The 103-nmi transit to a newly approved location for Site 1263 (proposed Site WALV-8E) was accomplished at an average speed of 10.8 kt. The vessel was positioned over the new site by 1515 hr on 29 March 2003. The corrected precision depth recorder estimate for the water depth was ambiguous, within a range of 67 m. As a result, we tagged the seafloor with the bit and then picked up the drill string ~5 m to obtain a mudline core.
The Drilling Sensor Sub (DSS), a measurement-while-drilling tool for measuring and recording drilling-dynamic data near the bit, was deployed for the first time in Hole 1263A. The first model of the DSS is a memory tool, which is 10 ft long with an 8
-in outside diameter and a 4
-in through-bore to allow for core retrieval. It is made of nonmagnetic drill collar material and is positioned in the bottom-hole assembly (BHA) above the outer core barrel. The sensor's electronics and batteries are packaged in the collar wall. The tool measures weight on bit (WOB), torque on bit, annulus pressure, bore pressure, and annulus temperature. The sub was designed to Ocean Drilling Program (ODP) specifications and manufactured by APS Technology.
Four holes were drilled at Site 1263. Coring intervals, times, nominal recovery rates, core barrels that required drillover to be released from the sediment, and the deployments of the Advanced Piston Corer Temperature (APCT) tool, Tensor core orientation tool, and nonmagnetic core barrel are listed in Table T1.
After two failed attempts at initiating Hole 1263A resulted in empty core barrels, the driller tagged the seafloor again, this time at 2726 meters below rig floor (mbrf). A mudline core was retrieved, and the seafloor depth was estimated to be 2728.2 mbrf (2717.1 meters below sea level) based on the recovery of the first core. Piston coring advanced to 284.1 mbsf, where the formation became too indurated for the APC. The bit was advanced by recovery when incomplete strokes were achieved on Cores 208-1263A-25H and 31H. The hole was deepened with the XCB system to the target depth of 345.6 mbsf. Active heave compensation (AHC) was used during XCB coring. AHC was turned off when the WOB indication began increasing without driller input. The operations engineer reported that the AHC deviation remained small (±0.12 ft), whereas the cylinder force (WOB) continued to increase. The software running at the time was a version modified by Maritime Hydraulics (MH) with a velocity gain reduction and a valve overlap increase. At the next opportunity, another modified program from MH was loaded into the programmable logic controller. This software version only used the velocity gain reduction and appeared to improve performance. The AHC was used while coring Cores 208-1263A-34X, 35X, and 37X through 40X.
The hole was flushed with a 40-bbl sepiolite mud sweep and subsequently displaced with 120 bbl of sepiolite mud. The drill string was pulled back in the hole, and the bit was positioned at 82.2 mbsf for downhole logging operations. The first logging run with the triple combination (triple combo) tool string reached the bottom of the hole (347.0 mbsf). The lockable float valve closed during logging, and it required more than an hour of working the pump and logging winch controls before the tool was retracted into the drill string. The subsequent deployment of the Formation MicroScanner (FMS)-sonic tool string could not pass a bridge or tight spot at ~158 mbsf, and the instrument was recovered for a wiper trip. In a further attempt, the tool could not be lowered below 174 mbsf because of a constriction in the hole. A short logging run was made from 172 to 74 mbsf. Further logging plans were cancelled. The bit was pulled clear of the seafloor at 0125 hr on 2 April, and the vessel was offset 20 m north-northwest.
Hole 1263B was initiated at 0225 hr on 2 April and was drilled without coring to 46.0 mbsf. Coring with the APC advanced from 46.0 to 261.9 mbsf (214.8-m interval). A small interval from 196 to 197.2 mbsf was drilled to maintain a stratigraphic overlap with Hole 1263A. The APC achieved incomplete strokes on Cores 208-1263B-14H, 17H, 18H, and 19H, and the cores were advanced by recovery. The hole was deepened with the XCB from 261.8 to 338.5 mbsf. The uppermost part of the PETM interval was recovered in the core catcher of Core 208-1263B-28X (~284 mbsf). The recovery of this critical interval was compromised because of chert jammed in the core catcher. The AHC was online during the cutting of Cores 208-1263B-32X and 33X. The bit cleared the seafloor at 1330 hr on 3 April, and the vessel was offset 20 m south-southeast.
Hole 1263C was initiated at 1445 hr on 3 April, drilled without coring to 90.0 mbsf, spot-cored with the APC from 90.0 to 118.5 mbsf, drilled ahead to 193 mbsf, and cored from 193.0 to 285.7 mbsf. The last APC core (208-1263C-15H) contained the entire PETM clay layer. One XCB core advanced the hole to a total depth of 290.8 mbsf. Cores 208-1263C-7H, 14H, and 15H were advanced by recovery. The bit cleared the seafloor at 1830 hr on 4 April, and the vessel was offset 20 m south-southeast.
Hole 1263D was initiated at 1955 hr on 4 April and was drilled without coring to 272.0 mbsf. Cores 208-1263D-1H through 4H were obtained from the interval 272.0–286.6 mbsf. All cores were advanced by recovery, and another sample of the critical PETM boundary interval was successfully recovered.
The cored interval for the site was 778 m, and the recovered interval was 710 m (average nominal recovery = 91%). The total interval drilled without coring was 484 m.
Four downhole temperature measurements (Hole 1263A: 31–116 mbsf) and one bottom water temperature measurement (Hole 1263B) with the APCT yielded an initial temperature gradient estimate of 2.5°C/100 m.
The bit was pulled clear of the seafloor and positioned at 364 m above the seafloor. Site 1263 was abandoned at 1015 hr on 5 April, and the vessel was offset in dynamic positioning mode 3.5 nmi east to Site 1264.
