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doi:10.2204/iodp.proc.342.105.2014

Operations

All times are local ship time (Universal Time Coordinated – 2.5 h). See Table T1 for coring summary.

Hole U1404A summary

• Latitude: 40°00.7997′N
• Longitude: 51°48.5990′W
• Water depth below sea level (m): 4742.3
• Date started: 1030 h, 20 June 2012
• Date finished: 2040 h, 22 June 2012
• Time on hole (days): 3.2
• Seafloor depth (m drilling depth below rig floor [DRF]): 4753.8
• Seafloor depth estimation method: mudline core
• Rig floor to sea level (m): 11.5
• Penetration depth (m drilling depth below seafloor [DSF]): 308.8
• Cored interval (m): 308.8
• Recovered length (m): 281.02
• Recovery (%): 91
• Total cores (number): 36
• Advanced piston corer (APC) cores (number): 32
• Extended core barrel (XCB) cores (number): 4
• Drilling system: 11 inch APC/XCB bit with 136.00 m bottom-hole assembly (BHA)
• Objective: core from seafloor to ~250 m DSF
• Result: target exceeded; objectives achieved

Hole U1404B summary

• Latitude: 40°00.7999′N
• Longitude: 51°48.5856′W
• Water depth below sea level (m): 4747.6
• Date started: 2255 h, 22 June 2012
• Date finished: 1310 h, 24 June 2012
• Time on hole (days): 1.7
• Seafloor depth (m DRF): 4759.1
• Seafloor depth estimation method: mudline core
• Rig floor to sea level (m): 11.5
• Penetration depth (m DSF): 228.7
• Cored interval (m): 228.7
• Recovered length (m): 228.04
• Recovery (%): 100
• Total cores (number): 27
• APC cores (number): 27
• Drilling system: 11 inch APC/XCB bit with 136.00 m BHA
• Objective: core from seafloor to ~250 m DSF
• Result: target and objectives achieved; problems with the core liners after achieving the main science objectives forced the abandonment Hole U1404B

Hole U1404C summary

• Latitude: 40°00.7890′N
• Longitude: 51°48.5857′W
• Water depth below sea level (m): 4747.5
• Date started: 1445 h, 24 June 2012
• Date finished: 1945 h, 24 June 2012
• Time on hole (days): 0.3
• Seafloor depth (m DRF): 4759.1
• Seafloor depth estimation method: Hole U1404B depth
• Rig floor to sea level (m): 11.6
• Penetration depth (m DSF): 44.5
• Cored interval (m): 28.5
• Recovered length (m): 28.98
• Recovery (%): 102
• Drilled interval (m): 16
• Drilled interval (number): 1
• Total cores (number): 3
• APC cores (number): 3
• Drilling system: 11 inch APC/XCB bit with 136.00 m BHA
• Objective: capture interval of science interest; deepen per direction
• Result: target likely overshot because of variable seafloor depth

Description

The vessel arrived at Site U1404 after a 4.2 nmi transit from Site U1403 and stabilized over Site U1404 at 1455 h on 19 June 2012. The plan for this site called for drilling three holes to a depth of ~250 m DSF. After completion of Holes U1404A and U1404B to 308.8 and 228.7 m DSF, respectively, Hole U1404C was drilled to 16 m DSF and then cored to 44.5 m DSF in an attempt to recapture a zone hypothesized to contain gas hydrate. The total time spent at Site U1404 was 124.75 h (5.2 days). The XCB was deployed four times, and the APC was deployed 62 times. The XCB-cored interval was 37.8 m with a recovery of 23.05 m (61.0% recovery). The APC-cored interval was 528 m with a recovery of 515 m (97.5% recovery). The overall recovery for Site U1403 was 95.1%.

Hole U1404A coring

The drill bit was spaced out to 4715 m drilling depth below rig floor (DRF) for the first attempt at a mudline core. The calculated precision depth recorder (PDR) depth for the site was 4718.4 m DRF. A mistake in the pipe tally resulted in an APC wireline run to ~4705 m DRF. The depth of the bit was repeatedly lowered until mudline was established at 4753.8 m DRF (4742.3 mbsl), which was 35.4 m below the PDR depth. Hole U1404A was spudded at 1030 h on 20 June. Three possible explanations for the discrepancy between the PDR depth and the drill pipe depth were offered:

1. Strong currents were causing the drill pipe to bend in an S-shape,

2. The acoustic signal was significantly affected by thermal or current layering in the water column, or

3. Seafloor bedforms caused local seafloor depth to vary considerably.

The second explanation is supported by the poor quality of the acoustic signal received from the acoustic beacon on the seafloor.

Cores 342-U1404A-1H through 32H were recovered using nonmagnetic core barrels and the FlexIT core orientation tool. The liner of Core 4H shattered, presumably from hitting a manganese nodule. Nodules as long as 10 cm were recovered in Core 1H, and others, perhaps even larger ones, may have been washed into the bottom of the hole. In Core 22H, the formation began to firm up, and the first partial stroke was recorded. Cores 22H through 32H were partial strokes, and the hole was advanced by recovery. The XCB was deployed for Cores 33X through 36X to a final depth of 308.8 m DSF. The drill bit cleared the seafloor at 2040 h on 22 June, ending Hole U1404A. Overall core recovery for Hole U1404A was 281.02 m for the 308.8 m interval cored (91% recovery). The total time spent on Hole U1404A was 77.75 h.

Hole U1404B coring

The vessel was offset 20 m east. The bit was spaced out to 4752.0 m DRF in an attempt to recover ~7–8 m of the mudline core. Hole U1404B was spudded at 2255 h on 22 June, and a 2.48 m mudline core established the seafloor depth at 4759.1 m DRF (4747.6 mbsl). Cores 342-U1404B-1H through 27H were recovered to a depth of 228.7 m DSF using nonmagnetic core barrels and the FlexIT core orientation tool. The liner of Core 7H returned shattered and collapsed for unknown reasons. Cores 21H through 27H were partial strokes, and the hole was advanced by recovery. Eight core liners either collapsed or broke, and three of those had to be pumped out of the core barrel with a high-pressure pump. The bit cleared the seafloor at 1310 h on 24 June, ending Hole U1404B. A total of 27 piston cores were taken over a 228.7 m interval with a total recovery of 228.04 m (100% recovery). The total time spent on Hole U1404B was 40.5 h.

Hole U1404C coring

The vessel was offset 20 m south. Hole U1404C was spudded at 1445 h on 24 June and was drilled to a depth of 16 m DSF. The seafloor depth was assumed (perhaps incorrectly) to be the same as that for Hole U1404B (4759.1 m DRF; 4747.6 mbsl). Cores 342-U1404C-2H through 4H were recovered to a final depth of 44.5 m DSF. The total advance was 28.5 m, with 28.98 m of core recovered (102% recovery). The bit cleared the seafloor at 1945 h on 24 June, ending Hole U1404C. The drill floor was secured, and the vessel began moving to Site U1405 in dynamic positioning mode at a speed of 0.9 kt. The total time spent on Hole U1404C was 6.5 h.

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