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doi:10.2204/iodp.proc.308.107.2006

Summary of operations

Hole U1323A

A summary of operations in Hole U1323A can be found in Table T1, and a more comprehensive description of MWD/LWD operations can be found in “Downhole measurements.” A beacon was deployed at Site U1323 at 1854 h on 15 June 2005. Hole U1323A was spudded at 2025 h as the driller tagged the seafloor at 1271.0 meters below rig floor (mbrf) (precision depth recorder = 1278.4 mbrf). The vibration-isolated television (VIT) camera was recovered and MWD drilling advanced to 206 mbsf. A sand layer, ~1.5 m in thickness (as interpreted from natural gamma ray resistance data from the MWD bit), was detected at 204 mbsf. Simultaneously, a 150 psi jump over background drilling pressure in the pressure-while-drilling (PWD) log was observed. A residual backpressure of 150 psi was also observed by the driller when he shut down the mud pumps. We pumped 50 bbl of 10.5 ppg mud in the hole and noted that the backpressure went to zero. When this mud was displaced with seawater, the overpressure returned. The pipe was filled with 110 bbl of 10.5 ppg mud and a wiper trip was made to 51.1 mbsf and back to 204.6 mbsf. The overpressure remained, and it was decided to continue to drill ahead at a very low rate of penetration (ROP), gradually increasing to 30 m/h, with “pumping and dumping” 10.5 ppg mud. At 242 mbsf, a rapid drop in gamma radiation, suggestive of a second sand interval, was observed in the data. At this point, it was decided that to maximize the amount of science and to conserve mud, we should move to the location of Site U1324 (BP Block MC 897) and plug and abandon Hole U1323A. We displaced the hole with 73 bbl of 13.5 ppg mud. The VIT camera was deployed and the top of the hole was observed to confirm that there was no flow. A free-fall funnel was deployed and inspected again with the VIT camera. We reentered Hole U1323A at 0300 h on 17 June. An obstruction or hole collapse at 140 mbsf prevented further penetration into the hole, and Hole U1323A was displaced with 31.8 bbl of 14.0 ppg cement that applied a cement plug from 140 to 40 mbsf. The drill string was then recovered, clearing the seafloor at 0550 h and the rotary table at 1010 h on 17 June.

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