Next Section | Table of Contents
doi:10.2204/iodp.pr.302.2005
OPERATIONS
Mobilization of the Vidar Viking, Aberdeen, Scotland
The Vidar Viking came under contract on Thursday, 22 July 2004, when mobilization began in Aberdeen. By 26 July, all equipment for the Vidar Viking had arrived, including information technology equipment bound for the Oden, and the derrick was load tested and certified. The Vidar Viking took on a full complement of fuel at Aberdeen.
Test Coring Site: Witch Ground, North Sea
The Vidar Viking set sail for Landskrona, Sweden, on 28 July. While the ship was en route, a first test of the drilling equipment was conducted in the Witch Ground area of the North Sea, ~8 h steam from Aberdeen. A test borehole was drilled in 152 m water depth to a depth of 37 m using both the advanced piston corer (APC) and the extended core barrel (XCB). Cores were obtained with both systems. The APC recovered >4 m in all runs (maximum = 4.5 m). The Vidar Viking left the test coring site at 1900 h on 30 July and proceeded to Landskrona.
Meanwhile, the mobilization of the Oden proceeded at Gothenburg, which included loading the laboratory equipment. On the evening of 31 July, the Oden set sail for Tromsø, Norway.
Mobilization of the Vidar Viking, Landskrona, Sweden
The Vidar Viking reached Landskrona on the morning of 1 August. The stern notch, a 100 ton section required by the Vidar Viking when working in ice, and the helideck were installed. The remaining containers were loaded onto the deck, including the core curation container sent from Bremen, Germany. Other mobilization work continued until the morning of 3 August, when the Vidar Viking departed for Tromsø.
Mobilization of the Vidar Viking and Oden, Tromsø, Norway
The Oden arrived in Tromsø on the evening of 5 August. The Vidar Viking arrived on the morning of 7 August. Two helicopters, required for ice reconnaissance missions, landed on the Oden and were secured.
Rendezvous of the Three ACEX Ships
Expedition 302 officially began when the Oden left Tromsø, Norway, at 2350 h on 7 August 2004. The Vidar Viking remained in Tromsø for the next 12 h to wait for dynamic positioning (Konsberg) spare parts to arrive.
Oden transited to 81°56'N, 44°59'E to meet the other two ships in the ACEX fleet, the Sovetskiy Soyuz and Vidar Viking, at the edge of the polar ice pack on 10 August. The fleet entered the ice together with the Sovetskiy Soyuz leading, the Oden following, and the Vidar Viking bringing up the rear.
Transit to the First Site
During the transit to the operational area, ice reconnaissance and personnel transfer flights began on 12 August. The fleet made an unprecedented headway of 8–10 kt in sea ice.
The fleet arrived on site at 2350 h on 13 August and began preparations for drilling and operations for maintaining position in the sea ice.
Preparations for drilling began with clearing ice from the moonpool. Once this was done, a steel skirt was deployed through and below the moonpool to protect the drill string from ice impact. Once the ice protection skirt was in place, the drill floor and iron roughneck were installed. The drill floor was ready for operations by 0900 h on 15 August.
During this time, the fleet's ability to maintain station was tested by positioning the Sovetskiy Soyuz and the Oden upstream of the Vidar Viking. The initial stationkeeping tests were successful, and the Fleet Manager gave approval to start drilling operations at 1100 h on 15 August.
Site Operations
Cores were recovered in five holes (M0002A, M0003A, M0004A, M0004B, and M0004C) (Tables T1, T2, T3). Hole M0001A was abandoned after a BHA was lost. Logging was attempted in two holes and data were collected over a 160 m interval in Hole M0004B.
Table T4 documents the allocation of time, broken down into (1) waiting for better ice conditions, (2) operational breakdown, and (3) drilling operations.
"Breakdown time" is defined as operational time consumed as a result of equipment or mechanical failure. The loss of a BHA, for example, regardless if caused by human error or mechanical failure, necessitated a drill string trip. If the trip time is caused by equipment failures, it was considered as breakdown time "B." Waiting for better ice conditions was labeled "W." Similarly, if waiting on ice conditions required pulling pipe and subsequent preparations to begin drilling operations, these times were included in the "W" category because that time delay was caused by the "waiting for ice" situation.
Site M0001 (Shotpoint 2720 on Line AWI 91090)
We reached Site M0001 at 1100 h on 15 August. Later that day during drill string deployment, the high-pressure mud valve was damaged. The valve was removed, the rest of the drill string was run, and then the broken valve was replaced. Pipe trips were slowed or stopped intermittently to allow overheated hydraulic fluid in the new drill rig to cool.
By 16 August, the drill string was deployed to the seafloor and the first piston corer was deployed at 0600 h. After pumping for 30 min, pressure was not obtained and the piston corer was retrieved without having fired. Damaged seals on the piston corer were replaced. Ice conditions were marginal, and at 0900 h operations were stopped and the drill string was lifted from the seabed. Ice conditions improved by 1400 h, and operations continued. The piston corer was deployed again, and no pressure developed in the drill string. Upon retrieval, the piston corer had not fired. It was suspected that the piston corer had not latched into the BHA. The XCB was then deployed but was not recovered, which indicated that the BHA was lost. At 2000 h, the drill string was tripped and the BHA and XCB losses were confirmed.
Beginning early on 17 August, a new BHA was assembled and we began to lower the drill string. When >800 m was deployed, the high-pressure mud valve on the swivel was damaged again during pipe handling; we decided to trip the drill string because the operator did not want to risk leaving the drill string hanging in the water column for an unspecified period of time. After tripping pipe, the damage was assessed and Oden's chief engineer was tasked with manufacturing a new valve using materials from a spare pup joint. As an interim solution, a conventional valve assembly was installed.
Ice conditions deteriorated between 0900 and 2200 h, and the time was utilized to move the Vidar Viking to a new position (Hole M0002A). Because there were no mud valve spares, the Swedish Polar Research Secretariat (SPRS) began making arrangements for a Swedish Air Force C-130 airdrop of two new valve parts and one conventional valve assembly.
Site M0002 (Shotpoint 2560 on Line AWI-91090)
Based on a strategy developed by the ice management team, the drill string was lowered while drifting onto location. By 2200 h on 18 August, this strategy put the Vidar Viking within 190 m of the proposed site. The final positioning was done by icebreaking this short distance to Hole M0002A. Once on location at 0820 h, three more drill pipes were added and coring started. Because the mud valve was not yet repaired, the XCB was deployed instead of the APC. A first attempt at coring was unsuccessful, but after adding more pipe and drilling another core run, some core was retrieved. The first core on deck arrived at 1335 h at a water depth of 1209 m. Drilling operations continued throughout the afternoon. The newly fabricated mud valve from the Oden arrived late in the afternoon, and preparations were made for its installation during a wireline trip. The temporary valve was replaced before more drill pipe was added for the next core run. By midnight on 19 August, a depth of 31 mbsf had been reached.
Drilling and XCB coring continued until 23 August when the Fleet Manager ordered the drill pipe to be pulled to 40 mbsf because ice conditions were deteriorating. Permission to continue drilling operations was given midday, and operations continued until 2100 h when the ice conditions forced the termination of Hole M0002A at a depth of 271.69 m.
The drill string was tripped to the drill deck during the morning of 24 August. After waiting for ice conditions to change in the afternoon, a transit began at 1930 h to a position from which the Vidar Viking could drift onto location while tripping in drill string.
While we waited on ice conditions and set up for the next site, an air gun seismic survey was run from the Oden to tie Site M0002 to the next site (M0003).
Site M0003 (Shotpoint 2521 on Line AWI-91090)
The Vidar Viking reached the ice-drift position at 2100 h and awaited ice reconnaissance results. The iron roughneck, which had been removed to repair oil leaks, was installed after repairs; the ice protector tube was lowered; and the drill floor was prepared. At 2300 h, the BHA and drill collars were run. At 0240 h on 25 August after 400 m of pipe had been deployed, the housing of the iron roughneck cracked and had to be removed for major repairs. Operations resumed at 1400 h using power tongs. The seafloor was reached at ~2300 h, and at 0110 h on 26 August, the first APC core was recovered from Hole M0003A (Table T2).
A second APC core with a shattered liner was recovered. The third APC core became stuck in the BHA. While trying to release the corer, the wireline parted at the mechanical termination, and it was necessary to pull the string. Hole M0003A was terminated at 0440 h.
The ice management team conducted ice reconnaissance surveys, reviewed options, and recommended that the fleet move to a location farther west, where a longer-term prediction of relatively good ice could be made. Once the site was selected, the ice team predicted an upstream ice position for the Vidar Viking to start to drift onto the new location. The fleet steamed to the updrift ice position, arriving at 0630 h on 27 August. During this time, wireline termination repair, APC service, and iron roughneck the testing/refitting took place.
Site M0004 (Shotpoints 3006 [A, B] and 3004 [C] on Line AWI-91090)
At 0755 h during pipe tripping, the high-pressure mud valve was damaged again. The valve was removed, and the remaining string was run to 1150 m depth while the valve was repaired. At 1800 h, the Vidar Viking was on location (Hole M0004A). Once on station, the repaired mud valve was installed and the drill string was run to the seabed. At 2230 h, drilling operations in Hole M0004A commenced and the hole was advanced by washing ahead 17 mbsf (Table T3) before a piston corer was deployed.
Shortly after midnight on 28 August, the APC became stuck in the BHA but was freed after ~1 h. Once on deck, the plastic liner in the core barrel was found to be shattered and 3.5 m of the core was stuck in the barrel. In light of these problems with the APC, in particular the risk of junking the hole again, it was decided to switch to XCB coring. Two XCB cores were recovered to a depth of 30.5 mbsf followed by washing down to 265 mbsf using the insert bit. This decision to wash ahead was made in order to recover sediment deeper than that recovered in Hole M0002A. By 2240 h, a depth of 265 mbsf was reached.
XCB coring operations continued for the next 3 days (29–31 August), where the hole was advanced at varying rates with good to poor recovery. During this time, the drilling was very slow (e.g., 1 m/h) and recovery in many cores was zero (Cores 302-M0004A-13X through 18X). Different strategies were tried to improve the advance rate. At times, the hole was advanced by washing ahead in an attempt to make faster progress but was ultimately abandoned after it was found that the washing rate was almost the same as the coring rate. On 31 August from 0200 to 0500 h, for two coring runs in a row, no core was recovered. The XCB shoe was switched to a coring shoe for a third attempt at recovery. This coring run cleared a blockage in the bit as the pump pressure dropped significantly. Following this core (with good recovery) and after clearing the blocked bit, core recovery and advancement improved over the next 12 h until basement was reached in Core 302-M0004A-35X. Basement penetration was difficult (8 m penetration in 12 h with low core recovery), and a decision was made at 0900 on 1 September to stop coring at total depth of 428 mbsf and conduct logging in Hole M0004A.
The logging tools were moved to the rig floor and the tool string (FMS-APS-NGT-SGT) and wireline rig-up proceeded simultaneously. The run into hole commenced at 2130 h. This was done at low speed in order to allow the tools to warm up. Communication with the tool was established, and it was lowered to the end of the drill pipe. A computer malfunction caused a communication loss to the tools. The problem was corrected by 0200 h. The tool was powered up, and attempts were made to get the tool to pass through the BHA into the open hole. All efforts failed at the same depth (~1366 mbrf); so, while at rest at this depth, the calipers were opened on the FMS to check whether it was free or lodged. The calipers had some movement, which indicated that the tool string was free.
The landing ring for the core barrel is the narrowest section of the whole pipe string (95 mm) and lies ~6 m above the bit. All the logging tools had been checked through a landing ring dockside in Aberdeen, but there was no hole calibration ring onboard that could be used as a second check. Sequentially, four more logging attempts were made. Each time, it was assumed that the logging tools were too large in diameter and the string diameter was further reduced by removing the larger diameter components. The APS bowspring was removed first, followed by the knuckle joint. Finally, only the narrowest velocity-density string was deployed, which failed to clear the bit at the same depth as the previous runs. After the fifth attempt failed, the logging time allocated had been used up and attempts to log Hole M0004A ended at 1045 h on 2 September.
After the logging gear was cleared away and the drill string was lifted out of the seabed, preparations were made to start a second hole (M0004B) at the site. During preparations, the inner barrel was deployed but did not latch. After an improvised downhole hammer was deployed and worked for 2 h, a short length of core (~10 cm of mudstone), which had been partially blocking the BHA, was recovered.
By 2030 h on 2 September, the Vidar Viking was at the new position for the next hole (M0004B). Coring in Hole M0004B started at a depth of 10 mbsf using the XCB because the APC was deemed too risky. After retrieving the first sample, the hole was washed to 20 mbsf for an in situ temperature measurement. The BGS temperature probe was lowered to the base of the hole, pushed into the sediment, and programmed to record the temperature every 5 s. The probe was left to record temperature for 40 min, after which it was retrieved. Plans to wash to a depth of 215 mbsf, core to 230 mbsf, and then wash to 250 mbsf and log were stymied by problems with drilling pressure lines/gauges freezing at –10°C. Because of these problems and the limited time left, the hole was only advanced to a depth of 220 mbsf. Temperature measurements were made at 60 and 100 mbsf.
At 0000 h on 4 September, the pipe was pulled to 65 mbsf to prepare for logging. Rigging of the wireline and tool string occurred concurrently, and rig-up of both was completed by 0415 h. The tool string comprised the FMS-BHC-NGT-SGT; the choice of tools was such that it could be run as a straight-through tool string without the need for articulation and eccentralization subs. The logging string was run slowly to the bit to warm the tools before powering them up. The logging string passed through the bit at 0530 h, and the first pass was completed at 0610 h. Logging operations were completed at 0710 h. Rig-down of the logging tool and wireline was completed by 0905 h, and preparations began for a third hole (M0004C). Hole M0004C was spudded at 1200 h on 4 September, and the first APC core was recovered at 1420 h. Two more APC cores were recovered during the next 10 h. An attempt to make a temperature measurement at 9 mbsf using the Adara tool on the APC failed because of a dead battery. At a depth of 14 mbsf, the APC core barrel became stuck after being fired. The period from midnight to 0530 h on 5 September was spent trying to retrieve the piston tool. Various attempts to recover the tool included flush only, hoist only, mixture of flush and hoist, and hoist and leave at top of hoist for some time. The APC was freed and recovered by 0530 h, and the barrel was slightly bent (the liner was easily removed). Because of the risk of getting stuck again, coring continued using the XCB with a modified Adara shoe to complete two more temperature measurements to a depth of 37 mbsf. Drilling operations ended at 1500 h. The drill string was retrieved by 0500 h on 6 September.
The Oden came alongside the Vidar Viking to transfer 400 T of fuel, and all three ships of the fleet carried out required maintenance before the return transit. A seismic survey was attempted from the Oden but was abandoned because of difficult ice conditions. The operational phase of the expedition ended, and the return transit began.
Transit from the ACEX Coring Sites to Tromsø, Norway
The convoy left the study area at 1930 h on 6 September and headed toward the North Pole. Progress was slow in the first half of the day but improved later, and the fleet arrived at the pole at ~2230 h. The convoy departed at 0100 h on 7 September and made good progress toward Tromsø in almost continuous open water. The Oden arrived in Tromsø at 2300 h on Tuesday 13 September.
The Vidar Viking parted company with the Oden at the ice edge in the early hours of Saturday, 11 September and headed due south. A crew change and demobilization were effected in Tanager, Norway, on 16 and 17 September. The Vidar Viking then sailed for Landskrona in Sweden, where the helideck was removed together with the European Science Operator core and curation containers and the deep freeze samples. BGS/Seacore personnel continued the reconstruction of the deck, while vessel and shipyard personnel removed the moonpool and other expedition-linked items.
On 22 September, the Vidar Viking sailed for Aberdeen, Scotland, to complete the demobilization. Upon arrival in Aberdeen at 0800 h on 24 September, the remainder of the expedition equipment was demobilized and the vessel was cleared for her next charter by 2200 h that day. Formal end of charter, following tank cleaning and reinstatement and off-hire recertification, was completed on 25 September.