Eight holes were drilled at Site 1251 (Table T1), under good weather conditions. Wind speed was 0-11 kt, gusting to 21 kt; seas were 3-7 ft; swell was 5-10 ft; and the prevailing sea-surface current was from the north at ~0.5 kt. Hole 1251A was drilled without coring on 22-23 July 2002 to obtain the initial LWD data for this site, which was followed by coring Holes 1251B-1251G on 26 July-1 August. As planned before the leg, during this period the Sonne and Atlantis conducted their scheduled research programs at the Hydrate Ridge summit. The Ewing was scheduled to arrive on location on 12 August to assist with the seismic profiling experiments. We returned to Site 1251 on 16 August to drill Hole 1251H for wireline logging and seismic profiling.
Hole 1251A was spudded at Site 1245 on 22 July to obtain the initial LWD data for this site (see "Downhole Logging"). Drilling proceeded at a moderate rate of penetration (ROP) of 25 m/hr and 15 strokes per minute (spm) circulation to mitigate formation washout below seafloor. No real-time measurement-while-drilling (MWD) or nuclear magnetic resonance (NMR) data were recorded over this interval. The ROP was increased to 50 m/hr at a bit depth of 30 mbsf and maintained to a total depth (TD) of 380 mbsf. As a result, the vertical resolution of the Resisitivity-at-the-Bit (RAB) tool images is ~10 cm and the NMR spectral data may have lower quality. The LWD string included the RAB tool, MWD, Nuclear Magnetic Resonance (NMR-MRP) tool, and Vision Neutron Density (VND) tool. The LWD operations involved changing the Azimuthal Density Neutron (ADN) tool and replacing the RAB battery prior to running pipe to the seafloor. LWD tools were pulled to the rig floor at 0900 hr on 23 July for a total bit run of 18 hr.
Hole 1251B was APC cored to 194.6 mbsf, with an average core recovery of 80.6%. At this depth, lithified sediments significantly reduced the penetration of the bit, prompting a change to XCB coring, which proceeded to 445.1 mbsf, with an average recovery of 85.5%. Hole 1251B was terminated ahead of the proposed depth of 620 mbsf, as it appeared that the primary scientific objectives had been achieved and hole stability was deteriorating.
In addition to the XCB coring, all pressure coring tools (PCS, FPC, and HRC) were used in this hole. Three PCS cores were retrieved under pressure from Hole 1251B, two above the BSR depth (which at Site 1251 is at ~200 mbsf), and one below the BSR. One FPC and one HRC were also retrieved from this hole. Whirl-Paks and perfluorocarbon tracer (PFT) were used in 13 of these cores, and the Drill String Accelerator (DSA) tool was run twice in this hole (see Table T4 in the "Leg 204 Summary" chapter). Other special tools in Hole 1251B included four APCT tool and two DVTPP runs.
Hole 1251C was spudded at 0330 hr on 30 July with the APC. When the APC failed to advance, we attempted to recover an XCB core across the same interval, which recovered 5.45 m. The hole was terminated at 17.6 mbsf.
Hole 1251D was spudded at 0715 hr on 30 July, using the XCB to collect the first three cores to 26.9 mbsf, with a recovery of 40%-90%. These cores were followed by APC to refusal at 173.4 mbsf and subsequent XCB coring to 226.5 mbsf. Whirl-Paks and PFT were used on microbiology Cores 204-1251D-22X, 25X, and 26X.
A series of special tools were deployed in Hole 1251D. Temperature measurements were obtained with one run of the APCT tool and two runs of the DVTPP. Four PCS cores were retrieved to complete the depth profile at this site, and deployments of each of the FPC and HRC were conducted as engineering tests for these pressure tools (see "Downhole Tools and Pressure Coring").
Holes 1251E through 1251F were each cored by APC to 9.5 mbsf for high-density sampling. Whirl-Paks and PFT were used only in Hole 1251E (see Table T3 in the "Leg 204 Summary" chapter). No special tools were used in these holes.
Hole 1251G was washed to 2.5 mbsf before one APC core was taken for special sampling of turbidite layers. The hole was then washed down to 20 mbsf, where an additional PCS was deployed (Table T18).
Hole 1251H was drilled to a depth of 445 mbsf as a dedicated hole for wireline logging using separate runs of the triple combination (triple combo) tool string (Temperature/Acceleration/Pressure [TAP] tool/Dual Induction Tool [DIT]/Hostile Environment Litho-Density Tool [HLDT]/Accelerator Porosity Sonde [APS]/Hostile Environment Gamma Ray Sonde [HNGS]/Inline Checkshot Tool [QSST]) and the Formation MicroScanner (FMS)-sonic (FMS/Dipole Sonic Imager [DSI]/Scintillation Gamma Ray Tool [SGT]) tool strings. Vertical and offset vertical seismic profiles were attempted with the JOIDES Resolution and the Ewing (located at an offset of ~700 m) alternating shots (see "Downhole Logging").