cores 22H through 47H. Drillover prior to removal from the formation was required for 22 cores and full stroke was achieved on all but 4 cores (31H and 45H through 47H). Shear pressures were consistent throughout the coring process at 2800 psi. Core liner issues were relatively mild with only two cores recovered with imploded liners (Cores 10H and 12H), although several barrels were bent during the coring process and several piston rods had to be adjusted and repinned because of overtorqued threads that caused misalignment of the rod grooves. Overall core recovery for the APC was 104%. The drill string was pulled clear of the seafloor at 2015 h on 14 June, officially ending operations in Hole U1338C.

Hole U1338D

Operations in Hole U1338D officially began when the drill string cleared the seafloor at 2015 h on 14 June. The ship was offset 20 m to the west of Hole U1338C. This hole was primarily planned to recover a few "instructional" lab demonstration cores to be used during Expedition 323 scientist orientation. Hole U1338D was spudded at 2150 h on 14 June, and the 4.89 m recovered with Core 1H established a seafloor depth of 4212.6 m DSF. Three APC cores were cut to 23.9 m DSF. APC core recovery was 104%. Official APC/XCB coring totals for Site U1338 include 139 total cores, 1261.9 m penetrated, and 1220.41 m recovered, for 97% recovery. The coring tools were secured and the drill string was pulled clear of the seafloor at 0145 h on 15 June. The top drive was set back, the knobby joints were laid out, and the drill string was recovered. Once the drill collars were laid out and the rig floor was secured for transit, control was transferred from dynamic positioning mode to the bridge. The ship was placed in cruise mode at 1030 h on 15 June for the anticipated 7.6 day (1811 nmi) transit to San Diego, California.

Transit to San Diego

The vessel departed Site U1338 ~4.5 h ahead of the projected schedule on a northerly course. The 1811 nmi transit from Site U1338 to the San Diego pilot station required 7.3 days at an average speed of 10.5 kt. Expedition 321, the second and final segment of the PEAT program, was officially concluded at 1715 h on 22 June with the first line ashore Berth 10-7 at the Tenth Avenue Marine Terminal, San Diego Harbor.

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