Leg 172 Operations Report

To Site 1063
To Site 1064

SITE 1062
(Proposed Sites BBOR-1, -1B, and -1C)

The 61-nmi transit to the survey area of Site 1062 was accomplished at an average speed of 11.3 kt. At 0600 hr on 14 March, the vessel slowed as the GI air gun and seismic streamers were deployed. The vessel then steered a westerly course as a seismic survey was conducted over BBOR-1, BBOR-1C, BBOR-1B, and then BBOR-1A. The vessel came about and performed crossing profiles: first, a southwest-to-northeast seismic profile across BBOR-1A, then a northeast-to-southwest profile over BBOR-1B, and finally a south-southeast to north-northeast profile over BBOR-1.

Site 1062 includes eight holes drilled into a single mud wave. Holes 1061A, B, C, and D are on the east side of the mud wave, Holes 1061E and F are on the west side, and Holes 1061G and H are near the crest. The far west and far east holes are 1050 m apart. To properly position the vessel over the holes on both the east and west sides, two beacons were required. Normal practice would be to refer to the holes on either side of the mud wave as two different sites, since two different beacons were used. Because the holes comprise a transect across a single mud wave, we instead requested that they all be referred to as a single site, which was approved. The total core recovery for the site was greater than 100% with 1000 m of core recovered.

Drilling operations began at Hole 1062A (BBOR-1) at 1045 hr on 14 March. The drill string was run to 4743.0 mbrf, while additional stands of 5.5-in drill pipe were measured and rabbited. The bit was lowered to 4758.0 mbrf, which was 20 m shallower than the PDR. The first attempt at an APC mudline recovered only water, though a second attempt from 4767.5 mbrf successfully established the seafloor depth at 4763.3 mbsl (4774.8 mbrf). APC coring advanced to refusal at 180.7 mbsf. During coring at this hole in the early morning of 15 March, ship motion became severe enough (2 to 3 m of heave and 2 to 3 degree rolls, combined with 520 kips of string weight) that knobby joints (heavy-wall drilling joints) were used rather than drill pipe joints after recovering Cores 1062A-8H, 9H, and 10H. The weather had calmed by mid-morning and the knobby joints were removed and replaced with drill pipe joints. Adara temperature tool heat flow measurements were conducted at 30.7 (Core 1062A-4H), 59.2 (7H), 87.7 (10H), 116.2 (13H), and 144.7 (16H) mbsf. Cores 1062A-4H through 9H and 10H through 16H were oriented.

Hole 1062B was spudded 13 m north of Hole 1062A and with an initial bit position 9.5 m deeper. APC coring advanced to APC refusal depth (156.7 mbsf), after which coring continued with the XCB. No cores were oriented in this hole.

While attempting to retrieve the core barrel after cutting Core 1062B-27X (239.0 to 248.6 mbsf), it was discovered that the XCB shaft, the core barrel, the core, and miscellaneous hardware were missing. Since this hardware was left at the bottom of the hole, further progress to the depth objective of 250 mbsf was not possible.

Hole 1062C was spudded 12 m north and 7 m east of Hole 1062B at 0740 hr with the bit positioned at 4772.0 mbrf. The seafloor depth was estimated at 4772.1 mbrf based upon recovery of 9.39 m. APC coring advanced to a total depth of 132.9 mbsf by 2145 hr on 17 March. Cores 1062C-8H through 14H were oriented.

Hole 1062D was spudded 6 m north of Hole 1062C, and the bit was positioned at 4768.0 mbrf. The recovery of 5.81 m established the seafloor depth at 4771.7 mbrf. After the core barrel was recovered, a downhole water sampler, temperature, pressure (WSTP) probe was run down the pipe to a level just above the seafloor and a water sample was obtained. APC coring resumed and advanced to a total depth of 81.8 mbsf. No cores were oriented in this hole.

To prepare for the offset for Hole 1062E (BBOR-1B), the end of the drill pipe was placed at 4656 mbrf. The beacon was remotely commanded into standby mode to preserve battery life, and then the vessel was slowly offset west. At 1109 hr on 18 March, a second beacon was deployed on the GPS coordinates of BBOR-1B. The bit was positioned at 4772.0 mbrf, ~10 m shallower than the new PDR depth of 4782.4 mbrf. The first attempt at a mudline resulted in a water core and so the bit was lowered to 4780.0 mbrf, where Hole 1062E was spudded. Hole 1062E is 1044 m west and 62 m south of Hole 1062D. APC coring advanced to the refusal depth of 136.8 mbsf (Core 1062E-16H). Coring resumed with the XCB and advanced to the target depth of 208.8 mbsf by 1600 hr on 19 March. APC Cores 1062E-4H through 10H and 12H through 16H were oriented.

Hole 1062F was spudded 11 m north and 16 m west of Hole 1062E and the bit was positioned at 4783.0 mbrf. APC coring advanced to a total depth of 83.1 mbsf by 0230 hr on 20 March. No cores were oriented in this hole.

The end of the drill pipe was positioned at 4670.0 mbrf and the vessel was offset 725 m to Hole 1062G (BBOR-1C). As the drill pipe was being picked up, the second beacon deployed on this site was recovered. The first beacon was commanded out of standby mode as the vessel settled over the coordinates of BBOR-1C. Hole 1062G is 724 m east and 30 m south of Hole 1062F and is 330 m west and 50 m south of Hole 1062A. Hole 1062G was spudded with the APC bit at 4759.0 mbrf, which was 8.4 m shallower than the new PDR reading of 4767.4 m. This time, however, a full core barrel was obtained and so the hole was abandoned.

The bit was picked up to 4754.0 mbrf, where Hole 1062H was spudded 3 m southeast of Hole 1062G at 0902 hr on 20 March. The recovery of 6.5 m of core established seafloor depth at 4745.3 mbsl (4757.0 mbrf). APC coring advanced to a total depth of 63.5 m (Core 1062H-7H) by 1615 hr on 20 March. Cores 1062H-3H through 7H were oriented. By 0145 hr on 21 March, all drilling equipment had been secured and the vessel got underway to the Bermuda Rise.

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SITE 1063
(Proposed Site BR-1)

After leaving Site 1062, we had a 943-nmi transit at an average speed of 11.6 kt to the Sohm Abyssal Plain, where we conducted a short seismic survey over a potential supplemental site (SAP-1). At 1130 hr, the JOIDES Resolution slowed to deploy seismic equipment. The ensuing seismic survey consisted of a west-to-east line that passed about 1 km south of the SAP-1 site, a broad turn to the south, and then a crossing line which traversed from south-southeast to north northwest across the original line and over SAP-1. This survey covered 28 nmi and was conducted at an average speed of 6.4 kt.

We then proceeded to the Site 1063 survey area, and prior to coring, conducted a 13 nmi seismic survey. This survey began with a south-southeast to north-northwest profile over Site 1063, followed by a crossing west to east line. The survey was conducted at an average speed of 4.5 kt.

Coring began in Hole 1063A at 1035 hr on 25 March. Following the first core, a near-bottom water sample was obtained with the WSTP for isotopic studies. APC coring advanced to 201.4 mbsf, which was considered APC refusal. Cores 1063-3 through 9H, 11H through 17H, and 20H through 22H were oriented, with gaps in orientation occurring during the interval in which data were being downloaded from the only operational Tensor tool. Hole 1063A was deepened with the XCB to 418.4 mbsf, which was 68 m deeper than originally planned.

In preparation for logging, Hole 1063A was flushed with a 30-bbl sepiolite sweep and the drill string pulled back to 377.5 mbsf. The drill string was pulled up to 99.1 mbsf with a maximum drag of 20 kips observed and then run to bottom where it contacted 16 m of soft fill. After a go devil (a tool that free-falls down the drill pipe) was dropped to insure opening of the lockable float valve, the hole was swept with 50 bbl of sepiolite mud. The hole was then displaced with 190 bbl of 8.9 ppg sepiolite mud. Finally, the drill bit was positioned at the logging depth of 105.0 mbsf.

By 0700 hr on 28 March, the Schlumberger equipment was rigged up. Logs were collected in the interval from 416.8 to 105 mbsf using the Triple-combo (DITE, HLDT, APS, HNGS) and the FMS (FMS and SDTC) logging tools.

Hole 1063B was spudded 29 m south of Hole 1063A, and the bit was positioned approximately 2 m deeper than at Hole 1063A. The seafloor depth was established at 4594.7 mbsf based upon 7.83 m recovery in the first core. Cores 16H through 18H and 23H were not fully stroked, but due to the interest in high-quality cores for magnetic studies, piston coring was advanced by the core recovered to a depth of 213.8 mbsf. Hole 1063B was then deepened with the XCB to a total depth of 351.6 mbsf. Cores 3H through 9H, 11H through 17H, and 19H through 21H were oriented with the Tensor tool. The Adara temperature tool heat flow shoe was deployed at 55.3 (Core 6H), 74.3 (8H), 93.3 (10H), 112.3 (12H), and 140.8 mbsf (15H).

Hole 1063C was spudded 14 m south and 7 m west of Hole 1063B, and APC coring reached a total depth of 212.7 mbsf using advance by recovery. Cores 3H through 10H, 15H through 21H, and 23H through 24H were oriented.

Hole 1063D was spudded 17 m south and 6 m west of Hole 1063C, with the bit positioned 2 m higher than 1063A. APC coring advanced to 163.8 mbsf (Core 18H) without incident, although, while coring, the seas began to get rough with 5-6 m swells and up to 4 m ship heave. While attempting to recover Core 1063D-19H (163.8 to 173.1 mbsf), the wireline parted, leaving the sinker bar assembly, Tensor tool, pressure case assembly, and the inner core barrel with Core 19H in it in the hole. This hardware and the core were later retrieved. The wireline failure was attributed to the poor weather conditions, which continued to deteriorate. Winds were gusting to 52 kt as a massive cold front passed over the location during the early morning on 2 April. Coring operations were halted while we waited for conditions to improve. At 1700 hr on 3 April, there was a momentary lull in the storm, which allowed the vessel to retract hydrophones and thrusters and come about. With time running out for Leg 172 and the storm showing little signs of abating, we decided to transit to Site 1064 (SAP-1). By 1730 hr, the vessel was underway to the last site, leaving behind two positioning beacons, which we were unable to recover owing to weather and sea conditions.

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SITE 1064

The 73-nmi transit to the last site of the leg was accomplished at an average speed of 11.0 kt. The vessel's track from Site 1063 took the storm on the starboard quarter, which was responsible for the very good transit speed.

A beacon was deployed at 0032 hr on 4 April. Shortly after deployment, the signal was lost and a back-up beacon was prepared and launched at 0114 hr. The back-up beacon started to behave erratically and a third beacon had to be deployed later in the day. As the vessel positioned over the beacon, the bottom hole assembly (BHA) received the routine end-of-leg magnetic particle inspection while drill pipe was being run into the hole.

Hole 1064A was spudded with the APC at 2310 hr on 4 April after the first two attempts resulted in water cores (APC cores that were shot into water above the seafloor). The seafloor depth was established at 5580.0 mbsf, but Core 1H had 101% recovery, which indicated that the mudline was probably not recovered. The previous water core, however, was shot from a bit position 6 m above the bit position for Core 1H. The end of the core catcher from the water core had a little mud on it, which indicated that we should have recovered about 6 m of sediment in Core 1H, rather than the 9.6 m recovered. The larger-than-expected recovery might be attributed to variation in the inclination of the drill pipe, ship heave, dynamic stretching of the more than 5.5 km of drill pipe, or some combination. Indeed, the weight on bit varied by as much as 50,000 lbs and the seas were still rough. The exact amount by which we missed the mudline is uncertain, but seems unlikely to exceed ~10 m because of the two previous attempts at 6 and 13 m above the drilling-estimated mudline. Seismic information indicates a possible 10 m of missing section, whereas extrapolation of chloride concentrations from pore-water samples indicates as much as 19 m are missing. In addition, the WSTP was deployed 10 m above the inferred seafloor following the mudline core, in an attempt to obtain a near-bottom water sample for isotopic studies. The WSTP sample was heavily contaminated with mud indicating that it had contacted the seafloor.

APC coring resumed and advanced to 28.5 mbsf. After recovering the third APC core (28.5 mbsf), the driller heard an unusual noise emanating from the drawworks, which upon investigation revealed a major failure of the forward drawworks traction motor. This failure left the drawworks with limited capability, ended coring at Site 1064, and ended Leg 172 approximately one day early. The drill string was raised slowly to the surface and the ship was underway toward Lisbon by 2215 hr on 5 April.

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