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doi:10.2204/iodp.proc.308.104.2006

Summary of operations

Hole U1320A

A summary of operations in Hole U1320A can be found in Table T1. The JOIDES Resolution arrived at Site U1320 on the evening of 7 June 2005, and a beacon was dropped at 0040 h on 8 June. The vibration-isolated television (VIT) camera was launched and the drill string lowered to 1469.6 meters below rig floor (mbrf), where the seafloor was observed. When what seemed to be a man-made object (possibly a plastic bag) was observed under the bit, the vessel was offset 5 m north. After the driller tagged the seafloor at 1479.4 mbrf, he raised the bit to 1475.4 mbrf in preparation for spudding. Hole U1320A was spudded at 0420 h on 8 June. Recovery in the first core established the seafloor depth at 1480.4 mbrf, or 4.0 m shallower than the corrected precision depth recorder depth. Advanced piston corer (APC) coring advanced to 69.4 mbsf, where a thick sandy layer prevented further penetration with the APC. Because sediments at the top of the hole were predominately sandy, it was considered unsuitable for deployment of the T2P probe. Coring continued with the extended core barrel (XCB) to 126.3 mbsf (Core 15X), where a clay-rich interval was identified. The T2P probe was deployed for the third time during the expedition, this time with a thicker tip. The probe landed in the bottom of the hole for 45 min while a minimum circulation of 10 spm (60 gpm) was maintained. On this occasion, the probe was recovered with a slightly bent probe tip. Temperature and pressure measurements were successfully recorded.

XCB coring resumed and advanced to 203.4 mbsf (Core 23X), where a dedicated coring line trip was utilized to obtain a DVTPP temperature measurement at the bottom of the hole. After one more XCB core was obtained to deepen the hole to 213.0 mbsf, coring was again stopped for another T2P run. The T2P probe was deployed for the fourth time at 213.0 mbsf. For this run, the bottom-hole assembly (BHA) was placed only 1 m above the bottom of the hole, allowing better centering of the probe and possibly responsible for the tip of the T2P retaining its shape on this run. XCB coring resumed and the hole was deepened from 213.0 to 289.9 mbsf (Core 32X), where another DVTPP bottom hole temperature measurement was attempted. Coring concluded when one final XCB core deepened the hole to 299.6 mbsf. Because the scientific objectives for this hole were realized, it was not necessary to continue to the original projected depth of 340 mbsf. The APC cored 69.4 m with an average recovery of 101.9%. The cores were oriented starting with Core 4H, and fluorescent microspheres were deployed in all APC core catchers. Nonmagnetic hardware was used for all piston cores. The XCB penetrated 230.2 m and recovered 180.2 m for an average recovery of 78.3%. The total cored interval was 299.6 m with an average recovery of 83.7%. While coring was concluding in Hole U1320A, an oilfield supply boat (Emily G) arrived at 0415 h on 10 June and quickly discharged to our vessel the MWD drilling hardware and one Anadrill engineer (David Domalakes) via eight crane lifts. The vessel departed at 0520 h. Consonant with the protocol for arriving passengers, David Domalakes was provided with a health, safety, and environmental orientation by the Chief Mate. After these formalities were concluded, David joined his colleague, Kelvin Hoong (already aboard), as they began to unpack, assemble, and test the MWD hardware.

Downhole logging

In preparation for logging, the hole was flushed with a 50 bbl high-viscosity mud sweep followed by a wiper trip to 56.7 mbsf and back to bottom. After circulation of another 50 bbl sepiolite mud sweep, the hole was displaced with 96 bbl of logging mud. The bit was then pulled back to the logging depth of 62.5 mbsf.

Downhole logging of Hole U1320A was undertaken with three tool strings: the triple combo, FMS-sonic, and WST. All tools reached the bottom of the hole and the logs obtained were good. A contact between the turbidite fan sediments and the stiffer hemipelagic mud unit was clearly identified at 174 mbsf. WST measurements were undertaken, but in accordance with the Integrated Ocean Drilling Program (IODP) Marine Mammal Safety protocol, these operations were interrupted when a bottle-nosed dolphin was spotted 5 m from the vessel. After no more marine mammal sightings were reported for 45 min, the generator-injector (GI) gun was soft-started in accordance with protocol and 12 WST stations were completed without further incident. Once the logging equipment was rigged down, the VIT camera was deployed and the hole was observed as the drill string was pulled clear of the seafloor at 1930 h on 10 June 2005. As expected, logging mud quickly obstructed the view and the camera was promptly recovered. After the bit cleared the rotary table at 2245 h, attention was directed to make up the MWD drilling assembly. Before that occurred, the drill crew performed the routine slipping and cutting of 115 ft of drilling line.

Hole U1320B

A summary of operations in Hole U1320B can be found in Table T2. In accordance with the drilling plan, MWD augmented the coring and downhole logging data set at the Brazos-Trinity Basin IV sites. These sites served as a reference location for physical and chemical properties. MWD data provide information throughout the drilling depth on physical properties and are used to test spatial variations in rock properties associated with the flow-focusing model. MWD tools deployed in Hole U1320B include the GeoVision Resistivity (GVR) tool and Azimuthal Density Neutron (ADN) tool, and measurements included pressure (annular pressure while drilling [APWD]). The GVR provided azimuthal resistivity images of the borehole and gamma ray measurements, the ADN provided azimuthal borehole-compensated formation density, neutron porosity, and photoelectric factor (PEF) measurements, and APWD provided measurements of annulus pressure for identifying potential shallow flow and overpressure conditions. The MWD drilling array described above was made into a complete BHA by the addition of a 9⅞ inch Security M44NF mill tooth bit, a crossover sub to five controlled-length drill collars, a tapered drill collar, six joints of 5½ inch drill pipe, and a crossover sub. The total length of the BHA was 144.8 m. The trip to the seafloor was interrupted at 288 mbrf to function test the assembly with pump and rotation. The VIT camera was also deployed with the drill string. Hole U1320B was spudded at 0915 h on 11 June 2005, when the driller observed (via the TV monitor) the bit contacting the seafloor at a depth of 1485.0 mbrf. After washing in the bit to 14.9 mbsf, the VIT camera was retrieved. The MWD drilling program was initiated and continued at an average rate of penetration (ROP) of 25.4 m/h until the depth objective of 320.0 mbsf was attainted at 0325 h on 12 June. The bit was then pulled out of the hole and cleared the seafloor at 0520 h on 12 June. After the drill string was positioned 250 m above the seafloor, the vessel was offset 2.3 nmi on a bearing of 202° in dynamic positioning mode back to Site U1319. This move was accomplished at an average speed of 0.9 kt.

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