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doi:10.2204/iodp.proc.304305.103.2006

Operations

Expedition 304

Port call

Expedition 304 began at Ponta Delgada, Portugal, with the first line ashore at 0816 h on 17 November 2004, which ended Expedition 303. Cores from the previous expedition were offloaded for transfer to the IODP Bremen Core Repository (Germany), and the hardware for our HRRS deployments and the advanced diamond core barrel was brought aboard. Cores from Leg 209 (MAR at 15°45′N) were taken aboard to use as instructional material for Expedition 304 scientists. Maintenance on the active heave compensator (AHC) corrected an intermittent control problem, and the port call was completed in 3.5 days.

Transit to Site U1309

Our transit began with the last line away at 2012 h, 21 November 2004. The pilot was dispatched at 2024 h, and we were under way at full speed to our first site. During the transit, we averaged 11.1 kt over the 939 nmi distance. The vessel arrived at location (based on global positioning system [GPS] coordinates), and we launched a beacon at 0830 h on 24 November 2004, initiating operations at Site U1309.

Hole U1309A

Operations began with a subsea camera survey of the seafloor (Fig. F304) to locate suitable places to drill the pilot hole and install the HRRS. The survey was completed in <2 h, and an appropriate area (devoid of large boulders or rubble) was selected for drilling. A water sample and a temperature measurement were collected for microbiology and geochemistry with the WSTP just above the mudline. The first hole (Hole U1309A; 30°10.11′N, 42°07.11′W; 1642 mbsl) was a punch core with the RCB coring assembly that captured the seafloor sediments (Table T26). Hole U1309A was terminated when the bit cleared the seafloor at 2230 h on 24 November 2004.

Hole U1309B

Rotary coring commenced in Hole U1309B (same coordinates as Hole U1309A) at 0050 h on 25 November 2004. From our punch test at Hole U1309A, we determined there was ~2 m of sediment covering hard rock. Because we were effectively attempting a hard rock spud, we began with low weight on bit (4000 lb) and slow bit rotation (30 rpm) to minimize the potential of drill collar failure. Penetration rates started at <1 m/h, but by 25 mbsf increased to as much as 2 m/h, as we were able to increase weight on bit and rotation speed while advancing the hole. Final penetration was 101.8 m with 46.7 m of recovery. All coring in Hole U1309B (Cores 304-U1309B-1R through 20R) recovered nominally 4.5 m increments (half cores) to maximize recovery. Owing to excessive vessel heave (4–5 m), only passive heave compensation was used during coring operations at Hole U1309B.

Penetration in Hole U1309B was terminated when the bit ceased rotation and penetration after 86.25 rotating h. The mechanical bit release was activated, and the bit was released at the bottom of the hole. The hole was displaced with drill (fresh) water for logging (to minimize resistivity contrast between the formation and the fluid in the borehole), and the end of the pipe was set 25 mbsf for logging. The logging operation consisted of three tool string deployments, one each with the triple combo and the FMS-sonic and a third run to test the new logging winch heave compensation system. Logging results indicate that Hole U1309B deviated ~7° to the northeast (N43E). Hole U1309B ended at 0805 h on 1 December when the mechanical bit release cleared the rotary table.

Hole U1309C

The HRRS was deployed with three joints of 13.375 inch casing with a designed penetration of 31.6 mbsf. The hammer-in-casing design utilizes a bit style that engages the hammer to a cutting shoe welded onto the bottom of the casing. All components were assembled starting at 0805 h on 1 December 2004. The assembly was tested at the rig floor and construction completed at 0230 h on 2 December. The vessel was offset ~20 m west of Hole U1309B to a location where the subsea camera survey showed seafloor characteristics similar to our pilot hole location (30°10.11′N, 42°07.12′W; 1638 mbsl). The subsea camera was deployed as we ran the HRRS to just above the seafloor, and after a comparison of active and passive heave compensation behavior, we decided to initiate the hole with the passive system (again because of high heave). Hole U1309C was initiated at 0945 h on 2 December. Hammer drill operations continued to 1655 m (drill pipe measurement), or 6 mbsf. This depth was reached shortly after noon on 2 December, at which time penetration and rotation effectively stopped. High torque, slow penetration rates, and low bit rotation speed during this deployment made for challenging drilling, and the drillers noted that each time weight was applied to the drill string, rotation would cease. Raising the pipe off bottom allowed rotation, but even after 8 h of attempts, no new penetration was possible, even while employing the active heave compensation system.

Because it seemed apparent we could not make sufficient penetration to install our casing string, we decided to abandon the attempt in this hole and move to another location. The subsea camera was deployed to inspect the HRRS as we cleared the seafloor and to aid us in selecting the next drilling target. Once the camera was near bottom, we could see that the casing running tool had released from the casing. Our operations team concluded that the release had probably occurred early in the deployment and that penetration effectively stopped at the time of release. The casing was firmly stuck in the seabed, with >25 m of casing standing proud above seafloor, and because it did not fall over when we extracted the pipe, we surmise that it is still upright. The BHA was pulled back to the surface, and the pilot bit from the HRRS cleared the rotary table at 0755 h on 3 December, ending Hole U1309C. Disassembly of the running tool revealed no detectable reason for early release.

Hole U1309D

A new drilling location was selected within our subsea camera survey area with similar seafloor appearance to the earlier drilling locations but outside the potential falling radius of the abandoned casing string and outside of the area of influence of the deviation of Hole U1309B. The HRRS was deployed for the second time, now with two joints of 13.375 inch casing for a designed penetration of ~22.45 mbsf. We utilized the same hammer-in-casing design as deployed at Hole U1309C. We elected to use a shorter casing string on this attempt to reduce installation time but still provide a viable reentry system.

All components were assembled and ready for deployment by 1915 h on 3 December 2004. Hole U1309D (30°10.12′N; 42°07.11′W) was initiated at 0120 h on 4 December with a tagged drillpipe measurement of 1645 mbsf. Hammer drilling commenced, and at 0630 h, at a depth of 5 mbsf, penetration seemed to stop. The subsea camera was deployed to see if the running tool had prematurely released again, but everything appeared to be intact. Drilling continued with slow penetration until 0900 h on 5 December.

After penetration of 20.5 m, rotation on the drill pipe stalled, with excessive torque only relieved by lifting the bit off the bottom of the hole. Our engineers suspected the possibility of another premature release of the casing running tool, which was confirmed after deployment of the subsea camera. Fortunately, the running tool did not release until we had nearly achieved our target depth in Hole U1309D, leaving 4.5 m of casing above the seafloor (within the design parameters for HRRS deployment). The reentry cone was released, and a subsea camera survey indicated successful deployment of the reentry system.

As per our operations plan, we elected to open the hole beneath the reentry funnel to ~100 mbsf before moving to our second drilling site. Because drilling parameters and logging data indicated a clean gauge borehole at the pilot hole, we determined a nested casing system would not be required at this time. We elected instead to deploy a coring system to provide additional core as well as a head start for future deepening operations. The first reentry into Hole U1309D was accomplished in 10 min at 0240 h on 6 December. Cores 304-U1309D-1R through 22R were cut from 20.5 to 131.0 mbsf. The majority of the cores were nominally 4.5 m penetrations (half cores), but two ~9.5 m cores were cut to compare recovery to half cores. Penetration rates and operating parameters were similar to pilot Hole U1309B. The BHA was pulled after 60.75 rotating h. The bit cleared the rotary table at 1520 h on 10 December, suspending operations at Site U1309. Even though we attempted to be conservative on bit rotating hours, inspection after pulling the bit indicated excessive wear, with numerous missing teeth and three loose cones. The excessive wear might be attributed to coring through several intervals of diabase.

Following operations at Sites U1310 and U1311, we returned to Hole U1309D to continue deepening the hole. Reentry with a new RCB bit took about an hour, and was completed by 1305 h on 22 December. At 1705 mbrf (~49 mbsf), we encountered an obstruction in the hole. After installing the top drive, only a short rotation was required to pass the obstruction, and the hole was cleared to the depth of our previous penetration (131.0 mbsf). Coring began with Core 304-U1309D-23R and continued in nominally 4.8 m increments through Core 47R to 252.4 mbsf.

After a pipe trip to install a new RCB bit, the pipe was deployed into Hole U1309D, encountering the same obstruction at 48–49 mbsf. Again, it was easy to pass this obstruction with rotation. Coring continued from Core 304-U1309D-48R through Core 78R (252.4–401.3 mbsf), with total recovery for the hole in excess of 64%. With 56 rotating h on the bit and only a few days left in the expedition, we tripped the pipe out of the hole after conditioning the hole for logging and filling it with freshwater (to improve resistivity contrast between the formation and the borehole fluid for logging). Obstructions in the hole were encountered at 1704 and 1690 mbrf (~48 and ~34 mbsf).

Before pulling the pipe, we attempted two shallow penetrations with the used RCB bit.

Hole U1309E

Hole U1309E was initiated with the RCB system after our last full coring run in Hole U1309D. After the pipe was withdrawn from the HRRS, we moved the ship in dynamic positioning mode ~10 m east of Hole U1309D and cored without circulation to a depth of 3.8 mbsf (Core 304-U1309E-1R). Drilling-disturbed unlithified microfossil ooze with coarse sand and a few pieces of rock were recovered.

Hole U1309F

Continuing with efforts to capture the oldest sediments draping the central dome of Atlantis Massif, as well as the detachment surface itself, we moved the vessel in dynamic positioning mode to a site 275 m northwest of Hole U1309D. This location was selected to attempt to core through thin lithified carbonate and into basement, as was determined to be present based on seafloor images from an Argo still camera survey (Argo II run 039, cruise AT3-60). A short subsea camera survey revealed a surface with the characteristics of lithified carbonate, and Hole U1309E was cored to 4.8 mbsf (Core 304-U1309F-1R); ~6 m of drilling-disturbed, unlithified microfossil ooze was recovered. Because RCB coring was not successful in recovering material we could recognize as intact basement rock in either Hole U1309E or U1309F, we tripped the pipe in preparation for logging. Hole U1309F ended when the RCB coring bit cleared the rotary table at 1450 h on 31 December 2004.

Logging in Hole U1309D

A new advanced piston corer (APC)/XCB BHA was assembled for logging. We selected this assembly to log Hole U1309D and provide the possibility of attempting two more coring systems (XCB and APC) on a transect of shallow-penetration holes across the central dome. The bit was positioned in the 13⅜ inch casing, but after 6 h, the logging tool would not pass the obstruction at ~48 mbsf and the logging run was terminated. Shallow-penetration holes were attempted with the XCB/APC coring system (see “Hole U1309G,” below) before tripping the pipe to install a logging BHA.

With the logging BHA installed, we were able to set the bit below the obstruction at ~48 mbsf in Hole U1309D. Triple combo and FMS tool string runs were successful, but the UBI run was not attempted because the second FMS pass ended with fallen rock briefly trapping the tool in the hole. The tool was extracted with no significant damage, and the logging BHA was pulled.

Hole U1309G

With the XCB/APC BHA in place, we made the short transit from Hole U1309D to Hole U1309G. Our target was an area of extensive lithified carbonate identified during a seafloor submersible survey (cruise AT3-60, Alvin dive 3642) in 2000. We deployed the subsea camera and encountered a marker deployed during the submersible survey. The navigation offset between AT3-60 and Expedition 304 is 11 m, the 2000 position of the marker is registered slightly to the north of the position determined during Expedition 304. Hole U1309G was cored to 3.5 m, recovering just under a meter of sediment and drilling-disturbed hard rock. An APC barrel was deployed to see if we could recover an intact section through the sediment and into basement, but the core barrel parted and no core was recovered. Because the result of XCB/APC coring was inconclusive regarding the nature of the uppermost basement at this location, we elected to trip the pipe to complete logging in Hole U1309D.

Hole U1309H

After logging operations were concluded, there was sufficient time left in the expedition for a short bit run. We elected to attempt a shallow RCB core at the same location as Hole U1309G. Using the retired bit from our last coring run, we attempted coring to a depth of just >2 m below the soft sediment blanket, but the core barrel returned empty. With ~5 h of operations time left in the expedition, the bit was returned to the seafloor and Core 304-U1309H-1R was cut without circulation in the upper 0.5 m and low pump pressure for the remainder of coring (~3.5 m). The pipe was pulled and inspected, and we were under way for Ponta Delgada by 0700 h on 4 January 2005.

Expedition 305

Port call

Expedition 305 began when the first line was placed ashore at Pier 12 in Ponta Delgada on the island of São Miguel, Azores, Portugal, at 2120 h on 7 January 2005. The vessel arrived slightly ahead of schedule and was able to clear customs and immigration the evening before the scheduled crew change. The US Implementing Organization and Transocean personnel crossover took place on the morning of 8 January. In addition to the routine freight transfer and the loading of fuel (999.6 mT), there were three pacing items for this port call: an American Bureau of Shipping (ABS) Annual and Statutory survey, an overhaul of the drawworks transmission, and the replacement of the AHC hydraulic hose bundle.

The ABS survey was completed by the morning of 11 January. Also on 11 January, the new AHC hose bundle was filled with oil and tested. After testing, the return hose had stretched in length by ~1.5 m. The return hose appeared to be either defective or inappropriately rated. Because repair was not possible within the port call schedule, the AHC was not operational during Expedition 305. The completion of the drawworks transmission repair was dependent upon the arrival of hardware from the Transocean warehouse in Houston (Texas, USA). Customs clearance in Lisbon, Portugal, delayed arrival of these parts until ~1530 h on 12 January.

At 1715 h on 12 January, the last line was released from the dock, and after clearing the harbor entrance, the pilot was released at 1721 h and the vessel began the journey to Site U1309. The duration of the port call was 4.8 days.

Transit to Site U1309

The transit to Site U1309 covered 1002 nmi at an average speed of 10.7 kt. Weather-related course deviations resulted in a somewhat longer transit than the one during Expedition 304. During the transit, the ship’s clocks were retarded 2 h to –3 h UTC. On approach to Site U1309, we conducted a 17.8 nmi towed magnetometer survey near the site. The survey line began at 30°4.7′N, 41°47.0′W, and extended west-northwest to 30°07.9′N, 42°07.1′W.

Initial deepening of Hole U1309D

The vessel was positioning over Hole U1309D at 1600 h on 16 January 2005 using the GPS and the beacon that was deployed during Expedition 304. The drill crew made up a 10-collar RCB BHA affixed with a new C-7 rotary bit. At 0027 h on 17 January, we reentered Hole U1309D and deployed the WSTP to the bottom of the hole. To minimize contamination or disturbance of the borehole water column, the drill string was lowered to ~10 m off the bottom of the hole with minimum rotation and no circulation. After the WSTP was retrieved, a fresh core barrel was dropped and ~3 m of fill was cleaned from the bottom of the hole. The recovered core barrel was curated as Core 305-U1309D-79G (numbering continuing serially from Expedition 304), as no new penetration was achieved.

Between 17 January and 30 January, we cored from 401.3 to 837.4 mbsf (Table T26) using four C-7 rotary core bits. The average rate of penetration steadily decreased downhole, from 2.6 to 1.6 m/h, averaging 2.2 m/h for the 14 day coring operation, with recovery averaging >80%. Based on a conservative estimate of bit life, we elected to change bits after nominally 50 h of rotation. At the end of each bit run, the bits returned worn but essentially undamaged. Mud sweeps (20 bbl) were circulated every 10 m of advance to clean the hole. Fluorescent microspheres and PFTs were deployed episodically during cored intervals at depths where microbiology samples were requested. However, PFT use was discontinued after Core 305-U1309D-90R at the request of the shipboard microbiologist, owing to insufficient time to rapidly process samples. At the end of the fourth bit run (837.4 mbsf), the hole was conditioned for logging, including displacing the borehole fluid with freshwater to improve the logging signal.

Logging Run 1, Hole U1309D

In preparation for logging, the bottom of the pipe was set at 170 mbsf. This allowed overlap with previous logging runs performed during Expedition 304 and positioned the pipe below an interval where minor obstructions were encountered in the borehole during reentry. The first logging run with the triple-combo tool string covered the full length of open hole. Logging with the FMS-sonic tool string also covered the interval from the bottom of the hole to 170 mbsf. Following the completion of the FMS-sonic log, we completed a test of the WHC to evaluate the performance of the new drum-compensator and compare it with the performance of the older LDEO wireline compensator. The third logging run was a VSP utilizing the WST-3 and the generator-injector air gun. In accordance with IODP policy, prior to the VSP, a 1 h visual survey of the water within a 700 m radius of the vessel was undertaken to ensure that no marine mammals were present prior to the start of the VSP experiment. Also consonant with the policy, the generator-injector gun was soft-started (gradually increased intensity for the first 30 min of operation) at the initiation of testing. The marine mammal watch was maintained until the VSP was secured, and no marine mammals were sighted during the experiment. A single joint of pipe was removed from the string, placing the bit at 161 mbsf before deploying the tool. The fourth logging run utilized the UBI. The UBI was deployed with a sinker bar to enhance deployment speed. Owing to an inconsistent borehole geometry in some intervals of the hole and poor tool performance in the high-speed, low-resolution mode, only intervals from 824 to 724 mbsf and 704 to 503 mbsf were imaged with the UBI. A final logging pass was made with the GBM. The internal gyrocompass of the tool was oriented with the vessel heading prior to lowering into the pipe. The GBM recorded data in both directions as it traversed from 170 to 837 mbsf and back. The drill string was raised 10 m as the GBM approached the pipe. The internal gyrocompass was oriented a second time when the tool was recovered. Logging operations were completed at 1040 h on 2 February 2005.

Deepening Hole U1309D

Between 2 and 23 February 2005, we cored from 837.4 to 1415.5 mbsf (Table T26), using one C-7 and five C-9 bits. The C-9 bits are designed for harder formation coring. We elected to use C-9 bits in order to preserve the last two C-7 bits in inventory in the event we encountered softer rock at depth. Average rate of penetration continued at 1.6–2.4 m/h, with recovery averaging 78%. We experienced no significant difference in bit performance between the styles of coring bits employed. Our routine procedure included 20 bbl mud sweeps after every other cored interval to clean the hole. Coring in Hole U1309D concluded with the last core on deck at 1015 h on 23 February.

Over the entire coring program, there were only a couple of irregularities of note in routine operations. Shortly after initiation of the second coring interval (at ~929 mbsf), the pump pressure decreased from 1000 to 900 psi, indicating that the core barrel may have become unseated. After the core barrel was recovered, a bit deplugger was deployed and normal pressure was restored. In addition, at 1373 mbsf, 0.5 m penetration required 1.5 h, and the core barrel was recovered empty. Because we suspected the bit might be jammed, we ran a bit deplugger. The ensuing coring interval still proceeded quite slowly (2 h for 1.5 m of penetration), so the core barrel was again recovered early, this time returning fine-grained diabase. The hard formation was eclipsed during the subsequent coring interval, and our rate of penetration increased to routine values.

During our midcruise logging run, a temperature of ~60°C was measured by one of the magnetometer tool’s sensors. After communication with the manufacturer to confirm the configuration of the temperature measurement system (to ensure the thermistor was not simply registering the internal temperature of the tool, which is heated to maintain instrument stability), we elected to attempt to verify the borehole temperature in preparation for our next logging run. In our first attempt, an assortment of calibrated, heat-sensitive, adhesive strips were affixed to a modified APC brass core catcher spacer deployed in a dedicated core barrel run. The core barrel was deployed at 1162 mbsf (a few meters above the bottom of the hole at the time) and allowed to equilibrate for 17 min without circulation. Upon recovery, the temperature strips indicated a minimum temperature of ~70°C. During the ensuing bit trip, we decided to deploy the WSTP to collect a water sample and temperature measurement. Before deploying the sampler, our technicians determined the thermistor on the WSTP was broken and no exact replacement was available. The shipboard electrical technician fabricated an ad hoc arrangement of the APC temperature (APCT) tool on the WSTP and found an uncalibrated thermistor to install on the WSTP. In addition to these two temperature measuring devices, an assortment of the adhesive temperature recording strips were also affixed to the WSTP. Owing to a failed O-ring, the APCT failed to record a temperature. The thermistor on the WSTP recorded a maximum temperature of ~60°C. A subsequent bench test determined 60°C was the maximum recording temperature for the new WSTP thermistor/datalogger assembly. The adhesive temperature strips indicated a minimum temperature of 110°C.

Logging Run 2, Hole U1309D

After hole conditioning on 23 February 2005 (once coring operations were completed), the borehole was filled with drill water to improve the logging signal. A logging BHA was deployed, and the bit was set at 194 mbsf. Two passes were completed with the triple combo tool string, the first from the bottom of the hole to the logging bit (1415–194 mbsf) and a repeat pass (as a calibration check) from 1284 to 1094 mbsf. The second logging run utilized the FMS-sonic tool string, but the telemetry link failed when the tool reached the bottom of the hole. The tool string was pulled to the rig floor, where the logging team determined the sonic tool had broken. The sonic tool was removed from the logging string, and the FMS was redeployed. Two logging passes were completed with the FMS. The first pass covered the interval from the bottom of the hole to 754 mbsf (to overlap with our midcruise logging run), and the second covered the interval from the bottom of the hole to 629 mbsf. At this point, the FMS tool string was recovered to allow time for a daylight VSP experiment.

A marine mammal watch was instituted at daybreak on 24 February, and after an hour with no marine mammal sightings, the generator-injector gun was hung from the port aft crane and a gradual power increase firing process was initiated. The WST-3 was deployed to the bottom of Hole U1309D, but voltage at the tool head was intermittent. The tool was raised to ~1200 mbsf, but only brief continuous communication could be established. A final attempt to communicate with the WST was attempted at ~700 mbsf, but when this attempt failed the tool was recovered. The single-component WST was deployed, but shortly after the tool was into the open borehole, sea state (heave in excess of 5 m) had deteriorated to the point where the logging heave compensator could not operate within safety limits. Only a single station was occupied with shots recorded before logging operations were terminated. The drill string was recovered and we began preparations for our transit back to Ponta Delgada. Operations in Hole U1309D concluded on 26 February.

Transit to Ponta Delgada

Prior to departure from Site U1309, a towed magnetometer survey was conducted. A survey line was laid out from 30°09.0′N, 42°14.2′W to 30°07.8′N, 42°06.3′W to complete the flowline path begun during arrival at Site U1309 at the start of Expedition 305. Initial problems with the port winch and with the logging software delayed acquisition of useful data until ~2.5 nmi along the line. Acquisition with the starboard magnetometer was successful and continued beyond the endpoint of the first line, along a track toward Ponta Delgada, until 1200 h on February 26. The 950 nmi transit required 104 h at an average speed of 9.1 nmi/h. Expedition 305 concluded with the first line ashore at Ponta Delgada on 1805 h on 2 March 2005.

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