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doi:10.2204/iodp.proc.311.106.2006

Operations

Hole U1328A

After completing LWD/MWD operations at Site U1327, we transited in dynamic positioning (DP) mode ~1.9 nmi to Site U1328 (proposed Site CAS-06A; Collett et al., 2005). The drill string was tripped to the seafloor and the vibration-isolated television (VIT) camera was deployed for a survey of the seabed to ensure that no chemosynthetic communities would be disturbed by operations. Hole U1328A was spudded at 1555 h on 24 September 2005, with an estimated seafloor depth of 1268.1 meters below sea level (mbsl; 1279.0 meters below rig floor [mbrf]). The hole was initiated with a controlled spud-in with 100 gallons per minute (gpm) circulation and 10–15 rpm rotation. At 10 mbsf, top drive rotation was increased to 40 rpm and then again to 60 rpm at 29 mbsf to maintain a 50 m/h rate of penetration (ROP) with a minimum circulation of 270 gpm. This controlled ramp-up was conducted to maintain hole stability and avoid blowing out the top of the hole. During drilling of Hole U1328A, no corrective action was required based on the safety protocol (see "Downhole logging" in the "Methods" chapter). At 0415 h on 25 September, the hole reached the total depth (TD) of 300 mbsf. After displacing the hole with weighted sepiolite mud, the drill string was tripped back to the ship, with the bit clearing the rotary table at 1100 h, ending operations in Hole U1328A. During the pipe trip, the ship moved 9.9 nmi in DP mode to Site U1329.

Hole U1328B

After completing operations at Site U1327, the ship was relocated ~1.9 nmi to Site U1328 and the VIT camera was deployed to inspect the seafloor for the occurrence of chemosynthetic communities. We conducted a 120 m camera survey along the proposed coring transect across the vent site (Fig. F10). We did not observe any living clam colonies; however, widespread carbonate outcrops were observed. Before spudding the first hole, we deployed the water-sampling temperature probe (WSTP) to collect a bottom water sample. Hole U1328B was spudded with the advanced piston corer (APC) system at 1310 h on October 11 2005. Recovery of 4.8 m of sediment indicated a successful mudline core. The estimated mudline seafloor depth and the visual observation of the seafloor tag during the camera survey agree within 0.3 m. Table T1 reports the visual seafloor tag depth of 1267.8 mbsl.

Core recovery in the second APC core was only 1.7 m with an incomplete stroke. The next core was taken with the XCB system to the target depth of the first PCS deployment (Core 311-U1328B-4P) at 14.5 mbsf. The APC core taken after Core 311-U1328B-4P was again an incomplete stroke, with only 1.89 m of core recovered. We switched back to XCB coring and advanced the hole to the target depth for the second PCS deployment (Core 311-U1328B-7P) at 26.0 mbsf. Both PCS deployments yielded core under pressure. Three additional APC cores were taken to 56.5 mbsf. Operations were suspended at 0315 h on 12 October because of strong winds and severe ship heave conditions. By 0745 h, conditions had deteriorated to a level (heave >8 m) that necessitated pulling out of Hole U1238B. Six APC, three XCB, and two PCS cores were collected in Hole U1328B with an average recovery of 73% (Table T1).

Hole U1328C

After waiting on the weather for 16 h, sea conditions improved enough to allow drilling and coring operations to continue. We offset the ship by 15 m from the location of Hole U1328B, spudded Hole U1328C at 2030 h on 12 October 2005, and drilled to the maximum depth of Hole U1328B (56.5 mbsf) to resume APC coring.

Hole U1328C was advanced to 75.5 mbsf with three APC cores, after which we switched to the XCB coring system and deepened the hole to 92.0 mbsf. A pressurized PCS core (311-U1328C-5P) was recovered from this depth and the rest of the hole was cored with the XCB system to 300 mbsf. The total average recovery for Hole U1328C was 80.3%. Temperature measurements were made on Cores 311-U1328C-2H, 3H, and 6H with either the advanced piston corer temperature (APCT) tool or the third-generation advanced piston corer temperature (APCT-3) tool (Table T1). Temperature measurements with the Davis-Villinger Temperature-Pressure Probe were carried out at 148.9 and 197.1 mbsf, but the data from both runs were degraded by an apparent electronic problem in the tool.

After reaching a TD of 300 mbsf at 1000 h on 14 October, the hole was prepared for wireline logging with a short wiper trip. At 1650 h, the triple combo tool string was lowered to 294 mbsf. The uphole triple combo run was completed without incident and the tool was back on the rig floor at 1940 h. Next, the FMS-sonic tool string was deployed at 2140 h, reaching the same depth as the triple combo logging run. Two passes of the FMS-sonic tool string were completed without incident and the tool was back on deck at 0245 h on 15 October. After rigging up for the VSP, the marine mammal watch began at 0730 h, followed by the 30 min ramp up of the generator-injector (GI) air gun at 0830 h. The VSP began at 0900 h with the first clamping position at 286 mbsf. The VSP was run successfully to the shallowest clamping position of 106 mbsf. Shallower positions were too noisy as a result of interference with the drill pipe, which had been set back to 76 mbsf. After pulling the tool back to the rig floor and rigging down logging, the drill string was pulled clear of the seafloor at 1615 h, ending operations in Hole U1328C.

Hole U1328D

The ship was offset 35 m to Hole U1328D for a high-resolution combined microbiology and geochemistry study of the SMI. The first two deployments of the APC system resulted in bent core barrels, so we switched to the XCB coring system. Hole U1328D was spudded with an XCB core at 1955 h on 15 October 2005, followed by a second XCB core, and then the deployment of the FPC at 14.0 mbsf. The FPC did not recover any core. The drill string was pulled clear of the seafloor at 2345 h, ending operations in Hole U1328D.

Hole U1328E

After offsetting 50 m from Hole U1328D, Hole U1328E was spudded with the XCB system at 0040 h on 16 October 2005. The primary focus of Hole U1328E was to recover pressure cores, with XCB spot cores from the top 40 mbsf. LWD data and previous scientific coring suggest that this interval contains the highest gas hydrate concentrations at this site. XCB coring advanced the hole to 8.5 mbsf, where the HRC was deployed with Core 311-U1328E-3E but did not return under pressure. Following an XCB core, a PCS core was deployed at 15.1 mbsf with Core 311-U1328E-5P but did not return pressurized. Another XCB core was taken and then the FPC was deployed with Core 311-U1328E-7Y, but it also failed to return a core under pressure. Two XCB cores advanced the hole to 46.0 mbsf, followed by deployment of the center bit to drill the hole to 92.0 mbsf. PCS Core 311-U1328E-10P was deployed and returned under pressure. A Davis-Villinger Temperature Probe (DVTP) temperature measurement followed. The center bit was redeployed and the hole was drilled to 197.0 mbsf. The FPC pressure core system was deployed with Core 311-U1328E-11Y, but it improperly retracted into the autoclave and failed to yield a pressurized core. An additional DVTP survey was conducted at 198.0 mbsf after the last FPC core run. The hole was then drilled to 215.3 mbsf, where the HRC was deployed (Core 311-U1328E-12E) but recovered without pressure. The hole was then drilled to 233.0 mbsf for a PCS run (Core 311-U1328E-13P), which returned with a pressurized core (Table T1). With ship heave conditions increasing to 7 m, the planned DVTP deployment at the bottom of the hole was cancelled, ending operations in the hole at 235.0 mbsf. After the hole was displaced with weighted mud, the drill string was tripped to the surface and cleared from the seafloor, ending operations at Site U1328 at 0715 h on 17 October.

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