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doi:10.2204/iodp.proc.311.105.2006

Operations

Hole U1327A

After completing LWD/MWD operations at Site U1326, the drill string was pulled back high enough to place the bit at a safe distance above the seafloor. We transited in dynamic positioning mode 8.5 nmi to Site U1327 (proposed Site CAS-01B; Collett et al., 2005). Hole U1327A was spudded at 1830 h on 23 September 2005, and the seafloor was tagged at 1321.1 meters below sea level (mbsl; 1333.0 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 optimize parameters for maintaining a 50 m/h rate of penetration (ROP) while maintaining a minimum circulation of 270 gpm. The LWD/MWD safety protocol was followed without incident (see in the "Methods" chapter) and required no corrective action. By 0815 h on 24 September, the hole reached the target total depth (TD) of 300 mbsf. The hole was displaced with weighted sepiolite mud, and the drill string was pulled clear of the seafloor in preparation for transiting to Site U1328.

Hole U1327B

Following a 9.2 nmi transit from Site U1329, we arrived at Site U1327 at 0415 h on 2 October 2005 (Fig. F9). We spudded Hole U1327B at 0855 h and returned a full core, which indicated we did not recover the mudline. We therefore terminated operations in Hole U1327B to obtain a mudline core from a new hole.

Hole U1327C

The bit was picked up 5 m and Hole U1327C was spudded without offsetting, with first core on deck at 0950 h on 2 October 2005. A 6.l m recovery for Core 1H, including the mudline, provided an estimated seafloor depth of 1304.5 mbsl (1315.4 mbrf). The hole was advanced to 92.9 mbsf (104% recovery) with the advanced piston corer (APC) system and to a TD of 300 mbsf with the XCB system (81% recovery). Seven temperature measurements were made, four with the Advanced Piston Corer Temperature tool, two with the Davis-Villinger Temperature-Pressure Probe, and one with the Davis-Villinger Temperature Probe (Table T1). Three PCS runs were made, which returned Cores 6P at 44.1 mbsf, 15P at 121.8 mbsf, and 24P at 197.3 mbsf. Core 6P was returned without pressure. After reaching TD, the hole was displaced with weighted mud, and the bit was pulled clear of the seafloor at 1545 h on 4 October, ending operations in Hole U1327C.

Hole U1327D

After completing operations in Hole U1327C, we offset 15 m to the northeast to spud a dedicated tool and logging hole with first core on deck at 1710 h on 4 October 2005. Two APC cores were taken to 16.4 mbsf for high-resolution sampling for pore water, gas, and microbiological analyses. The hole was washed to 83.0 mbsf and the first PCS run returned Core 3P without pressure. By 0240 h on 5 October, we had drilled to a depth of 124.3 mbsf in preparation for a run of the HRC pressure core system. The recorded ship heave had increased to >4.5 m and it was determined that it would be impossible to keep the HRC or any of the other pressure core systems on the bottom of the hole. Competing swells from the west and east caused ship heave conditions to worsen throughout the day. The heave conditions improved by 2245 h and preparations began to return to coring.

The HRC (Core 4E), XCB (Core 5X), and FPC (Core 6Y) systems were first deployed within a 16 m thick, high–electrical resistivity zone previously identified from the LWD/MWD logs (Table T1). The HRC was recovered under pressure, but during the transfer for P-wave velocity and X-ray scanning, the transfer system lost pressure. The first FPC core system fired prematurely (similar to the problem experienced in Hole U1329E) and recovered a sediment core without pressure. The hole was advanced by XCB coring to 155.1 mbsf, where the PCS was deployed and yielded a complete core under pressure (Core 10P). The hole was advanced by XCB coring to 170.5 mbsf, where the HRC was deployed with Core 12E and recovered sediments under pressure. The FPC was deployed at 203.3 mbsf and recovered Core 13Y under pressure. The hole was advanced by drilling to 217.7 mbsf, and the HRC was deployed and recovered a complete core under pressure (Core 14E). Two additional XCB cores (Cores 15X and 16X) were taken through the depth interval of the BSR. The hole was drilled to 246 mbsf where the PCS was deployed and recovered a complete pressurized core (Core 17P).

At 1256 h on 7 October, a helicopter arrived with the Canadian marine mammal observer and an IODP marine laboratory specialist. After unloading passengers and supplies, the helicopter departed at 1325 h. By 1615 h, Hole U1327D had been drilled to a TD of 300 mbsf, but adverse ship heave conditions (>3.0 m) were not conducive to logging. Rather than wait on weather, the time was used to condition the hole with a wiper trip and the bottom 20 m was reamed out and followed by a mud sweep. By 2330 h, the heave conditions had improved. The pipe was pulled up to logging depth and the triple combo tool string was rigged and lowered to 295.4 mbsf. The hole was logged without incident until near the top of the logging run when the combination of a large ship heave event (>3.0 m) and the oversized borehole damaged the density tool caliper arm. The damaged triple combo tool string was returned to the ship without further incident.

The VSP logging program in Hole U1327D began at 0720 h on the morning of 8 October with a required 1 h marine mammal observation period. After this period, we ramped up the firing pressure for the generator-injector (GI) air gun. At 1000 h, the VSP Well Seismic Tool (WST) reached TD at 276.4 mbsf and the VSP began. The WST was moved up the hole in 5 m increments and had completed 16 positions when, at ~136 mbsf, it was unable to clamp although the caliper log from the triple combo run showed that the hole should have been suitable for clamping. Suspecting that it had been damaged, we decided to pull the WST back to the ship for inspection. Unfortunately the tool became stuck and we were unable to pull it back into the drill pipe. Two attempts to clamp the logging wireline with Kinley crimpers were unsuccessful; however, the WST was worked back into the drill pipe and pulled to the surface by 2300 h. Operations in Hole U1327D ended at 0400 h on 10 October after the drill string was tripped back to the ship and the rotary table cleared.

Hole U1327E

Because of the critical nature of the downhole acoustic logging data to achieve the goals of the expedition, we decided to drill a dedicated wireline logging hole and to acquire additional PCS, HRC, and FPC pressure cores from several critical intervals not successfully cored in the previous holes at this site. The ship was offset 15 m to the northeast and Hole U1327E was spudded at 0850 h on 10 October 2005 as a special wireline logging and pressure core tools hole. The hole was started by drilling to 3.0 mbsf and then taking a single APC core for high-resolution geochemical and microbiological sampling. An earlier attempt to sample across the sulfate/methane interface (SMI) in Hole U1327C was unsuccessful, so Hole U1327E was an opportunity to sample the SMI. The hole was then advanced by drilling to 40.0 mbsf, where PCS Core 2P yielded a full, but unpressurized, core. The hole was advanced by drilling to 80.0 mbsf and a second PCS core (Core 3P) was acquired, this time with a full and pressurized core. The hole was drilled to 128.0 mbsf, where the HRC was deployed. Core 4E contained sediment but was unpressurized because the flapper valve did not completely seal. A deployment of the FPC was planned at 134.0 mbsf but was canceled because of growing ship heave conditions that exceeded 3.5 m near the end of the HRC deployment. Thus, we decided to drill Hole U1327E to the target TD of 300 mbsf, which was reached at 1630 h on 10 October. This completed pressure coring operations at Site U1327 with a total of thirteen pressure core deployments, of which nine were recovered under pressure (five PCS, three HRC, and one FPC).

Because of the continued high ship heave conditions throughout the day (ranging from 2.5 to 4.5 m) we decided to make only one logging run with a nonstandard, caliper-free tool string. The tool string included the Hostile Environment Gamma Ray Sonde (HNGS), Phasor Dual Induction Tool (DIT), and the Dipole Sonic Imager (DSI), which provide natural gamma ray, resistivity, and acoustic transit time data. The tool was lowered to 287 mbsf and logged to the setback drill pipe at 72 mbsf without incident. A short repeat pass of the lower 100 m was completed for quality control, and the tool string was returned to the surface. After rigging down logging, the bit was pulled clear of the seafloor at 0400 h on 11 October, ending operations at Site U1327.