161 Preliminary Report
OPERATIONS
Site 979
(Proposed site Alb-3C)
The original proposed site Alb-3A site was situated <0.5 nmi from the reported location of a telecommunications cable, and drilling there was not permitted. Prior to arriving on site, we received permission to offset and drill about 0.75 nmi north of the cable at proposed site Alb-3C. After the 63 nmi transit to Site 979 (5.5 hr; 11.45 nmi/hr), we deployed two beacons at 0745 and 0945 hr, 21 June, respectively. Hole 979A was located at 35°43.427'N, 3°12.353'W. The elevation of the DES above sea level was 11.90 m for Hole 979A.
Hole 979A
We used the same APC/XCB BHA at this site as at all other APC/XCB sites during this leg. We spudded Hole 979A at 1730 hr, 21 June. Core 161-979A-1H was taken with the bit at 1066.0 mbrf and recovered 1.46 m; therefore, the seafloor was defined to be at 1062.1 mbsl. Cores 161-979A-1H to -15H were taken to 134.5 mbsf and recovered 140.42 m (104.42%). Cores were oriented from Core 161-979A-3H, and ADARA temperature measurements were taken during Cores 161-979A-3H, -6H, and -9H.
Cores 161-979A-11H, -14H, and -15H were partial strokes, and we terminated APC coring after Core 161-979A-15H. The cores contained significant amounts of gas, and small holes were drilled into the liners prior to cutting them into sections to minimize gas expansion. All of the cores expanded against the inside wall of the APC core barrel, making visible contact ring marks on the lower part of the liner once it was extruded. Cores 161-979A-11H, -14H, and -15H, which were partial strokes, become stuck in the inner core barrel and had to be pulled out with a winch.
XCB Cores 161-979A-16X to -62X were taken from 138.3 to 580.9 mbsf (1208.5 to 1654.9 mbrf, respectively) and recovered 442.69 m (99.17%). Despite the expansive nature of the sediment, XCB recovery was very good, although the cores were quite biscuited. Coring parameters were 10,000 to 25,000 lb WOB and 50 to 70 rpm with circulation rates of 30 to 45 spm at 200 to 500 psi. The hole was terminated because there was insufficient time remaining to penetrate to 600 mbsf and also log the hole. Overall APC/XCB recovery for Hole 979A was 100.4%.
The maximum methane gas detected in the APC cores was 29,757 ppm (Core 161-979A-7H), and high methane concentrations near the seafloor were due to biogenic processes and did not present any safety problems. The maximum concentration of hydrocarbons from the headspace analysis occurred in Core 161-979A-31X, where the following contents were reported in (ppm); C1:37,130, C2:17, and C3: 13. C1/C2 ratios remained relatively constant with depth below Core 161-979A-26X, ranging from 700 to 1000.
We conditioned the hole for logging with a wiper trip to 79 mbsf (1153 mbrf). Three tight sections of hole were observed at 447, 494, and 528 mbsf (1516, 1568, and 1602 mbrf, respectively), and no fill was encountered in the bottom of the hole. The pipe was pulled back to 79 mbsf for logging. The quad-combo log was run into the hole, but met a bridge at 246 mbsf (1320 mbrf). We decided to log this part of the hole before moving the pipe down to attempt logging deeper in the hole. The caliper data in the APC and XCB portions of the hole were quite different, with the APC section being much more in gauge than the XCB section. This was also seen in Hole 977A.
After the upper portion of the hole was logged with the quad-combo, we removed the tool from the hole and lowered the pipe to 277 mbsf (1351 mbrf). When the tool was run back into the
hole, it encountered numerous tight sections and had to be worked down the hole to 464 mbsf (1538 mbrf) until no further advance could be made. We then logged from 464 to 251 mbsf (1538 to 1325 mbrf, respectively). Caliper data indicated that the hole was moderately washed-out with few continuous sections of hole in gauge. After completing the quad-combo logs, there was not enough time remaining to attempt the FMS log or to move the pipe lower in an attempt to log the lowermost 100 m of hole. Logging was completed and the tools rigged down by 2400 hr, 24 June.
The pipe was raised to 79 mbsf (1153 mbrf) and 63 bbl (200 sacks) of cement was pumped
into the hole prior to abandoning the hole. The bit cleared the seafloor at 0200 hr, 25 June. We circulated seawater through the pipe to clean any remaining cement residue before tripping back to the ship. While tripping out of the hole, the inner diameter of the pipe was coated with rust-inhibitor.
The bit cleared the rig floor at 0600 hr, 25 June. The backup beacon was recovered at 0230 hr, 25 June, while the drill string was being retrieved. The primary beacon would not release, despite the installation and testing of a new release mechanism immediately prior to deploying it at this site. The ship was secured for transit and departed at 0715 hr, 25 June, for a rendezvous with the M/V RESE, approximately 20 nmi off of Malaga, Spain. The transfer occurred at approximately 1400 hr, 25 June.
TRANSIT TO LEITH, SCOTLAND
After picking up two passengers and provisions off Malaga, the vessel headed toward the Strait of Gibraltar to begin the sea voyage to Leith. The 1831-nmi sea voyage from Site 979 through the straits to Leith required 179.25 hr at an average speed of 10.42 kt. At 2400 hr, 28 June, the clocks aboard JOIDES Resolution were retarded by 1 hr. Due to very favorable weather and sea conditions, the vessel made excellent time and arrived 24 hr ahead of schedule. The pilot was picked up at 1530 hr, 2 July, and JOIDES Resolution entered the harbor locks at 1700 hr. The ship docked at the Imperial Fuel Dock #5, with the first line ashore at 1730 hr, 2 July, ending Leg 161.
Total transit distance covered during Leg 161 was 2930 nmi, requiring 287 hr at an averaging speed of 10.21 kt. Surveying amounted to 130 nmi in 23.25 hr at an average speed of 5.6 kt.
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